1:9 bullet weight

[CrossFire]

I have DPMS M4gery with a 16' 1:9 barrel. It was sighted with a GI 25 meter target and gets a 3 shot group sub 1/2 inch, no problem. However, at 100 meters 3 shots may not even be on the paper.
I have used mainly 55 gr ammo which worked well in several other guns and is used by 2 friends with matching rifles.
DPMS has advised that I should be using ONLY 64 gr or heavier bullets in this barrel. They seem to have a pretty extensive list of ammo I should not be using, including USGI milsup, any & all reloads or any imported ammo.
Anyone have any experience with lighter, ie 55 gr, ammo in fast twist barrels?

[SSwee]

All I have on that platform is a Carbon15 7-1/4" barrel 1:8 twist. It shoots the 55gr tight at 100 yds. One of my shooting buddies has a Bushmaster M4 16" barrel with a 1:7 twist. He has problems with anything over 55gr. I have a copy of a write up on AR barrel twist rates and bullet weights that goes to extreme elaboration if I can find it.
SS

[Otis61]

I thought faster twist rates in .223 barrels (I.E. 1:7, 1:8) were for heavier bullets. 60-75gr. But it's the other way around?

[SSwee]

Your right Otis. I need to check again what twist rate is on my buddies but I'm positive on the bullet size.

Not the one I was looking for but a quick idea
http://www.triplebreakproducts.com/FAQ/twist_rate_for_barrel.htm

SS

[Beprepared]

Edit: The Higher the twist rate, the heavier the bullet...
I have standardized on 55gr BT or Spitzer from Sierra. Using 24 grains of H335 I have been able to get sub MOA three shot groups at 100 yards. This is milsurp brass with a SB RCBS die set.

While I have a 1:9 twist barrel on one AR, other .223s I use have a 1:7 twist. In the offhand I can do 5" groups at 100 yards with the above load. With more practice I'm sure I could get better.

55gr loads run just fine in my 1:9 twist 16" DPMS.:rockon:

[jfowl31]

Edit: The Higher the twist rate, the heavier the bullet...

TYPICALLY this is true. AR's are a slightly different ammo though. 1:7, 1:8, 1:9 all have funky characteristics about them as far as what weight ammo they can shoot. My 1:9 barrel could shoot any bullet weight I threw at it and group tightly (MOA with a big scope). But then I've shot a 1:7 carbine that couldn't stabilize a heavy bullet but shot 55's like a dream.

A lot of it has to do with the ammo too. Thin jacketed stuff made to fragment on impact might not do well in a fast twist barrel. Whereas thicker jacketed ammo of the same weight might do just fine.

You ask this question anywhere and you'll get tons of differing opinions. The real truth is that you have to figure out what shoots good in YOUR rifle as AR's seem to be weird about their twist rates.

[CrossFire]

I am relatively new to ARs and to be honest I grabbed it just because I figure no safe is complete without one.
I've been happy with the function but was surprised at the 100 meter results after getting these great groups off hand at 25 meters w/ the red dot.
Hell, off a bench 25 meters will do one ragged hole.
That makes the 100 meter results so frustrating.
I really wanted to like this gun.
The CAI Galil I bought can do a 3"-4" group at 100meters with the same ammo. That's benched with iron sights. I have to get a red dot on the Galil.
Thanks for the info on twist, it confirms what I had been told about twist and normal weight.
I just found a few boxes of Wolf 64 gr JBT so I will try it this week. I'll let you know how it works out.

[tump]

cheap ammo will usually give poor results. if you want better groups shoot match ammo. the ar i use to have would do 3-4 in. groups a 100 yards with wolf but 2 inch groups with rem. fmj.

[Eagle 1]

1:9 shoots and stabilizes up to 77 gr bullets. Mine loves 55gr Nosler BTs. 3/4" groups at 100 yards. A 1:7 twist with light jacketed HP varmint bullets driven at 3200+ fps can have a tendency to have the bullets literally blow up in flight.......the rotational forces are more than the jacket can withstand. Reportedly what you see is a small grey puff in midair downrange with a "maggies drawers" at the far end. Jfowl31 had it exactly right, you'll need to see what your rifle likes. A 16'' 1:9 is different from a 20" 1:9, whatever you have hanging on the front end, ie. lights etc. can have an effect.

Eagle 1

[drine]

1:9 shoots and stabilizes up to 77 gr bullets. Mine loves 55gr Nosler BTs. 3/4" groups at 100 yards. A 1:7 twist with light jacketed HP varmint bullets driven at 3200+ fps can have a tendency to have the bullets literally blow up in flight.......the rotational forces are more than the jacket can withstand. Reportedly what you see is a small grey puff in midair downrange with a "maggies drawers" at the far end. Jfowl31 had it exactly right, you'll need to see what your rifle likes. A 16'' 1:9 is different from a 20" 1:9, whatever you have hanging on the front end, ie. lights etc. can have an effect.

Eagle 1

Good info. I was wondering what weight was the highest I could go. I shot several rounds at one target and never stopped to check. In the end I find 5 different neatly arranged groups. Left, right, high and low. Remington, Hornady, Centurion, Privi, and Winchester. The Privi was dirt cheap and shoots like it. Groups about 3" at 50 yards. The Hornady Varmit bullets group like a dream and if I had a scope and decent bench it would make one hole I'm sure. 16" DPMS open sights and red dot.

[nevada]

I've read in many other forums that it is the length of the bullet body that contacts the rifleing, not the weight, that determines the best bullet for the twist rate. Length and weight are related of course, heavier usually means longer.

My Mini-14 has a 1/9 rate. I've tried bullets weighing 55gr to 79gr looking the most accuarate weight. The standard 55gr was best. The heavier bullets were significantly worse. Just my experience.

[drine]

I've read in many other forums that it is the length of the bullet body that contacts the rifleing, not the weight, that determines the best bullet for the twist rate. Length and weight are related of course, heavier usually means longer.

My Mini-14 has a 1/9 rate. I've tried bullets weighing 55gr to 79gr looking the most accuarate weight. The standard 55gr was best. The heavier bullets were significantly worse. Just my experience.

I'd say that is a huge factor too. Handloaders get better results. I'm wondering what they are using the 100gr 5.56 bullets in.

[CrossFire]

I am very familiar with the bullet length issue.
While I am just setting up to start loading 5.56 I have loaded BPCR in 45-70 and 45-110 for years. When loading for long range shooting with heavy weight bullets, 525 gr and up, key holing was common with high muzzle speeds out of faster (1:47 in a 32' barrel, don't laugh too hard) twist barrels.
At faster bullet speed (say, 1800 pfs:icon_biggrin:) the softer lead cast bullets would stip out of the shallow rifling. The issue was resolved by using bullet profiles that had less area in contact with the rifling.
The same factors are in play with the smaller 5.56 and lighter bullets.
I tried getting to the range today but the wind(45mph gusts)was so bad that my targets blew off the board before I got back to the bench line.
And I was only 25 meters away!

[CrossFire]

I forgot to post back on my range trip. I tried some 62 gr Brown Bear first.
I zeroed on the USGI 25 meters target and had a great group at 25 meters.
100 meters had all three shots on the paper with a standard 50 yard pistol target. That's better than I ever had with any 55 gr round.
I tried 64 gr Barnull and it required almost no adustment at 25 meters and did even tighten up a bit. At 100 meters I actual had a fairly decent group, three rounds about 3'.
I guess they have a point about the rifle needing a heavier bullet but am I wrong in thinking that a 1:9 rifle should be able to at least put 55 gr rounds on the paper at 100 meters?:icon_confused: