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View Full Version : Rounded base ...like bevel base?? Am I too picky



10mmShooter
07-17-2010, 04:33 PM
:veryconfu

Okay guys am I just being too picky???....and does it matter??

Pictured below are 6 samples of my 10mm RCBS 180g Flat Nose, they are positioned upside down so the we can discuss their bases. From the LEFT we have 3 samples that show slightly rounded bases, the 3rd one from the left being the most rounded. The samples on the right are what I consider acceptable and do not exhibit any rounded bases very sharpe edges on the bases.

I've shoot both types no difference in accuracy at <25yrds and no leading in either case. Charge is 7.4g of AANo5 at roughly 1000fps

So should I care about the round bases?? And how are the rounded base any different than the actual beveled base bullets. Seems to me they are really the same, because the bevels are simply beveled to improve bullet seating to avoid shaving lead.

Normally while casting I pitch the rounded base ones in the reject pile to recast, some slip through and this what prompted the question. I normally reject them while lubing and final inspection before loading on the 650.


http://www.keithrussell.net/roundbase.jpg

randyrat
07-17-2010, 05:04 PM
I don't think you'll find much lack of accuracy in a pistol boolit with a slight rounded base... Now if your talking long range rifle boolit, if they ain't perfect you would see a difference in accuracy in long range shooting.

Blammer
07-17-2010, 05:23 PM
I have found that sharp bases on my pistol boolits matter at distances past 25 yards.

I shoot at 50 and 100 yds with my 44 and 41 cal and rounded base boolits don't do nearly as well as the good square base ones.

From my perspective, no you are not being too picky!

Cherokee
07-17-2010, 07:34 PM
You've already answered your question - you can not tell the difference in accuracy. Longer range as said, diff would show up. I shoot rounded bases all the time but 3" @ 25 yd is norm for me now days.

canyon-ghost
07-17-2010, 08:41 PM
I'll second what has been said, you don't shoot the 10mm past 50 meters. The more distance, the more it would show, 100 meters and you'd see quite a difference in groups. Although, to a guy shooting an automatic, 100 meters seems extreme. I shoot 32-20 in a TC Contender to that distance, also other calibers. Some, I don't shoot that far and it does make it more difficult to tell any change at all. I immediately miss my scopes and distance.

It's all the type of shooting you do-
Ron

softpoint
07-17-2010, 09:24 PM
The only one I might reject would be the #3 on left. Some mixes of alloy that are perfectly good for pistol bullets just will not cast perfectly razor sharp edges every time. But those boolits are fine.:coffee:

Echo
07-18-2010, 02:30 AM
If really anal, re-melt the ones on the left. If only partially anal, use them for plinkers or practice.

(You must be some anal, to have asked the question)

geargnasher
07-18-2010, 02:50 AM
Just make a bigger puddle on the sprue plate and they'll all be sharp!

I reject rounded bases on everything, but that's cuz I have an OCD!

Gear

Bret4207
07-18-2010, 07:30 AM
Yup, what Gear said and cast a little faster. Hot moulds make good boolits.

The difference between a rounded, incompletely filled base and a BB is consistency. It will show in the best loads, best guns, best shooters even at short range. At longer ranges it really shows. Not being a fan of BB designs i will point out you can get rounded, incomplete BB too, but it's harder to see.

qajaq59
07-18-2010, 03:09 PM
One thing that really helps accuracy is consistency, so being picky is a PLUS!

mdi
07-18-2010, 03:50 PM
"Being picky" is a matter of opinion. The bullets you show are not completely filled out. Tin, temperature control , and casting speed can all improve the boolits poured. I personally like the sharp edges on the boolits to be just as sharp as the edges in the mold, but, I enjoy casting, don't have a quota and I'm casting boolits for me so I can be as "picky" as I want!:wink:

geargnasher
07-18-2010, 05:09 PM
I come from the school of "If something is worth doing, it's worth learning to do a well as you possibly can".

Again, just my opinion.

Gear

qajaq59
07-18-2010, 05:38 PM
I always figured that if I wanted bullets that were almost right I could go to the store and buy them. But to each his own.........

243winxb
07-18-2010, 06:33 PM
Sizing in a die or in the barrel makes them look better.
I've shoot both types no difference in accuracy at <25yrds and no leading in either case. Proof is in the shooting. Now test at longer yardage and report back.

