Oh darn it those Sportarget bolt tail peeps are nigh on impossible to find now. They also go for darned silly money when they do turn up. Lyman made one like it too.

The Parker-Hale ones an yes I see yours is marked AJP Bisley Works same company just a bit earlier are usally dovetailed in the firing pin nut. That's the first one I have seen sleeved over it and sweated on.

Really nice rifle you have there..