Sensible and appropriate AR ammo?
 

O.K. I have an AR with a 1:7 twist. After reading several articles as well as the ABC's of Reloading, I realize that with my twist rate, I can shoot pretty much any weight of bullet, from 50gr. up to 80 gr. First off, do you agree with this assumption? Secondly, if this the case, what is a good CQ bullet weight? And also, what would be a good longer range weight, say past 200 yds.? Lastly, what would be a good weight for 100-200 yds? Does it really even matter at 100 yds? TIA

Personally, I stay away from the 50 grainers in a 1:7 and consider 62gr to be my minimum for stability. I generally shoot 69 gr out to 300 yds, and 77 - 80gr beyond 300. But that's just me.... ;)

+1 to what Highpower said. I have an RRA with a 1:8 and it shoots 69gr. Sierra's and 68 gr. Hornady HPBT's very accurately. 55Gr. Remington FMJ's don't group any tighter than about 1.5 - 2". I've never shot anything heavier than 69gr., but I'm willing to bet that the 75-80 gr. bullets will shoot better than the 69gr. bullets. National Match competitors use 77 - 80 gr. bullets out to 800 yds., the only problem is that they have to be loaded singly, since they will not fit in the magazine.

Your initial assumption is correct: your barrel will stabilize anything from a 50 grain to an 80 grain bullet. There does exist a 90 grain bullet, which your barrel will stabilize as well.

For my shooting, I tend to 55gr FMJ for anything from the muzzle to 300 yards.

1.) One should not expect anything greater than 2" groups from a 55-grain FMJ at 100 yards. The exposed lead at the base of the bullet has a lower melting point than the copper jacket. The lead will melt slightly during the firing process and throw the concentricity of the bullet out of whack.

2.) Depending on the ranges, 69 grain bullets should shoot better. The 69 grain bullet has a better ballistic coefficient. The 75-80 grain bullets tend to be used at longer ranges because the shooter does not have to compensate as much for the wind.

3.) The Sierra Matchkings in 77 grain and the 75 grain Hornady bullets can be seated to magazine length. In fact, soldiers and Marines in the Squad Designated Marksman role are using 77 grain Sierra MatchKings.

Sierra recommends a 1:6.5" twist barrel.

Absolutely correct. Which ticked me off awhile back because I drove all the way out to the Sierra factory (3 hrs from home) to purchase some "seconds" and they were completely out of them. (ALL bullet types!) I talked with one of the ballisticians and was told that the plant was producing one bullet - and one bullet ONLY at that time. The 77gr MatchKing (cannelured) -- for the US military.

I'll be glad when they get back to a "normal" production schedule. :)

Thanks for the feedback guys. I'm heading to the range on Thurs. and I'm bringing some Hornady 75 gr. Match ammo and some Federal Fusion 62 gr. for comparison at 100 yds. However if I can get comparable accuracy @ 100 yds with 55 gr. I'll use those for practice ammo.

Quoted from Sierra's 4th Edition 50th Anniversary Manual:

As for loadings and recommended powder charges given for this bullet, the following also appears under the 80gr. MatchKing HPBT in the same manual:

You would be hard pressed to find SAAMI approved reloading data that endorses seating a long, heavy bullet to an OAL of 2.26". Additionally, depending on the type of chamber you have, you may not even be able to chamber a round using an 80 gr. bullet which has been properly seated to an OAL of 2.550". Many modern chamberings are of the .223 Remington variety, and do NOT posess the longer leade of the military 5.56 or Wylde chamber.

Please re-read the highlighted section.

Please re-read the underlined text...:rolleyes:

First of all numbnuts, I'm giving the OP information on the 80gr. bullet which he mentions in his question, secondly, while a 77gr. bullet CAN be seated to the max OAL of 2.26", most National Match competitors, as well as knowledgeable reloaders who strive for accuracy, seat their longer heavier bullets out to meet the lands and grooves because this yields better accuracy. Anything heavier than 77 gr. will NOT fit in a magazine and should NOT be seated to the same depth as the 77gr. bullet. I responded when I saw the 80 gr. bullet mentioned because many reloaders go out and buy 80 gr. bullets without realizing that they will NOT fit in their magazines, and seating them deeper so that they do fit, can be dangerous!

At ease, gentlemen. No need for name calling. Lets calm down a bit and remain civil.

Back on task... My 1/7 barrels shoot just fine (1" or so) with 55 gr FMJ handloads. WWB M-193 does not do as well. You should avoid the light weight "match" or "varmint" bullets as they tend to have thinner jackets. The combination of high velocity, thin jacket and fast twist can easily lead to bullets vaporizing shortly after leaving the barrel. The gray puff about 15' down range is a pretty good indication you have surpassed the rotational max for a given bullet.