45r
07-19-2010, 12:41 AM
Put the nozzle almost all the way in the sprue hole and pressure pour till you see lead start to spirt out lower mold and pour a big sprue with the mold leaned to the side so it doesn't go in the other hole.Get the second sprue big and overlap the first to keep sprue plate hot.Cut the sprue soon as it hardens.Keep the mold hot with fast pouring or high enough alloy temp,If the mold gets too hot cool it with fan cooling or pat top and bottom on wet towel.The inside seam area will start to shrink and get grey sometimes when mold is getting too hot.I like to use around 3 percent tin for better flow and fillout.Your bases should always be sharp.The right 3 would be OK for a gascheck boolit.I would recast the left 3.

mooman76
07-19-2010, 08:15 PM
I don't mind slightly rounded boolits as long as they are rounded even all the way around. I also agree that at 25 y or < you won't see any noticable accuracy loss. Lifes to short to be that picky but if that's what you or anyone else wants then go for it.

HeavyMetal
07-19-2010, 08:51 PM
I garontee if you load the boolits on the left, say 50 rounds, and then 50 of the ones on the right and go to a machine rest and fire 20 or 30 5 round groups you will see a difference in group size as well as group shape!

About now everyone is gonna say group "shape" ?

Yeah group shape! This intails a lack of vertical stringing, possible "short" flyers anything that makes the group seem not symitrical.

I realize this sounds wierd but a load that shoots a nice round group is going to score better long term!

This means boolits that might have been a 9 are now 10's because they are grouping symitrically.

I've seen a lot of groups in gun mags that were 2 inch at 50 yards, but the group itself was oblong in some way.

The base of any boolit is critical as to how straight it flys. The boolits you show on the left will perform just as if you had a damaged crown on the barrel, you'll get some flyers maybe some lite stringing maybe a shot out of the group by 1/2 inch or so.

Suffice it to say I want the best ammo I can make when I shoot for score and the stuff on the left would not pass Q.C. at my place and would never get to the lube sizer let alone near the Dillon.

I have had, and still have, this issue with casting. My cure has been to heat the mold, on it's side, on a hot plate, with the sprue plate in contact with the plate that I use to keep the mold warm.

My theory is that rounded base's don't come from having the mold to cold but from having the sprue plate to cold!

The proof of this is in the casting. Using two 6 banger Lee molds I have reduced the reject rate in my castings greatly since I started turning the molds on thier sides during rotation on the hot plate device!

Hope this makes sense to you guys.

casterofboolits
07-19-2010, 10:39 PM
Looks like your sprue plate may be too tight. Loosen the sprue plate a bit and the bases should should square up. Also make sure you have plenty of lead on the sprue plate.

44man
07-20-2010, 11:34 AM
Pressure pour is a myth. It does not matter if a ladle is half full or full or the whole pot is full of lead or half empty with bottom pour.
What counts is if the bullet when shrinking can pull molten lead in from the ladle or spout and NOT THE SPRUE. Ignore sprue size, it means zero and if you get a huge divot in the sprue, you have cast wrong.
My bases are so sharp I cut the rag when wiping lube from the base.
Pouring fast and trying to have a boolit pull lead from the sprue is silly because it sets up faster then the boolit in the mold.
Sprue plate tightness also has nothing to do with base fill out. It should be adjusted for each mold to lay flat on the mold top, nothing more or less. Some need tighter then others and if you see light between the blocks and plate, change the tightness. YOU SHOULD NOT SEE LIGHT IN BETWEEN THEM.
Speed casting makes more bad boolits then anything. Why would you cast 200 boolits and throw half back in the pot when I make 100 perfect boolits without a singe reject? Who is farther ahead?
Speed casting is like speed loading where you jam boolits in the brass so fast it shaves lead from the boolits.
Casting perfect boolits is so easy it can't be explained and it is NEVER to see how many you can dump in a short time. 100 perfect boolits is always better the 100,000 scrubs.
How I wish I could have all of you here. I would show you how to relax, slow down, make perfect boolits from ANY mold and shoot better then you ever could.
There is no magic or special process with any mold. It is plain and simple logic with a mechanical system.
Casting is so easy and no different with steel, aluminum or brass molds. Only the alloy governs the lead temps with softer needing hotter. A million posts telling you what you have to do and I will cut it to ONE post. If something is not right I can change it before the next boolit and all of you should too. There is no excuse to keep pouring bad boolits.
My confession is that I can not bottom pour without trouble so I plug the hole. It is not worth the trouble.

montana_charlie
07-20-2010, 12:55 PM
Round corners on the base occur when air cannot vent between the sprue plate and the top of the mould blocks.
It happens when the sprue plate pivot screw is too tight, and it occurs when you hold too much pressure on the sprue plate with your ladle (or bottom spout) while the bullet solidifies.

If you simply must keep the plate down tight, break the top corners of the block faces to create a vent groove for the escaping air.

