98Z5V

This is awesome.

Topside. Internal depth from the top of the base/back, to the very edge of the top where the tape comes out. I'll use a wooden chopstick, pushed into the top back, and knife-mark that thing right on the very edge where it comes out of the tube. Measure that chopstick from the end, up to your mark. You can't get an accurate measurement on the bottom of the tube (inside), because some of these tubes have a protrusion or "flare" there, to further capture or almost enclose the detent.

Not necessarily - hear me out on this one... With the 18", he's hitting the BCG during cycling. If the recoil system was correct, that wouldn't be happening. No other way around that, it's 100% accurate. Same lower. Something is up with the recoil system in this lower, or the 18" wouldn't be slamming it. 16" upper on that lower - it functions... with an issue in the recoil system... So, is that 16" undergassed, and it's not slamming the BCG? But just maybe almost there?... It's undergassed, and just missing that contact of the BCG and the tube... You put a proper recoil system in this lower, so BCG contact is impossible - like it's supposed to be - and I'll bet that 16" doesn't run as well then...

For what it's worth, OP, I bought ONE AP carbine receiver extension, for my first AP 308 build. Weird shiit happening with the cycling, so I checked it out - 7.100" internal depth. For a DPMS-based 308 recoil system, running a 2.5" long 308 carbine buffer, it needs to be running in an exact AR-15-lengthed carbine receiver extension - 7.000" internal depth. When I had that problem, I shitcanned the whole DPMS-based carbine extension business, went all Armalite AR-10 carbine recoil system, and never looked back - with flawless operation. I've built 3 other 308AR carbines since, and they all run the Armalite AR-10 Carbine recoil system. No guesswork, no diagnosis - if I have a cycling issue, it's not in the recoil system, it's something else.

That was closer to 1/3rd mile on that one - up your bragging a little. It was beyond a quarter mile. 581 yards from the survey gear, shooting line was about 6 yards in front of it - 575 yards. 440 is a quarter mile. 586.66 yards is a full third-mile. You guys come out next time, and we'll punch 880, no issues. Half mile.

Damn great job, Boot! I like to see that Faxon Pencil barrel gettin' it done! Wasn't I just talking about a Faxon Pencil barrel for hunting, for a .308AR in another thread?... @washguy, you out there, brother?...

Cool. What's the internal depth on the receiver extension?... They ONLY way your BCG is going to hit your buffer tube, and the lower receiver ears, is because the BCG is contacting those parts before the buffer can do it's job - which is bottom out in the receiver extension.Your recoil system is not working right. When I asked for recoil system details, you listed gas system details - those are two separate things that work together, but they accomplish two completely different things. IF you have an issue in your recoil system (and you do, or you wouldn't be hitting the buffer tube - and the lower, if you look close), so... IF you have an issue there and this is only coming up on the 18" gun - then you have a gas system issue on that 16" upper - because it doesn't have enough gas to throw that BCG into the buffer tube and lower... Make sense?

That is AFTER I left you in the parking lot, still packing up... I thought you were gonna choke me out...

Go grab a chunk of the Intro Section while you're at it, and tell us about yourself.

This spelled it all out, right here.

You have a recoil system issue in that 18" gun. List your recoil system parts for the 18" gun.

Hank is pissed...

HEY SUSAN!!!!!! Doc is busted, ain't he?...

^^^ Snatch 'em.

NICE!!! You ARE smooth, man... SMOOOOOTH...

No worries, man. When I'm not on here giving people shiit, I actually try to help once in awhile...

PSSST!... DOC! She's looking over your shoulder, brother!...

I'll bet with those recoil system fixes, and some lube, this thing will run well.

Both Armalite (AR-10) and DPMS-based (LR-308) rifle buffers are identical in dimensions. Wouldn't really matter what you get for that - I haven't seen the aftermarket screw that up yet, on rifle buffers for these big ARs. Just verify that the buffer you're buying is 5.200" long (within a thou or three wouldn't matter), and it should weigh about 5.4oz. Or pretty close.

Machine your own aluminum one, then - in Cali, don't you have to register it anyway?...

Yep - correct receiver extension, WAY wrong buffer and spring. You need a 308AR Rifle Buffer in that thing, measures 5.200" long. Might as well toss an Armalite EA1095 spring in there as well. That spring just runs, and there's only a couple alternatives for rifle-length recoil system springs on the market. Tubb Flatwire spring is another good option.

Wrong buffer and spring - at least for that buttstock. That's a DPMS-based carbine buffer for a 308. Same shortass buffer spring. Lemme ask you - is that buttstock secured on the rifle? Cna you just pull it right off? Or, is it secured with the vented buttstock screw (the one on the buttpad, at the top, should screw into a threaded hole in the back of the receiver extension...)?Was there any kind of a spacer in the receiver extension, after you pulled out the buffer and buffer spring? EDIT - I'm surprised you don't have "slam marks" on your lower receiver, where the BCG would crash into it. Seriously.

Tryptophan... strong enough to level an AD/HD bastard....

...but, it was definitely inevitable...

Well, that has to be a rifle receiver extension (buffer tube), or the stock wouldn't bolt on (screw on). The buffer should be 5.200" long, or it's not a 308 rifle buffer. Hopefully, the spring isn't an AR-15 spring. Measure the relaxed length of the spring, and we can tell you for sure...