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GA, USA
Posted: 4/24/2026 12:23:49 PM EDT
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I’m trying to diagnose what appears to be a mechanical compatibility / geometry problem in a PCC build, not a simple ammo or cleaning issue. Setup: Matador MAT-9 upper Foxtrot Mike Ranch Rifle lower Mean Arms ExoMag with ejector Problem: I’m getting a failure-to-fire / abnormal function issue, and I suspect the cause is somewhere in the interface between the bolt, hammer, lower geometry, and magazine positioning. Since I’m using an ExoMag with built-in ejector, I do not think this is just an ejector-absence problem. My working theory is that the issue is more likely one of the following: bolt-to-hammer interference / excessive drag hammer or trigger geometry incompatibility mag height / mag catch depth / round presentation issue overall tolerance stacking between the MAT-9 upper and FM Ranch Rifle lower This does not feel like bad ammo or a routine break-in issue. It feels like something in the system is mechanically not agreeing. What I’m trying to determine: what the single most likely interference point is whether the first thing to investigate is hammer profile, bolt drag, or mag positioning what the cleanest fix is before I start swapping parts or removing material Questions for people who know these systems: With this setup, is hammer profile / bolt drag the first place you would look? Has anyone run a MAT-9 upper on an FM Ranch Rifle lower successfully? Are there known hammer / trigger combinations that play well with this sort of setup? How much suspicion would you place on ExoMag height / mag catch depth versus FCG geometry? I’d especially appreciate responses from anyone who has dealt with bufferless AR9/PCC uppers on unusual lowers or solved a similar drag / FTF issue. I can add close-up photos of wear/contact points if helpful. |
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Need more details, but is bolt ramped or not. On the back tail of the trigger, see if the hammer tail is denting the hell out of it or the tail of the disco, or even leaving a white line. Note, this would the tell tale that you have hammer/trigger wedging, with the tail of the bolt too long/ need to round the top of the hammer FP contact pad isntead. Next, pull back on the charging handle, and tell me how far behind the bolt catch, is the face of the bolt able to retract past it. It should be only 1/8"~1/4" and in some cases where the face of the bolt is allowed to come much farther back then this, will need to get a receiver extension space that goes into the tube before the buffer and recoil spring are installed. Do not touch the trigger with upper shotgun'd opwn, cock the hammer back until its rear sear is as close to the disco sear, and what is the free gap distance between them (should only be .004"/thickness of a sheet of copier paper. Next, pull the FCG, and go back to make sure that the disco channel for the trigger pin, and even the trigger slot, is not bur'd/ causing the disco to bind in the slot. When you reinstall the disco spring, large coil side goes down into the trigger slot (will have to use a set of pliers to set the spring in the trigger channel), not the other way around. https://www.reddit.com/r/ar15/comments/76nrkk/my_ar15_was_fun_to_shoot_with_the_hammer_trigger/#lightbox And hammer legs have to be on top of the trigger pin. If ejector was the problem (not riding height enough, and bolt face close enough, then would be leaving/defecting spent case back in the action. If mag was the problem, then would be causing feed problems. So, the question comes down to if the bolt is taking the hammer all the way back down to the disco on full stroke, if the disc is catching/retaining the hammer while you still have the trigger pulled back during the the shot, hammer tail is not slamming the disc so hard that is dancing it/sticking it down to allow the disco to release the hammer with trigger still pulled back, and if the disco is retaining the hammer back until you dam near get the trigger allow the way back to its resting position, until the disco releases the hammer. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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