If a base corner 'looks' rounded, it is badly rounded.
It is not a 'square' corner unless it feels sharp when you drag your finger over it.
If it looks square but doesn't feel sharp, it's a rounded corner, too.

CM

fredj338
07-20-2010, 01:54 PM
The proof is always in the shooting. The only issue I would have is if the base rounding isn't uniform. If it's more rounded on one side, it will throw as a flyer.

Down South
07-20-2010, 05:05 PM
I'm picky, round base boolits go back in the pot. I really don’t have any problem with round bases once everything is up to temp and my alloy is right. I usually just throw the first few castings back in the pot. After that everything is honkerdory. Like 44man said, casting is easy once you get a few basics down.

oldtoolsniper
07-20-2010, 05:26 PM
What would be the difference in a round base and a bevel base? I know it is the mold design, I am talking shooting wise? Seems to me they are one and the same as far as gas cutting and flinging boolits willy nilly all over the target.

Recluse
07-20-2010, 06:29 PM
I'm FAR more concerned and picky with the bases on my boolits than I am the noses. A rounded base goes right back in the furnace. I don't even think twice about it--back it goes.

Why go through all of the work to clean your brass, deprime it, size it, prime it , measure your powder, etc etc only to put in a less than perfect boolit? And perfection IS something we, as boolit casters, have control over.

:coffee:

Down South
07-20-2010, 08:20 PM
A rounded base boolit most likely will not be uniform at the base due to poor fill out. If it is rounded a little more on one side than the other, it causes a problem when the boolit leaves the barrel. The side with "more round" will have a pressure release on exit on that side compared to the "less rounded side causing the boolit to cant. It's the same difference as having a bad or damaged crown on the barrel. The boolit needs to have a uniform pressure release around the circumference of the base of the boolit on exit of the barrel for the best accuracy.
Hope this makes sense!!!!

oldtoolsniper
07-21-2010, 01:22 PM
Perfect sense! Thanks!

fredj338
07-21-2010, 01:43 PM
What would be the difference in a round base and a bevel base? I know it is the mold design, I am talking shooting wise? Seems to me they are one and the same as far as gas cutting and flinging boolits willy nilly all over the target.

Like I said, if the base is uniformly rounded, probably not an issue. If the base is more round on one side than the other, it will likely throw a flyer.

Elk Country
07-21-2010, 02:22 PM
Rounded bases used to get rejected because I sized and lubed with a Lyman 450. Sizing a rounded bullet in the Lyman was a PITA cause the rounded base acted as another lube groove. Now I use a STAR and rounded or flat, the STAR doesn't care!!! STAR's RULE!!
ALL of my cast bullets are used for plinking so I don't care if they shoot 1.5" groups at 50yds.

Elk Country

mpmarty
07-21-2010, 02:26 PM
Quit looking at the cast boolits as you drop them from the mold! That is a waste of time and allows the mold to cool off too much. I cast steadily until the pot is more than half gone and then add ingots and look over the boolits while the pot melts again. Your boolits on the left may well be due to your messing around looking at things while the mold cools off.

45r
07-21-2010, 06:10 PM
Lots of good info hear.I use a rcbs bottom pour and don't completely cover the hole so it can vent and I drag an aransas stone across the top mold block face to get a little vent line under the sprue plate.I let the sprue be able to pivot on its own when turned sideways.I think loose is better than too tight.With a little tilt and barely touching the plate with the nozzle it heats the spueplate while the lead is flowing into the cavity and when you keep it there momentarily while lead starts to pour over the side it has plenty of time to draw and make a big sprue when you lower and level the mold.Sometimes you can see the sprue suck down before it hardens.Sometimes it doesn't.I don't think you have to cast at a fast heavy pour rate to make good boolits but the mold and plate makes perfect boolits when they are hot enough.Better to be a little hot than cold and its easier to me to keep a mold hot by using 1 mold.I got to try ladle casting,It seems like it is a lot easier to get perfect boolits.You can make a lot of boolits fast with a bottom pour but you have to cool the mold with fan or wet towel to keep a iron mold from getting too hot when using one mold.I can get a few hundred sharp base boolits within a few hours even with a single cavity.Actually they can be easier because the middle doesn't get too hot like a 2 cavity.I wish somebody would make a perfect boolit fillout article,book or something.When the boolits are filled out perfect with sharpe bases everything is great,anything else seems not good enough.

AZ-Stew
07-21-2010, 08:46 PM
What Down South said.

