What Defines Bullet Expansion?

gelandangan

slimjim wrote:

Thanks, gelandangan. I should have thought of doing an article but there are a couple of disadvantages the biggest one being when the site software gets updated, the articles get dumped and have to be resubmitted.

Slim,
If you have the study done as an article, it can then be read as a single continuous study.
I doubt articles are dump unless there are problem with the backup, and Dallan has been pretty good in keeping up to date with the backups.

slimjim · Posted: Mon Aug 05, 2013 5:53 am Post subject:

repeat

MacD

Slim; fasinating study. I am using Barnes TSX bullets 168 grain in my 308 hunting rounds. Muzzle velocity 2600 - 2700 if I recall correctly. I chose them primarily because they are accurate in my rifle and I needed something that would punch through the chest of a moose including the rib bones without coming apart and sending bits and pieces all over the place. The longest shot I have ever taken was about 300 paces but most shots are within 150 yards. I haven't used thr TSX on a moose yet so no personal experience to back up my thinking. Was the TSX the right choice? I also considered the TTSX and the Hornady SST. I guess my main question is how well do you think your test results carry over into the field?

slimjim

MacD, the TSX is a great choice for your application. It will expand better than the .277 130gr because its ogive is not as long. SST is a fragmentation bullet. The TTSX is longer with a better BC but you will give up case capacity and muzzle velocity.

The test results compare very closely withfield results. You can see the GMX recovered from an elk above. I will post some other comparisons for you.

English Mike

The GMX looks like it does what it's supposed to, so I might have a box to try come November.
Hopefully it'll be more consistent than the SST, which produced disappointing accuracy when we tried it a while back.

slimjim

The GMX in my rifle has been as accurate as Berger VLDs. My hunting buddy uses the GMX Superformance in his 300 Win Mag and is achieving less than 1 MOA. The GMX are fully expanded by the inside of the near-side rib cage. They don't expand quite as much as the Nosler E-Tip or Barnes in close but they are very consistent and have become the favorite for hog hunters.

slimjim

Here is a comparison of 6.8mm AccuBond and TTSX bullets recovered from testing and from game.

slimjim · Last edited by slimjim on Thu Aug 08, 2013 4:55 am; edited 1 time in total

Even negative performance has been correlated in testing. The .277 Berger VLDs, 130gr-150gr, have always yawed, turned 180, and penetrated tail-first in terminal performance testing. No fragmentation whatsoever. It hasn't matter if fired from a 6.8 or .270. Here is a hunter that found his 140gr VLD shot from a 6.8 on top of the snow behind a caribou he shot. The copper jacket has enough strutural integrety to remain intact upon impact. I've shot them from 100 to 500 yards and watched the bullet leave a waterjug undisturbed and leaking water. The picture belows shows the VLD yawing through the foam board that is positioned just behind the water jug.

Berger is a great company and their bullets are very accurate. The .277 VLD bullets just do not have the terminal performance I expect in a hunting bullet.

Azar · Member Joined: Jan 04, 2010 Posts: 275 Location: Utah

slimjim,

You've obviously put a lot of work and effort into this.

Thanks for sharing your findings! It's quite interesting.

Ominivision1

Very interesting indeed, good work Slim.

shrpshtrjoe

You do a great job documenting your tests slim . Its presented very well.. Thanks for sharing your results with the Nuts Very Happy

.. Good Info

slimjim

Thanks guys for taking the time to read and comment. I really enjoy the challenge of testing and trying to figure out how bullets perform.

MacD

Thanks again Slim. Looks like my TSX loads will work out fine. No moose license this year but I may go for a spring bear.

Vince

Slim...you have done a magnificent job putting this research together mate, although it was no doubt a labour of love. Thanks for all your hard work mate.

Whilst the calibre is different to what I shoot, the data should apply to my rifle in . 243 Win.

slimjim · Last edited by slimjim on Fri Aug 09, 2013 5:06 pm; edited 2 times in total

Vince wrote:

Whilst the calibre is different to what I shoot, the data should apply to my rifle in . 243 Win.

Thanks, Vince. You are right, I have done most of my testing with .277/6.8mm but I also have tested plenty of .223/5.56mm (which is why I switched to a 6.8mm) and some limited .308 that my hunting buddy was using for our elk hunt. Some simple logic applies.

- Like bullets of different calibers usually perform the same but the larger caliber will have larger expansion.

- Now that I realize that energy defines bullet expansion, I know why a 165gr GMX shot from a .300 Win Mag expands more at 500 yards than a 130gr GMX shot from a .270 Win even though their velocities are close to being the same (larger caliber plus more energy).

- What may surprise you is that the .270 will out penetrate the .300 Win Mag with like-construction bullets. A bullet with more expansion will penetrate less than a bullet with less expansion, sometimes even when it has less kinetic energy.

- I've also noted that almost all bullets penetrate deeper at longer ranges because their expansion decreases faster than kinetic energy. For a bullet to penetrate less at longer ranges, it has to very consisten expansion across its velocity range.