BSA 240 Magnum modifications?

[Shed tuner]

Thread resurrection

Just got one of these pistols and am going to have a looksee / play. Not too worried about power, just want it to be easier to cock and accurate. A new spring guide seems a basic starting point, but as it's hard to cock (well, it's not that tough in absolute physical terms, but it's just wrong that it should take that much effort) I'm going to find a more suitable spring first.

First stage is to play with it as standard and see how it shoots...

[Shed tuner]

First impressions.. much better than I expected actually..


The good: accuracy with hobbies. 5 shots groups ranging from 1/2" - 3/4" at 8 yards, which for a lightweight spring pistol is pretty good IMHO. trigger also quite light and fairly predictable. Weight quite light, so I will probably add some mass to aid stability. A longer barrel would achieve this perfectly, but I doubt the old one will come out easily.

The bad: not that bad really, but a little too much cocking effort, and definitely too much recoil - it wants to take off sideways and downwards. A loose grip defo needed for accuracy. Needs a softer spring / lighter piston or both.

The weird: huge amount of sight elevation - presumably due to the downwards recoil which must be moving the muzzle way before pellet exit. Also the grips are just stupidly weird - narrow at the top where your hands are widest


So it's all about recoil reduction (and some new grips in the future). And maybe adding a little muzzle weight.

[Shed tuner]

Stripped her down - very easy.

Very very dry in there.

First thing was to chop a coil off the spring, heat, and close, and dress on the grinder. I wanted to reduce the cocking effort a little regardless, so no choice there.
Piston washer was in good condition and a nice fit in the bore, so nothing to do there except a smear of moly on it, and on the front and tail of the piston. I contemplated lightening it at bit, but thought I'd do the basics first.
Made a beer can piston sleeve, lubed it all up and installed
Took a fraction off the rear spring guide OD, possibly even a smite too much, and then lubed it up and re-installed

Last thing - the bore of the plastic block that sits at the muzzle was 6.5mm - I thought that was a bit tight for a 5.5mm pellet, sitting 2 inches from the end of the barrel, on a lively recoiling pistol - so I opened it out to 7.5mm (which just kissed the crosspin, but barely). If I decide I need some muzzle weight, I'll replace this block with steel.

Reassembled and shot a few... cocking effort definitely reduced a bit, as is recoil. Power up from 3.5 to a very consistent 4.3 FP with hobbies, and the POI has gone up 3", which is good, as the weird recoil is dragging the POI down, so that effect has reduced.

I think I'll just leave it like this to be honest. I could lighten the piston, but it's not at all bad right now, so it's not crying out for it. Also it might cause issues with the trigger if I trim the outside, so would prob have to mill a couple of large slots lengthways well away from the trigger - e.g. 10 o'clock and 2 o'clock.


So there you go; not much more than a simple spit and polish is all this little beastie needs really.