The Down Range Forum
Member Section => Building America's Rifle => Topic started by: kmitch200 on October 04, 2023, 06:14:38 PM
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I was plugging in some bullet weights in Berger’s spin stability calculator.
Specifically looking at 77gr in 1/9 twist. At first it was “ahh, that’s marginal.”
Then I added in the elevation I live at now (4700’) and it was {thumbs up} GTG.
Does this match your experience?
This curiosity was started when I saw a show featuring Da Boss of Black Hills Ammo shooting the commercial version of the military MK 262 MOD 1.
While we can’t buy that, (for ourselves but we can buy it for others ::)) we CAN buy its commercial equivalent, the MK 262 MOD 1-C.
Same accuracy requirements:
these rounds come with the same no-nonsense lot acceptance accuracy test (10 groups of ten shots each at 300 yards) provided on military lots. No lot will ship unless it shoots sub 2″ groups (.64 MOA maximum/10 shot groups).
Not having that load, I picked up some 77gr Fiocchi and 75gr Hornady.
Range trip!!!
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I haven't shot any for accuracy yet, but I have 77-grain ammo to try in both a 1/7" and a 1/9" twist barrel. If the 77-grain fails to perform well in the 1/9" twist, I also have some 69 grain ammo to try out. I generally shoot M193 ball or its equivalent out of any barrel, whether it's theoretically over-stabilized or not. Mostly because it's still relatively cheap. I also like 62 grain ball ammo. 62 grain FMJ ammo, and JSP for that matter, usually has better accuracy than green tip ammo and still has SD better than 55 grain ammo.
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So the range trip went GREAT!
Now granted, it was only at 100yds for the test fire but my post ban Colt HBar 20“ 1/9 (NOT an AR, no deadly bayonet lug) loooved the 77gr match.
The Colt is bone stock except for the Geissele large pin trigger. My God how I love that!
(The Hornady 75s not so much but I was more interested in the 77s anyway and didn’t really give them all the attention I should have.)
After plinking away at bullseyes I put up a counter-sniper target.
5 rds in the ear that were about .75 MOA. Next stop, 200 and beyond on the steel! :)
What’s neat about the 77s is the wind call is yardage squared for a full value 10mph wind. 300 yds - 3x3 - 9 inches. Gets you in the ballpark so you can +/- 10 mph and whether it full value or not.
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That yardage thing is neat. I'd never heard of that before.
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That yardage thing is neat. I'd never heard of that before.
Yeah, me either.....very interesting.
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Yeah, me either.....very interesting.
Trust me, I didn’t think of it. (I wish I did but I’m not that smart) It was from the show I saw featuring the MK 262 MOD 1-C.
Plugging in the MV from my rifle with the Fiocchi load the wind calls are really close to the yrds squared formula.
I plugged in a 69gr Sierra MK in the calculator and guessed at a MV and it was kinda close but the 77 was more accurate in the calculator I have.
(Ballistic AE app)
I’m going to chrono some 69 GMM I have out of the same rifle and see the true speeds, plug it into the app and see what comes up.
I REALLY wish I could use that formula for another caliber/bullet weight but haven’t found anything remotely close. I tried heavy, light, medium using a 308 bullet and got brain fry by the time I was done playing around. :o