Home Forums Hunting & Shooting Hunting Rifles Low MV = Long Range Bullet Performance?

In some recent threads I've seen it referenced that bullet performance on game with a close range impact of a bullet started with a low muzzle velocity (~60% of full power velocity) = bullet performance of a bullet started at high velocity hitting game at long range at approximately the same impact velocity. In my mind this theory has pretty much been debunked, bullets started at low velocity do NOT perform the same as bullets started at higher velocities that impact at the same velocity as the low velocity round. My understanding was that the prevailing theory for this discrepancy was due to not achieving the spin rate on the bullet due to low initial muzzle velocity.

Bullet spin is virtually unaffected by atmospheric conditions and whatever spin is imparted to the bullet at the muzzle will remain on impact despite signifcant velocity losses to a long range projectile. Increased bullet spin helps the bullet open, imparting centripital force.

I looked for old threads on the subject and couldn't find any. Hoping we can get some discussion from long range shooters and/or those that have conducted significant bullet testing.

David

Interesting concept regarding the effects of rotational rate. May also be why some advocate softer than normal bullets for close range game with reduced loads. There may not be enough speed or rotation to cause them to come unhinged. I've had good results with standard Ballistic Tips with velocities in the range of 2,100-2,400fps. They expanded well enough to wreck lungs on whitetails inside 100yds.

Yeah, math.

MV x (12/twist rate in inches) x 60 = Bullet RPM


I do believe faster RPMS show up in bullet upset.

Without a danged doubt. Twist has never hurt even with plain old Bullets. And it certainly helps a bunch with tougher hunting Bullets.

Orangutans are skeptical.

Have a friend who cuts his .30-06 back to .308W velocities. He no longer is shooting what is stamped on the barrel, but a .308W. At some point it isn’t a .30-06, which shouldn’t be surprising, but if a .308W is GTG with a specific bullet, he is also.

Thinking that if rpm was a significant factor re: terminal performance there might be a correlation in regards to how much energy is found in the bullet radius based on mass/rotational velocity. Boys, it ain't much at all............and the difference between full throttle and half throttle is likewise unimpressive.

Where's Mathman when we need him, hey?

There isn't much energy tied up in the angular velocity, but the force that wants to peel the jacket off the bullet ought to grow with the square of the angular velocity if I remember right.

Interesting....

I remember BobNH talking about higher RPM equaling greater penetration... and citing some specific tests/studies. He knew his stuff pretty well, and I tend to withhold decent unless my personal experience is contrary... even then I’m fairly prone to question myself.

You’d think, that if more revs helps the bullet open up better.... that would decrease penetration.

I know shooting reduced velocity loads at close range, and comparing them to the same bullet at great speeds/ranges... isn’t Apples to Apples.

This is correct. Short range simulation of low impact velocities by reduced MV does not represent what actually happens.

I think Bob was probably talking about the test Steigers did with BBCs. If you drove them FAST and turned them hard they would penetrate like crazy. It was the reason those guys were using 7-8 twists in 300’s, 7mm’s, 338, 375’s back in the day outta blown out H&H cases. Steigers also listed the RPMs needed for his bullets to maintain optimum penetration on the package.

It said if you can’t get the RPMs needed to drop back to the next lightest Bullet. I’ve messed around with a pile of them now and it bears out what they were doing. I don’t think regular cup/core sorta bullets at those speeds would’ve faired as well since they’d probably get very torn up. BBCs, and similar tough bullets like That really work well though using that old recipe.

But I’d bet at more sane speeds wouldn’t hurt them as much and probably get the desired effects.

Using the Seafire method....

90 grain SGC at 2500 out of a 1-9” = 200,000 RPM

Same bullet at “normal” .243 velocity....

90 grain SGC at 3125 out of a 1-9” = 250,000 RPM

There’s several examples of these bullets at normal velocity/RPM, from 275-425 yards, where impact velocities/energies would be similar to Seafire’s famed “failed” 90 SGC... that starkly contradict his findings.

Do y’all think that extra 25% in RPM was the reason some of these bullets performed nearly identically (close to perfect)... and Seafire’s “failed”.

I think a crap shot won’t alter the outcome enough for us to tell. I’d like to try the loads in jugs and see what the difference is. Betting it isn’t enough to matter. No speed or twist will make up for gut shooting.

(250000/200000)^2 = 1.5625, i.e. 56.25% increase in rotational forces, assuming my growth as the square comment holds.

Agreed on the increase in “force”.... but how much more work can that delta in force really do?

By stressing the jacket more it *may* allow the impact forces to more violently expand the bullet. How much? I ain't saying.

200K or 250K per MINUTE which is somewhere between 3,300 to 4,000 REVs per SECOND............... and how many NANO-seconds does it take your bullet to get to STOP after hitting hide????? AND, it's making one turn every 9 inches, even if the forward velocity is slowed by half and the RPM remain, it's still only 1 turn in 4 1/2 inches........

I think adding .007 inches of bullet diameter, to certain calibers, would produce more measurable results.....

My guess is that the difference in performance isn’t significant until you get to the edge of the impact velocity that the particular projectile is designed for. At the edge it might make a difference in performance.

David

Might the spin (1 in 8" 180 ELD-M impact @2800) help shatter bone like this entry, although it didn't appear that the bullet came apart? It looked peculiar for an entry to me but I don't know chit besides it was overkill +P.

No. I'm pretty sure it was the gut shot.