Rounded bases are NEVER uniform, either on the same boolit or within a batch. They'll shoot cr@ppy compared to boolits that have square (sharp) base corners. Took me a long time (thick head) to figure this out. And, NO, they're not the same as a properly cast bevel base. Square corners shoot best, BBs shoot worse, rounded base corners shoot really bad.

Regards,

Stew

West Creek
07-21-2010, 10:13 PM
I think 44 man has identified what I find to be true. By the time my lee 20 lb pot is 2/3 empty I am pouring the best bullets - less pressure slower pour rate and I get perfect bullets. melt and mold are at a good temp - I always hate to quit to restock the pot because everything is going so well.

Dannix
07-21-2010, 11:08 PM
Talking just aerodymanic here, fill out et al regardless, I read somewhere, here I believe, the slower the speed and particularly once you hit subsonic, the more bullet base starts to matter. I can see how a good sharp edge would make the difference the previous posters have mentioned.

Came across this the other day. Just thought I'd share. I wish he had a shadow photo of a rebated boat tail for comparison.

Edit: There's some really cool, geeky stuff at that site. My mind started going mushy after reading just some of it. I'm putting it on my to-read list. Will take a while. :)

source (http://www.nennstiel-ruprecht.de/bullfly/micro.htm)
http://www.nennstiel-ruprecht.de/bullfly/fig2.gif
A .308 Winchester (7.62 x 51 Nato) FMJ bullet traveling at approximately 2800 ft/s (850 m/s). Note the change in flow type from laminar to turbulent at the bulletīs cannelure.

http://www.nennstiel-ruprecht.de/bullfly/fig3.gif
A 9 mm Luger FMJ pistol bullet, moving slightly faster than the speed of sound

http://www.nennstiel-ruprecht.de/bullfly/fig4.gif
A cal. .32 ACP (7.65 mm Browning) pistol bullet, moving at a speed considerably below the speed of sound. Only turbulences (the wake) can be observed behind the bulletīs base.

44man
07-22-2010, 07:34 AM
It would be interesting to see a WFN at about 1700 fps.
I have always said the pressure wave at the nose will move tissue in a deer out of the way into a secondary wound channel that collapses if the boolit is too fast. Be nice to see the wave.

Bass Ackward
07-22-2010, 08:11 AM
Wanted to watch where this went.

A lot of times, this is the reason for large diameter bullets shooting well. If you mold it poorly or load it and shave or reduce down, you can still end up with a fairly square base if the bullet sizes down enough with pressure on the base to square it up. Another reason that many older PB designs had wide rear drive bands so the C of B wasn't disturbed enough to affect flight at common handgun ranges.

On the other hand, you can have a perfect bullet base and end up with poor muzzle fit for a multitude of reasons. That's the war the GC fights.

Easy to see. Just load case with no powder and let the primer run it up the barrel sizer far enough that it engraves. Then drive it back out and look close. Coarse this doesn't cover the pressure damage or repair aspect, but it will show you why the big bullet technique can tend to do better and why sometimes rounded bases shoot better than one would expect. (short range anyway) And thus why you have varied opinion yet again.

Old timers used to say that the base was the steering wheel of the bullet. But since it can be damaged so that a great sharp base isn't, I just say it's all in the launch.

Dannix
07-28-2010, 10:52 AM
Just load case with no powder and let the primer run it up the barrel sizer far enough that it engraves. Then drive it back out and look close.
No matter how hard I try, I'm failing to understand this. Could you elaborate a bit?

MtGun44
07-28-2010, 01:01 PM
It is not the inflight shape that is the issue with a rounded base, it is the
non-uniform release from the muzzle crown. If one side opens up just a hair
before the other, you get a tip.

Bill

Blammer
07-28-2010, 01:51 PM
In this really good book I borrowed and read. (yes I learnt to read. :) )

the gentleman doing the testing could deform a portion of the base of a boolit and make it repeatedly hit a different spot (boolit lined up the same way in the barrel each time) from the normal group that was fired with the non deformed bases.

So yes, uniform bases are important.

Dannix
07-28-2010, 02:50 PM
Something I was thinking about just recently about the aerodynamics aspect -- gas checks aren't sharp-edged, so that may be a reason to not use a GC for slow stuff (besides unnecessary time and money expenditure). We could be talking about utter trivialities here though.


Bill, iirc, that's why some long range guys use rebated boat tail instead of 'standard' boat tail. Apparently the sharp edge of the rebated part makes for a more sure uniform release.


the gentleman doing the testing could deform a portion of the base of a boolit and make it repeatedly hit a different spot (boolit lined up the same way in the barrel each time) from the normal group that was fired with the non deformed bases
Wow, I'm get stoked just think of such a demonstration of geekiness. What's the book title?