375 cal barrel twist and projectiles?

[LR3]

Just to add my .02 cents, Dave V has been just outstanding in building my 30-378 and working with him on my 375 Snipetac, including solid GS rounds, and I would trust his opinion on anything he advises.

 

[Augustus]

I fired some of the ZA 6.5 cal 397 gr out of a 13-6.5 gain twist today. 3070 fps sub-moa out to 900 yds. I will stretch them on out tomorrow. I was using 1.15 BC. This was out of a standard 375/408 case.

 

[Chas1]

Augustus, you mentioned a 13-6.5 gain twist. Is the 13 the barrel length?

 

[groper]

no mate, the barrel starts with a 1:13 twist at the throat, then the rifling twist tightens as it gets closer to the muzzle and finishes with a 1:6.5 exit twist. Theres only one game in town doing them, bartlein...

 

[Chas1]

groper, thought it might be barrel length of 31 backwards. Thanks for responding.

 

[BobbyL]

I fired some of the ZA 6.5 cal 397 gr out of a 13-6.5 gain twist today. 3070 fps sub-moa out to 900 yds. I will stretch them on out tomorrow. I was using 1.15 BC. This was out of a standard 375/408 case.

This is great but i have a few thoughts. Yes these may be 47 grains heavier then the other solids but why is the BC so low? Im getting BC's close to that in a 350 grain bullet im firing 200fps+ faster. I hope that you can get a accurate BC measured on these and its higher then that. What have you seen for long range performance out of the banded solids. I have looked at thousands of rounds fired over doppler radar data from older banded solids/regular solids and the banded ones really seem to start to fall off just after 2000 and become unstable. Have you seen anything like this happen?

 

[Augustus]

Bobby what banded slolids have you personally witnessed flying out to 2000 yds. What weight, length, who made them. What solid bullets are you getting 1.15 from and do you have a fouling problem. Is the bullet you refer to a jacketed or soilid. If you have a 375 bullet that is 355 gr. with a 1.1 or higher BC and can push it to 3270 without a fouling problem then we are beating our heads against the wall trying to perfect these 6.5 and 7 cal banded solids.

In answer to the question of the 6.5 Za at extented ranges. I will be shooting them past 2000 today if I can get away for a few hrs. To be honest I dont Know what they will do until I fire them.

 

[Augustus]

Bobby, thats impressive, what bullet are you referring to. I will take the 6.5 cal ZA to 2250 or so today if I can get loose for a couple of hrs.

 

[BobbyL]

The jamison/lost river type solids i am getting over a 1.1 bc out of with a mv of 3200. Yes there is slight fouling after 15-20 rounds but with treatments i have found lately im actually getting closer to 50 rounds before running into fouling problems. With the new nitriding we may see 75 to 100 rounds because of the massive decrease of the coefficient of friction with this process.

 

[Augustus]

Bobby, I shot the ZA 375 cal solids to 2560 yds today. These are 6.5 cal. in length and weigh 397 gr. They were stable and seemed to be shooting nice. I only had three left when i got dialed in. I had a thunderstorm going on and the wind was switching directions constantly, verticle despersion was around 1/2 moa. I did not attempt to dope the wind. I just let it drift. I recovered one bullet and it had hit point first and looked like a drill bit. It was very obvious it was still spinning very fast.

 

[groper]

excellent news augustus! do you have any more left so that you can test them at 3000yds or more?

Also, are you planning on testing any from a conventional fixed twist barrel, instead of gain twist? or has this already proven not to work?

 

[the claw]

Man this twist/projectile thing is evolving on a daily basis!...

I might just sit on the fence and wait this one out for a while before jumping into the 375 cal...

I think I have almost decided on a 338 version...

 

[Augustus]

Groper, I dont have any more but will have more around July 8, I have a few 6 cal 369 gr. I will shoot in the meantime. These have already been proven out of a constant 8 twist. I fired three of these out of the 6.5 gain twist and they made a ragged hole at 100 yds. In answer to your question concerning a constant twist used in conjunction with the 6.5 cal, all I can tell you is a constant 8 twist will not fully stabilize them at top velocities. If they were fired from a constant 6.5 I would expect them to do OK if the bands cuould stand the forces applied to them. The gain twists are noticably more pleasant to shoot than the constant twists. From what I have learned over the last couple of yrs I will go ahead and predict the 421 gr 7 cal 375 will act very much the same way as the 6.5 cal provided the 7 cal is fired from a 5.5 exit twist. A gentleman in Navada will be firing 6.5 cal 338 out of a 5.5 exit twist within a few days. This should be interesting but I think the results will be similar to what I saw from the 6.5 cal 375.

 

[Augustus]

wooops