I don’t want to burst your bubble on this but if I recall correctly all boat tail bullets have a 7 to 11 degree angle to them. An angle greater then 11 degrees will INCREASE the drag and I am not talking bevel base bullets either.
I am very interested in this project of yours and would like to see it come to a complete success with drop figures for long range shooting.
I knew about the 7-11 degree angles of your typical Boat-Tailed rifle bullets. In fact, before settling on the angle I put on
these Boat-Tailed Gas-Checks I actually measured the angles of a few different rifle bullets.
One of them was a Barnes X bullet. The angle on those types of Boat-Tails is right at 7 degrees. Another bullet was a pulled full-metal-jacketed bullet off of an old 303 british round. It also measured right at 7 degrees.
The other two bullets I measured the angles of were both A-Max bullets. Both the 155 grain and the 168 grain bullets had Boat-Tail-Angles of 18 degrees. Possibly 18.5 degrees if I measured correctly. (and I'm pretty sure I did)
On all the bullets I measured, the length of that "Angled/Beveled" section was just a fraction over 1/8" long. In that respect they all seemed to be the same.
The Angle I decided on was way steeper than any of the above angles; more like twenty degrees.
Why did I choose such a steep angle???? Because; if these new Boat-Tailed Gas-Checks turn out to be finicky enough that even the slightest imperfection would adversely effect their flight characteristics, then a steeper angle on the Boat-Tail should amplify any problems I run into and in theory, in theory, in theory help me pin-point the source of the problem.
I don't know if that makes any sense to anyone but myself. I don't know how to explain it any better than that right now but, I would like to reiterate the following.
"Bare in mind that these are just prototype components. Once I get everything working right I can then go in and refine and re-shape the dies."
With the 12L14 metal rod I'm now using, going back and re-reaming the angles on the Forming-Rod and the Forming-Cup is not as difficult as it may have been with the harder metal I was using.
Thanks for your input. It's good to know we're on the same page.
I shall return.
HollowPoint
Last edited by HollowPoint; 03-17-2013 at 08:16 PM.
You could also look at making it a rebated boat tail and make the gas check to look like a donut with a hole in it, with the boat tail section sticking through it.
My original plan with these Boat-Tailed Gas-Checks was to make them "Rebated Boat-Tail" Gas-Checks. The logic behind it was that the Beveled Tail ends of such a cast bullet without the Rebated section would direct the hot gasses toward the outsides of the cast bullets while moving through the bore. That "Rebated Section" would be what stopped the Hot Gasses from Gas cutting.
In my mind the Boat-Tail design I'm using now has the possibility of inducing Gas-Cutting where there might not otherwise be any with conventional Gas-Checks.
After tinkering with the dies I discovered that the angles I'd have to bend the Rebated Gas-Check Cups into in order to achieve the "Rebated Boat-Tail" profile was just to difficult for me to achieve. It would be easier to make a "Rebated Boat-Tail Gas-Check" for a bullet with a larger diameter because there's more material to work with.
HollowPoint
How about taking a regular gas check and punching a hole in the center just large enough for the boat tail to stick through.
The gas check is not for heat, the base of the bullet is not exposed long enough to melt the lead.
The gas check adds compressive strength to the base of the bullet right where it contacts the barrel, preventing it from being distorted from the gas pressures while maintaining accuracy at a higher pressure.
Originally Posted by Doc Highwall
I think we might have apposing views about wether such a setup, with the Beveled Cast Lead Tail being exposed to the heat and the pressure, would be distorted enough to negatively affect accuracy. I believe it would. Remember, the tail end of a Boat-Tailed cast lead bullet would be a smaller diameter than the body of the bullet.
I picture in my mind the corner edges of the smaller tail end of the bullet being battered by the hot gasses and particles pushing it along. Regardless of how short the time of exposure, I see it as an instant loss of symmetry on the tail end of the bullet.
There's no way I could prove it. It's just how I envision it transpiring.
HollowPoint
The big problem would not be the making and shooting the bullet, but the recovery of an undamaged bullet to see actually what happened to it would be.
I agree. Although I have seen pictures of recovered cast bullets posted on this forum showing the various amounts of deformation at the tail ends of flat bullets.
The deformation was caused not only by hot gases an pressure but, by other contributing factors.
HollowPoint
I've had a week of sporadic small jobs this week that gave me time to go back and tweak a few things in the design of these Boat-Tailed Gas-Checks.
