Cutting Edge 425/13-6.5 Gain twist

[Chaddman]

Augustus or Kiwi Greg or anyone else with good and recent .375 data. I am planning on building a .375 rifle to start playing with you guys in ELR. I have read about every post that I could find from you and others concerning the .375 bullets and twist rates required by those bullets. I want Kirby Allen to smith the rifle and chamber it in his .375 Allen Mag. I spoke with Bartlein and they will be running .375 barrels around January 2015 so I want to get on that run list. I was originally thinking about a constant 9 twist barrel but not sure if I want to get into the gain twist game. Kirby Allen seemed to be shying me away from the gain twist barrels a little. I would like to chamber and throat the barrel for the SMK 350's for mag length purposes but also play around with the Cutting Edge designs (I.e. 352, 377, 402, 425 gr.)at the same time. I know this is somewhat of a tall order but just hoping. Can you give me any suggestions on barrel twist rates for gain twist rifling if you where trying to shoot any or all the bullets that I listed? I was thinking of going with a Bartlein 12.0/7.0 twist maybe. Thanks.

 

[Kiwi Greg]

I have done very little with the 350 SMK in gain twists but I would strongly recommend that you stop thinking about trying to shoot it in a 7 exit twist unless you like cleaning copper fouling.
I too will be getting some 375 barrels in the next run, once I finalise the exit twist, there is a group buy on here.
http://www.longrangehunting.com/forums/f17/bartlein-375-cal-group-order-134706/
I shot some custom CEB 450 grain Lazers recently out of my 7.25 exit & they shot well at 2000, so maybe we are overspinning the projectiles ?

My 7.25 exit shoots all the CEBs from 350-425 grain accurately, but the heavier ones give better ballistic performance than the ballistic calcs suggest.
A friend shot the CEB 425s with my old first 375 DCM, 7.25 exit & they were accurate & stable past 4K.
It is possible that you can shoot a heavier projectile than previously thought in a straight twist barrel but it could be a lottery.
I appreciate that mono projectiles are spendy, especially compared to the 350 SMK, but I think of it this way, if you owned a Ferrari why wouldn't run it on the best fuel you could, to get the best results you can.

 

[Chaddman]

Thanks for the great info Greg. I'm not dead set on only shooting the SMK's. I was advised by my gunsmith to stay away from the gain twist barrels. I'm not sure why as I didn't ask him but I was trying to give credit to him by taking his advise as he is known and respected as knowing his stuff.
That being said I'm still very interested in the gain twist barrels so I may end up buying one of each style constant and gain just so I could experiment with all bullet types. I too do not want to limit myself to just one bullet type and weight.
You say you may be over spinning the 425's and the new 450 proto. What would a more conservative twist rate be if you had to guess? In other words what would the minimum twist be that you could get away with right before accuracy potential starts to drop off and still be stable at 2K and 3K ranges?

 

[Kiwi Greg]

I'm not sure ?
One guy I know shoots 400s in 1-10 good so far to 1k, another 425s 1-9, good to 2k I've been told.
I have a 1-9 on the way to have a play with myself.
Saying we might be over spinning them doesn't mean its necessarily a bad thing.
The 350s at 3400+ with an exit of 7.25 are hauling some serious RPM & still shoot mint & don't foul, clearly they will shoot very well in a 10-11 twist, they certainly don't require anywhere near 7.25.
I've been very happy with my velocity & accuracy at 2k with my 7.25 & my friends accuracy at 3.6 & 4+k is unbelievable.

 

[Chaddman]

Hmmmm. Of coarse you guys never make it easy on the new guy to choose a twist rate. Just giving you a hard time I guess I will probably decide on a 12.0/8.0 gain twist or a 11.0/7.5 gain twist. Or even step it up a hair to a 7.25 like you are your friend are running. My thought process is to hopefully get at gain twist combo that will shoot most if not all the CEB's well or very well and then let the barrel choose which bullet(s) it likes the most. I also want to stay away from a twist that has an excessively radical transition in twist between the breech end and the muzzle like 13.0/6.0 or more. But even that is not as scientific as it sounds due to lack of testing in twist rates. You've said it yourself that your still testing the waters so I surely don't know either.

