Gunsmithing 6.5mm Barrel Twist weigh in's

[Jayman_10X]

To my Sniper's Hide Brothers,

I recently acquired a 260 Rem with a 1:8 twist x 22" bbl. I'd like to try it at 600 yards using 140 gr SMK's (have them on hand). Any concern about overstabilization with this caliber/twist/bullet combination?

Any experiences to prove/disprove that it will work?

As always, thanks for your thoughts!

Jason

 

[427Cobra]

Re: 6.5mm Barrel Twist weigh in's

I run a 8 twist with no problems what so ever.

 

[Bugholes]

Re: 6.5mm Barrel Twist weigh in's

At 260rem speeds from a 22" barrel, you won't have any trouble. At 2850+ FPS I have seen problems from overstabilization between 600y and 1K with the 139/142s

 

[JCH]

Re: 6.5mm Barrel Twist weigh in's

8 twist (6.5 CM)and I run 140 amax's...no issues.

 

[ChadTRG42]

Re: 6.5mm Barrel Twist weigh in's

You're good!

 

[head2h2o]

Re: 6.5mm Barrel Twist weigh in's

You'll be fine. I run the 140's out of a 1 in 8 all the time with no problem.

 

[Niles Coyote]

Re: 6.5mm Barrel Twist weigh in's

I was just checking stability this morning on this caliber using Bryan Litz’s software and came to the conclusion that the 8 twist would be the best to stabilize the long range bullets in all weather conditions that I would be shooting it in.

8.5 would work but the data suggested I may be cutting it a little close when the temp dips with some bullets.

I would not worry about over stabilizing unless you were shooting some real light weights, with thin jackets.

 

[Jayman_10X]

Re: 6.5mm Barrel Twist weigh in's

Thanks Guys,

I also want to try some 120 grain Nosler's in the same barrel for hunting. As such, my shots would likely be within 400 yards. Any potential issues with that bullet?

Jason

 

[JCH]

Re: 6.5mm Barrel Twist weigh in's

the 120gr Amax didn't shoot as well in my 8twist. I just shot factory Hornady loaded rounds and didn't do any load development but the groups were still sub-moa. I basically just wanted to foul the barrel up good and get some extra pieces of brass.

I wouldn't worry at all.

 

[LRI]

Re: 6.5mm Barrel Twist weigh in's

8 twist was the defacto practice for a very long time, then guys started slowing it down to an 1:8.5

I'm betting you'll be fine.

Just remember: twist rate and velocity has a direct impact on bullet RPM and this is what your ultimately concerned with.

A 3000 fps muzzle velocity rotates that little bullet at 270,000 rpm.

That's buzzing right along. As you pour on the steam (powder charge) the rpm increases as well. At some point something has to give and it's usually the jacket of the bullet.

Good luck.

C

 

[Jayman_10X]

Re: 6.5mm Barrel Twist weigh in's

Thanks Guys

 

[ChadTRG42]

Re: 6.5mm Barrel Twist weigh in's

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">8 twist was the defacto practice for a very long time, then guys started slowing it down to an 1:8.5 </div></div>
Yes, I prefer an 8.5" twist. I'll be running a gain twist to 8.5" soon. Another hunting rifle we did that had the same barrel had more velocity and shot very well for a factory gun with a Bartlein on it.

 

[border_reiver]

Re: 6.5mm Barrel Twist weigh in's

The 6.5 x 55's had both 8.66" and 7.87" twist rates, can't remember which the current SAAMI/CIP standard is for them, but made them in both twists for ammo companies worldwide. That's 1/220mm and 1/200mm respectively. Swedes were at one time using the 160grain(?) round that looked like a tube of lipstick, 4 wide lands for rifling, I suppose on their european moose.

260 Rem velocities, shooting the 120-140 I'll usually recommend 8" twist, though 8.5 does fine. Built a few 260's and 6.5 x 47's at 9.3" twist that shot the 120's extremely well.

 

[Greg Langelius *]

Re: 6.5mm Barrel Twist weigh in's

Been shooting .260 since early on with bullets ranging from 95gr to 142gr, all in a 1:8" twist, one barrel 24", 2 more at 28".

Remington initially narketed their rifles with 1:9" twist.

I have fired 120gr in 1:8" twist at 1000yd and saw some yaw that might have indicated overstabilization. Drop was a lot more than calculated, but oddly, accuracy was still in the 2MOA range. The bullet holes were elongated some, but all the points were pointing roughly upward. I can't say with certainty what all is happening, but I won't try it again.

I think that it may be possible to fire 139-142gr in a 1:9" barrel, but I'd not be so sure about a short one.

The 95's (HDY V-Max) were shot at well above 3000fps and 200yd and shot very well in the 1:9".

I think that 1:9" is GTG for 120gr and lighter, and may order a long (28") 1:10" for testing lightweights at extreme velocities (3400+fps).

Greg

 

[6.5x61Super]

Re: 6.5mm Barrel Twist weigh in's

..1 in 8 Pac Nor, 139 gr. Lapua Scenars @2,970fps....1/4MOA when I do my part.

I also have a Bartlein 1 in 8.5 sitting in my safe...