There has to be pressure against the bolt when assembled no gap. Not sure if that's going. Check out the JP SCS instructions they make note of that and the different Ar10 buffer tube lengths.
Reassemble the upper and lower assemblies with the front pivot pin and slowly lower the upper into position. Watch carefully as the receivers are closed to verify that the SCS buffer head contacts the bolt carrier. If you are not certain if there is a gap, finish reassembling the rifle and then shake it back and forth gently listening for the sound of the SCS sliding back and forth in the buffer tube. The unit should not be moving freely. The precise length of the SCS was chosen to accommodate most rifles, but if you detect a gap between the bolt carrier and SCS, this is due to slight variations in the manufacturing tolerances of the buffer tube, bolt carrier and receivers. To shim this gap, the best solution we’ve found is to simply place a quarter in the buffer tube before installing the SCS. It will not be necessary to use more than one, and you should not use extra shimming to “preload” the SCS. We offer alternate rate springs for this purpose. If you find the SCS protruding too far out of the buffer tube into the receiver and the rifle is having trouble locking back, you can shorten the plastic spacer as needed, but take care not to remove too much material. The bolt carrier and SCS should be slightly tensioned against each other in final assembly and should not move freely in the rifle. THANKS FOR YOUR BUSINESS! JPSCS-
AR15: Unit does not currently function with any Primary Weapon Systems (PWS) bolt carriers. The back bore on the PWS bolt carriers is not compatible with the JPSCS.
JPSCS-AR10: Unit will not function with longer Armalite carbine-length extension tubes unless the spacer is modified to accomodate the extra length. It will also not function with the HK MR762, the Sig Sauer 716, or the Rock River Arms LAR-8 due to its longer bolt stroke.
