HW77 springy underlever

[AC all day]

Questions for the educated.....
I have just been given an old 25mm 77.....it's rust free and also finish free, not sure which way to go yet....leave as is, have reblued or wrapped....but that's not the question....
When I got it the underlever required a slight pressure to return it closed( it's fitted with a ball catch silencer) and frequently pops open. I had this before when lead swarf built up in the breech area, it's not that....also the breech seal is flatter than a flat thing( now removed no change). I have stripped it down and wondered my next move, could the cocking link be short and causing this? or looking at the face of the piston sleeve it is not dead flush with its sides, can and has this moved? Do I try a new sleeve?
Over to you guys??

[T 20]

Check the cocking arm or lever isn't slightly bent, which would cause your problem

[piggy589]

Check the cocking arm or lever isn't slightly bent, which would cause your problem

I had a 97 with the same problem,yes indeed, a cocking arm like a dog's hind leg

[TonyL]

Check the cocking arm or lever isn't slightly bent, which would cause your problem

I had a 97 with the same problem,yes indeed, a cocking arm like a dog's hind leg

Yep, agree.

Also, guessing it's a Mark 1, check that the sides of the foresight unit / underlever retaining recess aren't damaged and also that, if the unit has ever been removed, it's securely fastened (Loctited) in its rearwards most position.

[Rickenbacker]

Barrel bent upwards would give the same symptom.

[AC all day]

Thanks guys.....things to check for sure!