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School me on barrels
- Thread starter P51MA
- Start date
Bumping my post because the latest BA barrel I bought is producing 0.55 to 0.67 MOA groups at 100 yards- from a 6mm ARC AR build after a reasonable amount of load development. Excellent barrels for the money and this one was on sale for relatively cheap.
Pin and weld is done, so the only thing missing is some proper glass. Has some cheap irons for function testing.
Aero sort of came up lacking with the anodizing on the upper; the shade is a bit off. You don’t notice unless it’s under bright light (like my flashlight here). The strike industries modular stock is very handy but it’s kinda meh aesthetically.
I know the love seat is ugly too, but it’s a pre-94. Has a MA legal folding bed.
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Made it to an indoor range. Only put about 30 rounds through it but she ran flawlessly.
Time to locktite down the gas block, and the my scope and mounts should arrive tomorrow.![[smile]](/xen/styles/default/xenforo/smilies.vb/001.gif "Smile [smile]")
I also got a few mags through the black rifle. I confirmed that it will not last shot hold open with USGI or PMAGS. It was cycling ok when I fed it mags with only 5 or 6 rounds, but choked on the last mag I gave it which was a full 30 mag, failing to feed every third round.
I think it’s just under gassed?
Time to locktite down the gas block, and the my scope and mounts should arrive tomorrow.
I also got a few mags through the black rifle. I confirmed that it will not last shot hold open with USGI or PMAGS. It was cycling ok when I fed it mags with only 5 or 6 rounds, but choked on the last mag I gave it which was a full 30 mag, failing to feed every third round.
I think it’s just under gassed?
Adjustable or standard gas block? If factory ammo, under gassed usually points to the gas block. If standard, could be slightly out of position. I think less common, but some budget barrel companies have been known to make mistakes on the gas port dimensions.Made it to an indoor range. Only put about 30 rounds through it but she ran flawlessly.
Time to locktite down the gas block, and the my scope and mounts should arrive tomorrow.
I also got a few mags through the black rifle. I confirmed that it will not last shot hold open with USGI or PMAGS. It was cycling ok when I fed it mags with only 5 or 6 rounds, but choked on the last mag I gave it which was a full 30 mag, failing to feed every third round.
I think it’s just under gassed?
The barrel is a part of this complete upper. I assume it's BA? Idk. Ran all Igman m193 5.56 today. Standard aero gas block.
Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver Includes Coupon Available w/ Free S&H — 3 models
Shop Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver | 5 Star Rating on 4 Reviews for Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver Coupon Available +...
www.opticsplanet.com
I posted the picture a week or two ago showing that the gas block is not perfectly aligned with the center of the bottom MLOK on the handguard.
I did some googling and failure to last shot hold open seems to be almost certainly an under-gassed situation. I guess I should pull the gas block off? Now that I've built another rifle I think I'd be confident doing this.
Probably gas block alignment. Getting the gas tube pin out and back in is a pretty big PITA, so if you are not experienced with that I'd leave it in and just try to better align the gas block. I will usually get the alignment without the gas tube installed then mark it for reassembly after I pin the gas tube into the block. Once the tube is in, I prefer to leave it alone. Also there's an 80% chance you will install the gas tube upside down.The barrel is a part of this complete upper. I assume it's BA? Idk. Ran all Igman m193 5.56 today. Standard aero gas block.
Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver Includes Coupon Available w/ Free S&H — 3 models
Shop Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver | 5 Star Rating on 4 Reviews for Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver Coupon Available +...
I posted the picture a week or two ago showing that the gas block is not perfectly aligned with the center of the bottom MLOK on the handguard.
I did some googling and failure to last shot hold open seems to be almost certainly an under-gassed situation. I guess I should pull the gas block off? Now that I've built another rifle I think I'd be confident doing this.
![[laugh]](/xen/styles/default/xenforo/smilies.vb/012.gif "Laugh [laugh]")
Probably gas block alignment. Getting the gas tube pin out and back in is a pretty big PITA, so if you are not experienced with that I'd leave it in and just try to better align the gas block. I will usually get the alignment without the gas tube installed then mark it for reassembly after I pin the gas tube into the block. Once the tube is in, I prefer to leave it alone. Also there's an 80% chance you will install the gas tube upside down.
Ohh believe me I know all about gas tube pins. It was the worst part of assembling the entire gun. Took me about 45 mins of struggling until I realized I could push the pin in with a vice.
Been meaning to order a proper set of punches and a starter punch for this. Half of the struggle with building a rifle was figuring out what tools are wants vs needs. All of the online guides just assume you have every tool under the sun at your disposal.
That said, I think I can just adjust it with the gas tube still attached.
you just need a regular pencil and a ruler. make a mark on the gas block sides to indicate position of the hole.
with a ruler, draw a line along barrel top to indicate the hole, and a vertical line as well. then just align 2 sets of lines.
if you will move the gas block enough - i would measure the gas port in the barrel also, just in case.
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Unfortunately I don’t have the means to measure the gas port diameter, and I wouldn’t have a drill to widen it even if I did.
Looks like the alignment was OK. Is it possible that it’s leaking gas out of the gas block pin hole? Looks like somebody had a hard time getting it in there back at the aero factory.
Soundwave
NES Member
My 20" criterion barrel for my AR-10 had to be sent back to have gas port enlarged. My 18" ballistic advantage had no issues and has been great.
Soundwave
NES Member
I think we had that same love seat.
There’s definitely some gas escaping where the gas block and gas tube meet. But this isn’t all that unusual. Often times gas escapes between the gas block and barrel too, but yours seems fairly tight, judging by the soot ring around the gas port.
What’s your buffer/action spring setup?
