Twist rate and penetration: also factors effecting penetration and wound channels in general

[Formidilosus]

If a bullet reliably tumbles and fragments every time, and creates consistent wound channels, I see no problem with it. I would want a large sample and I doubt this is the case, even with Bergers.

I forget the thread, perhaps the 223 thread, but it is discussed how the nose on Bergers reliably collapses, which is why the are consistent. Other match BTHP bullets have a different tip construction and depend on tumbling, which is why they give inconsistent performance.

Notice, not a single recommend bullet in the 223 thread depends on tumbling to initiate fragmentation.

Bergers yaw (tumble) frequently- especially below +/- 2,400fps impact. Below around 2,000fps impact often they don’t fragment heavily.
Almost all (nearly all) HPBT bullets yaw, and if with sufficient velocity- fragment. Yawing, in general, is not as consistent for most bullets as conventional upset. However, when a bullet does consistently yaw early in tissue, wounding is very good.

 

[ElPollo]

Bergers yaw (tumble) frequently- especially below +/- 2,400fps impact. Below around 2,000fps impact often they don’t fragment heavily.
Almost all (nearly all) HPBT bullets yaw, and if with sufficient velocity- fragment. Yawing, in general, is not as consistent for most bullets as conventional upset. However, when a bullet does consistently yaw early in tissue, wounding is very good.

Form—The nose ringed DTAC bullets seem to work on the same model as Bergers and Scenars where the yaw causes the tip to crush or detach and initiate fragmentation. What do you think separates the performance characteristics of these bullets? Is it an issue of how readily the tip deforms or detaches, the jacket thickness, something about the shape that induces yaw, or a combination of those factors? Is greater velocity the primary reason why you are opting to use bullets of this type in 6 mms? Do you think there is a velocity threshold where this type of bullet excels over the plastic tip bullets like the ELDM and TMK?

 

[Mountainrancher]

Bergers yaw (tumble) frequently- especially below +/- 2,400fps impact. Below around 2,000fps impact often they don’t fragment heavily.
Almost all (nearly all) HPBT bullets yaw, and if with sufficient velocity- fragment. Yawing, in general, is not as consistent for most bullets as conventional upset. However, when a bullet does consistently yaw early in tissue, wounding is very good.

Are you referring to all bergers or just the “non” hunting ones? Does the thinner jacket of the hunting bergers allow for more conventional upset/expansion from the front expanding or are they yawing to create fragmentation as well

 

[Formidilosus]

Are you referring to all bergers or just the “non” hunting ones? Does the thinner jacket of the hunting bergers allow for more conventional upset/expansion from the front expanding or are they yawing to create fragmentation as well

Yes to all. Sometimes the nose collapses or shears off and they fragment from the front, sometimes they yaw and then fragment. And it’s all Bergers. The thin jacketed VLD and Hunting ones fragment at a lower velocity than the thicker jacketed target ones.

 

[Mountainrancher]

Yes to all. Sometimes the nose collapses or shears off and they fragment from the front, sometimes they yaw and then fragment. And it’s all Bergers. The thin jacketed VLD and Hunting ones fragment at a lower velocity than the thicker jacketed target ones.

Makes sense thank you for the reply form

 

[mother_plucker]

I have studied this a bit. The rotational energy is very small to begin with and changing to faster twist increaes very little (think neighborhood of 10 ft-lbs) Ballisticians across the board dismiss twist as having any impact on terminal performance - assuming a bullet is stable to begin with and expands. There is just very little energy there. Internet experts say a lot of different things but nobody who studies ballisitcs and forensics and published books or papers thinks it does

As for tumbling inside game - no amount of rifling twist will keep a bullet stable in flesh. Flesh is roughly 1000x more dense than air so consider amount of spin increase needed to make stable

What keeps a bullet penetrating straight is shoulder stabilization. You can google this but there is a reason flat front solids track straight…

So what does faster twist do. In general 3 things:

Decrease angle of incidence. Any bullet tip is “wobbling” some when it leaves the barrel. After 80-100 yards this is pretty much gone. Faster twist can decrease this wobble some. Not much of an issue with soft points, tipped, big hollow points etc. as they are more forgiving to start expansion. However some bullets with long narrow hollow points may start to tumble at closer ranges before reaching terminal shape.

