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As I'm bored and not shooting anything, I thought I'd do some mods to the loading port of my Mossberg I use for PSG. I'd stripped it down, degreased it and was in the process of marking out where I was going to enlarge the port, when I saw a proof mark on the lower receiver next to one of the front corners of the said loading port.

It got me thinking, if I do any modifications, would it need re-proofing? I can't think how in a million years it is pressure bearing. Plus everyone and his dog seems to do this mod as a standard were I shoot and youtube is full of UK shooters telling you how to do it yourself (never mind the US youtubers).

Are there any implications in doing this modification on a part that is proof marked?

the cynic in me says that is purely money making, as after you enlarge the port, it then won't have a proof mark, so if you want to sell, it will need reproofing.

Which model Mossberg is it? The pumps and older guns aren't suitable for dual/quadloading because of the lifter design so it would be a waste of time.

I presume its a 930/940 and have seen several (930's) with port jobs. AFAIK none of them were reproofed. I would imagine however removal of a proof mark, assuming there isn't another on the receiver, could potentially be a problem when it comes to selling the gun though

There is a debate in the practical community as to how far is too far when it comes to port cuts before a gun should be reassessed but i'm yet to hear convincing arguments/see anything judicial to sway me either way.

I've been tempted to finally get around to doing my M2 but haven't found the time/scrotal fortitude to do it yet!

Cheers for the responses, I jibbed out in the end and went to plan B and did some comfort reloading! Just to prove to myself I wasn't losing the plot, I check my other guns and all had proof marks either on the barrels and/or on the receivers at the point the barrel attaches. Similarly on the muzzle end of the barrels if they had been threaded. All areas I would associate with pressure bearing.

Its a 930 JM Pro and its the only proof mark on the receiver. Perhaps I should practice more precise dual loading!

I'm going to have to make a massive effort to use the "lack of scrotal fortitude" comment at work when ever possible.......brilliant!