MKII lowers, what controls position on upper receiver?

[c310pilot]

I have an upper that the lowers are going way to deep in. I am trying to figure out exactly what has changed between the upper receivers. Its not the obvious as the rear ledges on the receiver measure out the same.

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[Peter Laidler]

It is the outer ears of the buffer plate that dictate how far the butt slide enters into the body of the gun. It is these ears that enter and seat against recoil shoulders in the gun body that control the 'primary recoil'. That is the initial recoil of the gun as it fires. The gun barrel and body recoils together AGAINST the outer ears of the buffer plate compressing the buffer spring against the buffer nut and friction ring. Later, when the buffer has resasserted itself, the secondary recoil takes place (In fact, what happens next isn't strictly recoil, but.........). The piston extension assembly comes to the rear and strikes the buffer plate in the centre, about the return spring rod and this also compresses the buffer plate against the buffer spring and friction collar.

Anyway, that's a long winded answer to what really only neede a short few words reply. But that's why when an Armourer picks up a Bren he always pushes the butt down against the flash eliminator. If the gun buffer is defective, you're going to have an uncomfortable day shooting the gun. It REALLY does work.

In truth, the butt plate buffering mechanism on the old early Mk1 guns was a total frill if not a complete fraud. But the financial penalty for any changes to the manufacturing rights/drawings were prohibitive - so it stayed! But not for long because when the war came, we just did it!

[c310pilot]

AHHH. I didn't even think that I had my buffer removed. Thanks!