7-10" twist barrels.

Is this true? I thought 9" would only stablilize up to 70 grain bullets.

Thanks

CRC

Depends on the barrel length and how hot its loaded.  Longer barrel = higher RPMS = more stable.  I am sure they are talking about 24" barrels as usual.

DevL,

Thanks. I didn't consider that.

CRC

CRC, as i have a sierra bullet poster above my computer desk on my wall, I see that Sierra reccomends that their 77gr HPBT MAtchking #9377 should be fired in 7-8 twist barrels.

The bullet would probably fly apart before you could stabilize it in a 1:10" twist barrel.

I'm probably wrong here, but I thought that "flying apart" was a symptom of too fast twist while "wobbling, bad trajectories and keyholeing" were symptoms of too slow.  Am I wrong?

The ability to stabilize bullets is also dependent on altitude and temperature (higher is better for both).

Just my two cents as I recently shot 40 rounds each of Federal Matchking bthp Sierra 69 and 77gr and they both gave 3/4" groups at 125yds out of my AR180B.  Thanks Dieseldog!

What I meant was, you'd be pushing some crazy velocities in a 1:10" twist bbl to reach the kind of stability you may get at NATO-like velocities out of a 1:9" twist bbl (which isn't much as it is).

Look at the [url=http://www.ar15.com/forums/topic.html?b=3&f=16&t=150906&page=8]bottom of this page at Forest's post[/url]. This was in the thread about the Nosler 77gr OTM round. His testing indicates that it shoots just fine out of a 1:9 barrel.

He was also shooting only 3 shot groups.  When I fired the same ammo from a 1/7 14.5" Bushmaster I got substantially higher velocity and in winds up to 25 mph I got 1.9" 5 shot groups with a wobbly bench.  I am sure I could have gotten sub MOA had I been prone with bags in no wind and higher magnification than that 3X mini ACOG. Brouhaha shot a couple groups that started off at .10" his best 3 shot group was probably 1/2 MOA.  Thats with a non free floated chrome lined barrel.  I guess you could say the 1/7 twist not only gives greater accuracy on the order of 2-4 times but greater velocity too in the 45 fps range (greater barrel resistance keeps it in barrel longer and yeilds higher pressure).  Hell my rifle had not even had 50 rounds through it and was not broken in while his had thousands through it.

The 77 grain may be good enough for government work in a 1:9 at self defens ranges but I think it is capable of turning milspec barrels into sub MOA shooters with a 1:7 twist.  Also past 100 yards is where the semi stable bullets start to open up the groups.

Edited to add:  We shot crappy as hell and were almost too embarased by our shooting that day to post results.  We did not "call flyers" either.  We just shot and wrote down what happened.  We did all our shooting during the last session of the day and were pressed for time as we had jacked around and not gotten busy.  I would like to see a side by side comparison at 200 yards on the same day...

DevL:

I agree that 1:9 is iffy, but for CQB or <100 yards, I think that 2" groups are more than adequate. If you're planning to use it for competition, then all bets are off. Depends on what the intent is...

At the same time, I'd definitely want to try it out of MY AR before spending a lot of money on the round. Might have to fire up the ol RL550B.

My take and current load info:

Sierra 77 MatchKings are my load of choice and the most accurate round we've found outta my CR6724. This is an "Elite" barreled 24" 1/9 twist rifle. They will hold sub MOA out to 800 yards on a GOOD AIR day, if I do my part, but these are moving [b]AT MAX VELOCITY[/b]. Many have been suprised at how well these custom loads shoot in the 1/9 CR6724 from the 600 yard line in "F" class competition. They move around 2850fps outta this rifle and are max loads, we NEVER push them harder, guess ya can if ya want blown primers and stuck cases due to the pressure, we don't.

I have attempted to shoot these same "hand-loaded" rounds thru 16" M4s that are 1/9 twist from RRA and Colt and [b]NEITHER[/b] produced groups I was happy with, due to the velocity loss experienced by the 8" shorter barrel.

I am currently working up loads to get to the velocities exhibited by Tat and brouhaha's 77 OTM thread, using LC brass and our powder/primer combinations. I got to test 3 different loads last Sun, but am not there yet, although the last 5 rounds were loaded at the max weight of the SMKs. Still no flatten primers or pressure signs and I'm stepping up a bit more in powder weight with the loads (hoping the thicker brass will help me get faster but still safe enough pressure wise, as normally my accuracy load goes into Remington brass) and intend on using 2 more different powder/primer combos, hoping to get there using "safer" loads (lower powder weights, but fast'r powder), but we'll have to wait and see, as chrono is at the farm. I am doing some loading this week at home as I have a couple single press set-ups there.

Once I get there (pushing the 77 OTM at the 2740 fps shown by Tat and brou) I do intend to give the 1/9 Colt and RRA M4s another shot, based on Forest's comments, as he is a guru to be listened to, and the Nosler 77 OTMs are entirely different bullets than the 77 SMKs, which probably make a difference.

FWIW, tho I bought a DPMS M4 in 1/7 twist especially for these heavier rounds and intend to match a load to it for SHTF purposes.

The loads shot last Sun, started at 2580 fps, then 2640 and progessed to 2680 (all avg of 5 rounds) Dad was not impressed 'cus most groups were just staying in the 2" diamonds with smallest under 1.5". Where the 6724 will put 5 of the 77 SMKs in 1/4-3/8" most all day at 100 yards, he lacks the understanding of a chrome barreled M4 vs the Elite stainless steel and 8" additional barrel length, (this man kills crows daily at ranges from 300-500 yards, so it's no wonder he thinks 2" groups suck).

I had the red-dot removed and the Leupy off the 6724 installed in order to get the best sight-pic possible and will continue to test in this manner as red-dot is not precise enough for my puposes, which is to get the OTM hot enough and not sacrifice any more accuracy than I have to. Eventually when I have the OTM load I want the Leupy will return to the LR rifle and the ML2 will again take it's place on the DPMS M4.

This is where I'm at at the moment and I will post more when I get further data.....

Hope this helps some,
Mike