I'm afraid I made the mistake of doing a fair amount of additional research on Boat-Tailed bullets in general which lead me to change the angle of the bevel that makes up the Boat-Tail end of my cast bullet.
The actual change was strictly to the angle of that bevel. I went from 20 degrees to 11 degrees. Eleven-degrees being the middle ground; so to speak.
That "research" I mentioned turned up several different numbers concerning the optimum angles that a given Boat-Tail Bullet should have. They went all the way from a low 7 degrees to as steep as the 18.5 degrees I measured on the Hornady A-Max bullets. (these are all for 30 caliber rifle bullets)
I also tweaked my final forming die to the same degree of bevel so once the Gas-Checks have been installed I can then press them into that forming die to give me a more uniform angle-shape on the finished Boat-Tailed Gas-Checks.
Yesterday I turned my latest candidate for the bullet design that I'll be using to wear these new Boat-Tailed Gas-Checks. I was going to use one of the two others I'd turned on the lathe but they were made with a twenty-degree bevel on the tail ends. This latest cherry now has the newer 11-degree bevel. All that's left to do on it is cut the flutes.
There was an upside to going to the 11-degree bevel. I found that with the 20-degree bevel that I had incorporated previously, the checks came out generally uniform but, if I looked real close, about one in every five Gas-Checks were slightly lop-sided. I believe this was due to the diameter on the end of my Forming-Rod being so small. As it lifted the check up to form the Boat-Tail cup, it must have been shimmying to one side or the other just enough to cause it to produce an non-symmetrical Gas-Check.
With my little chinese made bench lathe, it's hard enough to maintain any kind of accuracy as it is so, even a slightly lop-sided check was sure to throw a monkey wrench in the works. Everything has to be as close to perfectly concentric as I can get it. I believe that any problems I may encounter will be due to machining inaccuracies.
With the larger diameter of the 11-degree bevel I'm now getting consistently uniform Boat-Tailed Gas-Checks. Hallelujah!
I'll be back later to post a pic of that latest cast bullet cherry. (without the flutes)
HollowPoint
Last edited by HollowPoint; 03-23-2013 at 10:30 AM.
HP
I want to applaud your work and effort. I believe there is a market for a boat tailed cast bullet. I purchased the 311365 GB for long range .308 practice. Adding a boat tail would provide an increase in effective range.
Should your concept work (and I think it will), it should be possible to add a spacer to a normal mold and use a modified cherry with the same profile as the mold but fluted only for the boat tail to cut the spacer plate. This would permit any existing mold to be converted to a BT design. In fact, it may not even be necessary to have a full length cherry. It may only require a tool to cut the BT profile on the spacer. Of course, the spacer would be attached to the mold blocks with screws. This would afford the use of the same mold for both styles of bullets.
In fact, there may be interest in a mold that normally produces a plain base "plinking" bullet of say 160 gr - then by changing "spacers" one could produce a 170 gr normal GC bullet and have another "spacer" for a 180 gr BTGC bullet.
Again, very good work. Pushing the envelop is how we learn and improve.
Well Done!!!
dverna:
If I am thinking correctly if you add to the bottom of an existing boolit mold to make it an boat tail boolit you would have to start with a nose pour mold????
If the boolit was poured from the base then the sprue cutter would have to be moved to allow for the difference on the top of the mold????
It sounds like an interesting idea though.
NRA Life Member
When you add say .200" of material to the top of the mould you just mount the sprue plate on top. The only problem is the original mould block is drilled and tapped for the screw that holds the sprue plate will need a longer screw by .200”.
Thanks for the vote of confidence. What you've stated makes sense to me. In fact, if you haven't already, some of my previous replies and pictures show that this is basically what I've been using as a loose guide as I've developed this project.
My only hinderance has been the inaccuracy of my metal lathe.
I believe that the specs for the NOE 311365 group buy bullet are available online but, I am unable to keep such tight tolerances with my setup so it would be difficult for me to make a Boat-Tailed cherry of any kind that was based on those exact specs.
That last cherry in the pic above had to be made by eye-balling it to the general dimensions that I was looking for. It's strictly for testing purposes. Even then I wasn't able to shape it directly on the lathe to its final profile. I had to turn it to just slightly larger than the .311 diameter and then do the rest with fine metal files and emery cloth. It's as concentric as I could get it and I think it will work for its intended purpose but, I wasn't able to make it like one would if they had an accurate lathe and the experience to do so.
