first new 5.56 build in a long time

[stagpanther]

Inspired by the "one AR that does it all" thread I decided to put a new build together on the first new barrel for 5.56/224 that I've bought in 14 years; a fulton/criterion 20" hbar in 8 twist. Really should have got a faster twist, but I should be satisfied with the 70 gr +/- bullets I'll be limited to--even if I modified the mag to take longer bullets the receiver magwell limits me to about 2.32 anyway. Shot some bulk M855 yesterday at 187 yds but couldn't do any better than 2.5 MOA--switched to a handload of 70 gr rdf's and the first two charge weights I managed to reduce group size to 1.5 MOA but that's still unsatisfactory in my book, Hopefully I'll find a good node eventually. I couldn't set up the labradar because it was far too windy so I don't have any velocity data.

[Shadow9mm]

That's one sexy looking rifle! A little tuning of your hand loads and it should tighten up. just have to find the good seating node.

[stagpanther]

Thanks--yeah, I figure I'll have to do some "fishing" to find the "mother node."

[Shadow9mm]

I usually just seat 0.020 off the lands, or max mag lenght, whichever I can get. Then start pushing back in 0.003 increments until I get 2 to 3 groups that shoot well. Then I pick the one closest to the lands so as the barrel wears out it will still be in the node for a while. It's not all technical and fancy, but it's methodical, repeatable and simple.

[stagpanther]

I usually just seat 0.020 off the lands, or max mag lenght, whichever I can get. Then start pushing back in 0.003 increments until I get 2 to 3 groups that shoot well. Then I pick the one closest to the lands so as the barrel wears out it will still be in the node for a while. It's not all technical and fancy, but it's methodical, repeatable and simple.

The chamber seems to have a shortish freebore, even so, most bullets engage lands well beyond what the limitations of the magazine well allow. No biggie--I run into that frequently with AR's. I haven't yet tried a full ladder range of different charge weights. While I have thousands of .224 bullets--they are mostly smaller ones for a slow twist 22-250 and bigger ones for a fast twist 224 valkyrie and I suspect the sweet spot in bullets for this barrel will lie somewhere between 62 and 75 gr bullets.

[stagpanther]

Well, I fired it a couple of more times and continue to get mediocre results; very frustrating for a match grade barrel I paid about $350.00 for. I have less than 50 cartridges total down the barrel including a few that shoot very well out of my other 5.56 AR's.

I decided to take a second, more thorough look with my Hawkeye borescope and found this:



I know a bit of wear at the port is normal--but I have AR barrels that are 10 years old with many thousands of rounds through them that don't look 1/10th this worn. Notice the port was drilled with the groove to land wall going right down the middle of the port opening. The erosion inside the port is spectacular with a flare of copper arching forward--and this is after I spent an hour hitting the bore hard with bore tech copper eliminator.

Other than that the gun has always shot without a hiccup.

[Shadow9mm]

I recently watched the In range TV Q&A series with faxon on barrels. It was an amazing series. I can't remember which vid or the time stamp. But what they said is lots of testing was done. It does not matter if the gas port is in a land, in the groove, or overlapping. It made no difference in accuracy. Granted I believe it was military testing, but I believe faxon did their own as well.

here is vid 3 that deals with gas ports. Great series.
https://www.youtube.com/watch?v=R3FDLiWMUTc

[stagpanther]

Some top-scoring AR competition shooters use barrels with ports positioned just like this. Others say they put them in the grooves. Problem is, you can easily see in this bore that would be more or less impossible considering the narrowness of the groove and the size of the port. I've never seen damage this profound--or quickly--on any port positioned in any way. The gas system functioned perfectly from the first shot--never noticed anything unusual in the normal functioning (other than the less than stellar accuracy/consistency, which I usually figure is my fault).

[stagpanther]

here is vid 3 that deals with gas ports. Great series.

Thanks for that, interesting interview.

[Shadow9mm]

Originally Posted by stagpanther

Thanks for that, interesting interview.

There are 4 vids in the series I think. All were super informative. I initially went looking for info on nitrided barrels and ended up watching all 4 in one day. There were a lot of things I had a basic understanding of that I feel I understand a lot better now. And a lot of things I never even considered.

[bedlamite]

Originally Posted by stagpanther

Really should have got a faster twist, but I should be satisfied with the 70 gr +/- bullets I'll be limited to

8 twist works just fine for anything you can fit into mag length, up to and including the 77gr sierra. The reason the .mil went to 7 twist was for tracers.

[Shadow9mm]

and for the frangible stuff. pulled a 50g one apart the other day, was shocked by the monster bullet.

left is 55fmj, center 50g frangible, right 75g OTM

[stagpanther]

The fine folks at Fulton not only offered to replace the barrel; but upon checking their website I noticed they had a chrome-lined 1:7 twist barrel in stock and I asked if they could send me that instead, and they did, despite production commitments. It arrived today and the bore was pristine sparkling clean and the port looked superbly cut as well as nice sharp and clean rifling at the muzzle and crown.



Now before you tell me the twist and chrome lining are unnecessary--I have a "military grade" 1:7 chrome lined barrel I've been using for about 15 years and it can still group MOA which is pretty darn good for having had countless thousands of freedom seeds down the bore. I'm not looking for match-winning grade so much as very good and reliable accuracy for a long time.

[stagpanther]

I put it together and took it out for a test run and ran into problems almost immediately, grouping was erratic as was cycling. I noticed that opening up the port on the gas block all the way didn't change much in the felt recoil, so I figured chances were that somehow I misaligned the gas block on install. Took it apart and sure enough I was way off--not quite sure how I messed up that badly. Realigned and put back together and now shoots wonderfully, even with the 15 year old bulk FC ammo I could get MOA. The really interesting part is how far off the shots were landing with the gas port not tuned properly. Very happy with the barrel and eagerly look forward to developing loads for it.

[Shadow9mm]

That's great!

[stagpanther]

Gonna try a few handloads next.

[DaleA]

Us lurkers like it when a plan comes together.
Congratulations.