Also, for bullets with no means to expand (think otm/fmj) the more stable a bullet is going in the longer it will penetrate before tumbling. This is why there are mixed reviews on m16 coming out of viet nam. Sometimes tumbled and came apart and did a lot of damage. Sometimes penciled through as never tumbled. So less stability is your friend there.

The centrifugal force can cause a bullet to expand more quickly. By far the dominant force in expansion is dynamic pressure (ie from foward motion) but particularly with very thin jackets with nothing to control (jacket thickness/partition/bonding) this happens. I doubt a big factor in big game bullets unless maybe somebody uses match type tipped bullets or uses a way faster twist than bullet is designed for

This last one is more my opinon and never seen mentioned in literature. More spin for “petal bullets” can present more frontal area in shorter distance for bullet to transfer energy. Not a big deal with normal mushrooms but petaled bullets (ie barnes x, etc) have space between them. They penetrate deep because there is less surface area crushing tissue as they penetrate. Spinning them faster presents more frontal area in the same distance. Of course that will decrease penetration some. Think of the swirlies (which by the way are caused by material flowing off tips of petals) in the gel videos. Faster twist should show more swirls and possibly wider but shorter wound

People say there is “cutting” going on with petaled bullets but I highly doubt that. #1 the temp cavity forms as the bullets is passing so the sides of the bullet are not touching anything until the bullet slows down. This is why even in media you see a bullet spin. Much like air this is because the bubble forms around it and nothing to degrade spin Once the bullet slows down and media touches the sides of bullet near end of peneration. the rotations stop pretty quick - since there is very little energy there

Lou

Just curious if you have seen some of the kills with an 8.6 Blackout and solid bullets out of the 103 twist? Pretty impressive rotation in those where the petals on the bullet are actually turned 90* to the body of the bullet.

 

[Lou270]

Just curious if you have seen some of the kills with an 8.6 Blackout and solid bullets out of the 103 twist? Pretty impressive rotation in those where the petals on the bullet are actually turned 90* to the body of the bullet.

I have not except for some of the youtube videos from the company. I do know The swirlies one sees in gel is just the material flowing off the tips of the petals as a bullet travels through gel. The swirlies don’t typically show up in a traditional flat mushroom as the material is flowing off the face of bullet more uniformly, but the bullet is still spinning as it penetrates. The more spins the more the swirlies. I don’t know if this increases damage or increases illusion of damage but if it does increase damage would likely be minor and only in bullets that expand with petals. At least that is what I think.

Faster twist may increase fragmentation which can be good or bad depending on where the fragmentation happens during penetration

Lou

 

[Bluefish]

Just curious if you have seen some of the kills with an 8.6 Blackout and solid bullets out of the 103 twist? Pretty impressive rotation in those where the petals on the bullet are actually turned 90* to the body of the bullet.

I know maker has to design bullets differently for the 8.6 vs other subs. They also have a velocity limit which I expect is due to the petals opening due to fast enough spin rate. I have started to hunt with 45-70 subs and am impressed. Rpm is super low, only 64k rpm. At 500g they offer lots of penetration, more than needed for whitetail.

I would like to see some comparisons between the 8.6, 45-70, and 450 bm. I think between those 3, the 45-70 would come out of top simply due to the ability to handle a lot heavier bullet. Subsonic is interesting as velocity decreases much slower than sonic, even with low BC. Drop is almost the same with all cartridges as speed is the same starting and BC doesn’t matter much. Then it’s only how heavy for how much energy you can put on target.