J-Rob Posted August 17, 2012 Share Posted August 17, 2012 I finally received my JP SCS from Brownells backorder and installed it in my rifle. I'm running a LaRue 16" 5.56mm PredatAR with Magpul PRS stock with the JP SCS. I have ran close to 500 rds so far with this setup and about 40 of those rounds were loaded 1 at a time in various magazines and not once did the bolt lock back. I did this after firing 2 full 30rd magazines and noticed the bolt failed to lock on both magazines. I'm thinking the spring might be a little too strong and isn't letting the bolt back to the rear far enough for lock back. Is anyone else having this problem? Link to comment Share on other sites More sharing options...
AFH Posted August 17, 2012 Share Posted August 17, 2012 I had a similar problem at RM3G, turned out to be worn out gas rings. They were replaced by the JP rep at the match, and everything ran fine afterward. Thanks JP!!! Don't know if that's your issue, but it's worth a look. Andy Link to comment Share on other sites More sharing options...
APL-G35 Posted August 17, 2012 Share Posted August 17, 2012 My dad is having the same problem in a brand new build using the jp lo-mass operating system with a syrac gas block. It won't lock back even with full gas. Link to comment Share on other sites More sharing options...
kurtm Posted August 17, 2012 Share Posted August 17, 2012 Your dad has a misaligned gas block. I don't know how many Syracs I have seen like this as of late. They like to move when tightened, and the shoulder isn't the same length as regular gas blocks causing them to be installed half a hole off. Once installed properly, it will run with an aluminum carrier, or a titanium, which is much lighter than your setup. Link to comment Share on other sites More sharing options...
J-Rob Posted August 17, 2012 Author Share Posted August 17, 2012 The PredatAR is new and I inspected the gas rings and it's not them. The only other thing I can think it might be is the full weight carrier but that's just a guess. Link to comment Share on other sites More sharing options...
APL-G35 Posted August 17, 2012 Share Posted August 17, 2012 Thanks for the info Kurt. I'll have him check it out. We are trying to get everything dialed in for a 3 gun match next month Link to comment Share on other sites More sharing options...
Colodrew Posted August 18, 2012 Share Posted August 18, 2012 I went from JP's low mass buffer to the captured spring and did not even have to adjust the gas system. Practiced and shot RM3G without a hitch so far.The JP spring works keep looking for other issues as the guys recommended. Link to comment Share on other sites More sharing options...
Blaise1 Posted August 25, 2012 Share Posted August 25, 2012 Kurt, I just ordered a Syrac for Julies rifle, which way is the gas hole off? Will I need to file down the shoulder on the block or use feeler gauges and increase the gap? Also where are can I find one of those ultra lightweight carriers your talking about? Link to comment Share on other sites More sharing options...
J-Rob Posted August 30, 2012 Author Share Posted August 30, 2012 So after another trip to the range the JP SCS was still not allowing bolt lock back and I also felt more recoil. I talked to one of JP's armorers and they are sending me a lighter spring to try out. They said the SCS system was really designed for rifles with adjustable gas blocks that could have the gas and SCS systems tuned together. So I hope swapping the spring will solve the problem. So, if you're having the same problem I suggest getting a lighter spring from JP. Link to comment Share on other sites More sharing options...
APL-G35 Posted September 4, 2012 Share Posted September 4, 2012 Range update, Mr. Miller was correct the alignment of the gas port hole was incorrect with the syrac block. Now the gun will lock the bolt back correctly on an empty mag. Thanks for the help. Link to comment Share on other sites More sharing options...
dukduk Posted September 4, 2012 Share Posted September 4, 2012 what was off the distance from the taper in the barrel or the L&R alignment? Link to comment Share on other sites More sharing options...
gng4life Posted September 4, 2012 Share Posted September 4, 2012 Thanks for letting us know... Link to comment Share on other sites More sharing options...
