bullet expansion test results

Great point Steve!! I've played around with rotational inertia as it is effected by the center of mass and stability a bit. I have found that the farther aft the center of mass resides in a bullet the higher the rotational velocity has to be to keep it moving point forward and expand in what we consider a normal' fashion without exhibiting yaw and subsequently tumbling. Simple. Do you want the bullet to yaw and tumble? Maybe, maybe not.
The behavior of a bullet can be most easily thought of in terms of a gyroscope. As in gyroscopic stability, the faster you spin it the more likely it can resist an upsetting force and recover the rotational orientation and path that existed prior to the introduction of the upsetting force. Now this brings us to tumbling. Do you want the bullet to yaw and upset or hold it's orientation? Tumbling can leave a very substancial wounding track, don't get me wrong, however it is problematic in that it is seldom predictable in its upset track, fragmentation or in the depth that it initiates.
The farther aft the center of mass is the more likely a bullet will tumble and the sooner it will do it. Is it desirable or not? Maybe, it depends...
Next it brings us to the jacket, if there is one. If the jacket is heavy enough or hard enough to resist the forces acting on it the bullet will trade front to back and simply continue on in that orientation until it runs out of energy. This generally doesn't create a desirable hunting type wound. If the jacket is thin enough or soft enough to not be able to resist the forces acting on it, it will fragment or deform which can show dramatic wounding effects. Provided it happens quickly enough to shed into the vitals you are probably golden. If it is too delayed it will pass through the animal and make a large exit wound.
There is a lot at play that contributes to how, why and even if a bullet performs as we hope it will, we have seen this in the thread. Bravo Yorke, kudos to you for taking the time to put together this thread. I have enjoyed it and learned from it. Thank you.
 
I don't think I can add anything worthwhile to what Steve and Trnelson said.

My experience through the testing pretty much matches Steve's assessment that an SG of 1.5 or higher is needed for good results. A couple of the bullets had an SG of below 1.5 and still shot good groups but the bullets didn't expand well. The 140gr Berger VLD in 6.5mm comes to mind here; specifically when shot from the polygonal rifled 6.5 Grendel. The groups were good but the bullets tumbled and didn't expand on impact. When shot at a slightly higher velocity but from a conventionally rifled barrel they expanded much better.

I presume that a relatively low SG is the reason that a bunch of the bullets failed to expand as expected. Like Steve, it's making me reassess my bullet choices in a couple applications.
 
I don't think I can add anything worthwhile to what Steve and Trnelson said.

My experience through the testing pretty much matches Steve's assessment that an SG of 1.5 or higher is needed for good results. A couple of the bullets had an SG of below 1.5 and still shot good groups but the bullets didn't expand well. The 140gr Berger VLD in 6.5mm comes to mind here; specifically when shot from the polygonal rifled 6.5 Grendel. The groups were good but the bullets tumbled and didn't expand on impact. When shot at a slightly higher velocity but from a conventionally rifled barrel they expanded much better.

I presume that a relatively low SG is the reason that a bunch of the bullets failed to expand as expected. Like Steve, it's making me reassess my bullet choices in a couple applications.

Question for you. What was the muzzle vel and twist rate when you caught the 150 Dead Blow?

Steve
 
Thanks a ton yorke-1 for going to the trouble to do all that! Very informative- Between you and a few others chiming in with their experiences, I too have decided to make some changes in my hunting bullet choices.
 
I looked back. Assuming you have a 10" twist the stability factor would have been above 1.5sg. Reason I asked is we test with an 8" and a 10". Don't remember which we used with that bullet. Know we were able to get under 1800fps performance. Once we get performance at or below 1800fps we stop as we see no point in going lower.

Steve
 
Very nice work Yorke! I learned a few things from your testing, and confirmed some other things that I have experienced. That was a LOT of work, and I for one appreciate the effort!...........Rich
 
I realize this is an older thread. I would love to see some expansion tests on the new .30 cal Sierra Matchkings, particularly the 230. I am interested in 1400-1500 FPS impact results from a fully stabilized bullet.

Looks like I can use some Trailboss in a 10 twist 300Win but my SG will be around 1 and nowhere near stabilized to give me accurate low velocity results. Yorke, do you have anything that could perform this test?
 
I realize this is an older thread. I would love to see some expansion tests on the new .30 cal Sierra Matchkings, particularly the 230. I am interested in 1400-1500 FPS impact results from a fully stabilized bullet.

Looks like I can use some Trailboss in a 10 twist 300Win but my SG will be around 1 and nowhere near stabilized to give me accurate low velocity results. Yorke, do you have anything that could perform this test?
We do low vel impact testing using trai boss all the time. You are correct that your test will be flawed with the low sg of the bullet with the reduced load. The only way to get good low velocity data is with a bullet that has a min of 1.5sg. So you will need a faster twist barrel to test at short range with reduced loads or set up a bullet trap at long range with full vel loads.

Steve
 
We do low vel impact testing using trai boss all the time. You are correct that your test will be flawed with the low sg of the bullet with the reduced load. The only way to get good low velocity data is with a bullet that has a min of 1.5sg. So you will need a faster twist barrel to test at short range with reduced loads or set up a bullet trap at long range with full vel loads.

Steve
I have always looked at the reduced velocity test this way: If it expands at a given velocity with a reduced load, it will "certainly" expand with the same weapon fired with a full load with the same impact velocity at distance!
 
I might also add, and I think this agrees with Steve, if it Won't expand with a reduced velocity load, it doesn't necessarily mean you are done testing. I am also a believer that rotational velocity affects expansion!
 
I might also add, and I think this agrees with Steve, if it Won't expand with a reduced velocity load, it doesn't necessarily mean you are done testing.
Right! That's why it would be nice to run this 230 in an 8 twist so it would be stabilized at 1500fps. No guessing. Although I will probably still pick up some Trailboss and do it anyway...something about curiosity and a cat
 
Like the others said, the results would be a little off because of the low SG. That's one of the most significant influences I saw in poor expansion. I still think it would be a good test though!

I was actually thinking about setting up to do some more testing. I was given a decent recipe for home made ballistic gel that I think would work really well combined with the leather. If I find the time this winter/spring I'll try and get some more tests done.

I'm still irritated that Photobucket decided to charge so much for their photo hosting and all my pics got nuked on this thread. I'm willing to pay, but not $400 per year! I just need to take the time now to go back and edit this thread and update all the photos.
 
Like the others said, the results would be a little off because of the low SG. That's one of the most significant influences I saw in poor expansion. I still think it would be a good test though!

I was actually thinking about setting up to do some more testing. I was given a decent recipe for home made ballistic gel that I think would work really well combined with the leather. If I find the time this winter/spring I'll try and get some more tests done.

I'm still irritated that Photobucket decided to charge so much for their photo hosting and all my pics got nuked on this thread. I'm willing to pay, but not $400 per year! I just need to take the time now to go back and edit this thread and update all the photos.
I just went through many pages of your testing tonight and all of the photos were available. Hmm?
 
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