AR15 mil-spec buffer tube length or fitment issue

J

JRDuffman

Member
Rating - 100%
4   0   0
Location
London Ontario
I'm currently building my first AR15 and I have a Norinco stripped lower that I built up with a LPK including a mil-spec buffer tube. The problem is the length or fitment doesn't seem to be correct.

I bought the kit together inc the back plate and castle nut. I screw the buffer tube into the receiver until the lip just holds the buffer retaining pin as I've seen done before and then tighten the castle nut on. The issue seems like the tube is screwed in too far. When I put on a Magpul MOE stock I can not get it to grab the inner most adjustment hole on the tube because the stock hits the castle nut before it can get that far. I have another M4 style stock that does fit all the way on but the Magpul doesn't. The thing is I've tried both stocks on another AR15 and they both fit on no problem. The tube inside the receiver comes right up %100 flush to the front side where the upper ramps down and I just don't know if that is correct. I seem to recall the few I've looked in having a little bit of a gap meaning the threaded end of the tube isn't flush with where the upper meets the lower. I could be wrong about that but it would explain why I can't get my stock on all the way as in the tube is threaded in too far into the lower. The thing is if I loosen it just one turn around it doesn't catch the buffer retaining pin. The buffer tube also has a slot cut in the bottom where the threads are that's just wide enough for the tip of the retainer to poke through but I'm not that far in to where the tip would be actually in the slot, it's in where it would be if the cut wasn't there. Screwing it in to the point that the tip would be in the slot would put the tube right though the lower and interfere with the upper for sure. I also don't recall seeing this type of slot cut into the bottom of the threads of a buffer tube before either. Seems strange and doesn't make sense when my issue is already that the tube may be in too far to reach the retainer so why would you want a lot in there to allow it to go in even further??

What's going on here???? I also wondered if the castle nut is simply too long? That would cause the issue here too. But has anyone ever heard of that before?


Thanks for any advise!
 
Last edited:
Sorry pics might have helped but it's really hard to tell just by looking at it. But I found another tube and put them side by side and it is actually a little bit longer overall than the previous one. Put that one in the AR and it's perfect.

Lucky I have a Ruger SR-22 rifle that uses a mil-spec buffer tube ONLY to hold the stock on (no actual buffer/spring) so I was able to put the shorter one in that since it doesn't have to be screwed in to a certain point to hit the buffer retaining pin. Now they're both fine.

So I guess the mil-spec buffer tube I got wasn't so mil-spec after all! I know mil-spec is a iffy term to begin with BUT how is the overall length not a common spec between them?? But I guess it worked out in the end.
 
It's my first AR build ever and so yeah, sorry if I wanted to make sure I wasn't doing anything wrong, didn't have a bad receiver or, you know, just simply wanted it to work properly...
 
Do you have the buffer retainer detent and spring installed? If the lower is mil-spec and the tube is mil-spec the depth of the tube will be bang on because it stops at the detent. Also the mil-spec tube is marginally short from a Commercial tube.
 
Where the threads are on the receiver extension (buffer tube), is the bottom slightly longer than the top? What brand?
Try another brand R.E. to see if the problem is the R.E. or the lower. It's a Nork so my money is on the retainer hole being out of spec, however, some companies make some pretty awful R.E.s



Anywhooters, your options are these:

a) live with it - the stock can't collapse any further so it won't be an issue whilst shooting

b) return the buffer tube kit to where you bought it for a new one after convincing them the issue isn't your Chinese lower ;)

c) don't use the buffer retainer - you'll be able to lock up the stock but you'll have to be careful not to launch you buffer/spring when you open it up
 
Sqr said:
Do you have the buffer retainer detent and spring installed? If the lower is mil-spec and the tube is mil-spec the depth of the tube will be bang on because it stops at the detent. Also the mil-spec tube is marginally short from a Commercial tube.
Click to expand...

You didn't actually read the OP.....did you? lol
 
Magpul CTR/MOE/ACS/ASC-L Stocks have the provision to add or subtract the ".55" extended butt pad spacer" that is used to aid in the fitment on some applications. If yours is installed it will not reach the first buffer tube hole.
 
-[Crosshair]- said:
wat
Click to expand...

It's not required with a JP silent captured spring. Also when a lower has been poorly machined and the detent hole location is out of spec and a symptom is the buffer face is scared by the detent. You can purchase an offset detent to minimize the mil-spec buffer damage or as I have pointed out remove the detent entirely. It's not uncommon as the only caveat is owner needs to be more careful when braking the receivers apart for work or cleaning. Not the best solution but it avoid throwing the lower away.
 
Sqr said:
It's not required with a JP silent captured spring. Also when a lower has been poorly machined and the detent hole location is out of spec and a symptom is the buffer face is scared by the detent. You can purchase an offset detent to minimize the mil-spec buffer damage or as I have pointed out remove the detent entirely. It's not uncommon as the only caveat is owner needs to be more careful when braking the receivers apart for work or cleaning. Not the best solution but it avoid throwing the lower away.
Click to expand...

So instead of using a properly manufactured lower receiver the solution is some BS bandaid setup where your return spring and buffer are now free to fly all over hell's half acre every time you open up the gun.... bright choice..
 
*MALICE* said:
He tried that. Retainer pops out.
Click to expand...
.......ok.....short version.....leave it out. Done! Nothing is going to happen.

When removing the upper the buffer and spring actually get stopped by the trigger so the retainer pin is actually not needed at all. It was also stated that the pin/spring can be a point of failure.

Here is an offset pin for out of spec lowers. They work fine.


8f07d2206c51b26b6ea8ff0d21529c78_zpsc4zkneko.jpg


It allows the ability to back the buffer tube out of the receiver.

3bd3973da3e758a2df369a9bd44f990c_zpsdihyoc4w.jpg
 
Last edited:
Kidd X said:
So instead of using a properly manufactured lower receiver the solution is some BS bandaid setup where your return spring and buffer are now free to fly all over hell's half acre every time you open up the gun.... bright choice..
Click to expand...

Throw the lower away...not a chance because it's a solution and I would use it because it is only for convenience and not an operating requirment. It's only free to fly if the owner is careless.

If not this can happen.

7f78e8fba7bd288c65bf0e17ca621053_zpsvvidmxv2.jpg
4721d3a5eca3175bf40fb08e3b86f563_zpsizhjfxr1.jpg
8f10c6707cb75ded7d79d1cdda31a2ea_zpsqx53bkda.jpg
 
Last edited:
Sqr said:
Throw the lower away...not a chance because it's a solution and I would use it because it is only for convenience and not an operating requirment. It's only free to fly if the owner is careless.

If not this can happen.

7f78e8fba7bd288c65bf0e17ca621053_zpsvvidmxv2.jpg
4721d3a5eca3175bf40fb08e3b86f563_zpsizhjfxr1.jpg
8f10c6707cb75ded7d79d1cdda31a2ea_zpsqx53bkda.jpg
Click to expand...

Right, that damage can occur on OUT OF SPEC lowers. Get a lower that was made properly and it is NOT an issue. Lowers are cheap, and out of spec ones are cheaper yet. Oh and the trigger doesn't stop the return spring from flying out, the hammer does. The trigger pokes out the bottom of the receiver. ;)
 
You must log in or register to reply here.
Back
Top Bottom