Unexplained Bullet Instability - HELP

[SteveK]

I just shot a few new bullets I loaded up and am baffled by the results.... Keyholes at 100 yards!

These were Berger, 70 grn BTHPs with 25.4 grn. Ramshot X-terminator. The gun is a bastard, comprised of an MR556 H&K upper (16.5 in. bbl/1 in 7 twist) and a Colt M4 lower. The grouping was none too great either... about a 5 inch group.

What the hell is going on here?

[Artful]

What's the length of that bullet? What's the speed of that load?

Looks like 2,900 to 3000 fps ish?
http://www.ramshot.com/wp-content/up...ec_1-23-14.pdf

[CHeatermk3]

My HBAR 1/7 twist didn't like them either, nor did it like the 77 gn Sierras.

It shot the 69gn BTHP match well and surprisingly did well with the winchester 64gn powerpoint in either with or w/o cannelure.

Good luck I got rid of that 1/7 bbl in favor of a 1/9 twist.

[Remiel]

im setting up to build an ar and found this to be helpful on twist rate.

http://www.gunsandammo.com/ammo/pair...st-rates-ammo/

[Comrade Mike]

I rock a 1:8 and have run into 0 problems

[frnkeore]

When you have stability issues with jacketed bullets, ALWAYS measure your twist rate.

I have purchased 3 barrel blanks, over the years that where mis-marked. Two 25 cals, both marked 12 twist, one was 10 twist and the other was 18! The barrel that I'm now shooting is a 33 cal, marked .338 x 10, it is actually .337 x 15!

Douglas only guaranty's 1/2" in there twist rates because the button can't be depended on to follow exacty.

Because of my experiance, I highly recommend checking twist rates, even if you don't have stability issues now, with a new, longer bullet, it could still raise it's head.

Frank

[JSnover]

Since you can't change your rifling, change your velocity or bullet length (weight). What else have you loaded for this rifle? How did the others shoot?

[Motor]

Steve. Is it possible that your barrel has a worn throat? 1 in 7 is FAST and if the rifling is worn the bullet may not be engageing the rifling but sliding through it.

Check the bore especially the throat for copper fouling.

[KYCaster]

What the hell is going on here?

You're two grains over the max recommended load.......BACK OFF!!!...........

...........or, better yet, use a slower powder.

Jerry

[nhrifle]

I'll pass on a little magic trick I know: Varget.

Buy some, beg some, acquire it somehow.

[Twstanley]

yah, I am with kycaster, recheck your load data, you are 2 grains over max for that bullet weight and powder. With that much pressure and that quick of rifling the bullet is probably just sliding over the rifling and not stabilizing at all.

Any flattened primers or ejected brass with bright rings near the base?

[triggerhappy243]

my sons ar did that too. either too slow or too fast.(velocity)

[RG1911]

And it just may not like that bullet. (Although 2 grains over max seems to be a bit much.)

My old Chanlynn AR-15 barrel (1-in-8 twist) loved the Sierra 69-grain MatchKing and the Hornady 60-grain V-Max. My new Krieger barrel hates them both, but loves the Hornady and Sierra 55-grain bullets and the Sierra 77-grain MatchKing.

Richard