Bullets Spinning Apart

[PapaB0415]

At while ago, I had a 1 in 7 3 groove in 7 Rem mag. A friend built a 7 STW with same barrel configuration. We both shot 180 VLDs. The 7 STW began to damage bullet jackets at round count 150 or so. His bullets would diverge from POI by inches at 100 yds. Mine did the same thing at just over 200 rounds.

I emailed Bryan Litz and he suggested I switch to 180 target VLDs with their heavier jackets. That helped for a while then the bullets would show signs of damage and shoot several inches off POI at 100 yds. I tried moly coating the bullets and it worked for a while.

Other members told me before I built the rifle not to use a 3 groove with such a fast twist and they were right. The 3 groove is the issue as it damaged the jackets in the throat area once it got rough. Accubonds and TTSX bullets shot fine in that barrel after I quit using the VLDs.

RPMs:
7 mag 180 VLD @ 2950 fps 303,428
7 STW " @ 3100 fps 318,857

So will a 5 groove be less susceptible to this?

 

[Lefty7mmstw]

The 8" twist bbl. on my 7rum (brux) loves to pop match bullets too... The 170 sierra will literally blow its nose and land sideways on target at 100 yards. I suspect the berger would too but the accuracy was lacking... Right now the 175 eld-x seems to be the ticket, but I only have a couple groups from the rifle using that bullet...

 

[AZShooter]

While I still use a 3 groove in a 257 weatherby with lots of velocity the twist is 1 in 10 so there are no issues with the 115 Berger VLDs. 265,104 rpm

I had a 5R bartlein 1 in 7.5 twist 6mm-284 that shot 105 berger hybrids at 3500 fps with no issues for life of barrel. 336,000 rpm

repeat from earlier post, two 1in 7 twist rifles with issues:
7 mag 180 VLD @ 2950 fps 303,428
7 STW " @ 3100 fps 318,857

I realize this is not a good scientific control but that 6mm-284 created higher RPMs yet the Berger hybrid survived the journey for the entire barrel life. I would say that a 5 groove would be better than a 3 groove with twist of 1 in 8 or faster.

 

[J E Custom]

some seeing this with the .22 creedmoor shooting too fast through a fast twist. forget the 55 gr they blow up on exit

I barreled up the 223 WSSM with a 1 in 15 twist after hearing some of the horror stories of some hot rod cartridges by some expert builders to minimize bullet destruction but still reached critical RPM with some bullets.

This rifle was special built for speed and has never failed to impress me. It remains to be seen what the barrel life will be. With the bullet I use (A 40 grain ballistic tip) it will exceed 4600 with good accuracy (1/4 MOA) and I am testing the 30 grain to see how fast it will go with out destroying it's self.

With today's trend to go with fast twist, bullet issues appear often.

J E CUSTOM

 

[Orange Dust]

While I still use a 3 groove in a 257 weatherby with lots of velocity the twist is 1 in 10 so there are no issues with the 115 Berger VLDs. 265,104 rpm

I had a 5R bartlein 1 in 7.5 twist 6mm-284 that shot 105 berger hybrids at 3500 fps with no issues for life of barrel. 336,000 rpm

repeat from earlier post, two 1in 7 twist rifles with issues:
7 mag 180 VLD @ 2950 fps 303,428
7 STW " @ 3100 fps 318,857

I realize this is not a good scientific control but that 6mm-284 created higher RPMs yet the Berger hybrid survived the journey for the entire barrel life. I would say that a 5 groove would be better than a 3 groove with twist of 1 in 8 or faster.

Not an expert by any means, but I always thought fast 3 groove barrels were at their best with monos. Maybe just an old wives tale, may be some truth to it. I do know for a fact you can blow up bullets pretty consistently with a long bullet, fast twist and lots of powder if you have the wrong combination of such.

 

[PapaB0415]

So with a mono 145 gr out of my 7 Sherman Short 1:7 barrel, going 3200 fps, would produce 329,000 rpm's. Do you guys think this is over stabalization of the bullet and it will wander or do you think it is in the realm of okay rpm's for accuracy?

 

[Orange Dust]

So with a mono 145 gr out of my 7 Sherman Short 1:7 barrel, going 3200 fps, would produce 329,000 rpm's. Do you guys think this is over stabalization of the bullet and it will wander or do you think it is in the realm of okay rpm's for accuracy?

I think it will help the bullet to open up at greater distances. You have to just test for accuracy.