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sixb0nes · August 14th, 2015, 23:01

Hey folks,

Finally got around to opening this recent trade (SRC M4 SD GEN III) up for some cleaning, and to put in a 363mm inner barrel. I noticed some upper/lower separation early on but didn't put any thought into it.

Now that I've opened it up, I'm seeing the problem. With these SRC bodies (I don't know how common this is as I'm not a big M4 collector yet) it appears there are no lower tabs to allow for a pin through on the rear of the receiver. The upper appears to stay in place both by the conformed shape around the gearbox and a ring of tongue/groove around the rear which lines up to the upper receiver.

See pics below ...

Notice the rearmost bolt/pin are still in place - no need to remove as there are no tabs. Also notice the broken tongue that was obviously sheered off by the previous owner unbeknownst to me. This tongue should pretty much encircle the upper part of the buffer area, but in my case there is only a few mm left of coverage:

This next picture shows where the groove is on the upper that would fit up to the tongue on the lower. There are also two set screws there which I haven't muddled with, but you can see a square tab on the upper that may coincide with them, again to prevent movement (I think):

Back together and see the gap:

Now after squeezing:

So. Kinda sucks. I had a few ideas in mind to alleviate it the movement aspect, as seen between the last two pictures; but, I wanted to hear from the community or maybe someone who runs this configuration and has experienced this and how they solved it. I don't know what kind of force was exerted here to break it ... so this may not be common at all? I also don't think this is a common design, but again, I could be wrong.

My thought was to run something like thin 3M tape along the inside of the upper, away from any moving parts. I think that would cause a permanent gap (or not depending if I mount tape on upper or lower part of curve), but better than movement.

Hope someone has some ideas aside from replacement.

August 14th, 2015, 23:01	#1
sixb0nes Trader rating Join Date: May 2009	SRC M4 Upper/Lower Joy Hey folks, Finally got around to opening this recent trade (SRC M4 SD GEN III) up for some cleaning, and to put in a 363mm inner barrel. I noticed some upper/lower separation early on but didn't put any thought into it. Now that I've opened it up, I'm seeing the problem. With these SRC bodies (I don't know how common this is as I'm not a big M4 collector yet) it appears there are no lower tabs to allow for a pin through on the rear of the receiver. The upper appears to stay in place both by the conformed shape around the gearbox and a ring of tongue/groove around the rear which lines up to the upper receiver. See pics below ... Notice the rearmost bolt/pin are still in place - no need to remove as there are no tabs. Also notice the broken tongue that was obviously sheered off by the previous owner unbeknownst to me. This tongue should pretty much encircle the upper part of the buffer area, but in my case there is only a few mm left of coverage: This next picture shows where the groove is on the upper that would fit up to the tongue on the lower. There are also two set screws there which I haven't muddled with, but you can see a square tab on the upper that may coincide with them, again to prevent movement (I think): Back together and see the gap: Now after squeezing: So. Kinda sucks. I had a few ideas in mind to alleviate it the movement aspect, as seen between the last two pictures; but, I wanted to hear from the community or maybe someone who runs this configuration and has experienced this and how they solved it. I don't know what kind of force was exerted here to break it ... so this may not be common at all? I also don't think this is a common design, but again, I could be wrong. My thought was to run something like thin 3M tape along the inside of the upper, away from any moving parts. I think that would cause a permanent gap (or not depending if I mount tape on upper or lower part of curve), but better than movement. Hope someone has some ideas aside from replacement. __________________ ┌────────────────────────── ─ ── ∙ │ He who dies with the most guns, wins. └ Last edited by sixb0nes; August 14th, 2015 at 23:30..