Ok so I'm shooting along (Bushy M4gery) and the bolt just freezes up as far back as it will go...hmph?

...magazine isn't empty, what the hell?

racked the charging handle and got nothing (it didn't even get far back enough to TOUCH the bolt)

last resort time, tap (rather forcefully, lol) around different parts of the gun to try and knock it loose, shake it a bit,  yada yada yada....
So I give up, remove the mag, and go to having fun with my Glock for a while....I'll screw with the rifle later at home...

So when we're getting ready to leave the range, I pick up the rifle, and in one last fit of desperation, I shake it and tap it a little and the bolt inches forward a SMALL BIT very slowly. ??? So I do it more and the bolt finally snaps forward...okay?
What the hell just happened? Someone suggested a piece of ammo debris stuck around the bolt somewhere? I dunno, odd?

What do your buffer and spring look like?

Posted By Tweak
"What do your buffer and spring look like?"

I would second Tweak on this.

I've seen this happen where the buffer retaining pin came loose, popped up, was caught by the bolt carrier and wedged itself between the carrier and the buffer tube.  Retaining pin came up because they were shooting the rifle with a loose buffer tube, as the tube unscrewed slightly, the pin popped up. Very pretty scrape inside.

DING DING, good call guys, thanks.

Upon taking the rifle apart (yeah I'm just now getting to it) I found the buffer retaining pin and spring tumbling around in the bottom of the reciever, I'm just wondering how in the hell they got loose enough for the bolt to finally snap forward and allow the pin and spring to fall down into the reciever, just confuses me.
Screw that though, now that I know what happened and have the rifle apart, how do I stop it from happening again? I could probably use Loctite on the threads of the buffer tube, but that would screw me if/when I decide to change buttstocks again won't it? What's the most common solution for this aside from constantly tightening the buffer tube?

Nope, it's the ACE ARFX shorty stock, perhaps someone has pics, sorry I don't.
It's fixed, and very tubular in build, basically consists of the buffer tube, a lower tube forming the shape of a standard stock, and the buttplate.
Still waiting for a reliable fix to this problem before I put the rifle back together.....

Well, I did put it on myself....but was quite sure I had it right...lol

I didn't use anything to screw the tube into the reciever, just reefed on it with my hand as hard as I could...LOL, and actually found that to be TOO tight, because the tube screwed itself right OVER the hole the buffer detent pin goes in, so I backed it out a touch...hmm.

perhaps I'll just touch some loctite to the tube and screw it in far enough to not cover the buffer detent pin hole and see what happens....eh?

Thetube must be torqued or locked mechanically with a locknut.  Unless you can do this, leave the buffer retainer out as this is sure to happen again.

Sounds like something is out of spec, perhaps milling the buffer tube so it can be properly torqued and be in the correct position to retain the buffer retainer.

I wasn't aware that leaving the buffer detent out was an option? Everything will/should function fine without it? Hell, I'll just do that...

<----runs to put rifle back together minus buffer detent....

I hope this doesn't come off as being a smartass but, I feel the proper fitting of all the parts in any firearm to be a sign of a well cared for and well built one.
I have read where it is suggested the buffer detent be left out so this type of malfunction can't happen. If the buffer tube is correctly fitted by shortening the threads and filing the bottom for a strong positve retention of the detent the malfuntion won't happen anyways. Take your time, see how it all works and fit the parts slowly.

just .02


mark mcj    

Well...no offense taken
I will say that this is my first AR project and I'm still in the process of feeling out how the whole thing goes together and works.
I'm gonna try putting it together minus the buffer detent, and if anything seems remotely off I'll probably just throw the stock buttstock assembly back on and bring it to Bushy (I live about an hour from their shop) and see what they can do for me.

The buffer retainer is there to retain the buffer and spring when "shotgunning" the upper for maintenance.  It is for convienience and does absolutely nothing when the gun is fully assembled.

As mentioned above, the correct way to resolve this is to find the cause and correct it.  It probably will require some fitting.  But, the gun will run fine if you leave the jamm-o-matic feature out for now.

Do see to it that the buffer tube stays tight, though.  If it loosens up a bunch, it could lead to some damage to the lower.

