A Beginner's attempt at Boolit Design - Critique Welcomed!

[DrCaveman]

I am probably in over my head, but I like CAD so I went ahead and came up with a few boolit designs for 38/357 guns. I would greatly appreciate any comments from people who have submitted their own drawings for custom molds, and who may have had to change certain aspects based on the reality of CNC capabilities/proper mold fill-out/boolit release from mold, etc.

I am pretty ignorant of proper lube groove depths or widths, but I think this is an area of significant flexibility... but any insight is very welcome.

Or, if you just think the design is a bad idea, for whatever reason, let me know!

http://castboolits.gunloads.com/imagehosting/thum_226994f92ffa55f41b.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=4884)

This has a pretty standard SWC front, but I gave it some extra length to bump up the weight and increase the length of full-diameter driving bands. I am attempting to combine Tumble lube grooves with more standard lube grooves. My thinking is that low pressure loads just get tumbled, while magnum loads would get pan treatment in addition to being tumbled.

The odd shape of the two larger lube grooves was also intentional, my thinking that the liquifying of the lube would create small eddy's near the bottom of the groove, keeping the lube in the groove a little longer. Maybe pure hogwash, but it kinda makes sense.



http://castboolits.gunloads.com/imagehosting/thum_226994f92ffa5aaeee.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=4885)

This one is intended as a big-boy hunting/SD round, shot around 1000-1200 fps with pretty stout loads. I drew this one first, and I have a feeling that all the square corners may pose problems in fabrication as well as mold operation. All that can change easily, but for now I just wanted to see what everyone thought of the general shape and groove placement.

As with the previous design, I am attempting to combine large lube grooves with small ones, since I would like to find a boolit capable of shooting within a variety of temperatures at a variety of pressures. Again, I figure that the bottom groove will be filled with some heavy duty pan lube, while the top grooves will be more like Tumble lubed. This boolit has a full 50% of its length at full diameter.

Thoughts? Thanks in advance. I am still very new to all of this, and my skin is thick. Dont be afraid to beat me up, or knock some sense into me.

[excess650]

Radiused bottoms or angled sides in the grooves will make for a stronger boolit. Too, it will be easier to make tooling for radiused corners, angled grooves, etc and boolits will drop more easily from the molds if the corners aren't as sharp.

If these are to be shot from a revolver, the distance from the crimp groove forward plus case length needs to be shorter than the cylinder. If for a lever action, the OAL will need to be less than the maximum the lifter will allow for.

Take a look at Ranch Dog's designs or NOE's version of the RDs and NOE's .360 WFNs.

[geargnasher]

+1 on radius and draft angle. The boolits won't drop from the mould unless everything, including the larte meplat, is angled. Note most boolit designs have a minimum angle on all things like the top of the crimp groove and even the front shoulder on the boolit.

Gear

[DrCaveman]

Alright, these are the types of comments I was looking for!

A couple things:

I determined the distance from crimp groove forward by measuring loaded rounds that work fine in my gp100. The large front driving band on the larger boolit may be an obstruction, I need to test a little more to know for sure. In short, I was working with .32" as my max protrusion from a 357 case.

Gear, what is meant by 'minimum angle'? I can easily draw the boolit with an angle at every location, but when do I specify a particular degree, and what should that degree be? Presumably, different at almost every location, but is there a rule of thumb for 'straight' edges?

For instance, I worked off of Lee's drawings of their tumble lube groove to determine the dimensions of the lube grooves on the 187 gr swc boolit. This was 26 degrees from straight, 0.04" groove width with 0.01" band between.

For supposed 90 degree corners, what is typical back-off? 2 degrees? And will the custom mold makers adhere to this, or just do what is easier? Or, to my chagrin, do exactly what I request?

[MT Gianni]

I get no leading with the 358429 or the 358156. I don't think that you need as much lube groove as you have shown in the top boolit.

[runfiverun]

it's a draft angle that will allow the boolit to come from the mold.
you have to use it for everything from fiberglass to lead.

you really don't need a lube groove any deeper than the height of the lands.
the riffle effect of the lube grooves is not applicable.
it works fine in water but lube is not alway's liquid [it has different stages],and you don't want it rolling around in there when it is.
this will cause cavitation and heat, you could also compress the air [created by the cavitation] or cause a dieseling condition.
it needs to flow along the cuts made from the rifling sealing any passages that the gas could follow,and lay down a friction barrier to prevent galling.
think about lube as ski wax.

[DrCaveman]

I get no leading with the 358429 or the 358156. I don't think that you need as much lube groove as you have shown in the top boolit.

Ok, fair enough, as I haven't seen any leading from my TL boolits anyway. Are you saying that I could just ditch one of the large lube grooves entirely, and maybe have a full diameter driving band instead?

I may be putting words in your mouth, but this seems to be where it's headed. Maybe I knock a few hundredths off the length to keep things around the 180-185 gr range, while getting rid of one large lube groove. Getting closer to Keith design.

[DrCaveman]

it's a draft angle that will allow the boolit to come from the mold.
you have to use it for everything from fiberglass to lead.

you really don't need a lube groove any deeper than the height of the lands.
the riffle effect of the lube grooves is not applicable.
it works fine in water but lube is not alway's liquid [it has different stages],and you don't want it rolling around in there when it is.
this will cause cavitation and heat, you could also compress the air [created by the cavitation] or cause a dieseling condition.
it needs to flow along the cuts made from the rifling sealing any passages that the gas could follow,and lay down a friction barrier to prevent galling.
think about lube as ski wax.

