AR Sponsor
Posted: 5/22/2012 1:46:15 PM EDT
|
Hi all,
I seem to have screwed the goat with an 80% receiver I'm working on. The hammer and trigger holes are not quite in the right place, and the disconnector won't release the hammer. Any ideas of how I might be able to fix this, and not have to scrap the lower? Thanks |
| Don't scrap the lower yet. The spacing between the trigger and hammer pin holes is somewhat tolerant to spacing problems. Try another disconnector or file a small amount off the front of the disco hook until the timing is correct. If too much is removed the hammer may miss the sear notch when the trigger resets after a bolt carrier cycle and may travel all the way forward to the firing pin when coming off the disconnector. If this happens you may be screwed. |
|
Quoted: why cant the holes be welded up and redrilled? Because the weld will be harder than the surrounding metal and the drill tends to wander off-center. IMO the best bet is to center-up on the proper hole location and drill the holes over-size for bushings which will allow the use of standard FCG pins. |
|
the receiver is what it is, there's no going back.
double check your dimensions as previously stated, especially the depth of the pocket behind the trigger it sounds like the trigger isn't going forward enough (the tail of trigger isn't going down enough at the rear, which moves the disconnect away from the hammer) try different FCG components (yeah they should all be the same, but they're not) modify the fcg parts to fit,(NOT as in NEVER grinding on the engagenment surfaces, use common sense) or use a self contained drop in FCG assembly. sometimes called a cassette, or a module, its a one piece FCG that drops in and just uses the pins to hold it in. Timney's are one such. welding on 7075 can be done, and its easy to clean up ,but in the end you're going to use the same jig and drill the holes in the same place. |
|
OK,
The FCG pocket is actually a little deeper than specs. I have tried several FCGs and all get the same thing. I had been working on modifying the hammer, but what I am afraid of is that by the time I get enough removed for it to work, I'm not going to have enough of it left. To be clear, I've been removing material from the round portion of the hammer on the bottom. |
|
Drill the holes to .240"ish, Ream to 0.2495, press in a plug, redrill.
Voila! Also, drill the holes before you cut the FCG pocket. Quoted:
Quoted:
why cant the holes be welded up and redrilled? Because the weld will be harder than the surrounding metal and the drill tends to wander off-center. IMO the best bet is to center-up on the proper hole location and drill the holes over-size for bushings which will allow the use of standard FCG pins. That should not be an issue with proper drilling technique, use of a good spotting or center drill will reduce you headaches ten fold and they are maybe $6. Posted Via AR15.Com Mobile |
|
Quoted:
find a good tig welder and have him weld up the holes and start over.pay him for his time and bring him some beer, so when you do it again he'll hook you up the next welding session.  Good welder or otherwise, the 7075 alloy is not considered to be weldable. A weld my look OK but will have little strength. |
| You say you have built other lowers using the jig that drilled this lower and the other lowers worked fine. Have you compared the trigger hole to hammer hole spacing between the suspect lower and one of the lowers that works? Any difference? Have you put the lower back into the jig and checked for misalignment? |
AR Sponsor