PDA

View Full Version : How far forward to screw buffer tube on ar15 and missing buffer and spring



Gene Hackman
07-03-2015, 02:11 AM
Today at my LGS I bought a single point sling adapter and had the shop owner install it for me. (I don't have a castle nut wrench) Anyway I didn't realize till tonight that he left the buffer and spring out and it I probably won't get it till next week now due to conflicting work hours. Also, I'm not sure so I would like to ask, does the buffer tube need to be tightened one more turn so that the nipple on that little pin is more inside of the groove on the buffer tube? Any help is appreciated. Please see photos.

http://i1370.photobucket.com/albums/ag273/Dano1987/20150703_010028_zpsozbxa5kb.jpg (http://s1370.photobucket.com/user/Dano1987/media/20150703_010028_zpsozbxa5kb.jpg.html)

http://i1370.photobucket.com/albums/ag273/Dano1987/20150703_010015_zpsj92tpu4f.jpg (http://s1370.photobucket.com/user/Dano1987/media/20150703_010015_zpsj92tpu4f.jpg.html)

http://i1370.photobucket.com/albums/ag273/Dano1987/20150703_002027_zps3mdzbezv.jpg (http://s1370.photobucket.com/user/Dano1987/media/20150703_002027_zps3mdzbezv.jpg.html)

CJB
07-03-2015, 06:21 AM
Whoever reassembled that lower has no clue....

If the parts are made correctly, the buffer tube will just cover the edge of the detent (nipple) and the adjustment holes wil be vertically aligned, at which point the castle nut can be tightened. There really is no need for the little half moon cut out, but... if ya gotta, so so the adjustment holes on the buffer are vertical... I guess ya gotta. Although, facing the buffer would have been the more correct fix. More correct, because removing the buffer (and spring) will require the detent to be depressed. That is not quite as easily done (and not how it was designed) with the little half moon cut.

The detent holds the buffer itself in place, preventing it from flying forward out of the tube upon opening the receiver sections. The buffer tube captures the detent, preventing it from flying out under its own spring pressure.

Bawanna
07-03-2015, 09:56 AM
I looked and looked at those photo's and I thought, what heck am I looking at? You got it CJB.

It looks like it could be backed out one full turn and still be correctly oriented, except now it wouldn't work with the notch in the tube.

Once the gun is closed there's not need for the detent, as CJB said, it only contains the buffer and spring when the gun is broke open.

Good pictures, I just couldn't figure out for a bit what I was looking at.

Gene Hackman
07-03-2015, 11:26 PM
Whoever reassembled that lower has no clue....

If the parts are made correctly, the buffer tube will just cover the edge of the detent (nipple) and the adjustment holes wil be vertically aligned, at which point the castle nut can be tightened. There really is no need for the little half moon cut out, but... if ya gotta, so so the adjustment holes on the buffer are vertical... I guess ya gotta. Although, facing the buffer would have been the more correct fix. More correct, because removing the buffer (and spring) will require the detent to be depressed. That is not quite as easily done (and not how it was designed) with the little half moon cut.

The detent holds the buffer itself in place, preventing it from flying forward out of the tube upon opening the receiver sections. The buffer tube captures the detent, preventing it from flying out under its own spring pressure.
So is there something wrong with how it's assembled?

SigGlockBoy
07-05-2015, 07:52 AM
One turn in would go too far.

I would unscrew the buffer tube about 2mm to just line up the detent in the notch so it moves up and down freely. I suspect it turned a bit when he tightened the castle nut down.

You can use the proper castle nut wrench or a strap wrench to loosen/tighten the castle nut.

Glad you looked over the work. It would have been a nasty mess if you would have been able to somehow chamber a round and fire it. Not too likely though.

CJB
07-05-2015, 08:22 AM
Yes its not together properly.

There are two types of buffer tubes. One is round, the other has a detent mechanism for adjustable stocks, and those generally have a slot at 6 o'clock to ride in a plate that has a little tab at 6 o'clock. The plate fits into the frame when the castle nut is tightened, and also holds the detent spring for the takedown pin.

Round one's have a flat on the end of the tube, and you just screw 'em down tight. The length at the buffer detent is set.

A tube for an adjustable stock can have its length set, by one thread increments. One thread, because you still need to line up the 6 oclock slot/tab to make it all work.

The receiver, and the buffer tube.... both.... are supposed to have threads that are registered withing certain specs. I "think" the spec on each is 1/8 revolution (maybe it's 1/4 rev, I can't remember it was a long time ago when I studied this). Anyway, by doing the thread registering - starting the thread at a certain position relative to the rest of the assembly, you can be assured that the assembled parts length will be within a certain parameter. And that length is relative to the registration, and the threads per inch. As an example, at 1/4 revolution on each part, you'd have a max of 1/2 revolution from "perfect". If you have 12.5 threads per inch, then you'd be out by no more than 1/25th of an inch (twice as fine as the thread count), or put another way, you could be off by no more than .040 inches (1/25th of an inch). Make the rest of the stuff work out so you can live with that amount of slop in the fit.... you're golden.

Registering threads, is not a total *****, but.... ya know... it can be if you're trying to do it on less than stellar production equipment. Or with buffer tubes, more likely, you don't know about, or don't care about getting it right. Hence, the little half moon cut out that someone had to put in the tube.

Could be the tube is good, and the receiver is not. Either way, just make it work. The half moon isn't really supposed to be there, but then again...its a means to an end. If the pin can be depressed, and if the tube holds the pin from flying across to the next county when you open things up.... its ok for a non-military use rifle. Military use, they want things interchangable.... you know that drill.