A tip for the dudes with Buckmaster PB12 tube-mags

[Wapiti]

This might not help too many of you, maybe some of your mates have one of these shotguns. Maybe even, ones similar in the way they work.

These shotguns have a (I suppose it's what it's called) gas block brazed to the barrel. The gas piston slips into it from the action end, and it has a steel piston ring seal on it.
However, the seal between the magazine tube and the gas block, the front side, has a thin O-ring inside the block. It seals (sort of) the gas from leaking forward, stopping some of the gas being lost out the front. So all the gas is used to reliably operate the action.
The O-ring is a 25mm i/d x 2.3mm section.
This is very important when using lighter loads, or reduced velocity ones.

However, a lot of them don't reliably extract and eject strongly enough with light 7.5 shot loads, some say that after a few 100 shots the things smoothen up enough to just work with these loads.

Mine didn't work at all, and on inspection I found that the O-ring in mine was completely missing from the factory.
So, in my many O-ring kits we keep in the farm workshop, I found an O-ring that fit very snugly, much more so that the original.
It is a 23mm i/d x 3mm section, a standard size in an O-ring kit.
I put it in whilst waiting for the original part to come into my local gunshop, which it did yesterday, along with a few more magazines for my wife's PB12-M style.
Use silicon grease to lube the O-ring up, so it doesn't perish from gun solvents and strange gun oils.
You can get tubes of silicon O-ring grease from easy joints like Super-Cheap etc.

Now, mine pelts out the light 7.5's and 9's fired shells we use for snakes and pest birds, just as hard as 00 Buck or slugs, really snappy and super reliably. Just like that.
So if you know anyone complaining about reliability issues with theirs with light loads, a better, tighter sealing O-ring fixes this immediately.
You can buy these in 10-packs online from bolt 'n nut places, bearing shops etc.
Look for Neoprene O-ring, 23mm i/d x 3mm section.
Section means, the thickness of the O-ring ring diameter itself, in this case 3mm, with 23mm meaning the internal diameter of the ring sitting unstretched, new.

So when I got the original O-ring from ASA (they were good about it and didn't charge me) I compared it to the one I used in my kits and no wonder people have mixed results with these shotguns, it doesn't seal well at all and is a very sloppy fit. I can't imagine why they cut a groove for an O-ring and fitted one that just flops about in the groove.