# Firearm answers

One question per page, answered against manufacturer documentation rather than forum consensus. Every source is linked.

## Optics and mounting

- [Will a Holosun 507K fit a Glock 43X MOS?](https://www.tactgpt.app/answers/holosun-507k-glock-43x-mos.md): 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.
- [What red dot fits a SIG P365 without an adapter plate?](https://www.tactgpt.app/answers/sig-p365-red-dot-footprint.md): Anything cut for the Shield RMSc footprint. The optic-ready P365 slide is milled for it, so RMSc-pattern sights mount straight on.
- [Does a Trijicon SRO fit an RMR cut?](https://www.tactgpt.app/answers/trijicon-sro-rmr-same-footprint.md): 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

- [Will a 300 Blackout round chamber in a 5.56 barrel?](https://www.tactgpt.app/answers/300-blackout-in-a-556-barrel.md): 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.
- [Can you shoot 5.56 in a .223 chamber?](https://www.tactgpt.app/answers/shoot-556-in-a-223-chamber.md): 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

- [Will a mil-spec AR-15 stock fit a commercial buffer tube?](https://www.tactgpt.app/answers/mil-spec-stock-commercial-buffer-tube.md): 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.
- [Are M-LOK and KeyMod accessories interchangeable?](https://www.tactgpt.app/answers/mlok-keymod-interchangeable.md): 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.
- [Will an AR-15 upper fit an AR-10 lower?](https://www.tactgpt.app/answers/ar15-upper-on-ar10-lower.md): 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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TactGPT can make mistakes. Always check important info for accuracy. The information it provides is intended for educational purposes only. It does not give legal advice; verify any laws cited. Always follow all applicable laws and safety guidelines.

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