Home Forums Hunting & Shooting AR and Tactical Rifles Well I may have messed up, opinions?

I built a 6x45, mcgowen 18" barrel, rifle length Gas system, magpul rifle stock and buffer kit, I think their gas port standard is .082.

Anyway I didn't read into it enough and apparently the 18" rifle length combo is troublesome in this caliber. The rifle is looking to be accurate enough but it's a single shot. It doesn't even attempt to cycle. Any opinions or suggestions before I scrap this $300 barrel 😬

Maybe a bolt swap and rechamber to 6 ARC, or 6 Grendel? The bigger powder/gas volume might be enough to get it running. I'd do the homework first though.

Really hard to say w/o having access to the gun.

I don't have a chart for sizing the gas port on a 6x45, but an 18" rifle gas 5.56 is .098 - .103, normally.

But even at .082, it should at least partially cycle.

I'd disassemble the entire gas system & verify no obstructions, tube correctly aligned in GB & GB correctly aligned to gas port. Verify gas to fit to gas ke; gas key tight on carrier.

I always measure the center of the GB port on the barrel & on the GB to verify exact GB location. Most need to have the GB about about .020 off the barrel shoulder on the GB journal for exact alignment.

Don't know if your GB is a clamp on or set screw version, but if a set screw, verify that the dimple aligns the GB to where you measured that it should.

If it has 2 set screws verify that both allow the GB to align correctly.

Some GB's have different spacing than others, .400" & .450" if I remember right.

Good Luck.

I’ve seen a Gas key not drilled all the way through.

I’ve also seen a gas tube inserted upside down. Don’t overlook the little stuff.

What Montana man said is a great way to start. After that, get a JP Enterprises silent capture buffer spring kit with multiple weights and start playing with the weight combos.

You didn't say what powder and how much you are using.

kwg

82 thou sounds way too small, especially if you are using a ball powder. Mil spec for the 18 inch Rifle Length Gas System port is 0.105 for Mk 12s. That's a little larger than a #37 (.104") drill and a little smaller than a #36 (.1065") (maybe it's a metric drill size?). I would start with a #42 (.935") and go up in diameter as needed from there.

To enlarge the port, run a piece of #4 or #3 lead buckshot into the barrel until it's under the port. Lube the port with some WD40 and run your drill in @ 1,000 - 2,500 rpm. Don't be a pussy with this or you will get the bit stuck and probably break it off. When you see lead chips rise up, you are done. You can do it all at once or a little bit at a time. Just keep the RPMs high when you do feed it in.

If there's a commercial 6x45 load available, I've never seen it. I'm not saying it doesn't exist because I simply don't know for sure...I never look for that one due to lack of interest.

So, assuming you're handloading I would suggest taking a look at your powder choice and charge weight to begin with. The amount of gas generated will be roughly proportional to the charge weight, so using a heavy charge of the slowest burning powder that will combust completely (or near so) should supply your gas system with an ample volume of gas. A powder that burns too slowly generally won't burn completely because a good burn requires a certain amount of pressure be maintained as the bullet moves down the bore, and powders that are ill suited to the cartridge and bullet weight often do not burn completely and convert all the charge mass to gas.

If you choose a powder that burns too quickly you might not be able to generate the volume of gas necessary to operate the carrier.

Bullet weight choice might dictate a certain powder burn rate range also.

If the rifle is assembled correctly with correctly manufactured & selected parts AND you're using a load that should run that gas system, then the next thing I would look at is buffer weight. I think reducing buffer weight might help.

All that said, I'd check all the things suggested in previous answers first.

Or, to experiment with light buffers, just remove the rubber piece from the standard buffer and take out one or two of the weights in there and reassemble. 🙂 Most buffers seem pretty easy to pop apart with a small punch and a hammer.

Another option to play around with, but this one does cost money, is buffer springs. Sprinco makes a very nice lighter power spring (Sprinco Yellow). Or, if you want to go the other way, they make heavy power springs as well.

I think I'd keep the buffer full of weights rather than let them be slamming around inside the buffer. They make aluminum buffer weights.

Barring something screwed up with the gas hardware or installation, this is really the most likely next cause.

There's no reason to expect to need to use any buffer lighter than a Carbine (3 oz) buffer & anything lighter than a Sprinco Yellow (one step below "standard") spring.

If the gas port is right, ..........................along with the rest of the gas system, & assuming anything near a 52-55K PSI loading, or higher.

MM

I'm shooting a speer 75 gr hp over 27 gr of benchmark

That looks like a reasonable combination of components to me. I'd go over the rifle like others have already suggested, and if you find nothing amiss then Tyrone's suggestion that the gas port is too small may well be where you're at. At that point a lighter buffer and/or spring might help or it might not. You may well end up having to drill it out further, but that would be the last thing I would try on a $300 barrel that you already know shoots well. I guess you could resort to an adjustable gas block afterward if it turns out something stupid got overlooked, but it wouldn't (or SHOULDN'T) be the end of the world.

Just one more thing - swap out the BCG with a known good. Then move on to the other stuff.

Half the BCGs these days don't have sealant under the gas key. The screws can seem to be tight, yet these BCGs will develop leaks over time.

I think I figured it out. So I swapped out the rifle length buffer for a standard carbine buffer in a rifle buffer spring and it almost worked, it would eject but not load another round. I think a swap over to a full carbine buffer/stock system will fix my problem! Thanks guys!

Are you able to get the bolt to lock back manually? There are several ways to mismatch buffer tubes, buffer springs, and buffers.

Yep

Carbine buffer system was a no go, I'll swap out the bolt and lower in the morning to eliminate all those possibilities, and if that doesn't do it, I'll have my smith start on the gas port.

There used to be a company that offered it as Arrow Arms .243 ammo, of course loaded for AR's. I picked up 4x bags of it myself, it was all Hornady brass. Hornady was never able to tell me if they actually loaded the ammo or just offered the brass.

You could pick one of these up Teslong

Will probably be cheaper than what the gunsmith will cost. It will answer any alignment questions you may have and, in the end, you'd still have the borescope.