The Mercury and Mercury Challenger strips have both been covered by Guy (ggggr) and myself in the Idiots Guide posts 37/38 and 122. In both of these the barrel block was left attached to the breech jaws as there was no need to split the action at this point. Today though, I did split the action at this point. The rifle was a Mercury S with an initial chrono of 430fps (AA Field) so in dire need of a service. Cosmetically it was excellent although the breech seal was crumbling out and the action was quite resonant on firing. Strip followed the norm as given in previous posts but this time I also split the action at the breech jaws; simply undoing the securing bolt and removing it. Having the cylinder separate from the barrel did make re-assembly of the rifle easier. The piston was removed as usual by removing the cocking arm 'cage' from the cylinder. Gee, the securing bolts were tight ... pozi 2 bolts and I admit I feared for them rounding off. Did BSA employ gorillas on the assembly line? New piston O ring fitted (BS112) and a piston sleeve from a beer can. I left the original steel spring guide even though is was quite loose in the spring; which I also left as it seemed quite reasonable. On reassembly I noted that when you split the breech block from the jaws the securing bolt also acts as a securing bolt for the lock up plunger. In order to re-assemble you must locate the breech block in the jaws and then depress the plunger a few mm in order to fit the through bolt. I did this by pushing the plunger against a wooden block while holding the split action and feeding the bolt through. I did not know the plunger did this and I suspect that it could catch someone out as my plunger stayed in place and I did not realise it needed a slight push to allow the bolt to be fitted.
The old breech seal was completely defunct ... crumbling as it came out. A new one was made from urethane tubing, 8mm id and 12mm od x 4mm. This tubing was an excellent fit ... it is interesting to note that this 8mm x 12mm size is very common to many rifles. A 1m length costs very little and it is easily cut to length to suit whatever rifle you want.
All back together again after a relube with moly CV grease and we are now running at 750 fps. Very pleased. I would expect the fps to rise a bit as the O ring settles in ... it was a bit tight to assemble into the cylinder.
What a great way to spend a couple of hours on Boxing day.
I will add a few notes to the Idiots Guide Mercury strips.
Cheers, Phil