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Joined:
Apr 2026
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GA, USA
Posted: 4/28/2026 1:07:50 PM EDT
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All insight welcome. Thanks in advance! 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: (I know for a fact this should work in theory...  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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I had to look that up. Looks interesting, but no help from me. My 9 is a regular blowback/colt mag. https://www.uzitalk.com/forums/index.php?threads/matador-arms-mat-9k-brownells-brn-9-upper.99932/ Good luck. I have had to grind a touch off the hammer tip before to alleviate drag. |
If life was easy nobody would quit.
| I have no dog in this fight, but just recently stumbled upon the mags you mentioned, and looked into them. The mags are also mentioned in the retro ar forum on Reddit. Long story short - the mags were hit and miss and could cause problems. That’s all I got and I hope you get it sorted out. |
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