I've been praying to God for the money to buy a CNC lathe. That would certainly simplify things for me; as long as that CNC lathe had the accuracy.
I've also had that last turned cherry set up on my fouth-axis just waiting for the free time to mill the flutes. The actual mold blocks have also been set up in the Self-Centering Vice on my manual bench-top mill. I may have time tomorrow. It just depends on my work schedule.
Thanks for the input.
HollowPoint
Last edited by HollowPoint; 03-26-2013 at 08:50 PM.
I got a chance to mill the flutes on my latest Cherry candidate on Tuesday while I waited on a customer to drop off his Model-A.
The first flute was cut without a hitch, then when my 4th-Axis spun to the next position something went awry. My CAM-software must have spit out some bad G-Code because my end mill started cutting a little short of where it was supposed to cut. Funny thing is that I run computer simulations of my tool paths to confirm that my cuts are correct. I must have been holding my mouth the wrong way when I set the part up on my mill.
I let it run thinking that since I was cutting three flutes on this Cherry I could still get it to work with two out of three correctly cut flutes. I'd simply grind the rest by hand so that I had a sort of semi-D-Reamer instead of the three-flute Cherry I originally intended.
It looked good so I heat teated it like I normally do and attempted to cut my mold cavities. Son-Of-B!+¢⧦!!!I caught it before I completely ruined my newly made mold blocks.
The friction that was generated by trying to cut that first mold cavity turned that D-Reamer/Cherry into a cork-screw looking mess.
I'm going down tomorrow and pick up a length of 0-1 Drill Rod so I can do it all correctly this time. I hate having to do things two or three time before I get it right. I should be used to it by now but, I'm not. I've never had that happen before with a Heat treated Grade-8 bolt reamer.
Because of the shape of this bullet (large in the middle and two different smaller diameters at either end) I can't pre-drill the cavity to minimize the amount of cutting that my Cherry has to make. With this bullet profile, the Cherry has to cut nearly the entire profile of the bullet cavity. I'm not an experienced enough machinist to do it any other way. Heat treated tool steel should do the trick for me.
This will be my first time using a Drill Rod of any kind to make my Reamer/Cherry. I've done enough reading up on it the last couple of evenings that I think I have it figured out. Hope everything goes as planned. I'm real close to completing this project. Making that specialty bullet mold is the last thing on the list before I can go out and test fire a few of these Boat-Tailed Gas-Checked bullets.
I opted not to test fire the previous bullets I cast because I was afraid that to many of them may have been non-concentric at the tail end. Few things can be more disheartening than failure on a first attempt. It's best to wait till I get all my ducks in a row and quacking the same tune.
I was going to post a picture of that cork-screw looking D-Reamer/Cherry but it would have been to embarrassing for me. I'll save it for when I can post some pics of my finished bullet mold and a few cast bullets out of that mold. That way the positives will divert your attention from the negatives of such a project.
I'll be back.
HollowPoint
Last edited by HollowPoint; 03-28-2013 at 08:21 PM.
Just to much of a darn hurry.
For the last couple of weeks I've been swamped at work. Today I got a few hours of free time so I quickly set up my latest Cherry on the mill.
I ran my computer aided tool-path simulations before hand and everything looked good.(on the computer I mean) Everything looked good until my end mill reached the end of its first pass on the mill. Apparently I hadn't set my "Safe-Height" quite high enough so when the little quarter-inch end mill moved back to its starting position it crashed into the top of my newly turned Cherry.
The cutting end of my expensive 1/4" coated-carbide end mill was demolished and there was now a huge gash on the top of my Cherry. Thank God for the Emergency-Stop on my mill.
I went back into my CAM software and tweaked the "Safe-Height" then I generated some new G-Code.
I had left that unfinished Cherry still set up on the mill. I just loaded the new G-Code and let it ride. Now everything was cutting perfectly but I also now had a five-flute Cherry that was missing one of its flutes.
Now I have to turn another one as close to the dimensions of this damaged Cherry before I go through the process of heat-treating and then tempering it.
I did have another Cherry on standby just in case I screwed up this attempt as well but, that "Standby" Cherry isn't really what I want to use as my first Test-Bullet Cavity-Cutter for my Boat-Tailed Gas-Checks.
