Ok, so I just finished my first build with a stripped spikes upper and lower. This entire gun was pieced together. I am having a serious issue with the tolerances being very tight. I mean in regards to the last 1/16 of space between the upper and lower. It’s so tight it literally snaps into place. It almost seems like there is maybe an issue with the back of the bolt carrier and the buffer? The take down pins are also ridiculously tight, but I have read this is not uncommon(its luck of the draw). However I have never handled an AR with the upper and lower so tight it literally snaps together. Any ideas as to what this could be or if their is a fix?
Lucky. Always seems like they are too loose for me.
probable tolerance stacking making things tight. had a similar issue with my first build of a BCM upper mated to a DTI lower. i had to use a delrin punch to knock the pins out for dissasembly. after shooting for a bit it loosened up and now is fine. it also used to “snap” into place when seating the upper.
No such thing as too loose. That’s preferable to too tight every day.
I’m trying to decipher if that’s a personal issue or if the lowers that you’ve been trying to “mate” with have all been used & abused. Either way, that seems like TMI.
I do agree with Euro that the loose ones are definitely easier to mate with.
Well, if that’s not “Dicking the dog”, I don’t know what is. 
Ya got me…you caught the tater…
That’s what she said right? Guess I kinda walked face first into that one.
Seems like I have to put wedges in mine always. Even other handling people’s rifles or handling them at the lgs. I never never handled a tight one without play.
If my memory serves me well there is such a thing as too loose. If you can slip a 20 thousandth feeler gauge between the upper and lower one or both are out of spec.
Well it definitely sucks having to eat a can of spinach every time i want to push out my take down pins or need to mate my upper and lower.
Can’t tell you what the armorer standard is for replacement, but I can tell you that I’ve seen a Marine use a rifle which could fit a credit card in the space between the two halves still earn an expert award on the KD course of fire. To me, its a non issue as 999 out of 1000 times the people who worry about these things worry even though it is in spec.
I’ve had some builds that were tighter than others. Shooting & disassembly of the two halves will naturally loosen things up over time. I wouldn’t worry about it.
I have also read here somewhere that there is an actual spec for what is “too loose” however, it escapes me right now.
Army TM9-1005-319-23&P
Air Force TO 11W3-5-5-42
Page 3-68
d. Test
- With the upper receiver attached to the lower receiver, and the pivot pin and takedown pins in place, perform the following test:
(a) Apply hand pressure to push the upper receiver as far to one side as possible.
(b) Attempt to insert a 0.020" inch thickness gauge between the pivot pin lugs of the upper and lower receivers.
(c) If the thickness gauge penetrates to the pivot pin at all accessible locations, repair by replacement of the upper receiver (see (b) below) or replacement of rifle is required.
-
If the rifle fails the above test, remove the upper receiver and install a “NEW” upper receiver and perform the test again.
-
If the rifle now passes the above test, it shall be considered serviceable and continue in use.
-
If the rifle fails the test with a new upper receiver, this failure shall be considered a shortcoming. This shortcoming requires action to obtain a replacement rifle. Once a replacement has been received, evacuate the original rifle to depot for overhaul.
This leaves a lot of room for loose upper to lower receiver fit on a functional rifle or carbine.
If it doesn’t loosen up enough to pop out the takedown pins by hand after a few dozen times, you can take a file and gently sand a slight amount on the bottom part of the hole in the takedown lugs. Be very, very gentle and careful. But, whatever you do…
DO NOT PERFORM ANY SANDING ON THE LOWER RECEIVER.
Honestly, it’ll probably loosen up with time. But, in general, I prefer to be able to pop the takedown pins by hand.
Well I did some playing around and what’s going on is the back of the bcg is pushing against the buffer. So the last initial squeeze i am making that I have described as “snapping” into place is the back of the bcg pressing against the buffer.
That’s perfectly normal.
Yea, I have just never had a gun this tight before I guess, so it took me by surprise. Now I did forget to mention that I cerakoted it,…but I highly doubt it would drive the tolerance off this much. All assembly was a little tighter then normal but nothing drastic. First time I have dealt with this lol. I’ll find out how she shoots next weekend.
The back of the BCG should glide the buffer back with NO snapping action AT ALL. Your RE and/or Buffer detent hole may be out of spec… The RE may also be threaded in a full rotation TOO MUCH because of an out of spec buffer detent hole.
This “some are tight… no big deal” crap is too quick of an assumption with all the garbage being rushed to market lately.
The wear spec of .020 seems like alot. I guess I just need to stop thinking about it.
The play always seems more noticeable to me when using a vertical grip.
I hope this is not the case as its a registered lower, i have also notice if i squeeze and upper and lower together i can push out the take down pins by hand without the need for tools. It most definitely is not “gliding” on across the buffer.
Can you get a pic of the buffer retaining area from above and to the side of the lower with the upper removed… or at least with the receivers opened up???
(the back of the bolt carrier should be flush with the back of the upper receiver. The Buffer face should stick forward a little. Then the back of the Carrier (when closing the receivers) should push the buffer back to that it’s not touching the buffer retainer when the actions are closed.
If the back of the carrier is hitting the TOP of the buffer at all when you close the receivers, there are problems. It should only contact the face/front of the buffer… nowhere else.