MODERATORS: please move this thread and the previous one that asked the question to Collectables or General. I think we need to keep the Idiots Guide to instructions not questions.


But to answer the question: assuming that you have assembled the parts correctly...I suggest: If you can, mount gun securely and watch what happens when you try to cock it ... does the spring become coil bound? If you cannot see this, strip gun again and rebuild but without the spring. Try to cock and if the sears engage then there must be something that stops the piston moving far enough back.
Have you used a new spring? Does it have more coils than the original one? Have you added preload washers in piston or at the trigger block?
It is a matter of elimination that may need you to remove washers or a coil off the spring.
Cheers, Phil