Bullet talk

[Bison Butt]

What is the difference in performance between a flat base bullet and a tapered base bullet.

I ordered 32 gr Serria  Blitz king and 39 grain Blitz-kings. The .32 grain are flat base and the 39 grain are beveled based. I expect some difference in performance, but they could have been made either way as far as I know.

Thanks

[jpshaw]

Both will have the same sectional density since they weight the same but the beveled base will have a better ballistic coefficient rating since it is more streamlined in the rear.  Meaning, it should hold velocity a little better then the other.

Oops.  I didn't notice that they do not weight the same.  The bevel base should have a better sectional density and a better coefficient.  Meaning, again, that it will maintain its velocity better but the lighter one should have a faster velocity to begin with.  I would pick the 39 grain bevel base.

[BBF]

pick the one that groups best.

[OR-E-Gun Bill]

What is the difference in performance between a flat base bullet and a tapered base bullet?
Thanks

This from Sierra's website explains it well:

"The streamlined tapered base of the boat tail bullet greatly reduces drag, which results in higher retained velocity, greater striking energy, a flatter trajectory and less wind drift than comparable flat base bullets."

For long range, I would opt for the 39 gr. boat tail.

Bill

[buck460XVR]

a little info............

The final advancement in bullet shape occurred with the development of the boat tail which is a streamlined base for spitzer bullets. A vacuum is created when air strata moving at high speed passes over the end of a bullet. The streamlined boat tail design aims to eliminate this drag-inducing vacuum by allowing the air to flow alongside the surface of the tapering end, thus eliminating the need for air to turn around the 90-degree angle normally formed by the end of shaped bullets. The resulting aerodynamic advantage is currently seen as the optimum shape for rifle technology. The spitzer boat-tailed bullet ( Balle "D" ) was first introduced as standard ammunition in a military rifle in 1901, for the French Lebel Mle 1886 service weapon.

my understanding is at ranges less than 200 yards there is no measurable difference between the boat tail and the flat base.

[Lone Star]

my understanding is at ranges less than 200 yards there is no measurable difference between the boat tail and the flat base.

A quick look at any ballistic table will show that there is a 'measureable' difference in retained velocity.  The difference is not large at 100 yards, but with those small bullets it may make a small difference in performance on game. 

Example - Speer 52-grain bullets at 100 yards @ 3600 fps muzzle
HP - 2977 fps/1919 fpe
BT - 3131 fps/2122 fpe

That's a difference of 154 fps and 203 fpe at just 100 yards.  The difference at 150 or 200 yards would be considerably more.  How much these differences matter in the field however is open to opinion.


.

[calvon]

I've read that given two bullets of equal weight, equal diameter, equal nose conformation, equal everything else, except one being boat tail, the other flat base, the flight path from a single gun and a single powder charge will be identical until the bullet slows to below the speed of sound. From there on out, the advantage is with the boat tail.

Sooooo, if you're shooting at targets at a thousand yards, go with the boat tail. Otherwise ignore the difference because it doesn't amount to a pinch of snoose.

[LaOtto222]

What the guys have said about retained velocity is basically true. No one has addressed the accuracy angle. Some guns shoot the flat based bullets better than the boat tailed. Some shoot the boat tailed better. I think it depends on the exact shape of the crown right at the rifling. As a bullet exits the barrel the expanding gas escapes around the base of the bullet. The base of a boat tail will still be in the bore when the gas starts to escape. If the crown is just a little bit non - perfect the gas will push the base of the bullet just a little to the side, giving the bullet a little bit of yaw. This will, in most cases stabilize before it reaches 100 yards. The trouble is, will it still be on a true flight path? Most bench rest competitors shoot flat base bullets trying to extract the last little bit of accuracy out of their rifles. Of course most of them only shoot at 100 or 200 yards. You are going to have to try both to see which shoots best in your rifle. At extreme ranges, the boat tail has a clear advantage, in the wind drift, velocity, and drop departments. Another factor is the bullet length. The boat tail is slightly longer so if you are on the ragged edge of stability, the flat base may shoot better than the boat tail in the same weight. Every rifle is a thing onto itself. Shoot both and determine which shoots best in YOUR rifle at the expected ranges you are going to be shooting at. Good Luck and Good Shooting.

[BBF]

Excuse me Otto, but someone did mention accuracy. At least "pick the one with the better group" sort of says it

[murphdog]

45-70,
Your right.  Someone else did mention accuracy.  But I appreciate the detailed analysis that LaOtto222 gave us concerning the potential effect that bullet shape has on accuracy.  For me, his post was very worthwhile. 
Duane

[BBF]

The other benefit with the BT's are that they start down the neck a bit easier then FB's but accuracy is the top priority provided the weight, cal and construction of the bullet match the intended use.

 My wife's Mohawk in .243 just loved the 100 gr Sierra FB's but went wild with the BT's of the same weight and make.

[LaOtto222]

45-70... Sorry I missed your "pick the one that groups best" before I posted. Of course that is accuracy. That is what it is all about. Your wife's .243 is a perfect example of some guns liking the flat base bullets better. I had a heavy barrel 222 with 1-14" twist that loved Hornady 50 SPSX a flat based bullet. I also have a heavy barreled 223 with 1 - 14" twist that would not shoot that same bullet, no matter what I tried. I tried heavy loads of different powders, I tried medium loads and light loads of many different powders. I tried different seating depths, I tried different primers too. I wanted that rifle to shoot the same bullet in the worst way. Nothing worked, I sure tried. It does however love Hornady 50 V-Maxes a boat tailed bullet, go figure, but that is the way it is.

[Bison Butt]

I shot the 39 grain, .204 bullets I had worked up a load for.  A three shot group were all touching and no bigger than my little fingernail. They were started at 24.4 grains of Benchmark and continued upward at+.3 grains. The last group at 25.7, shown as max in the Hogdon manual were the tightest. Performance is fine.

Thanks for the input.

BB

[Catfish]

The boat tail on a bullet actually has a little more drag than the flat base at supersonic speeds. The boat tail do have a big advantage when they fall below supersonic, where velocity is concerned. The boat tail bullet, of the same weight as a flat based, will need a slightly faster twist to stabilize it due to its being longer.