The bolt wont bottom out on the back of the receiver as long as the recoil springs are changed after 5,000 rounds or so. I got to the point Id change them out after 3,500 rounds.....$30 set of springs vs a $28k-$32k receiver.....yeah thats a no brained.
The other part in an M3A1 that causes issues was the improved design of the guide rod back plate. The original M3 used a large plate, a lot of surface area to spread the stress across. The M3A1 used a small plate which put all the stress in one central area. Couple that with a non-maintained gun and yeah youll blow out the back. The improved version was down so you can take the bolt assembly out of an M3A1 without pulling the ejector housing out, unlike the M3. The large plate on the M3 wouldnt clear the ejector.
Id run an M3 guide rod assembly in your Medea build. Its better on the gun. If you want to be able to pull the bolt assembly out without pulling the ejector housing off-Machine an 1/8 slot into the back plate to create clearance for it to pass the ejector on the way out.
Suppresses on M3s will actually create faster spring wear due to increased pressures throwing the bolt harder. The feeling of it shooting softer is due to damn near doubling the over all weight of the gun. Put a suppressor on an Uzi and it really makes the gun shoot smoother but you can also feel more bolt speed to the rear. Same thing here-suppressed means more bolt speed rearward which means more spring tension needed to counteract that.
Edited by Got Uzi, 16 January 2021 - 09:25 AM.