I used a 93/MP-5 single arm locking piece to fit in the 91 A-3 housing, see first pic, it worked with the other parts, release lever, ratchet nut, etc, BUT......it appears the MP-5 arms are wider.
I tried 2, the one that came with the MP-5 stock parts, the newer scalloped pattern, and an older non scalloped.
I can fit the housing onto both rifles I have, Greek SAR-8 and a PTR32, but the stock will not slide on the receivers.
I tried both, measured the arms and they are about .005" wider from outer face to the inside where they fit into the grooves on the receiver.
Compared them to a number of different stocks I have, and the MP-5 stock arms are made wider, meaning the MP-5 receiver is JUST a little more narrow than a 91/G3.
I originally thought of this for the PTR-32, sort of a "poor man's HK-32".
It'll work, but, it would mean removing a little material from both stock arms the full length.
On the brighter side, extended, the MP-5 stock does give the same LOP as the 91, thanks to the larger butt pad, but adds about an inch and a half closed, again, thanks to the larger pad.
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