So removing the detent, and perhaps some loctite to the tube's threading is a place to start for now I guess, I'll bring it back up if anything else happens. Thanks guys!

Quoted: actually found that to be TOO tight, because the tube screwed itself right OVER the hole the buffer detent pin goes in, so I backed it out a touch...hmm.

The open end of the receiver extension should fit over the outer rim, and just short of/against the center post of the buffer retention pin when the extension is tightened to 35 lbs.  If your finding that the lip of the receiver extension is a tad too long, and binding the center post, the quick way to fit is to just pull the tube, and roll/flat file the end of the tube to get it to the correct length.  Keep the file 90* with the end of the tube (flat flat agaisnt both edges) and use your other hand to spin the tube to remove some length of the lips.  One you have the correct length,  then just use a small file to re-bevel (remove the sharp edges caused by shorting) of the opening of the receiver extension.  

When you install the receiver extension after fitting, a few drop of blue loctite works wonders on keeping the tube in place (as Tweak pointed out).  If you need to remove the receiver extension at a latter date, then just heat the tube up with a heat gun (600*) about 2” back from the receiver, which will break the loctite bond and allow you to spin the tube back out.

Note: You really don’t need to use the loctite if you torque the extension correctly, but if you need to clear a few jams by butt stock impacts (or just need to give a few butt rubbings) then it insures that the receiver extension will not spin and back out on it’s own.


As others have posted, leaving the buffer retainer pin out will cause nothing but problems in the long run.  Best case is that the hammer is un-cocked and the buffer just tags it as it slingshots into the front of the lower. Worst case is the whole mess slings out of the lower and you don't get all the crap off the spring/buffer (dirt from the ground), which makes it's way back into the extension, then migrates into the action to destroy the parts.

Ace Carbine receiver extension

Yes, there's a raised lip around the tube after the threading that snugs up to the reciever

Thanks for the pic...LOL

I've got the tube screwed in as tight as I can do by hand, the smoothness of it doesn't allow me to get a good enough grip with a wrench or tool of any sort to tighten it more, so the loctite might have to be the choice for keeping that in place.

Notice that that the back section of the extension where the butt stock screws into has two flats.  

This is where you use a wrench to tighten the extension to the receiver.

<---raises idiot flag

I never thought of that...

Quoted: CeeDub, What is the length of threaded section (flange to front) of your extension? Also, compare it to the one that was previously on the rifle. You may want to hold off modifying any part until you're certain which part is wrong.

Either the receiver extension open lip end is a tad too long (section forward of the stop collar), the stop collar was set too to far rearward on the tube, or the Bushmaster buffer retaining pinhole opening was milled too far back in the receiver.

My thoughts would be as long as the bolt hold open device works with the receiver extension flat bottomed out against the receiver, then the added length of the extension is a godsend (can be fitted to just kiss the buffer retaining pin).

More often, the buffer retaining pin oblongs the hole opening in the receiver, and on some pins/receivers, the pin can walk out from the retention of the receiver extension. With this tube, he can set/fit the tube to just kiss the center of the pin, which insures that even after wear to the receiver retaining hole in the receiver (oblonging over time), the receiver extension will retain even the sloppiest of fitting of the two.

Keeping in mind that if the current carbine receiver extension still allows the bolt/catch to function**, if he sends the tube back for replacement, then they will simple shorten the lip and send the unit back out.  Without having the rifle in hand to fit it, they may shorten the tube to the point that with a new lower receiver, the buffer tube is retained, but after years of wear, the retention of the retainer becomes a problem. This would put him back to square one, which is to either find a longer receiver extension to compensate for the oblong wear (which he currently may have), or to replace the lower receiver.


To sum it up, My thoughts are that I would rather have a part slightly over sized/long from the start, which allows me to fine fit the part to the rifle it is going to be installed in, then to have a part that is border line too short from the start, and which leaves you searching through your shop tools for a part stretcher (heating/penning/grooving) at a later date.  


** With the extension installed (collar bottomed out on the back of the receiver in the rifle), pull back on the charging handle and see where the bolt stops in relationship to the bolt catch.  The front face of the bolt should stop short of the rear of the ejection port, but at least 1/8" rearward of the back face of the bolt stop against the bolt face.