I may have to look at that 6 position tube if anything. I rarely have time to fire the M4 sadly. When I last fired it, I don't feel the play in the stock when pushing against my shoulder. We'll see, next time I fire it, if I notice the play I may need to replace the tube with RxArms version. The thud should did have me worried though until I was told it's normal. I'm like damn... the thud doesn't seem good. If I fire, will the stock just slam into the firearm because it's not grabbing to the indents in the tube? Anyway, good to know it's normal. Again, when firing the firearm, the thud sound doesn't make itself known. Could be due to the fact, a big BOOM masks everything else around me lmao.