Forgive me if this has been covered. I did a search and didn’t find anything in my first sweep.

Looking for expert opinions on the matter, not just one-off’s or anecdotal “evidence”, but answers from people who know more about ballistics than myself — not that that is difficult to do.


I have two AR-15s, one with a 16” ER Shaw barrel, heavy contour, fluted, 1:9 twist. the other is a Daniel Defense barrel, 10.3”, carbine length gas system, gov profile, 1:7 twist.

I have almost exclusively used the 16” under a scope, for predator hunting. I’ve shot anything from 40 gr tipped to 62 gr SPs, all with the accuracy that you’d expect for each round. What I’m wanting to do is SBR the 10.3” pistol, and switch over to using this one as my primary varmint gun, as I now have a 5.56 suppressor, and want to lose the length.

My question is, what should I be running — and, more importantly — what should I stay away from, as far as bullet weights? I know the tighter twist is made for heavier bullets, but will the 55gr SPs I usually run perform well, as a standard? I also don’t want to run the 40 or 45s if there really is a risk to the jacket coming apart and causing a baffle strike.

Right now, I have in my predator ammo box, a varied plethora of ammo choices, but far and away the majority is 50 gr tipped, 55 gr tipped and 55 gr soft.

What’s the overall advice in my situation? Thanks in advance!!

Start here:

https://www.shilen.com/calibersAndTwists.html

https://riflebarrels.com/calibers-and-twist-rates/

I’ve used 40 Nosler BTs for coyotes, and they work very well. But, they aren’t ideal for pigs. You could make the case that the 223 is a bit light for hogs, but I use it some, and lately am using Sierra 65 gr Gamekings. The 63 gr Sierra SMP works pretty well also. I also tried the Nosler 64 gr Bonded Solid Base, but I never could get the accuracy I wanted with that bullet. Being bonded, the 64 gr BSB may well be the best bullet I have for hogs, and I may try it again. The good news on the 65 gr GK is that you can again buy them and they are very accurate. Well, upon looking for that 65 gr GK, maybe they aren’t available now.

I have no experience with heavier bullets for varmints in the 223.

With the Shilen link, I’m understanding that I’m “good” up to 90 grains, and the other link isn’t that helpful, just showing the reverse perspective of what twist for certain weights. I ran across that one in prior research.

With the first link though, I’m nudged toward believing that I should be fine with anything in my 1:7. I won’t be shooting anything over 69 I’m sure. But I still worry about what I’ve been hearing, where, theoretically, I could have a jacket come apart on a 40 gr, should I try them and like the accuracy or something.

1:7 twist it is not difficult to over-spin, which is what you are talking about.

Long barrel or short barrel, being a hand loader and experimenter, rifles shoot best when the twist rate is paired with the right bullet length. To get longer, you have to get heavier. So, in a 1:7, I would be focusing on 60 gr bullets and heavier. 70-90 gr is where I would try to focus my efforts. They will be slower muzzle velocity, but if they shoot tight that's fine. And being a heavier bullet, it will deliver more payload.

Bullets I would definitely stay away from with a 1:7 twist are Speer TNT which are a very thin jacket bullet that even their loading data lists loads for them that are slow for the bullet weight in rounds 223 size and above for overspinning in standard loads for the construction of the bullet but they are very effective on small varmints.

I had a 16 inch 556 AR at one time that I tried the 40gr Ballistic Tips in and they shot ok for factory loads and the 55gr BTs did fine in it. With a 1:7 barrel that is only 10 inches you will be slower and I would expect them to work fine on varmints but if using on a hog I would definitely go heavier or stouter constructed bullet.

I have a 16” 1/7 twist AR. It is very accurate with 55 grain Sierra Gameking, 55 grain Nosler Ballistic Tips, 55 Grain Hornady SP, and 55 grain Hornady V-Max. No issues pushing any of these four as fast as I can. Your 10” barrel is going to give up a good bit of velocity compared to my 16” 7 twist. I can not say anything about other 55 grain bullets in a 7 twist as these are the only four I’ve tried.

It's RPMs that make a bullet vaporize, not just twist rate alone. RPM is a function of twist rate AND velocity.