I’m leaning towards the problem being a slightly undersized gas port more than gas leaking. But, you could probably use some high temp RTV where the gas tube goes into the gas block. Though, you’ll probably want to take the tube out slightly to apply, and then reinsert. Just a thought on the RTV. I’ve never actually had to do that before.
If you want to check the gas port diameter, you could pick up some pin gauges. A set that covers the 0.060”-0.090” or so.
Was the gas block flush back like that before? Or did it have a very slight gap? Many barrels are made with a slight gap. It was originally done so a handguard cap could fit behind an FSB gas block, and then some barrel manufacturers continued that vistigial dimension on barrels that only have a 1” gas journal and couldn’t mount an FSB anyway.
In any case, looking at the soot around the gas port, as long as you have the block back where it was, then it was lined up correctly.
you`l lbe surprised how easy is it to drill that. any regular cobalt bit will work fine, and you only need to enlarge an existing hole a bit, not a drill brand new one.
to measure it one uses standard punches, if you have 'em. but from the picture it looks fine, like what it needs to be.
it does not show side leaks neither. hole in the block is much larger than hole in the barrel, so, that should not be the issue.
i would try to put it all back, properly, and then play with swapping buffers/springs.
look it up here:
- Sprinco AR-15/10 Buffer Spring - AR15Discounts
Please take a look at the description below, to see which buffer spring will work best for your build.
ar15discounts.com
again, with 14" and shorter barrels, non-suppressed, it may end up to be sensitive to the load type and bullet weight. you may end up with one spring for 55gr m193 and a different one for 77gr custom loads.
pastera
NES Member
I had a cheap upper that was short stroking
Measured everything before pulling the gas block, measured everything checked the port size with a drill index (close enough) and everything checked out.
Reassembled everything taking care to align the gas block and everything worked perfectly after that.
Only thing I could point to was there must have been something blocking the gas port or block and I cleared it when disassembling it.
Measured everything before pulling the gas block, measured everything checked the port size with a drill index (close enough) and everything checked out.
Reassembled everything taking care to align the gas block and everything worked perfectly after that.
Only thing I could point to was there must have been something blocking the gas port or block and I cleared it when disassembling it.
on my brand new ruger sfar gas block was misaligned and not truly torqued at all. it happens.
i would think on any new gun, it is just a common sense to do a complete disassembly, check, lubrication and re-assembly, even if it is a pita sometimes.
on ARs - includes undoing barrel nut and lapping the upper. on almost all pre-made uppers they do not lubricate the nut threads - means incorrect barrel torque and, well, future pita to undo it.
Standard buffer and spring from a complete Aero m4e1 lower, although I tried a borrowed H2 with a different spring and no difference.
There was no gap on the gas block. The Yankee Hill gas block on the other barrel also calls for no gap. I'll check Aero's instructions on their gas blocks to confirm that no gap is actually correct; that is how they sent it to me though.
Closest I can measure for the gas port is holding a 5/64th allen key up to it, which in theory should be .0781 flat to flat. Gas port looks like it is .075 to .78. This is a really crude measurement though.
you`l lbe surprised how easy is it to drill that. any regular cobalt bit will work fine, and you only need to enlarge an existing hole a bit, not a drill brand new one.
to measure it one uses standard punches, if you have 'em. but from the picture it looks fine, like what it needs to be.
it does not show side leaks neither. hole in the block is much larger than hole in the barrel, so, that should not be the issue.
i would try to put it all back, properly, and then play with swapping buffers/springs.
look it up here:
- Sprinco AR-15/10 Buffer Spring - AR15Discounts
Please take a look at the description below, to see which buffer spring will work best for your build.
again, with 14" and shorter barrels, non-suppressed, it may end up to be sensitive to the load type and bullet weight. you may end up with one spring for 55gr m193 and a different one for 77gr custom loads.
Since it won't last shot hold open, the buffer and BCG just arent getting pushed back far enough. The standard buffer and spring should already be pretty light, no?
There's a shop down the street from me that can probably measure the gas port and widen it out a tiny bit for short money. Seems like it would be easier to add a heavier buffer if I end up with too much gas, rather than start making spring/buffer/bolt carrier lighter than standard?
pastera
NES Member
A sticky bolt can mimic under gassingThe barrel is a part of this complete upper. I assume it's BA? Idk. Ran all Igman m193 5.56 today. Standard aero gas block.
Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver Includes Coupon Available w/ Free S&H — 3 models
Shop Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver | 5 Star Rating on 4 Reviews for Aero Precision M4E1 14.5in 5.56 NATO Threaded Complete Upper Receiver Coupon Available +...
I posted the picture a week or two ago showing that the gas block is not perfectly aligned with the center of the bottom MLOK on the handguard.
I did some googling and failure to last shot hold open seems to be almost certainly an under-gassed situation. I guess I should pull the gas block off? Now that I've built another rifle I think I'd be confident doing this.
Strip your BCG and inspect, clean and reduce it.
That seems about what Ballistic Advantage uses. I think they use 0.078-0.079 for their 14.5 mid-lengths. And in general, 0.074-0.080 is an acceptable range. The lower end may start to get picky with light charged .223, and the higher end is likely a little over-gassed for 5.56. Daniel Defense uses 0.076.
What ammo are you using?
Igman 5.56 55s
winchester 5.56 55s
Bear in mind my method of measurement is mk1 eyeballs + an Allen key lol. Not exactly accurate.
I don’t think most people really have this problem, but in theory mid length + 14.5 is a pretty short dwell time vs a carbine 14.5, so it would be more prone to undergassing? Rifle length 18’s are even a hair less dwell time, but my 18 is specced for a big ole .093 gas port iirc
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