How important is it?

[Carl]

If they come apart shortly before a plate it can appear similar to a hit, otherwise it’s just a puff of dust.

 

[Forkyfinder]

So when they come apart how do you know that? Does anything hit the target or just pieces? I assume if they come apart the trajectory would be affected

From what ive been told - bullets basically disentegrate. The centripidal forces exceed the strength of the jacket and lead bond and it flies apart.

 

[BackofBeyond]

Hornady did a podcast over twist rate and they discussed over twisting bullets.

According to them, it’s a thing.

 

[rjthehunter]

Hornady did a podcast over twist rate and they discussed over twisting bullets.

According to them, it’s a thing.

I'd think they're a pretty reputable source. It's their line of business. So I like to think they've tested it. Do you have a link? Time to give it a listen!

 

[Forkyfinder]

I'd think they're a pretty reputable source. It's their line of business. So I like to think they've tested it. Do you have a link? Time to give it a listen!

Listened to that one.

This ones good too. Explains a lot of what i tried to.

Terminal Ballistics - Hornady Manufacturing, Inc

Terminal Ballistics Video Library...

www.hornady.com

Hornady has been changing the game with bullet technology and engineering for a long time now. They pioneered making slow twist, high bc, slow velocity expanding bullets out of long range cartridges like 300 prc.... for me to shoot deer at 200 yards with...lol.

 

[Wind Gypsy]

Yep. And twist. Another interesting variable. Do bullets spun faster work better? Monos probably, but what about the rest of bullet types? mtmuley

Depends on what one sees as better! With monos where there isn't a concern of things coming apart too fast it seems like better if anything.

With lead core it does make sense to me that a bullet spinning faster would come apart faster upon impact than one spinning just enough to be stable. When that is good vs bad probably varies a lot by application. The extent of every difference is probably dependent upon the bullet, just how fast it's spinning, and what it's hitting though (edit to add: maybe even how much the lands deformed the bullet and jacket as well). Enough to make things tough to quantify other than on one off instances.

taking things further down this rabbit hole.. we see ballistic gel terminal results occasionally at lower velocities but I think many times the data comes from greatly reducing muzzle velocity and thus RPMs compared to the real life scenarios they are trying to represent where the bullet is spinning at a much higher RPM because it had a much higher muzzle velocity. Makes me wonder if the results are skewed by having low RPMs.

 

[Doublecluck]

Depends on what one sees as better! With monos where there isn't a concern of things coming apart too fast it seems like better if anything.

With lead core it does make sense to me that a bullet spinning faster would come apart faster upon impact than one spinning just enough to be stable. When that is good vs bad probably varies a lot by application. The extent of every difference is probably dependent upon the bullet, just how fast it's spinning, and what it's hitting though (edit to add: maybe even how much the lands deformed the bullet and jacket as well). Enough to make things tough to quantify other than on one off instances.

taking things further down this rabbit hole.. we see ballistic gel terminal results occasionally at lower velocities but I think many times the data comes from greatly reducing muzzle velocity and thus RPMs compared to the real life scenarios they are trying to represent where the bullet is spinning at a much higher RPM because it had a much higher muzzle velocity. Makes me wonder if the results are skewed by having low RPMs.

We’ve taken say 10-15 animals with 168 vlds out of 30-06/300 wm

North of say 50 animals with 7mm 168 vlds



Ranges have varied 200-500 mostly. But very similar mv, same weight, same bullet design. By observation I always have felt like the 168/7mm combo just hit a little harder. Originally I thought it was just the obvious that the 7 was retaining more velocity/energy and had a higher sectional density. But there was enough crossover where it didn’t really add up. For example I shot an antelope doe at like 220 with the 300 and it ran like 40-50 yards. A week or so later my daughter shot a full size mule deer at 336 in seemingly the same spot center of lung with the 7 and it absolutely dropped it like normal. Vel would have been nearly identical. A while back I think I was listening to either Bryan Litz or one of those Hornady podcasts and it dawned on me that it might be the twist. If that’s the case it would seem even a subtle change 1-10 to 1-9 could have a dramatic effect. Not a huge sample size but makes sense.

 

[Carl]

taking things further down this rabbit hole.. we see ballistic gel terminal results occasionally at lower velocities but I think many times the data comes from greatly reducing muzzle velocity and thus RPMs compared to the real life scenarios they are trying to represent where the bullet is spinning at a much higher RPM because it had a much higher muzzle velocity. Makes me wonder if the results are skewed by having low RPMs.

From the people I know who’ve been involved in doing gel testing at a professional level, reducing muzzle velocity to get a lower impact velocity will skew the results for exactly the reason you’re thinking. I took it from our conversation that they sometimes go to the trouble of doing the gel tests at long range, but don’t know much for details beyond that. I’ve actually always wondered if you could use an extra fast twist barrel at low velocity to get meaningful results without having to do it at long range which gets complicated for a bunch of reasons.

ETA: not saying no one publishes results gathered by reducing muzzle velocity, I don’t doubt some do. Just that per my understanding it isn’t apples to apples to do so, due to decreasing the rpm.