You said a lot here, I think. Not sure what you mean by cavitation, but I presume it has to do with creating pockets of air. It sounds like you see these as a bad thing, I will take your word on that.

Lube groove no deeper than lands... What boolit out there adheres to this standard? While I can understand what you are saying, I have owned no boolits or moulds which satisfied this measure. It kinda sounds like you are saying: the shallower the better!

Since I like my Lee TL boolits so much, I will not argue, but this seems to be in opposition to mainstream mould design. Am I missing something?

In any case I will modify my dwgs and put out some new ones tomorrow morning based on the critique.

Thanks for comments thus far.

[subsonic]

I am no expert, but here's how I see it.

You can TL any boolit, so your TL section is superfluous and gives up bearing surface while weakening the boolit for no good reason and making the mold more complex.

My personal feeling is that the lead used for driving bands is put to better use at the front of the boolit where it grabs rifling first and tries to strip, rather than at the rear where it is mostly just functioning as a piston ring. This will also affect bore friction, which relates to engraving pressure and speed.

I would suggest making lube grooves DEEPER than the rifling depth by at least .002" per side. You want to leave some room for displaced lead while not adding bore friction for no gain. I would try for around .8gr of lube on these boolits.

A lot of the guys that get great revolver accuracy tend toward several (3-4) narrow lube grooves instead of one big Keith type groove. But some report great accuracy with the Keith type groove too.

Your drawing states these boolits will be 187 and 194gr. Be aware that the GP100 has a 1:18.75" twist, which is fairly slow. You may have an issue here - do your homework on this by seeing what others are experiencing with similar weight boolits in GPs, or try an existing boolit at 100yds in this weight range. You may only get longer range (past 10yds) accuracy at top level loads. Be aware that the SWC style boolit is longer for weight than an ogival design like a WFN, WLN, or even a TC. This length may add to the twist rate required. If you plan to shoot living things with this boolit , you want to make sure it is VERY stable in air, because stability in meat is even tougher to acheive.

Others may say I'm full of BS. They are welcome to critique my statements - but these are things I would definitley consider before cutting this mould.

While re-invinting the wheel may be a fun pastime, there are reasons why existing wheels are round. Don't overlook the theory of KISS.

[nfg]

Mountain Molds has a very nice bullet design program that also has links to specific information on almost all aspects of cast lead bullet design and a good place to look for information is www.lasc.us with included links to other sources.

I'm new to casting also, but have been designing bullets and turning them from brass and wildcats for a LONG time...cast bullets have some particular areas of concern that are outside "normal" bullet design so spend some time working out those particular "problems"...all that data is well covered in the above two links.

Nothing wrong with reinventing the wheel considering the long development from wooden to modern rubber tires.

[DrCaveman]

Man, the more I tweak my drawings, the closer the boolits look to Keith designs. I'm beginning to feel that this is an exercise in futility. I was hoping to come up with something groundbreaking, or at least inspire someone else into a new innovation.

One main goal was the ability to fully utilize two types of lube, to provide a wider range of operating pressures. I guess those 'tumble lube grooves' are an uneccesary addition, since an alox-type lube will coat all surfaces of the boolit. And if I just try to make little grooves the entire length of the seated portion of the boolit, 2-3 thousandths deeper than the rifling depth, I am basically looking at a standard Lee TL design.

Am I wrong, or does liquid alox work better with shallow grooves? And conversely, wax/hard lubes work better with a bit deeper grooves? If this is correct, then why don't more mould designs use two sizes of lube groove?

[subsonic]

I think the whole reason the Lee uses small, rounded lube grooves is because they are easier to machine and also fill out easier when casting. Your reject rate will be lower on molds and castings.

But if you get the temps right and have some tin in your alloy, the castability factor is a non-issue.

There is a reason why almost everybody likes Keith and/or LBT style boolits.

If you want to innovate, I think the direction things are heading for the innovators does not include lead.

[turbo1889]

DrCaveman, I am a man who has already traveled at least part of the road you are considering going down. I will attempt to give you some pointers as I see them based on my experience thus far.

I have designed and am using a total of three hybrid boolit designs that use both Lee type tumble lube boolits and conventional lube grooves combined together on the same boolit design. Here are some pictures which are clickable links to the boolits in question (clicking on the picture will take you to the web site of the mold cutter who made the boolit mold for me showing a CAD view of the boolit with dimensions). They are in order of development and they all have flaws and things I learned along the way:

Hybrid Design #1 ~ 35-cal maximum weight thumper boolit for 38-spl./357-mag./357-max.
http://farm5.staticflickr.com/4151/5066836222_5cc846df9d_n.jpg (http://www.accuratemolds.com/bullet_detail.php?bullet=36-210C-D.png)http://farm5.staticflickr.com/4148/5094831259_5c105b3ecd_n.jpg (http://www.accuratemolds.com/bullet_detail.php?bullet=36-210C-D.png)



Hybrid Design #2 ~ “fat” 30-cal rifle boolit for 303-Brit./7.62x54R/7.7-Jap/7.62x39
http://farm2.staticflickr.com/1404/5222722086_ce2bf91c15_n.jpg (http://www.accuratemolds.com/bullet_detail.php?bullet=31-180B-D.png)http://farm5.staticflickr.com/4091/5222133243_357e8c36a0_n.jpg (http://www.accuratemolds.com/bullet_detail.php?bullet=31-180B-D.png)



