How to ID MkII piston post??

[TactAdv]

Riddle me this....

How does one easily telll from external examination the Mk II post from the Mk I???

Am I correct in assuming that you CANNOT interchange Mk I & Mk II PLUNGERS.....I.e, one cannot use a short Mk I plunger in Mk II post??

-TomH

Information

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[Peter Laidler]

Difficult externally! But internally, the Mk2 post has a deeper hole internally for the longer piston post plunger. You could use a shorter Mk1 plunger in a Mk2 piston post but to achieve what? If you use a long PP plunger in a Mk1 PP, the end of the rod batters the end of the shallow housing and causes mayhem and jambs the spring onto the rod. This was all done to further cushion the violent unolocking cycle and help cure the high attrition rate of PP springs. It sort-of helped but the attrition rate remained high, even up to the last L4 Bren era. That's the reason why a spare PPspring was always part of the spare parts wallet.

[TactAdv]

Difficult externally!

Thanks, Peter. I guess I knew the internal differences, but what is a dilemma over here is that when I see one for sale no one here really is conversant enough USUALLY to make the definitive examination of the plunger hole depth, so they are advertised devoid any identification of Mark.

It matters to me- I'm shooting my original MK II MG a lot and I'm not looking for any more MK I piston posts!! I have a box of MK I posts I don't want, and was trying to see if there's a visual I.D. way to know before I go buy more.....

Plunger springs I have plenty of!!
-TomH

[Peter Laidler]

You could just deepen the hole to suit. It wasn't a feasible option in the 40's but now, with better quality drill bits they'd drill down easily I'd say.

The reason for the change started when the gas port was opened up in the Mk1* barrels and Mk2 gas plugs. It gave more gas but that in itself caused a more violent unlocking/primary extraction. Hence the need for a more cushioned PP spring and plunger. This violent action was also the reason for the double return springs and later on, caused the buffer plate to crack in a circle around the face. That is the reason why we always polished the front face of the buffer plate, so that you could immediately see whether it had started to crack or break.