“Lipped” buffer tube install procedures?

[bb223]

Hello,

Got this fluted buffer tube on sale from PSA (I know, I know) and wasn’t entirely sure about the proper install procedure. I screwed it down until it properly and fully retained the buffer detent but after I fully torqued and staked I noticed I could perhaps give it another full rotation.

Extra rotation or not, does this look to be installed properly or should I pull it apart and redo it?

Thanks and sorry for being a dumb dumb.

[georgeib]

To me, it looks like you're good to go. No movement?

[JediGuy]

Maybe check for install instructions for the PWS enhanced buffer tube? They use this idea. Off the top of my head...use a pin to push the pin down far enough to make another rotation? I don’t know if you can even do that.

[1168]

Drop a buffer and BCG into it without a spring or upper. I just checked a Sionics for reference’s sake, with the bolt fully extended/unlocked, I got ~0.1” to 0.11” from the bolt face to the bolt catch, and ~0.16 from the rear or the gas key to the top of the receiver ring. I don’t know what the exact or +/- specs are for this. I’ve heard 1/8” (0.125”) tossed around for bolt catch clearance.

[bb223]

Factory baselines:

6920:

Bolt face to catch .125
Gas key butt to web .1875

6920 upper/LMT factory lower:

Bolt face to catch .25
Gas key butt to web .375


Built lower in question:

Bolt face to catch .25
Gas key butt to web .125

That LMT lower/6920 upper is my workhorse with north of 30,000 rounds on it with no issues, so I guess the new lower I built is ok?

What do you think?

[Curlew]

I don’t know how you made the measurements, but something seems off. I think the numbers are too big to be plausible, especially the second pair. Maybe the bolt was pushed back in the carrier?

Thing is, there’s only so much wiggle room available between having the BCG pushed forward to where the (extended) bolt nose touches the bolt catch, or aft to where the key hits the receiver ring. By my measurements and figuring, the total clearance available is only about .265 or maybe .270, and this is consistent with what “1168” measured (.1 or .11 plus .16). You can trade off clearance at the bolt catch for clearance at the back of the key, but as best as I can see they always add up to .265 or so.

So when you say that on your new lower the bolt can be retracted to .250 behind the catch, I would think the key is about to kiss the receiver. But you also say there’s .125 of clearance back there. Not sure what to think....

[bb223]

Don’t know honestly, but I measured them the same with my Reloading calipers, though I rounded slightly up or down a few thou to make them end in 5s or 0s.

The newest lower is an Aero and looking at it seems like the rear web face is very slightly further back than the 6920 lower.

I just got back from shooting it and there’s no impact marks or anything slamming. All the buffers are the same length too so I guess it’s fine?

This is a pistol build and the Aero lower previously had a KAK Shockwave tube on it for thousands of rounds so all the parts have worked together just fine, the only difference now is the new buffer tube to support the new Shockwave Blade 2.0M.

Measurements aside is there something I should be paying attention to? I mean as long as the buffer retainer is captured and the BCG doesn’t bottom out is it good to go?

[Curlew]

I guess so. The test that 1168 suggested seems pretty definitive, so if you did that and saw a decent gap behind the key, then presumably there’s not excessive free space in the buffer/tube system. And if the gun is able to lock back ok, then it’s not too short either.

The only other thing that comes to mind for me in this area is to verify that when the upper and lower are mated, the carrier pushes the buffer back a bit, away from the retainer. But if it’s only the buffer tube that’s been changed, I don’t think that would have made any difference in this regard.