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sniper_jay
11-21-2006, 3:32 PM
the ammo box sez it's designed for "1 in 9 or slower twist barrels."
my CMMG upper came with barrel twist of 1 in 7. is that slower or faster than 1 in 9. did i get the wrong ammo? :confused:

SemiAutoSam
11-21-2006, 3:35 PM
1 in 7 is faster than 1 in 9

what this means is the bullet makes 1 complete revolution 360 degrees in the case of 1 in 7 7 inches of barrel length.

and same for 1 in 9 it takes 9 inches of barrel length to make 1 360 degree revolution.

ocabj
11-21-2006, 3:35 PM
1 in 7 is faster than a 1 in 9.

You don't really need to worry if your barrel has a faster twist rate. Unless you're shooting 40-50gr ammo at 4000fps, it's not going to be a problem in a 1 in 7 twist barrel.

blkA4alb
11-21-2006, 3:36 PM
The 1 in 7 twist is designed for heavier bullets, there is a possibility that the bullets could tear themselves apart from the faster twist of your barrel. A 1 in 7 twist is faster than a 1 in 9.

sniper_jay
11-21-2006, 3:46 PM
thanks for the info.. i guess i'll have to shoot them through my Stag upper build then.. the box sez 45 grain, 3600 fps btw..

i get it now. "faster" means faster spin by the bullet inside the barrel then? does that affect the velocity or the accuracy in any way??

what's the barrel twist in a mini-14? i have one of those too. i was under impression that i can shoot just about anything with that rifle..

thanks again for the info fellas.

jemaddux
11-21-2006, 4:05 PM
thanks for the info.. i guess i'll have to shoot them through my Stag upper build then.. the box sez 45 grain, 3600 fps btw..

i get it now. "faster" means faster spin by the bullet inside the barrel then? does that affect the velocity or the accuracy in any way??

what's the barrel twist in a mini-14? i have one of those too. i was under impression that i can shoot just about anything with that rifle..

thanks again for the info fellas.

45gr bullet is to light for a 1 in 7 twist. The bullet will do what is called keyhole which will cause you to have no accuracy at all. When you buy bullets for the barrel check a few rounds out. Try a 62gr or 68gr. You can find British rounds of 62gr for around $125 or so per 500, the 68gr Canadian you can find also. If you want you can go up to the 69gr and that gets a bit pricey with Black Hills and so on. But try a few out and see what shoots best for you.

Ubergeek
11-21-2006, 4:12 PM
what's the barrel twist in a mini-14? i have one of those too. i was under impression that i can shoot just about anything with that rifle..

A Mini-14 has a 1 in 10" twist.

IIRC, some of the folks on ARFCOM have shot 45 grain 5.56 ammo (Winchester varmint ammo) from 1 in 7" twist barrels, and have not complained of poor accuracy.

mltrading
11-21-2006, 5:03 PM
Oh-oh, the AR15.com Ammo Oracle site is down. You may find more info over there.

The 45gr is too light for 1/7 BBL. I am afraid that the 45gr bullet will be torn apart at such spinning rate.

If you are shooting 55gr and up, 1/7 should be proper.

6172crew
11-21-2006, 5:34 PM
Your 1 and 7 twist will really like the SS109 or even the heavy stuff blackhills sells.

Im going to buy some 77 grain just to see how it works at 700 yards.:cool:

ocabj
11-21-2006, 7:31 PM
You could probably shoot the 45 grain bullets out of your 1 in 7 twist. We had a guy trying to tear the jackets off of 45gr bullets at the range in a 1 in 8. Couldn't do it at 4000 fps.

As far as 77gr at 700 yards, it's doable. Wind drift will be worse than 80s, but if your wind call is ok, you'll be fine.

PIRATE14
11-22-2006, 12:21 AM
You could probably shoot the 45 grain bullets out of your 1 in 7 twist. We had a guy trying to tear the jackets off of 45gr bullets at the range in a 1 in 8. Couldn't do it at 4000 fps.

As far as 77gr at 700 yards, it's doable. Wind drift will be worse than 80s, but if your wind call is ok, you'll be fine.

As you get to the lighter bullets in the faster twisting barrels it's the bullet design of the jacket that will keep the bullet together.....some of the 45 grain thin jacket bullets can hack it others can't......if you have a shorter barrel you have less to worry about. As a rule of thumb stick to 55 grain or higher in a 1-7.

xrMike
11-22-2006, 8:00 AM
Your 1 and 7 twist will really like the SS109 or even the heavy stuff blackhills sells.

Im going to buy some 77 grain just to see how it works at 700 yards.:cool:Where's the best place to buy Black Hill's remanufactured ammo in those heavier weights? Is 69 grain a good one to try in a 20" 1:7 barrel, out to 300 yards max?

I've been shooting 55gr out of my 1:7 and I want to try some of the heavier stuff, just to see if it's more accurate.

ocabj
11-22-2006, 8:25 AM
Turners carries 77gr Black Hills blue box last time I was in there (several months ago). Midway has good C&R pricing on it.

Just go with 77 rather than 69. I was going to use 69gr SMKs at 200 yard (specifically offhand) and 77 for 300 (and 80 for 600). But rather than wasting time and money getting another bullet and keeping ammo sorted for all three distances, I just went with 77 for 200 and 300 (and 80 for 600). The only reason I considered 69 for 200 (offhand) is to have a faster velocity round to get the bullet out of the muzzle faster. But after much thought and advice from other shooters, I passed on the 69 for highpower use.

I'm shooting 77gr SMK at 2730fps in a 20" 1 in 7" twist service rifle legal barrel.

Also, quite a few people have stated they couldn't get 69gr SMKs shooting well in their service rifles.

xrMike
11-22-2006, 8:35 AM
Thanks! That's exactly the kind of advice I was looking for...

jlmurphy
11-22-2006, 10:48 AM
Mini 14's came with different barrel twist rates, so check yours. Also, every bullet has an optimum spin rate, but what really matters is the combination of barrel twist rate and length combining to give muzzle velocity. A slower twist barrel with a long barrel, or a really hot load can give a higher muzzle velocity/spin rate than a short barrel with a faster rate.

sniper_jay
11-22-2006, 1:15 PM
my ignorant ***** just went to walmart and bought the cheapest ones.. shows what i know about guns.. :o

i didn't even bother to check my cmmg upper's barrel twist rate until i noticed the "1 in 9 or slower" marked on the ammo box..

actually, i didn't even know those grooves inside the barrel came in different variations.. :( thanks again fellas!

Sydwaiz
11-22-2006, 2:07 PM
Some bullets have thinner or thicker jackets too depending on the manufacturer. But unless you reload, I wouldn't worry about it. Just buy some heavier bullets and try em and see what works.