Hybrid Design #3 ~ heavy weight 30-cal rifle boolit for 30-06
http://farm6.staticflickr.com/5184/5858723910_479017dcd2_n.jpg (http://www.accuratemolds.com/bullet_detail.php?bullet=31-216T-D.png)http://farm6.staticflickr.com/5226/5858172821_eeeb486471_n.jpg (http://www.accuratemolds.com/bullet_detail.php?bullet=31-216T-D.png)





Okay, now on design #1 I learned the following:
----- I had more “conventional” lube capacity then I needed and on most loads I had better accuracy if I only filled one conventional lube groove instead of both and there was enough lube and I didn’t get any leading but for some of the 357-max carbine loads I needed to fill both lube grooves because one was not enough to prevent leading but if I filled both although the leading at the end of the barrel went away the groups opened up a little because the boolit was “too slippery”.
----- The plain base worked fine for the 38-spl and most of the 357-mag loads but for some of the 357-mag loads and most of the 357-max loads a gas check would have helped as was confirmed by installing some thin pop can metal plain base gas checks that swag over the base of a plain base boolit in the sizing die.
----- For load data availability 210 grains was just a little too heavy. Not much load data for boolit weights over 200 grains and I would have had more load data to work from if the boolit had been just a little bit lighter since there are loads for 190,195, and 200 grain boolits that this boolit was just a little bit heavier then so reducing its weight by 10-20 grains would have been advisable for load data reasons.
----- The third drive band up from the bottom, the one directly above the upper conventional lube groove is too thin, narrow, and fragile and is crushed too easily when crimping in the bottom Lee type tumble lube groove directly above it at the base of the nose.

If I were to do it over again this is how I would change the hybrid boolit design #1 according to what I learned (original on right, improved to left):
http://farm6.staticflickr.com/5057/5434899198_9f151cd2af_z.jpg (http://www.flickr.com/photos/54455625@N04/5434899198/)

----- Capacity of the conventional lube grooves is reduced.
----- Base band is a gas check shank.
----- Length and thus weight of boolit is slightly reduced.
----- Thickness of third drive band up from the base is increased.




On design #2 I learned the following:
----- The problem with this design was the shape of the nose. I had originally specified the nose to be a flat tipped truncated cone shape with sharp crisp edges which although very accurate and effective on game was absolutely terrible for feeding. Not a single magazine gun I owned (disregarding the single shot break action 7.62x39) in the calibers in question would feed the boolit with the original nose shape from the magazine into the chamber without jamming up when that sharp end on the tip of the nose grabbing on any and every little edge in the guns action. They had to be fed into the guns chambers one at a time by hand. Other then that it worked great. The ultimate solution I arrived at to fix the mold I already had in my possession was to bore out the nose section on one of its two cavities with a 3/16” ball end mill cutter so that one cavity produced a round nose boolit profile. I also informed the custom mold cutter of the problem and he modified the design in his catalog (as you might have noticed when you clicked on the picture) so that the tip of the nose has a rounded edge instead of a sharp edge like it originally had.

http://farm3.staticflickr.com/2257/5721239538_ac495500eb_n.jpg (http://www.flickr.com/photos/54455625@N04/sets/72157626598172447/)http://farm4.staticflickr.com/3191/5720681663_fd100091e3_n.jpg (http://www.flickr.com/photos/54455625@N04/sets/72157626598175579/)

The resulting round nosed boolit produced by one of the two cavities on the mold now feeds no problem through all my guns including semi-auto SKS and AK-47 guns when loaded in the 7.62x39 cartridge. I got lucky though in that the angle on the nose along with the size of the flat on the nose allowed a common 3/16” size ball end nose mill cutter to match up so well to successfully convert the mold. If I were to do it again I would use a nose shape like found on the AM# 31-087T (Clickable Link) (http://www.accuratemolds.com/bullet_detail.php?bullet=31-087T-D.png) design which feeds very well and still maintains a 0.18” flat meplat on the nose for effective hydro-shock wave terminal ballistics and does not require a slow painstaking modification to be made to the mold after the fact.




On design #3 I learned the following:
----- The heaviest possible, longest possible boolit that will fit, feed, and be stabilized by the rifling of one’s gun is not necessarily the best choice for a cast boolit for big game hunting with cast boolits even though initial impressions may point that direction. The boolit is stable and accurate in flight when pushed to the top end of its velocity capabilities out to about 200-yards range. If shots at greater range are attempted and/or the velocity is reduced beyond a top end performance (for cast) load is used the groups open up. When the boolit strikes a living flesh and bone target it tumbles inside the chest cavity of the animal hit and does not hold true and punch through nose first all the way through. This has the desired lethal effect on both coyotes and deer but I can’t trust the boolit for heavier game like elk and although they don’t run far before lying down and dying I can’t help but wonder if a boolit that held stability better and punched through nose first in meat would make them “bite the dust” in their tracks right there where they were hit. A slightly shorter and lighter weight boolit or a gun with a faster twist rate in the barrel might produce better results.
----- There is a better and simpler way to do the DD rings at the base of the boolit tip at the end of the bore riding nose section (a triple set of them on this boolit). The small raised ring that engraves in the rifling is what is desired, forming a groove of smaller diameter then the main bore riding section in-between them is an unnecessary complication that serves no purpose. Just a simple raise ring (or two or three) is all that is needed like is used on the AM# 31-200N (Clickable Link) (http://www.accuratemolds.com/bullet_detail.php?bullet=31-200N-D.png) design.

