Firearm answers
One question per page, answered against manufacturer documentation rather than forum consensus. Every source is linked.
Optics and mounting
- It dependsWill a Holosun 507K fit a Glock 43X MOS?Usually not without an adapter plate. The screws line up, but the factory cut has four locating posts and a Holosun K optic only clears two.
- YesWhat red dot fits a SIG P365 without an adapter plate?Anything cut for the Shield RMSc footprint. The optic-ready P365 slide is milled for it, so RMSc-pattern sights mount straight on.
- It dependsDoes a Trijicon SRO fit an RMR cut?Mostly. The SRO uses the RMR footprint, but Trijicon requires a mounting kit on Glock MOS, Springfield OSP, Walther PDP and HK VP9.
Ammunition and chambering
- UnsafeWill a 300 Blackout round chamber in a 5.56 barrel?Yes, and that is the danger. It chambers and the bolt closes, but firing it can destroy the rifle. Never mix the two on the bench.
- UnsafeCan you shoot 5.56 in a .223 chamber?Not safely. The .223 chamber has a shorter throat, so 5.56 pressure climbs past what the rifle was proved for. The reverse direction is fine.
AR-platform parts
- NoWill a mil-spec AR-15 stock fit a commercial buffer tube?No. A commercial tube is about 0.022 inches fatter, which is enough that a mil-spec stock will not slide on. The other direction fits but rattles.
- NoAre M-LOK and KeyMod accessories interchangeable?No. KeyMod uses a keyhole opening and M-LOK a rectangular slot with a rotating T-nut. Neither system’s hardware mounts to the other.
- NoWill an AR-15 upper fit an AR-10 lower?No. An AR-10 lower is a physically larger receiver. Worse, AR-10 has two incompatible patterns that do not mix with each other either.
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