It wouldn't be so much of a hassle to turn another Cherry if it weren't that I have to do it by eye-balling it. They never come out exactly alike. I just have to get it as close as I can to the profile of the previous one so that I can use the same G-Code to mill the flutes.
On an up-side; the 5/16" 0-1 Drill Rod I'm using sure is a breeze to cut on the lathe. That's because it's already close enough to the finished diameter that all I really have to do is form the beveled tail end and the nose profile. I'm hoping it will be just as easy to harden and temper.
Here's a pic of the Cherry I screwed up today. In an effort to deflect some of the machining-shame I've also included that previous "Grade-8 Semi-D-Bit" Cherry I mentioned in my previous post. I figured it would be good for a laugh.
I'll be back once I get some more free time.
HollowPoint
Last edited by HollowPoint; 04-03-2013 at 07:12 PM.
I'd get with Oldpara for this kind of help. With his expertise in the CNC business I bet he could whip out a mold in no time.
Slim
JUST GOTTA LOVE THIS JOINT.
Yea, you're probably right.
There are lots of guys on this forum that could do in a couple of hours what it takes me several attempts to complete but, if I had them helping me then I would'nt learn as much.
I prefer the idea of completing my own projects and not having to rely on others to finish them for me.
Something that generally doesn't come across when I come on and post my mishaps or mistakes is the learning that takes place because of them. I know that with all the machining mistakes I've made since taking up machining as a hobby, I should be a freaken-machining-genius by now.
It doesn't matter as much to me as it does to some folks. I learn what I can in the time I have to do so.
What I've learned so far? I've learned that when I get in to much of a hurry, mistakes happen; yet, I'm still always in a hurry.
I include my mistakes on purpose. There's lots of guys here that have dreams and ideas of their own who never make an effort to bring them to fruition. I mean, Ground-Breaking ideas that every cast bullet guy could benefit from but, because there seems to be a prevailing assumption that you have to be someone who doesn't make alot of mistakes in order to bring such ideas into being, we'll never seen any of these "Ground-Breaking" ideas.
The mistakes I make could be considered failures if I were to stop at that point in any given project. If I keep on going, those mistakes and/or failures become just another rung in that proverbial "Ladder Of Success."
HollowPoint
Last edited by HollowPoint; 04-05-2013 at 10:26 AM.
Hollow point, any chance you could make a video of the cherry cutting the mold? How do you have your machine set up to cut the block with the cherry? I am not a machinist, but I would love to learn. I applaud your efforts!
With a typical flat base cast bullet mold I would generally pre-drill my cavities with a drill bit just a bit smaller than the actual diameter of the bullet in question. Then I'd go in with my Cherry and basically ream out the cavity to its final shape.
For me, this is done by using a self-centering vice. I just position the Cherry at the correct depth on the mold and carefully close the mold down around the Cherry as the Cherry is spinning.
That's basically the same way I'm doing it with this present Cherry as well. The slight difference is that because of the nose end and the tail end of my bullet design being smaller than the belly of the bullet, the "Pre-Drilled" hole can only be as big as the diameter of the tail end of the bullet.
This means that the bulk of my mold's cavities will have to be reamed/cut to final shape by my Cherry rather than by the "Pre-Drilling."
The mold blocks are cut on my CNC mill. The actual cavities are cut on my little harbor freight bench-top mini mill that I've had for the longest time. There's no real complicated science to it. Even so, I still make my share of mistakes.
I don't own a video camera. I kind of wish I did. I'll check with the relatives. Maybe one of them has a video recorder they can loan me.
HollowPoint
Thank you!
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| BP | Bronze Point | IMR | Improved Military Rifle | PTD | Pointed |
| BR | Bench Rest | M | Magnum | RN | Round Nose |
| BT | Boat Tail | PL | Power-Lokt | SP | Soft Point |
| C | Compressed Charge | PR | Primer | SPCL | Soft Point "Core-Lokt" |
| HP | Hollow Point | PSPCL | Pointed Soft Point "Core Lokt" | C.O.L. | Cartridge Overall Length |
| PSP | Pointed Soft Point | Spz | Spitzer Point | SBT | Spitzer Boat Tail |
| LRN | Lead Round Nose | LWC | Lead Wad Cutter | LSWC | Lead Semi Wad Cutter |
| GC | Gas Check |
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