[turbo1889]

Now, as to the specific theory or idea behind even using a hybrid design.

It is my personal belief that fit is one of the most important things for a cast lead boolit (and to a lesser extent a jacketed bullet as well) to obtain quality accuracy results. Specifically not only does the main body of the boolit inside the case neck need to be of sufficient diameter but in addition the part of the boolit that extends out beyond the mouth of the cartridge case should fit the throat of the gun and if applicable the lead into the guns rifling “like a hand in a tight fitting latex glove”.

That kind of perfect incredibly tight “hand in glove”, “zero slack”, “kissing gun metal”, “lightly engraving in the rifling” kind of fit is difficult to obtain with a purely conventional boolit design unless one makes a chamber cast or swaged throat impression of the gun in question and then cuts the boolit mold to fit that gun and that gun specifically and only with that kind of perfect fit between the boolit and the guns throat and lead into the rifling so that the boolit gets the best start possible into the guns barrel when the hammer falls and the powder is ignited.

Enter the Lee tumble lube groove profile. One of the biggest complaints about those little micro bands and grooves is that they are too fragile and squeeze down too easily. On some of the Lee boolits (a good example being their TL boolit design for the 9mm) just seating the boolit in the mouth of the case with the neck tension of the brass can squeeze down the boolits diameter a couple thousands of an inch which is enough to make a boolit which is the right size now be undersize and result in both leading and accuracy problems.

The idea is to turn this disadvantage into and advantage. What you do is make the part of the boolit that fits down inside the case neck with conventional full size drive bands and lube grooves that will hold their sized diameter and not get messed up and squeezed down by the neck tension or anything like that. But on the exposed nose of the boolit that is outside the case and fits in the guns throat you use the fragile little Lee micro sized tumble lube grooves and little micro bands and you make them oversize by a few thousands of an inch. Then when a cartridge that is loaded with such a boolit is chambered in the gun all those fragile little Lee tumble lube bands that are a few thousands of an inch oversize all squeeze down to fit the throat of the gun. Thus the simple act of chambering the round in the gun forms the boolits nose to exactly fit the guns throat and even lightly engrave in the rifling depending on the gun and the boolit design which may also use the tumble lube bands like the DD rifling engraving bands that Walt came up with many years before Lee even started making molds much less introduced the micro groove and band tumble lube profile. Because the drive bands are so much thinner all it takes is a minimal amount of force to chamber the round with those little bands on the nose squeezing down to fit the throat exactly and/or engraving in the rifling.

On a bolt action rifle you don’t even notice it unless you are really trying to use a pinky light touch on the bolt and feel for it. The semi-auto actions of the SKS and AK-47 slam shut and lock into battery without even so much as a hiccup and loading a revolver cylinder just takes firm thumb pressure to press each cartridge into the chamber the last 3/8” of an inch or so as the little nose bands squeeze down a couple thousands of an inch to tightly fit the throats of the chambers.






Now as far as tumble lube boolits that use only the tumble lube profile, tumble lube is a surface coat lube. It works just as well on a boolit that has completely flat sides with no lube grooves at all as it does on a boolit with tumble lube micro grooves and bands as far as lubrication is concerned. The little grooves are not there so much as to hold lube as they are there as “relief grooves” to give the lead that is displaced by the rifling somewhere to go. They are just like the little grooves in the sides of the Barnes copper solid rifle boolits and some other brands of monolithic solids that are lathe turned from brass or bronze rod stock. They do also grab a little bit of extra tumble lube with a wicking like effect but not much. And yes they do fill out well and are easy to cast with.

My main suggestion if you want to design a tumble lube only boolit that is to be cut for you by a custom mold maker such as Tom @ Accurate Molds is to simply modify the Lee tumble lube profile with slightly wider bands in-between the little grooves. Simply doubling the width of those little micro grooves from 0.01” wide as in the original Lee tumble lube profile up to 0.02” wide bands in-between the grooves makes a world of difference to make it far less likely the little bands will get squeezed down in diameter by the neck tension when you load them into the case mouth. There are many examples of tumble lube type boolits in the Accurate Molds catalog that use a groove profile that is nearly identical to the Lee profile but have been improved by having the little bands being made a little bit wider and thus not as easily squeezed down and hold their size better. A good example is AM# 36-140W (Clickable Link) (http://www.accuratemolds.com/bullet_detail.php?bullet=36-140W-D.png) and is only one of many that use this simple improvement of making the little bands a little bit wider on the tumble lube profile.

If you want the little bands to squeeze down easily as in using them on the nose of a hybrid boolit as I have explained then leave them as they are at a thin little band of 0.01” as used by Lee but if you are using them on the main body of the boolit inside the case neck and you need them to hold their diameter and not get squeezed down easily then double their thickness up to 0.02” you can even go a little thicker then that if you want but doubling them has worked great for me for when I want to stiffen them up.

[JIMinPHX]

+1 on radius and draft angle. The boolits won't drop from the mould unless everything, including the larte meplat, is angled. Note most boolit designs have a minimum angle on all things like the top of the crimp groove and even the front shoulder on the boolit.

