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I recently asked someone about getting a small slot cut in the lower of my Walther/Colt M4 .22 and there was a sharp intake of breath followed by 'If you do that you'll have to get it reproofed'.

My question is:-
Does any amount of work on a firearm require reproofing or are there limits? If I open out the magwell on my GSG 1911, should I get it reproofed or are there some guidelines as to what work would require a reproof?

Surely proof only applies to pressure-bearing components?

What can they 'proof test' about a mag well?!?

Seems like old-timer nonsense to me :)

As above, Proof laws only apply to (*Some) Pressure bearing parts.

*Some, interestingly some parts such as the firing pin, firing pin rod if used and shroud although technically being pressure bearing are not subject to test.

Thanks Ovenpaa.

Does the lower count as a pressure bearing part?
Could I do (or have done) whatever minor work I like to it? (within reason)

The lower is not a pressure bearing part as such however I have seen a few with Proof marks in the past.

Without knowing what you want to do it is hard to comment further :)

The lack of an external bolt hold open catch is bit of a pain.
There is an internal mag activated hold open catch which runs just inside the left side of the lower.
I'm thinking it might be possible to cut a narrow slot in the top edge of the lower to attach an external stud to the end of the actuator.
It wouldn't look genuine but it would be better than having to stick a finger up inside the mag well every time I need to show clear.

I think the gun smith is trying to seperate you from your cash.

38Super wrote:The lack of an external bolt hold open catch is bit of a pain.
There is an internal mag activated hold open catch which runs just inside the left side of the lower.
I'm thinking it might be possible to cut a narrow slot in the top edge of the lower to attach an external stud to the end of the actuator.
It wouldn't look genuine but it would be better than having to stick a finger up inside the mag well every time I need to show clear.

Tbe normal M4 has a bolt hold-open catch.
Is the one on the Walther not functional?

The Walther has something that looks like the standard AR hold open but it's just cosmetic.
The internals are very different to a normal AR.

I don't know the answer to this question or what tests were carried out but my CCMG has proof marks on both the lower and upper.