Low velocity impact testing

[RockyMtnMT]

We have been working with low velocity impact testing the last few weeks to make sure that our bullets do as they should. There have been some great threads on this in the years past. Discussions about twist rate of reduced loads and the effect that it has on the impact test. We have been working on finding minimum impact velocity for our bullets to open up. We were working with the .243 80g bullet. When fired from a 9" twist with a muzzle vel of 1800fps they would not open up. We then fired it from a 7" twist at the same vel and they opened perfectly. So my conclusion is that the faster twist gave better stability to keep the bullet oriented point 1st and ensuring expansion. This 80 bullet at 1800fps has a stability factor of 1.41 sg at our altitude in the 9" twist. Slightly low. In the 7" twist it is 2.33 sg, very stable.

So my conclusion is that stability factor may have more to do with terminal ballistics than previously thought. A bullet that is marginally stable will fly very well and will lose a but of bc. I now also think that that bullet that is a little marginal in stability may not work like it should when impacting an animal.

Steve

 

[Pdvdh]

Thanks for sharing this Steve. I've always suspected what you're reporting. It takes a lot of time and effort to test and demonstrate it. This will factor in my future twist rate decisions next time I purchase a barrel blank.

 

[elkaholic]

We have been working with low velocity impact testing the last few weeks to make sure that our bullets do as they should. There have been some great threads on this in the years past. Discussions about twist rate of reduced loads and the effect that it has on the impact test. We have been working on finding minimum impact velocity for our bullets to open up. We were working with the .243 80g bullet. When fired from a 9" twist with a muzzle vel of 1800fps they would not open up. We then fired it from a 7" twist at the same vel and they opened perfectly. So my conclusion is that the faster twist gave better stability to keep the bullet oriented point 1st and ensuring expansion. This 80 bullet at 1800fps has a stability factor of 1.41 sg at our altitude in the 9" twist. Slightly low. In the 7" twist it is 2.33 sg, very stable.

So my conclusion is that stability factor may have more to do with terminal ballistics than previously thought. A bullet that is marginally stable will fly very well and will lose a but of bc. I now also think that that bullet that is a little marginal in stability may not work like it should when impacting an animal.

Steve

Thanks Steve! I have been advocating for years that twist rates do indeed affect expansion. If you think about it rationally, going from an 8 to a 7 twist at 3000 fps increases the rotational velocity by thousands of rpm. This HAS to put more pressure on the integrity of the bullet. I also believe, that along the same line of thought, more tissue damage occurs because of this same increase in rotation with a jagged jacket.
I have posted this before but I think it is worth saying again. The dept. of defense did a test YEARS ago with 110 gr. bullets fired both from an '06 and a 30 carbine. I think the mv of the carbine was a little over 2000' and they fired the '06 at a distance that duplicated the velocity of the carbine at the muzzle. The bullets were fired into gelatin and the wound channel was photographed and measured. The results were amazing in favor of the '06. I should add that the '06 had a 10 twist and I believe the carbine was a 16. I have done a lot of bullet testing myself, and find no reason to dispute what the military found. Good luck with your business and keep on testing! This is an important issue and more people should be aware of how these things work together for better terminal performance.....Rich

 

[HARPERC]

Good work! Thanks!