BSA Airsporter / Merc trigger block issues

[edbear2]

Reading through the thread on the Merc elsewhere, I thought I would add this as I am in the process of fixing an Airsporter which was a bit rattly. The gun felt "loose" on cocking so after the grip and forend screws were tightened, a single shot was fired which showed a healthy 580 fps with wasps (bit shy of 11).

Anyhow, on stripping, the back block steel threaded cup which engages with the cylinder was quite loose, so I was relieved that the back block unscrewed by hand. For anyone who has never had one apart, the general arrangement is shown here;

https://www.flickr.com/photos/312284...57663274889756

The threaded cup is retained by the screw in part with the thin flange, the cup is drilled in three places around it, and in these places when the gun was new, the flange of the screw in part were upset by a punch or press tool to provide a locking function. Although my cup had about 10 degrees of "rattle" I still needed to drill through the holes to remove material that was preventing turning, this is a 2 min job, just use a close fitting drill and give each hole a couple of "pecks" till clear. I used an airline chuck locking tool with angles ground in it as a driver, these are often found at car boots cheap and I have a small biscuit tin full of the things as they are a great source of cheap flat stock steel, besides being a ready source to make into tools for jobs like this (Diana 50 stock bolt was another time one saved me!), Older bicycle spanners are good quality steel too, and are normally pence.

On this gun, I may now try and get the stud out and get it anodized as a TX block I had done recently came back in super order, I will then assemble using an oil tolerant high strength Loctite, maybe 602 but undecided as yet.

The radial anti slip grooving on these bits are a real bit of quality, and prevented my cup spinning and causing a disaster, even though the thing was loose, but obviously if you have any discernible movement....No excuses not to sort it out!

Couple of other things I could add, the ONLY way I ever get off BSA / HW blocks if tight is with a superplastic Thor. Nothing else comes close, never use a bar in a BSA as the leverage is nowhere near what a sharp rap with mallet will do...Think impact airgun on wheel nuts, A sharp rap has the same shifting effect.

I also will only use mousemilk or plusgas, a few moments with a hot air gun to cylinder joint, apply penetrating fluid, leave till cool to touch, one or two whacks with a mallet, has never failed....ever!

On HW's I use a block of steel which fits snugly in the trigger pocket and protrudes maybe 60mm, but must be a slip / light push fit to prevent marking.

ATB, ED