Neil Price is wok­ing on one of the most beau­ti­ful break-bar­rels ever made by BSA

Air Gunner - - Contents -

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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