"bam" underlever air rifle what model is it? Is it the same as smk ?

[metalmickey]

Hi learned members, I was given an old Chinese underlever air rifle in .22 cal. All in bits I have been told its all there, but it does need attention !! So I re-assembled it -- it cocks but the trigger sear does not engage positively and hold back the piston, which has a tendency to slip off as returning the underlever. The piston sear ramp did look a bit worn to be honest. I was told these are the same as a SMK db4/db5. So I ordered a new piston from T.W. Chambers but when it arrived this morning it measures 20mm longer. I have been trying to identify the exact model but the only marking on the action is "BAM"
the stock is a bland painted plank with a non defined cheek piece and an over sized hand grip which puts the trigger almost out of reach. The front sight has a single adjustable post inside an open hood, bit like the ak47 looking on the net all indications are of a b3- ? but there are so many variants. When ordering the piston "BAM" as a make is not available so went for the SMK db4 anyone had any experience getting parts for one of these old guns ? Chambers have said that because it is an old model they cannot help me any further. I have decided to see if I can get someone to splash a weld across the rear of the piston skirt and see if I can re-file the sear angle to suit.
If not I will put it up for sale to recover my outlay for a new piston seal. stock refurbishment paint job & postage costs. Around £35 + P&P Cheers mickey
"keep using the sun cream"