OK, so i bought a older JLD PTR91 a couple of weeks ago. The gun was super tight and shoots good. It came with the green plastic funiture and I decided i would put some of the old surplus wood funiture on it from RTG. When i swapped out the plastic stock with the wood stock I noticed that I have a little bit of front-to-back movement on the lower. Is this common with swapping stocks or using old surplus stuff? And is there anyway I can fix it?