This is in reference to my experience with Semi-auto remanufactured Bren guns here in the U.S., but the question should apply and actually originate from the original full auto Bren gun as there is no modification in that area of the U.S. conversion.

I see that barrel nuts (locking levers) are available from those with no numbers stamped at all ("originals" perhaps when a gun is new?), and then some having "0" stamped" and versions with numbers "1" thru "5".

I had thought these barrel nuts pushed the barrel slightly towards the rear (into final locked position) and allowed for another way to tighten headspace. I am now thinking that is not the case. So can someone explain to me how these barrel nuts worked in the process of locking a barrel? I mean I understand the overall method of interrupted threads and how the basic locking works. But what happens in the nuisance with these numbered locking nuts?

I have barrels that I have tried in my Mk I body, but the original barrel nut won't completely close on some of these extra barrels. I tried a "3" marked nut and it wasn't any better, in fact may have actually been worse, in the fact it did not get any closer to locking closed. The original barrel nut has no number stamped on it at all.

I looked up "barrel nut" in the search, but found nothing that explains what the alternative numbers mean or how they work.
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