I just got the new JP 9mm BCG in today and the 9mm Silent Spring should be here tomorrow so I decided to compare it to the CMMG 9mm BCG I currently have. At first glance they look identical, the finish is pretty much the same on both of them, but I just cleaned and oiled the CMMG yesterday so it's the shiny one in the pics. The differences I have found are minimal but I will list them anyway. The pin holding the extra weight in the back of the JP is actually a coiled spring pin and the CMMG is just a hollow roll pin. This should make the JP less likely to break and accidentally work its way out since it has some extra tension holding it in place. The other difference I notice is the extractor is silver colored on the JP and black on the CMMG, not sure if it's just the color playing tricks on my eye, but the JP extractor looks a little bigger and the bolt face is shaped a bit differently. The only other difference I see is the bottom surface of the bolt that provides a contact surface is considerably narrower on the JP, you can see this in the last 3 pics. The JP measures about 0.25" wide and the CMMG is about 0.33". This would explain the JP bcg being a tad lighter at 15.6 oz and the CMMG is 15.8 oz. I'm not sure what, if any effect this will have on cycling. Anyone got an idea?
Overall it's a very nice bolt that's not much different from the CMMG. The CMMG will work with the Silent Spring since you can remove the weight at the rear, so don't feel the need to run out and buy the JP if you already have the CMMG and want to get the Silent Spring. I haven't decided if I want to keep the CMMG as a spare or just sell it, I will hopefully get to test out the whole system this weekend.
JP is the one on bottom or the right in the pics
This pic probably best illustrates the difference in width of the bottom contact surface