AusVarmint

Took advantage of the rainy weather to spend the day in the shed fixing up an old BSA Mercury that I picked up.

Pulled the whole thing apart and gave it a good clean and polish. The piston head was pretty cracked and bent with the rubber buffer totally disintegrated. The breech oring was history so that needed replacement as well. Finally it looked like the previous owner had made a very bodgy cocking lever that was ugly as.

Machined up a new piston head from Delrin and mounted it on the piston. A new oring and a wipe of moly grease and it easily slid back into chamber. Made a top hat also from Delrin to help the spring rotate when compressed. Used a piece of square bar as the new cocking lever and machined a slot for the pivot arms.

Came up really nicely and a big improvement on the original. Next steps are to find a threaded bolt to replace the breech pin and tighten up the jaws. The other thing I noticed was that the breech seal when sitting proud of the end of the barrel, gets a small nick from contacting the transfer port. This also prevents the barrel from fully closing so I shaved it down with a razor blade. Looks a bit rough but the barrel closes properly. Test firing at the range, I put a piece of tissue paper over the breech and it didnt get blown off so asuming this means its sealing. I would like to fix this properly so has anyone had this problem?

Good way to spend a rainy day mate looks way better than it did thats for sure,
Shame you can't chrony it.
Cheers
Ol 55

Nice job - is it a .22 or .177?

The BIG 5.6mm bore on these can be a problem nowadays because of the lack of proper 5.6mm pellets that will fit properly.

Its .177 but the breech end is quite loose. The pellet stays in there but its not a tight fit. The front end is also drilled out I'm assuming to give it a big bore look

Yeah that's a BSA thing, the muzzle end is counterbored, allegedly to protect the very end of the muzzle.

I know on my mate's .22 Mercury, RWS pellets will drop a few mm into the breech which is way too loose and bad for the gun, not to mention bad for accuracy.

The old British made 5.6mm Eley Wasp were the way to go - when you could get them....

You can get the new Rhino pellets from the UK which were specifically made for the slightly larger but true 0.22 cal.

You could try the JSBs as the skirts are soft enough to blow out into the rifling. I have some non standard 4.53mm JSBs and you have some Crosmans which have a slightly lerger head albeit a bit heavier.