Setting up a fast 6.5 with heavies

[Chickentoast]

Planning on spinning up a 6.5 Sherman Short (26") and am conflicted between Berger LRHT's - 144's and 153.5's.

Will I overspin the 144's in a 7.5 twist around 3250 fps? I've read about the Hornady 147's vaporizing, but nothing on the Bergers. The 153.5 looks like it needs or at least prefers a 7.5.

 

[bobke]

Perhaps not exactly relevant because of lower expected velocity from 6.5 CM, but some insightful comments from Frank and others regarding compromise of twist, bullet weight, velocity and jacket construction that may be meaningful in your circumstance.

7 twist 6.5CM in 20” AR?

Have divested myself of .308 AR rifle and most of my supplies to focus on 6.5 cal AR’s and have question regarding advice of use of 7.0 twist for a new 20” +2 gas Krieger barrel. All of my experience with current inventory of 6.5GR, 6.5x47 and 6.5CM in either bolt or gas guns use 8-8.75 twist...

www.snipershide.com

 

[badassgunworks]

No you won't over spin it I use a 1 in 7 twist and also a 1 1/8 Twist on 160 grain bullets 6.5 caliber I pushed 140s at 3800 feet per second to that same Barrel no issues at all

 

[Chickentoast]

^Awesome, what cartridge for that velocity?

 

[badassgunworks]

My 6.5 perseus and the 6.5 romulus perseus is based off full length improved lapua case and the romulus is based off of a shortened cheytac

 

[Chickentoast]

I understand your goal is no come-up or windage. Ever! And maybe go through a few dozen barrels/yr.

 

[Ledzep]

I wouldn't go faster than 1:8 personally. There's no need, especially if you're going to be sending them fast. The 6.5 PRC barrels that I've seen that had 147's failing also failed 140 Bergers, 140 ELD's, and 150 SMKs. Can't speak specifically about the 144 or 153.5.

Keep the barrel clean and the throat in good shape and it will pay off for you later. Carbon rings, heat, fast twist, tight spots, tight bores, etc... are all contributors to bullet failures. Most barrels don't have issues with it but you start inviting problems near & over 300k rpm and twist rate is one of the variables that is entirely in your control.

3100* 12/7 * 60 = 319krpm
3100* 12/7.5* 60= 298krpm
3100* 12/8 * 60 = 279krpm

 

[THEIS]

Hi,

Any reason you are wanting to stick with jacketed projectiles since you are wanting to push as fast as you can with that cartridge?

Switch over to monos and not worry about spinning too fast.

Sincerely,
Theis

 

[Chickentoast]

From what I've seen, the monos are twice the cost with worse BC. Am I looking in the wrong places?

 

[Ledzep]

Twice the cost, yes. Worse BC... Depends on how you look at it. Typically BC for the weight is pretty high, but the cap on weight (length) is lower than with cup&core (lower density). Nonetheless, the cap on length is determined by twist rate and not worrying about the integrity does alleviate the spin issue (faster velocity and/or faster twist). The real length limitation is then how much twist you can get to bite and/or magazine/platform limitations.

Anyway, if you go crazy fast twist for heavy solids.. you're likely only going to be able to shoot solids. Or you keep a hybrid capable twist rate and shoot lighter solids that have similar BC to heavier cup & core. There are some other arguments and trends that go back and forth. Cup & core has some benefits that solids can't achieve and visa versa.

6.5MM 121gr FLAT LINE BULLET | Warner Tool Company

The 6.5 mm 121 gr Flat Line Bullet is a CNC lathe-turned copper solid, designed to boost speed and BC - shooting farther, faster, flatter.

www.warner-tool.com

 

[Chickentoast]

Thanks, yes, I've checked out Warner, Cutting Edge, and Hammer. I came to the same conclusion... they might benefit a 6.5 Creed or a 308, but not a 6.5SS, or a 300 RUM, and since they require more twist/new barrel, why not add some case capacity and win on both ends with a heavier, jacketed projectile as well.

I went through the thread below... it seems 7.5 twist with 5R rifling is doing ok for 150+ grains, but I didn't read anything about anyone having poor accuracy or tumbling bullets with 8 twist either. Still on the fence, no rush on the build.

You are being redirected...

 

[Lowlight]

Do a gain twist and not worry about it

Go 8.25 to 7.5 and you are money all the bullets will work

 

[Chickentoast]

Good idea - I did read your thread on gain twists but didn't find any gain barrels in stock when building my last rifle. Since no rush on this one, might as well order one.

 

[badassgunworks]

Yes your looking in the wrong place. By design is possable but to get a heavy 6.5 you need a super fast twist

 

[Chickentoast]

Did some more reading - there's a good deal of data on the Berger 156 EOL, and no one has had an issue with 8 twist (from Accurateshooter site), while some people have had issues with 7.5 twist. I'd still like to try the gain twist, but it seems Ledzep gave the right advice above - just go 8 twist because there's no need for more, even with long heavies.

 

[oinco]

If you talk to barrel people, they"might" be able to steer you right if your questions are sound... twists are not equal between manufacturers due to several things. The best gunsmiths will tell you who currently has the best 6.5 barrels or the best 6 barrels etc. it varies by caliber. Why? because tooling varies by caliber.

I have a 6.5SST 7.5 twist. 150SMKS work very well and 146 Matrix Ballistics VLD even better.

 

[Squibbler]

Yes your looking in the wrong place. By design is possable but to get a heavy 6.5 you need a super fast twist

Any recommendation for 6.5 optimized for a 7 twist?

 

[Ledzep]

Any recommendation for 6.5 optimized for a 7 twist?

Yeah, put a ".5" at the end of that 7.