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FRST said "Just to be clear- you can run around with the bolt behind the 8th round. It's just not advisable/safe as the slightest jolt will send the bolt forward."

Which means that it can hold 8...

Well damn, the plot thickens lol

I don't think 5 round clips would make it legal as it can still hold 8 internally. That's like only loading 5 rounds in a 10 round mag, or only loading 5 rounds into a 10 round shotgun tube.
You...

Ah ok, so the grey area is that you cant really keep the action open with the full 8 rounds in it, so as soon as you put it in you have 7 in the magazine and one in the chamber.
Interesting.

As I said im not really familiar with Garands, but I did a quick google search which suggested the stripper clips take 8 rounds.
So if the stripper clip can take 8, then you put it in, chamber a...

Im not really familiar with Garands - but I thought it can hold 8? If so, why would it not be an E-cat?

If it can hold more than 7 then its an MSSA. Mag does not need to be detachable. For example a semi auto shotgun that can hold more than 7 in its tube would also be an MSSA.