Bevel vs. flat Base bullets?


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bunnielab
June 7, 2008, 09:37 PM
I have see it written (by authors I trust) that bevel base cast bullets are not capable of the same level of accuracy as flat base ones.

The reason given is that the flat base bullet will "expand" (there is a better work for it, but I cant for the life of me think of it, somthing with an "o") to fit the bore. And that flat base bullets exit the muzzle more cleanly and with less disruption.


I have tried to test this myself, using soft swaged Flat base and 15BHN bevel base cast bullets under identical loads. I want to say that, yes, the flat base bullets are more accurate, but my test was far from scientific and there are a ton of factors (the load used, the gun used, how I was shooting) that make me not trust my results.

I have made some poor bullet purchases in the past and don't want another box I cant use sitting around my house.

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LB7_Driver
June 7, 2008, 09:46 PM
The main reason flat-base bullets are more accurate (at shorter ranges) is its easier to make them to very high tolerances. There may be something to how they exit the bore, though the barrel crown has greater effect.

Boat-tail bullets have a higher ballistic coefficient and are better a longer ranges. By 500 yards or so, the

If you're talking about cast bullets and not jacketed, then there are other more significant factors in play. Cast bullets, particularly softer bullets, will upset to fit the bore tightly upon firing. 22 rimfire and lead pistol bullets are known for this. A bevel at the base would allow for greater lead movement in strange (read: unpredictable) ways... leading to inconsistent accuracy.

My favorite 22 cal varmint bullet is the Nosler Ballistic Tip. It is a boat-tail design and capable of 1/4 MOA accuracy out of custom rifles.

ReloaderFred
June 7, 2008, 09:51 PM
The word you're looking for is "obturate", meaning to expand and fill the bore, when used in reference to firearms and ammunition.

There is less gas cutting around the base of the bullet with flat base bullets. The bevel base was invented to facilitate loading in progressive and automatic loading machines. It had nothing to do with ballistics.

Hope this helps.

Fred

bunnielab
June 7, 2008, 10:06 PM
The word you're looking for is "obturate"

Yes, thats the one.

So assuming all other factors are equal, a bevel bases lead pistol bullet will preform the same as a flat based one?

kennedy
June 7, 2008, 10:14 PM
check out a sierra match king boat tail, in .308 sub moa

Down South
June 7, 2008, 10:39 PM
You might want to post this over on Cast Boolits or do a search over there. There is a wealth of info on any subject dealing with cast there.
I've heard the same thing that flat base cast does better than a bevel base cast but I can’t prove it.

RyanM
June 7, 2008, 10:47 PM
Bevel base bullets and boattails are still going to be slightly less accurate, even if they're perfectly made. Some of the hot powder gas can slip around the rounded base and end up ahead of the bullet, which then has to fly through this hot, expanding, turbulent cloud. A flat base bullet will divert the blast, sort of like a muzzle brake.

You'd be hard pressed to notice any difference, though. Less than 1/2 MOA, definitely. Probably less than 1/4 MOA.

Sunray
June 7, 2008, 11:13 PM
"...boattails are still going to be..." All the match grade rifle bullets I've ever seen are HPBT's. Anyway, a bevel isn't the same thing as a boat tail.
The best lead .38 target bullet is an swaged HBWC.

243winxb
June 7, 2008, 11:42 PM
using soft swaged Flat base and 15BHN bevel base cast bullets under identical loads. A swaged bullet will win the accuracy test most ever time over a cast at slow target velocity. The cast bullet will have hidden flaws like air pockets or a difference in mould cavities,or alloy from the start of the pot compared to the bottom of the pot. The more you have to size down a cast bullet the less accuracy it will have because the bullet is deformed when sizing. A swaged bullet is formed under lots of pressure, a more perfect bullet. Flat or boatail bullets both can be accurate, but won't use the exact same load. In the 45acp using cast bullets i will take the Lyman 200gr swc bevel base over the flat base in round nose or swc. Not only does the BB load better, but there is less deformity of the BB bullet base. The metal displaced by the lands has to go somewhere and it tends to end up at the base of the bullet. This happens even if the bullet is sized to the exact groove diameter.

TexasSkyhawk
June 7, 2008, 11:51 PM
(Reloader) Fred said it well.

I have .45 moulds (.452 200SWC) in both bevel-base and flat-base. I have a hard time determining which one is more accurate, regardless of gun it's fired out of.

Bevel base is easier to load, flat base is easier to cast. As a general rule, I prefer flat-base bullets.

Jeff

243winxb
June 7, 2008, 11:59 PM
http://www.thehighroad.org/showthread.php?t=332274 Obturate http://en.wikipedia.org/wiki/Obturate Take note at what pressures are need for a bullet to obturate with different alloys/types/copper

CBS220
June 8, 2008, 01:35 AM
I can't tell the difference in accuracy.

I have heard it said that at close ranges flat based bullets do have the edge, but the ballistic performance of boattails gives them the edge further out.

Quite frankly, it seems to come down more to the shooter than anything else... if you're shooting a match bullet in an adequate caliber with a decent load, blaming the bullet tends to be just an excuse.

