Dan

I guess I started this by Not tieing it down to the exact measurement I just did a quick measurement wasn't trying to prove any one wrong or wright just a place to start looking. I worked with artillery and small arms for years in the manufacture and inspection. I know there are tight tolerances on these arms as there is a tolerance applied to all manufacturing whether it be in ten thousands of an inch or in inches i will be more exact on my measurements from this point so I don't confuse people who aren't familiar with weapons and manufacturing.I do appreciate your reply as I know you are correct.i wasn't trying to be stupid just trying to help I will be more precise on my comments in the future.

Thanks for the information the correct measurements were as you said I will consult that chart I'm new to this sight seems to be pretty good thanks again

That should of been dpms lower palmetto state arm upper

That was the problem you need the tube to be at least 7 3/4 to 8 inches I have a dons lower and a Omsk upper hope the fix will work for your set up

I'm having the same problem I have tried different spring lengths siding work so I have an armalite ar10 I measured the depth of the spring tube the armalite is approx 1 inch deeper I'm thinking this might be the problem I will ditch out the tube and see if it works. I will let you know if it works. DM