What contours are you and your friend running on your 7.25 exits?

Also when taking payment does Bartlein ask for money up front or when the barrel is complete and ready to ship?

 

[Kiwi Greg]

Hmmmm. Of coarse you guys never make it easy on the new guy to choose a twist rate. Just giving you a hard time I guess I will probably decide on a 12.0/8.0 gain twist or a 11.0/7.5 gain twist. Or even step it up a hair to a 7.25 like you are your friend are running. My thought process is to hopefully get at gain twist combo that will shoot most if not all the CEB's well or very well and then let the barrel choose which bullet(s) it likes the most. I also want to stay away from a twist that has an excessively radical transition in twist between the breech end and the muzzle like 13.0/6.0 or more. But even that is not as scientific as it sounds due to lack of testing in twist rates. You've said it yourself that your still testing the waters so I surely don't know either.

What contours are you and your friend running on your 7.25 exits?

Also when taking payment does Bartlein ask for money up front or when the barrel is complete and ready to ship?

The 12-7.25 does work very well.
I will probably go 12-7 for my next ones.
We just run a straight taper from a 5-6" knox down to 0.92.
No idea on the payment situation with Bartlein.

 

[Rocky Mountain]

Some interesting talk about solids and gain twist barrels, I know three years ago when I was trying to wade through all the miss information out there I finally chose between 8 and 6 twist ordering 12-7.25 which Kiwi Greg and others ended up getting to. Is it the right twist rate ?? all I know is that it works very well with 350gr through to 450gr CE. Dose this mean a bit more twist rate isn't a bad thing? I know having more twist rate opens up a lot more bullet options than if I had a state twist rate barrel Real world shooting by one of Kiwi Gregs friends out to 4000 yards with the a 425gr CE 7.25 twist in my 375 DCM chambering with all bullet stable is a very strong argument for more twist. I have heard that starting slower allows the bullet to settle before raising the twist rate, would a faster twist at the start be good or bad with the longer 375 Cal bullets.

 

[Chaddman]

Great point which was the essence of my next set of questions. Is it better to start out slow with a 12 or even a 13 twist and work your way to an exit of 7 or 7.25 or is it better to start our fast with say a 9 twist? I know Augustus has a 9.0-6.0 gain twist that he uses from time to time maybe we can raise him up for some input.

I hope this doesn't open up to many more questions. Eventually I would like to actually order the barrel twist that I settle on before Bartlein begins their next run.

 

[Rocky Mountain]

Some say a larger difference between twist in a gain twist barrel isn't as good as half that twist but out of the 4 barrels I know off with larger gap I can't see how you could improve there performance.

 

[Chaddman]

RM, these four barrels that you are talking about with great performance what twist rates are they running?

 

[Rocky Mountain]

I'm in no way saying other twist combinations aren't working well Augustus 9-6 shoots very well with the 425gr CE, just there isn't any real world advantage that I can see either way at this point in time. I just like the idea of being easier on these long solids when they first enter the barrel so sorry there isn't any right or wrong. The four barrels are 12-7.8 and three 12-7.25, the 12-7.8 for some reason didn't shoot the 425gr as well as the 350gr to400gr CE which it shot well.

 

[Augustus]

I have two of the gain twist 375 barrels. One is a 9 to 6 and the other is a 13 to 6.5, both shoots the 400 and 425 very well. Other folks testing seems to indicate exit twists around 7.2 will suffice.

Based on my experience and the testing of others, I think an exit twist of 7 would be optimum for the 425. If I ordered another gain twist barrel, I would probably try a 12 to 7. It will be a very long time before all question are answered about the .375. There has been millions of rds fired through a 308 and there are still discussions about what projectile and twist rate is best.

One thing is for sure, your pocketbook is going to get several grains lighter over the next couple of years if you continue down this path.

 

[Chaddman]

Hey Augustus good to talk with you. After talking to Kiwi Greg and Rocky Mountain the last couple of days the 12.0-7.0 gain twist is exactly what I was thinking too. I hope to place my order with Bartlein along with you guys this next round. Thanks again.

 

[Rocky Mountain]

I ordered a 12-7 with the group buy a week ago
Time will tell what is the best but the 12-7 is good guess for now.