Neil Price is woking on one of the most beautiful break-barrels ever made by BSA
Part Two of Neil Price’s refurbishment of a friend’s BSA Mercury S
11 The piston head is held on to the piston by a cross pin. This has to be removed with a thin pin punch and a hammer to enable the new buffer washer to be fitted behind it.
That is the piston head cleaned up to remove most of the score marks, the new buffer washer fitted and the new ‘O’ ring in situ. You can see from the photo that sometime in the dim and distant past, that even though I have cleaned up the piston head, there are still witness marks where someone in the past has gripped the piston head with mole grips or some such instrument of torture.
With a light smear of moly grease on the piston ‘O’ ring and the bearing surface of the piston body, the piston can be inserted into the action. Make sure that the cocking slot in the piston is lined up to the one in the compression cylinder. Again, I ease the edge of the new ‘O’ ring over the cut outs in the action with the blade of a small screwdriver so that they do not get bits chopped out of them by the sharp edges.
Put a coating of moly grease along the cocking lever slot.
Some moly grease is put on the cocking arm ears, and the ears are now located through the cocking slot and into the piston. Now the cocking arm with its spacing washer can be lined up with the hole in the barrel bracket, and the pivot pin knocked back in.
The cocking arm retaining bracket can now be replaced by tightening the two cross-head screws.
The ends of the new mainspring still had the rough marks from where they had been ground.
Polishing the ends of the mainspring with various grades of wet and dry paper will help the mainspring to rotate when being compressed and released.
Some moly grease on the two ends and the outside of the new mainspring and on the spring guide and we are ready to screw the trigger housing into the rear of the action. There is quite a bit of pre-load on these springs and I find them quite stiff and difficult to fit by hand. The curved shape of the back of the trigger block makes it awkward to fit into a spring compressor.
I decided to make a little jig so that a spring compressor could be used. I traced around the outline of the
trigger block onto a piece of 30mm thick wood and cut the shape out.
I then screwed two pieces of 6mm thick plywood onto the sides.
I drilled a countersink in the end, on the centreline of the action so that my spring compressor could locate into it and prevent it from slipping.
Here is the little jig located in my spring compressor. This allows me to compress the spring and engage the thread in the trigger block without swearing a great deal and breaking out into a sweat.
The trigger block can now be tightened into the action until the two previously scribed marks are lined up.
The stock can now be replaced, a few shots put into the pellet trap to settle things in a bit and we can do another chrono’ string to see what we have achieved.
That is much better, a 7 fps spread over ten shots and entirely legal.
After a few tins of pellets have been put through this rifle and the spring and ‘O’ ring bed in, the power will rise up 0.5 ft.lbs. and that will make this as good as the day it was purchased new.
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