Here's some info that may help, I installed one of JP's Captured Spring Buffers about 1000 rounds ago and have not had a single problem. Purchased the "Spring Pack" with the "Buffer" thinking I might need to use them for adjustments, but never even took them out of the bag.
Silent Captured Spring (patent pending) for AR-10-type rifles
Includes spacer to allow for installation in both carbine-length and rifle-length buffer tubes.
From JP's Website:
JP - Buffer Springs and Silent Captured Springs
Compatibility
The JPSCS-AR10 is designed to work in standard 7-inch M16/M4-length buffer extension tubes on .308 AR-type rifles like the DPMS LR-308. Armalite .308 rifles, likewise, use these standard M16 extension tubes with rifle-length stocks, so the JPSCS-AR10 will function normally when installed with the supplied spacer. However, Armaliteís .308 carbines use a slightly longer, nonstandard carbine extension tube. The JPSCS-AR10 can still be used with these extension tubes by installing the spacer, which must be modified to fit. Alternately, the system will function readily if the longer Armalite carbine tube is replaced with a standard 7-inch .223 carbine extension tube.
The JPSCS-AR10 is not compatible with the Rock River Arms LAR-8 because of its longer bolt stroke and subsequently longer extension tube.
SPRING PACK
The Auxiliary Spring Rate Kit for the JP Silent Captured Spring allow custom tuning of the device to a given rifle. While the default spring installed in the JPSCS is selected to offer the best performance for the widest range of configurations, a simple disassembly and reassembly of the JPSCS with a slightly different spring rate can yield truly optimized performance, particularly for rifles without an adjustable gas block.
In selecting a spring for your rifle, install a heavier spring in you feel the buffer head fully compress and bottom out while firing the weapon. If the bolt carrier will not lock back reliably on the last round fired, even when completely gassed (in the case of an adjustable gas block), select a lighter spring.
On large-frame rifles, a lower spring rate (i.e., heavier spring) with a properly tuned gas system can often yield a faster, lighter impulse that feels almost like an AR-15 in being very easy to clear or cycle for charging. Using the JPSCS-10 without a JP adjustable gas system will likely require a heavier spring to overcome the friction and extra mass in the bolt carrier relationship. Then again, since Armalite rifles use a McFarland gas ring and have a very low bolt/carrier internal friction, they can often strip, feed and go into battery with a lower spring rate. Because of the inevitable variability in platforms, this spring kit is designed to get any rifle cycling successfully with our JPSCS system.
The included springs from lightest to heaviest are listed below with the color with which they are coded:
JPSCS-SPRING10-100: 1 side red
JPSCS-SPRING10-105: 1 side blue and 1 side red
JPSCS-SPRING10-110: 1 side yellow and 1 side red