Gear

Make that +2.

A lot of people like square bottom lube grooves because they like the extra lube volume that the corners provide. My experience has shown that most boolits, especially pistol boolits, are over lubed & a radius in the corners makes the boolits drop much more easily from the mold.

[geargnasher]

To answer the "minimum angle" question, at least 15 degrees from perpendicular. Radiused lube grooves are the way to go IMO regardless of what Elmer thought, and as has been mentioned most lube grooves are way too deep. I have a variety of pistol moulds (some I designed, some I didn't) that have lube grooves only .010-012" deep and that's plenty. I've also found that, by and large, two narrow, shallow grooves are better than one, deep groove.

Gear

[JIMinPHX]

most lube grooves are way too deep.

A good example in support of this statement is the little round nose boolit that you get out of a Lee mold for a 9x18 makarov. The lube groove on that thing is about 1/4 of the size that I see on most other 9mm or .38 cal boolits, but they shoot great for me & never lead my bore.

I suspect that as the bearing surface of a boolit gets longer, then the multiple lube groove locations become more important. This is just conjecture on my part though.

[turbo1889]

Black powder loads is where you actually need deep square like lube grooves that hold a whole lot of lube.

[nfg]

I think the only way to get from the bed to the coffee pot is one step at a time...unless you are just married and your wife isn't working...no diss or flame intended.

My point being...it takes a whole lot of heads doing a whole lot of thinking and a whole lot of testing to come up with what we think is de Rigueur today but will be "Duh" tomorrow.

I also think that if whatever you're doing has a commercial basis and most shooters being very conservative, hard headed, prone to paroxysms' and fits over very small "truisms", if you want to "sell, sell, sell"...whatever bullet you DO make needs to be very close to what is considered "the right stuff"...with just a few innovations for the "snowjob" effect.

All the diehard testers of the "lead and dead" crowd are learning the real story and TEACHING the rest of us what that story it's all about.

Everytime a newby or and oldie asks this question a whole 'nuther world opens up for someone with a really "new" idea and there is a chance of a new "truism" being born.

Since I started definitively "learning about lead" I bought a 45-70 NEF BC and rechambered it to 45-120 and a 50-90 Sharps just to "plink" at long range with big, long, heavy, cast lead bullets...I've done everything else that has happened in this sport over the past 50 years and was getting totally bored. This "lead thing" has got my blood boiling again.:bigsmyl2:[smilie=w:

I think this "new to me game" is totally awesome and GREAT and lots of new stuff will be learned in the comming years and maybe new types of lubs developed that require even fewer and smaller lub grooves.

There is NO such thing as "Static"...everything moves...either forward to new things or backward as it gets left in the dust.:!:

I have a problem with the first bullet I designed for my 625 HB, like Turbo did with his illustrated bullet, but mine was a "too long a nose" and too little meplat". As soon as my "CasterMan" finishes this run of bullets I will take the mold home and re-configurel the nose cavity with a 135°, 15/32 drill bit to just beyond the flat nose, then use a 5/8" mill to enlarge the cavity a bit more. This will give me a slightly pointed, 75% Meplat and more lead in the nose hopefully to correct the bullets going sideways into the target at 15 yds. I will draw it up in TurboCad so I can work out the actual added area so I can calculate the amount of added lead weight.

It will DEFINITELY look WRONG as far as conventional wisdom goes, but if it works...it works...if not the money was well spent...knowledge always has a price. Hahahahahahahahah

[turbo1889]

. . . I will take the mold home and re-configurel the nose cavity with a 135°, 15/32 drill bit to just beyond the flat nose, then use a 5/8" mill to enlarge the cavity a bit more. . . .

If you don't have your own machine tools I can tell you from experience that the hardest part of doing this kind of modification is keeping the cutting tool centered and being careful not to cut too deep and take out too much material by accident. Here is a link to the thread that catalog my experience with modifing the tip of my AM# 31-180B to a round nose profile with a 3/16 ball end mill cutter. Might be something in there that might help you with your modification project:

http://castboolits.gunloads.com/showthread.php?t=100420





The OP might also want to take a look over at Cast Bullet Engineering’s catalog. They have a few bore riding rifle boolit designs with micro grooves on the bore riding part like my AM#31-180B and AM#31-216T designs have on them on pages 11,13, & 14 of their catalog including their design numbers 285-145GC, 309-150GC, 309-168GC, 309-180GC, 309-225GC, 313-174GC, & 314-190GC. Basically a range of boolits to fit all the 30-cal and “fat” 30-cal rifle cartridges with one for the 7mm cartridges as well. Here is a link to the CBE catalog pages in question that include the designs in question:

http://www.castbulletengineering.com/page0051.html

[nfg]

Thanks, Turbo...I have a manual lathe, mill, 3-4 Jaw and lots of dial-in cooters, tools, TurboCad and all that jazz, but thanks for the link. I've drawn up the design from several angles and nose shapes. Not much room for error OR to work with, but centering the mold block is no sweat .

I did back off from the 5/8" bit tho'...that is larger than the bottom of the grease grooves...Geeze, talk about a brain phaught...and settled on a 33/64 drill bit.a One reason I do a LOT of drawing and modeling before I get what I want.

