Tested My New .223 With 90's Today

[hogan]

COAL is acronym talk for Cartridge Over-All Length.

I was wondering what in hell you were doing with a 90gr bullet about .2 deeper than an AR-15 mag length seated bullet???? But you were Measuring to the ogive explains it...
Seems the established bullet maker recommended minimum twist to make a 90 grainer perform is 1:6.5 not much wonder 7 twist isn't delivering the goods.

 

[cmillard]

i think that that 6.5 twist is for 20" service rifle barrels

 

[FroggyOne2]

6.5 twist is for the Sierra 90 in a Service Rifle because of the reconmended muzzle speed of 2650 fps.

 

[hogan]

It ain't the velocity that is critical to stabilize the bullet, it is the twist.

Anybody seeking 2650fps with a 90gr bullet in any kind of AR-15 is playing with fire. Maybe if you AI the case, but how many AR-15s shooting .223AI when can shoot grendel or 6mm AR or even a PPC?

I am happy with 77/75 grain match bullets at mag-length for all-purpose.

Have you seen the Dominion Rifle Club of Canada Winter 08 article with the report on 1000yd shooting
w/90gr SMK & JLK from a 6.5 twist bolt rifle? Google will find it for you. The guy was firing 20shot groups
at 1000yds and getting a 2" average vertical dispersion. Not just a few times. Tons of data.

I doubt even with a super stout actioned boltgun if the guy was pushing 2650fps, but has been a while since I read the article.

I have a White Oak Precision Pac-Nor SR barrel in like new condition, 6.5 twist if you are interested and have an AR-15 to mount it with. make you a deal with 300 JLK & SMK 90gr if you are interested. Not a give-away, but a solid deal...

Hope you are having fun with your pursuits, just double-check that velocity thing related to twist. Might call Sierras techline and inquire if they put that "use only with 6.5 twist" label on the box for grins & giggles...

 

[FroggyOne2]

What I was trying to say is that to shoot the Sierra 90's in a service rifle, it is reconmended that one use a 6.5 twist bbl, the reconmended max V for that bullet is 2650 FPS. That is what the company says from what I know. But I don't fool with those! I am using the Berger 90's. And I know that they have worked well in a 7.7 twist bbl. But that is a bolt gun, just as I am shooting. I have not meddled with a gas gun in years!

 

[KenO]

I build a simular setup, but different stock. I shoot a Barnard P .308 for Palma matches in a offset Mastin stock with the V-block. So I put together another Barnard P for .223 and switch out the stock. I have a 30" Brux 7.5T barrel. I didn't know which chamber so I called Dave Kiff for guidence, he steered me away from the Wyde because he said it was a large chamber for gas guns. I got his .223 Match reamer, kind of tight, but no-turn neck (barely).

The barrel is real finiky for finding loads, went through many bullets, and both RL15 and Varget. I laddered up over a chrony and had pretty bad SDs and groups trying nodes. Then I tried the 82 Berger over varget and it tightened right up running 2880. Its been a real hammer! I shoot it mostly in 3X600 competitions in the Palma class. I shot a couple practices at 1000, it did fine, but trust the .308 more for that distance, and haven't shot a Palma or 3X1000 with it (yet).