RyanM
June 8, 2008, 03:56 AM
"...boattails are still going to be..." All the match grade rifle bullets I've ever seen are HPBT's. Anyway, a bevel isn't the same thing as a boat tail.

Just repeating what I've heard. Saw some slow-mo videos once showing the difference. The boattailed bullet did indeed have to fly through the expanding gas cloud, while the flat base one didn't.

Although, with gun manufactures porting absolutely everything nowadays, it's probably no longer a factor.

ChuckS1
June 8, 2008, 07:52 AM
I prefer plain base since I don't have to wipe off the little bit of lube that gathers in the bevel when I run them through the sizer. I think most commercial casters make them because it's faster on their machines.

243winxb
June 8, 2008, 09:34 AM
I prefer plain base since I don't have to wipe off the little bit of lube that gathers in the bevel when I run them through the sizer. This is one problem the flat base doesn't have. On the Lyman 450 sizer you can plug 2 of the bottom holes in the sizer dies with lead shot, tap it in flat, this help cut down on the lube on the bevel part, but does not get rid of it. You can have a custom die made with the inter sleeve/push rod cut to fit the base of the bevel. Stillwell tool & die in Texas did make them but looks like they might have gone out of business.

243winxb
June 8, 2008, 09:53 AM
When it comes to High Power Rifle Bullets, there is no difference in accuracy between a flat base or boatail bullet. They will need different loads to shoot well. A boatail is better in the wind, less bullet drift. As far as ballistic coefficient goes the ogive/nose angle/length of the bullet makes more difference . Check out the different bullet designs here. http://www.bergerbullets.com/

rcmodel
June 8, 2008, 02:20 PM
If we confine the answer to cast bullets, which the OP ask about, you will find flat base bullets more accurate then bevel base.

Perhaps not enough to notice by an average pistol shooter like most of use.

But the ne-ultra cast bullet shooters are the long-range BP Silhouette & Creedmore guys who shoot Buffalo rifles & cast bullets at 600, 800, & 1,000 yards or more.

You won't find any bevel-base or boattail cast bullets winning, or even used there!

rcmodel

The Tourist
June 8, 2008, 02:40 PM
This is one of those debates where I have to don my fireproof scivvies.

I don't find any differenence. And I mean in all of the 32 years I've been reloading.

First, cast bullets. With or without gaschecks. No difference, none. I found that a good case trimming, a careful chamfer and a good cull helped more. The one exception was using a 429421 with the original square cornered lube groove. I tighted my groups a bit, but a stranger might not notice.

As for .22 centerfires, I've used military, boattails, zippeedos, softpoints, ballistic tips, once fired brass, new brass, full-sized brass, and the one thing that tightens groups the most is to adjust your powder measure down one full grain when you find an acceptable load.

I've left barrels dirty, I've polished them with Nevr-Dull. I've shot off of sandbags, rolled up jackets and my own folded arm. The quality of the trigger actually seems more important that the load.

Oh, and BTW, I'm not a natural good shot. Hitting bullseyes came from monkeying around with conventional wisdom.

mach2plus
June 19, 2008, 12:41 PM
Greetings to all. I've been reloading for about 15 years. During that time I have never used cast bullets, so I have absolutely no experience in reloading them (though I have observed them being made). All my experience is with rifle cartridges, mainly 270, 7mmMag, and 223/5.56. After reading some of the responses in this thread I am now wondering if I have been reloading incorrectly all these years, given that I have no idea why there would be any lube at all on bullets that would need to be removed prior to seating. Is this something unique to using cast bullets, or am I doing things the wrong way??? As a side, I have never had ANY problem(s) whatsoever in seating a BT or flat based bullet (though BT's are much easier to seat), and I have never, ever used lube on any bullet. Also, after resizing, I have always used q-tips to wipe the interior (too include the necks) of my cases to remove any lube, etc.

thanks for the bandwidth -- m2+

rcmodel
June 19, 2008, 12:46 PM
Only cast bullets have bullet lube of some sort on them.

Those that have been run through a lubrasizer have stiff grease applied only to the grease grooves of the bullet.

Tumble lubed Lee cast bullets have a thin coating of liquid Alox all over the bullet from end to end.

Your jacketed bullets do not.
The copper jacket is the lube!

rcmodel

30Cal
June 19, 2008, 07:10 PM
All the match grade rifle bullets I've ever seen are HPBT's. Anyway, a bevel isn't the same thing as a boat tail.

Nah. The 150gr SMK plus plenty of custom 125-130gr match bullets are Flat Base.

All the LR application (heavy) bullets are BT's though.

mach2plus
June 20, 2008, 10:59 AM
Greetings again and thanks for the prompt reply. Nice to hear that I seem to have been reloading correctly, ha. On another subject, I haven't explored any of the other threads yet regarding this matter yet, so I apologize if this is a retread. But for Ryan M, do you (or anyone else) recall where you may have seen the video that you are referring to that shows the gas bypassing a beveled based bullet versus a flat based bullet?? It sounds like a very interesting video. M2+

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