That will leave 0.150" of original truncated bullet taper and I only have to drill 0.0140" deeper...and I will use a 118° drill. I have some leeway there also...I can just touch the original meplat and leave it full, drill an additional 0.046" and have a small pointy tit ala Madonna or go the full 0.092" and have a full 118° nose and ~82% Mep. They ALL look different from the usual RN/FN profile but should shoot just as well.

I think all the gyrations prior to doing a project is almost more fun than doing the project, finding it did work, then have to start on something else. Hahahahah

[DrCaveman]

Turbo, I first have to thank you for the lengthy and helpful post. Glad to see that I am not the first to consider the "hybrid" mould design, and that it has had a few chances to work itself out before I spend money on totally experimental mould designs. Surely, if I do take the plunge and pay someone to make one of these moulds for me, I will figure out something I could have done better, but that is for the benefit of the next person in line considering doing what we do/have done.

http://castboolits.gunloads.com/imagehosting/thum_226994f976a55899a0.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=4940)

Here is my revised attempt, and I have tried to take into consideration several things mentioned. Most influential were:

-barrel twist rate. I had not considered that before, though I have been loading heavy boolits pretty hot and getting mixed accuracy results. Just one more item that I need to have in my noggin at all times when making ammunition choices. The GP100 twist rate of 1:18.75" does make the heaviest boolits less stable at a given velocity. While I cannot plug any remotely realistic numbers into any formulas I find that will indicate "unstable", I took this advice generally, and reduced the weight down to 175-ish.

-angles on all edges. This seems to have removed any true flat front, so Im not sure how the effects on a flesh target will differ, but hey if thats what I gotta do to make 'em drop from the mould, then so be it.

-Tuble-lube style grooves in front of intended crimp point. I really took Turbo's description of boolit swaging as is enters the leade and rifling to heart, and I will see how influential it is on the shooting of the boolits. It makes sense to me on multiple levels, and could explain why some people are anti-TL. I instead chose to increase the bearing surface within the loaded round.

-smaller lube capacity overall. I didnt double check this, but I am pretty sure that I have less lube capacity than the first two designs. A recent comment in the thread regarding new, improved lube technologies struck home, and it stands to reason that we dont need the capacity that black powder shooters or ELmer Keith did.

Part of my thinking about this boolit was that soft, easily liquified lube could be applied both front and rear, while a thicker, harder lube applied to the middle. Maybe the lube in front bands provides initial "greasing" while the lube in rear bands provides initial seal. As temps increase, the middle band of lube liquifies, and provides a continuous stream of lube for the rear of the boolit to remain sealed. Lube in front bands is long gone by the time the boolit exits the barrel, and the two rear lubes get mixed a little, hopefully cashing out right when the base exits.

I dont really know what I am talking about, but I appreciate the input and genuine responses to help me along. I hope that I am contributing something, but if not, I am definitely receiving something!

and NFG, no commercial basis here. Since my piles of boolits are growing waaaay faster than I can shoot them, the thought has crossed my mind to sell them, but at this point I doubt I would have any takers!

[subsonic]

Your front section of TL ahead of the driving band isn't going to do much for you. I have never seen a revolver with rifling in the chambers. Now, if you want to use these in a short-throated fixed chamber gun, that might be an advantage.

Notice how much lead you had to take away from your driving bands to make the TL grooves.

[turbo1889]

I'm going to partially, but only partially disagree with what sub-sonic has said. My AM# 36-210C has primarily been used in revolvers and that is what it was primarily intended for and the tumble lube grooves on the nose do help it to for to fit the revolvers cylinder throats with a "hand in glove fit". I size it to +0.0005 to +0.001 over the throat size of whichever gun I'm loading for and thus when the rounds are thumb pressed into the cylinder chambers all those little tumble lube grooves on the nose squeeze down just a little bit in the cylinder throats to fit them just as "snug as a bug in a rug" and fully fill the throats and be centered and in position before the hammer ever falls.

That said, it is also true however, that I have a lot more tumble lube grooves and a lot more bearing length on my boolit that is outside of the case and down in the cylinder throats of the gun. Far more bearing length inside the cylinder throats then any conventional jacketed bullet or cast lead boolit that I know of. In fact the nose of the boolit darn near fills up the entire cylinder throat of the gun and that is how it was intended from the start:


http://farm5.staticflickr.com/4150/5066225503_fe8f2754bf_n.jpg (http://www.flickr.com/photos/54455625@N04/5066225503/)http://farm5.staticflickr.com/4146/5066836760_021caa562e_n.jpg (http://www.flickr.com/photos/54455625@N04/5066836760/)

So I know it works for a revolver boolit intended to be used in a long smooth throat that puts a lot of bearing length and a lot of little bands outside the case and in the throat. But the question thus becomes whether a boolit like drawn by DrCaveman which has three little driving bands outside of the case and approx. 0.16" bearing length across them in the throat is going to work with the same principle of a "slight squeeze to fit" that is known to work with a boolit which has seven little driving bands outside of the case and approx. 0.36" bearing length across them in the throat assuming in both cases the crimp at the case mouth is formed in the bottom tumble lube groove.

Slightly less then half the tumble lube bands to support the nose in the throat across slightly less then half the bearing length in the throat. Is that enough to properly support and center the nose in the long smooth cylindrical throat of a revolver or not? That is the question.

