
With the barrel pushed all the way in the breech there's a gap at the front. This is the same gap that I found inside the breech as the barrel was sliding back and forth.

I used loctite bearing retainer to seal the barrel in the breech. This will prevent any air leaks or movement.

I cut a metal washer.

Like so.

That takes up that space.

I found a sliding breech cover with appropriate "patina" on Ebay.

I made a new breech cover screw to fit.

Slotting...

One of the sight holes went plumb through into the barrel...

So I wrapped a thin scrap of teflon tape around that sight screw. Should prevent air loss.

Finally, I found a knurled nut in my pile of parts I purchased last year.
Now the barrel doesn't move, air leaks are minimized and loading is much easier.