Factory Norma Match .223 77gr SMK's 1-9 @ 100yds

[Chris Butler]

Shot this group with a Savage Model 12FCV .223, 5 shots off a bipod, no rear bag.
I understand that 77gr shoot better out of a faster twist.
Is this an anomaly?

 

[benchracer]

Nice shooting! ...and very surprising to see from a factory load. I don't think this is an anomaly. My 9 twist 5.56mm bolt gun shoots the 75 AMAX with amazing consistency (which, I believe, is longer than the 77 SMK) out to 500 yards, which is as far as I have shot it. The twist calculators say it shouldn't work that well.

The 9 twist causes bc to be degraded, which is reflected in my drop and drift, but I haven't tested another bullet that shoots this consistently, and I have tested bullets ranging from 53 to 75 grains. I suspect the same general phenomenon is at work with your rifle relative to the 77 SMK.

The other thing to consider is that, with a marginal twist for a given bullet weight, you may not get the same results in all conditions.

 

[Chris Butler]

Thanks

 

[kevinbritvec]

Shot this group with a Savage Model 12FCV .223, 5 shots off a bipod, no rear bag.
I understand that 77gr shoot better out of a faster twist.
Is this an anomaly?

 

[kevinbritvec]

My 26" 1/9 Winchester M70 loves Hornady 75 grain bullets. I believe the longer barrel adds approximately 100+ fps over a standard 20" barrel and helps to stabilize an otherwise borderline bullet.

I also tried to double check my barrel twist by using a tight fitting patch and counting revolutions as I pass the cleaning rod through the bore. My best guess is that my particular barrel is just slightly faster than the advertised rate of 1/9. I measured closer to 1/8.75.

Be glad that your rifle shoots them, realizing that in cold weather it may not. Also extended ranges may cause the bullet to destabilize because it will have lost a lot of velocity. Lower velocity requires a faster twist to remain stabile.

 

[Chris Butler]

My 26" 1/9 Winchester M70 loves Hornady 75 grain bullets. I believe the longer barrel adds approximately 100+ fps over a standard 20" barrel and helps to stabilize an otherwise borderline bullet.

I also tried to double check my barrel twist by using a tight fitting patch and counting revolutions as I pass the cleaning rod through the bore. My best guess is that my particular barrel is just slightly faster than the advertised rate of 1/9. I measured closer to 1/8.75.

Be glad that your rifle shoots them, realizing that in cold weather it may not. Also extended ranges may cause the bullet to destabilize because it will have lost a lot of velocity. Lower velocity requires a faster twist to remain stabile.

Thanks for the input!!
Much to learn from.