If it were me realizing I have less of the little bands to support the nose in the throat and a shorter bearing length that is outside the case and in the throat I would probably go with a heavier (like approx. 0.04" to 0.05") drive band above a conventional short crimp groove and then put tumble lube grooves above that. Basically a little heavier band at the bottom of the nose right above the crimp like a conventional boolit has to make up for the fact that I didn't have as many of the little TL bands in the throat over as long of a bearing length outside the case in the revolvers throat. That does change the angle of the TC nose. I would personally still go with three bands on the nose (now being one heavy and two light instead of three light) which pushes out the bearing length of the nose slightly and steepens its angle slightly but you wanted to keep a steeper nose angle you could just drop back to one heavy and one light band on the nose.

A quick mod of the OP's drawing is below, his most recent proposed design to the left and then my two mods with a heavier band at the base of the nose above the crimp on the right. My personal preference bending towards the middle one of the three:

http://farm8.staticflickr.com/7277/6967831416_8495a848f1_z.jpg (http://farm8.staticflickr.com/7277/6967831416_8495a848f1_z.jpg)

Not saying it wouldn't work to "squeeze fit", "snug as a bug in a rug" as drawn with only three TL bands forward of the crimp and the throat but it isn't going to provide the same level of nose support in the throat that my boolit that I know works in revolvers does. At the same time though I fully realize that not everyone is looking for a big flat nose double-decker wad-cutter that is about as aerodynamic as a flying brick like I was and a lot of people aren't going to want a nose with that much bearing length built into it. So making a little heavier band at the base of the nose above the crimp and putting TL bands above that is probably a good compromise. Especially since most revolver throats have a slight lead in taper at the entrance to their throats for the first 0.05" to 0.10" of the throat forward of the case that is slightly larger diameter then the rest of the throat diameter so the first band forward of the crimp isn't going to squeeze down as much or at all as the little bands further up the nose so making that band heavier shouldn't present a cambering problem from a band that is too heavy to easily squeeze down like the little bands will.

As far as taper for edges in a boolit mold for lead:
----- For a meplat flat on the nose that is under a 1/4" you can get away with it being totally flat 2-3 degrees of slope is nice though.
----- For a meplat flat on the nose that is over a 1/4" you need that 2-3 degrees but you don't need more unless you get really ridiculous with like 1/2" and larger.

----- For a shallow lube groove that is not a radius-ed lube groove you can get away with 10 to 15 degrees of slope. For deep lube grooves 35 degrees of slope makes things a lot nicer.

[DrCaveman]

Turbo,

Thanks so much for the quick and informative reply. I will have to do some testing on my gp100 to see what the real deal is on the chamber throats. Considering that I do not have a nice micrometer in my possession, do you have any suggestions as to determining the rate of taper, or anything else relevant to the allowable boolit shape for my gun?

I can picture slugging the cylinders to an established depth (or, distance from end of cylinder) then measuring diameter, re-slugging a little deeper, and so on, allowing me to extrapolate a reasonably accurate curve. Since I imagine this could require 5-10 sluggings of each chamber, I gotta wonder if there is a better way that I am blindly overlooking. Would one slug, driven flush with the face of the cylinder, then knocked back out the backside, tell me what I am looking for?

Something in me wants to keep some semblance of aerodynamics, so I will probably not go as far as your double-ended wadcutters, but it is great to know that it worked, and may push me to comfortably add one or two more TL bands out front.

I notice you did not remove my rear TL grooves on your altered drawings. Do you think these are worthwhile, or unnecessary tooling complications which reduce bearing surface? They don't seem to serve any swaging function as do the front grooves.

[turbo1889]

DrCaveman,

Sorry I haven't gotten back to you until now. Up until now the last half of the week for me was like being a squirrel trying to cross the Indy-500 speed way during the race. Just managed to get across without being turned into a furry speed bump so now I can catch my breath and continue our discussion.





First of all, revolver throats, and gun throats in general. I drew up a quick picture of what a "correct" modern revolver chamber and a "correct" modern non-revolver (rifle, auto handgun, etc . . .) should look like:

http://farm8.staticflickr.com/7197/7127459481_bdd7a00c83_z.jpg (http://farm8.staticflickr.com/7197/7127459481_bdd7a00c83_b.jpg)

The revolver chamber is on the top of the picture with a non-revolver chamber below it. Both chambers are pretty much the same. At the end of the chamber there is a sharp edged lip usually something about a 75 to 80 degrees hard angle that is just shy of a 90 degree right angle to take up most of the wall thickness of the brass cartridge case at the mouth. This is followed by a small cone shaped lead in with a light angle of usually about 2 to 3 degrees. The basic difference between a revolver chamber's throat being that this lead in cone doesn't extend into the rifling since their is no rifling in the throats of a revolver.

When you slug the throats of a revolver to get the main diameter of the long flat sided cylindrical portion of the chamber throats in the cylinder. As you allude to the exact profile of the lead in cone and how deep it extends is a whole lot more difficult to determine. The truth is that you really don't need to figure out its exact profile though and it is a whole lot simpler then that.

Lets say for example that one had a revolver where when you slugged the cylinder throats (pushing the slug all the way through and out the front of the cylinder chambers) they all came out perfectly all the same at 0.358" on the mark and when you slug your barrel you find out that it measures a major groove diameter of 0.357" on the mark, and when you seat a boolit sized to 0.359" in a cartridge case it slips right into each of the chambers no problem with a nice tight fit without any wiggle room but still slips in easily.

Now all you guys out there who have actually measured the critical dimension on a lot of revolvers at this point are probably laughing at my example. Yes, I know that life rarely works out that perfectly but it makes a good example.