 

[Wind Gypsy]

From the people I know who’ve been involved in doing gel testing at a professional level, reducing muzzle velocity to get a lower impact velocity will skew the results for exactly the reason you’re thinking. I took it from our conversation that they sometimes go to the trouble of doing the gel tests at long range, but don’t know much for details beyond that. I’ve actually always wondered if you could use an extra fast twist barrel at low velocity to get meaningful results without having to do it at long range which gets complicated for a bunch of reasons.

ETA: not saying no one publishes results gathered by reducing muzzle velocity, I don’t doubt some do. Just that per my understanding it isn’t apples to apples to do so, due to decreasing the rpm.

Lots of variables going on. In regards to using a faster twist at lower velocity - It makes sense to me that differing pressures, time under pressure, length of barrel travelled, and twist rate could all impact how a bullet's jacket is changed during the firing process and possibly impact terminal results even if the RPMs are the same. Maybe less so than drastic differences in RPMs but still.. Must be a PITA to try and center punch a 10" square gel block at 800 yards.

 

[Forkyfinder]

From the people I know who’ve been involved in doing gel testing at a professional level, reducing muzzle velocity to get a lower impact velocity will skew the results for exactly the reason you’re thinking. I took it from our conversation that they sometimes go to the trouble of doing the gel tests at long range, but don’t know much for details beyond that. I’ve actually always wondered if you could use an extra fast twist barrel at low velocity to get meaningful results without having to do it at long range which gets complicated for a bunch of reasons.

I guess im not following either of you here here. The bullet doesnt gain or lose rotation based on "where" it is. A 1 in 12 twist is always going to be twisting 1 time every 12" traveled. Whether its 4000 fps or 1000 fps or anywhere else in the trajectory. So it wouldnt matter if you tested the ballistics with a pud load at 10' or at 800 yards to get the same velocity - the rpm of the bullet will be same at impact in both situations. Rpm = mv x 720/TwistRate.

 

[mtmuley]

I guess im not following either of you here here. The bullet doesnt gain or lose rotation based on "where" it is. A 1 in 12 twist is always going to be twisting 1 time every 12" traveled. Whether its 4000 fps or 1000 fps or anywhere else in the trajectory. So it wouldnt matter if you tested the ballistics with a pud load at 10' or at 800 yards to get the same velocity - the rpm of the bullet will be same at impact in both situations. Rpm = mv x 720/TwistRate.

But velocity affects a bullets behavior at impact. mtmuley

 

[Forkyfinder]

But velocity affects a bullets behavior at impact. mtmuley

Right. What i mean is 1000 fps from a barrel with the same twist at 1' is no different than the same bullet hitting the same ballsitics gel at 900 yards (with the same barrel twist) with a 1000 fps impact.

 

[Carl]

I guess im not following either of you here here. The bullet doesnt gain or lose rotation based on "where" it is. A 1 in 12 twist is always going to be twisting 1 time every 12" traveled. Whether its 4000 fps or 1000 fps or anywhere else in the trajectory. So it wouldnt matter if you tested the ballistics with a pud load at 10' or at 800 yards to get the same velocity - the rpm of the bullet will be same at impact in both situations. Rpm = mv x 720/TwistRate.

The rotation of the bullet in flight doesn’t slow at the same rate as forward movement does. If it starts with extra rpm’s it hangs on to them down range. Thus, you can’t just lower the muzzle velocity, shoot at close range, and get the same results.

But velocity affects a bullets behavior at impact. mtmuley

Yep.

 

[Carl]

Lots of variables going on. In regards to using a faster twist at lower velocity - It makes sense to me that differing pressures, time under pressure, length of barrel travelled, and twist rate could all impact how a bullet's jacket is changed during the firing process and possibly impact terminal results even if the RPMs are the same. Maybe less so than drastic differences in RPMs but still..

You’d have to test it out against a control for sure, but if it was my full time job it’s something I’d want to try out.

Must be a PITA to try and center punch a 10" square gel block at 800 yards.

I’m sure! Not to mention if you’re trying to take high speed photos, and working with a product that’s quickly decaying.

 

[Forkyfinder]

The rotation of the bullet in flight doesn’t slow at the same rate as forward movement does. If it starts with extra rpm’s it hangs on to them down range. Thus, you can’t just lower the muzzle velocity, shoot at close range, and get the same results.


Yep.

Ah. You guys were right - i stand corrected.

Spin Rate Decay

We discuss how we measure bullet spin at the muzzle and downrange and how spin rate decay affects stability over distance.

thescienceofaccuracy.com

From the podcast - says 20% or spin decay at 1000 yards as an example. So a 1 in 10 is now twisting 1 in 12. Seems like itd be something theyd be able to model in software and replicate with different twist rates in test barrels.

 

[mtmuley]

One thing is fairly clear. More stability is better. I think that should also be paired with high velocity. mtmuley

 

[Forkyfinder]

One thing is fairly clear. More stability is better. I think that should also be paired with high velocity. mtmuley

Dont forget BC

 

[mtmuley]

Dont forget BC

I haven't. But a highly stable bullet at high velocity is as important as BC In my mind. Maybe I'm off base. mtmuley

 

[DFS]

most of the people talking know what works for them. If you got a system that works stay with it. It is fun to play around though.

 

[mtmuley]

most of the people talking know what works for them. If you got a system that works stay with it. It is fun to play around though.

I know what works. I think I might be on ti something that works better. We'll see. mtmuley