The next thing you would do is take a boolit, any boolit you can get your hands on so long as it has a good flat base and size it to your 0.359" sizing diameter and seat it in a dummy case upside down. Start with the back end of the boolit sticking out like a quarter of an inch out the mouth of the case. Then gently try it out in each chamber of the revolvers cylinder seeing if it will fully seat or not. It probably won't, most revolver throats aren't going to have a lead in cone depth that will allow a 0.359" diameter boolit to go a quarter inch deep down inside a throat that measures 0.358" for its main length after the lead in cone. So you adjust the seating die on your press to seat the boolit just a little bit deeper in the case and try it again. You repeat that until you find out what is the maximum amount that the 0.359 boolit can be sticking out the mouth of the case and fully chamber. At that point you don't know the exact profile or depth of that lead in cone but you have the information you need. Namely how wide you can make the big thick front driving band ahead of the crimp groove and the boolit will still chamber since that heavy band is fitting inside of the lead in cone. Any bands that are further out on the nose from there if they are going to be full diameter need to be the thin fragile little tumble lube bands that will squeeze down to fit.

This same process would be used to determine how long you could make the front driving band forward of the crimp groove on a revolver boolit design regardless of whether you were going to put smaller "squeeze to fit" tumble lube bands out in front of it or not.





Second, as to putting tumble lube grooves on the base as well. I haven't done that in a hybrid design and if you use a base first type lubra-sizer machine such as the Lyman, RCBS, or Saco machines your going to have a heck of a time putting conventional lube in the groove it is supposed to go in without also filling the tumble lube grooves below it as well. With a push through sizer that injects the lube at a specific point in the stroke like a Star or Mark-VI then it will be no problem. Which if you intend to tumble lube only for some loads and then lubra-size and tumble lube for other loads that need more lube that isn't necessarily a bad thing TL grooves can hold conventional lubra-sizer lube as well but usually it needs to be a hard lube that is tough and kind of elastic to hold in the little TL grooves without getting knocked off or wiped out of them. So far for all of the hybrid designs I have done I have put conventional lube grooves and bands on the bottom only and TL grooves and bands on the nose only. Sometimes I conventional lube only, sometimes I tumble lube only, and sometimes I do both depending on the load. The "squeeze to fit" action on the nose still works whether or not they are dry or have TL on them and the rigidity of the heavy conventional drive bands on the base of the boolit still hold up and don't squeeze down whether they are tumble lubed or have the grooves between the filled with conventional lube or not.





Third, as to tooling considerations. A lot of that is determined by who is cutting the mold for you and what method they are using. There are at least five major methods I know of that are used to cut molds that I know of and each has their own quirks as far as tooling is concerned.

It's almost 02:00 right now in my local time zone so I need to get to bed but I should have some more time tomorrow afternoon to discuss what I know of the various methodologies used to cut the mold cavities and what I know of the various tooling issues that result, or at least those I have encountered.

[nfg]

Check out ACCURATE MOLDS and MOUNTAIN MOLDS as to design limitations for their CNC type of mold making. Both list what they can and can't, will and won't make. You can also talk to the other mold makers or go online to their URL's for insights into their mold making.

While CNC machines can do wonders, the SIZE of the object and the machine tooling impact what can and can't be done...along with ecomonic considerations, some things just require an excess amount of "hand" work that add to the cost of making the mold

You have to also remember...there is a WHOLE lot of hot air as to what a "good" bullet actually is...go to any range and you can see all the various bullets being used, which ones actually shoot straight, etc...many of the most accurate go back a century or more as to the design. Hot air per se isn't good or bad, I'm not moralizing or dissing anyone...As Turbo is going to great lenghths to point out, some designs work best for revolvers, some for pistols, and some for rifles...and there are many bullet designs that work in several shooters.

Many times discussions on both lead and jacketed bullets filter down to nuances in arguments that really don't mean doodly...and it would take several lifetimes worth of constant development to see any difference...

In all this nuance of minutia we forget just WHAT the bullet is supposed to do and get mired in the molasses and can't move.

Just something to think about...where reality meets the ether. Hahahahahahah

[DrCaveman]

Turbo

Thank you once again for going above and beyond. Sorry for my lack of response, as I have been out of town and super busy this past week.

Since my last post I found a single cavity Ideal/Lyman 358429 at my local muzzleloading shop. I can't say that I have found a cooler-looking boolit than this one, and it took my casting and holding one in my hands to reach this conclusion. It seems to embody everything I was looking for, except the hybrid lubing aspect.

My mould has a slightly smaller front driving band, and a rounded grease groove, so I know it is not 'true' Keith design but I can also tell that the general design has a lot going for it. I am also able to crimp in the crimping groove in 357 mag brass with no cylinder issues (though it is pretty near flush with the front of the cylinder).

Unfortunately I havent shot it yet, but my hopes are high. I am going to take my sweet time with this custom design, but I think I have found a template from which I will restart my work.

I will try your backwards loading method to determine the max front band size, since that seems pretty important. Further, I am thinking that I could get away with a few TL bands in front of the Keith front band without causing any problems. Also could probably shrink the main grease groove a little bit, and shorten the whole boolit to maintain about 175 grains, and increase case capacity a little.

I really like the huge protrusion from the case with the 358429, and I hope to retain that at the very least.