APL-G35 Posted September 4, 2012 Share Posted September 4, 2012 Dukduk, not 100% sure since its my dads gun I'll ask him tomorow and repost again to let everyone know. Link to comment Share on other sites More sharing options...
APL-G35 Posted September 4, 2012 Share Posted September 4, 2012 Ok, apparently when the gas block was set back to the shoulder it was about 1/8th of a hole off. He had to move the gas block forward to get the correct alignment. Hope this helps Link to comment Share on other sites More sharing options...
dukduk Posted September 4, 2012 Share Posted September 4, 2012 oh man, that sucks. what barrel? Link to comment Share on other sites More sharing options...
Outsydlooknin75 Posted September 4, 2012 Share Posted September 4, 2012 Remember when putting gas blocks on that when the original is on there is a piece of sheet metal that keeps the fsb from going all the way back to the shoulder on the barrel. Not every manufacture takes that into account when designing their block, it may be necessary to leave a small gap between block and shoulder where the handguard cap would be. Sent from my PG06100 using Tapatalk 2 Link to comment Share on other sites More sharing options...
APL-G35 Posted September 4, 2012 Share Posted September 4, 2012 A black hole weaponry barrel Link to comment Share on other sites More sharing options...
J-Rob Posted September 6, 2012 Author Share Posted September 6, 2012 The JP replacement spring arrived today. I removed the standard spring tonight, and I noticed the replacement spring is longer than the standard spring. Does this sound right? Talking with JP they said I need a lighter spring weight than standard so I'm not getting why the "lighter" spring is longer. Link to comment Share on other sites More sharing options...
APL-G35 Posted September 6, 2012 Share Posted September 6, 2012 When it comes to spring rates I don't believe length really plays a factor. I think it has more to do with the diameter and how tightly coiled the springs are. Link to comment Share on other sites More sharing options...
Rolex40 Posted September 6, 2012 Share Posted September 6, 2012 The JP replacement spring arrived today. I removed the standard spring tonight, and I noticed the replacement spring is longer than the standard spring. Does this sound right? Talking with JP they said I need a lighter spring weight than standard so I'm not getting why the "lighter" spring is longer. Can you measure the current spring and the replacement spring you just got in. I would like to compare it with what I have. Also, I have been running the JP system without any problems in my Colt CRE. Link to comment Share on other sites More sharing options...
J-Rob Posted September 6, 2012 Author Share Posted September 6, 2012 Standard Spring measures at 10 1/4 inches Replacement Spring measures at 10 3/4 inches Replacement Spring also has yellow painted on one end Link to comment Share on other sites More sharing options...
Montrala Posted September 27, 2012 Share Posted September 27, 2012 I have problems with bolt lock back in my HK MR223 as well, with different type of mags. It is quite unexpected, as HK uses uprated recoil spring and heavy buffer so I thought that piston system will be "violent enough" for JP. Link to comment Share on other sites More sharing options...
dukduk Posted November 18, 2012 Share Posted November 18, 2012 ugh went to function check the guns today and no bolt lock back, I opened up the gas block maxed out and the issue remains. des you call or email JP for that spring? barrel is a Nordic 18" .223 with a syrac clamp on GB, LMOS bcg, CMC trigger Link to comment Share on other sites More sharing options...
hpnewby Posted April 29, 2013 Share Posted April 29, 2013 So how have any of the lighter JP springs worked. I've got a similar setup, 18" w/ rifle length gas, Syrac set screw edition, JP LMOS, and JP SCS. I never had any problems with commercial ammo, but have never gotten the bolt to lock back with CFE 223 reloads up to 69gr. I've double checked the GB port alignment and the rings are good. GB is wide open and I still got nothing. With commercial ammo I was in the middle of the GB adjustment range. Link to comment Share on other sites More sharing options...
midget Posted April 29, 2013 Share Posted April 29, 2013 So how have any of the lighter JP springs worked. I've got a similar setup, 18" w/ rifle length gas, Syrac set screw edition, JP LMOS, and JP SCS. I never had any problems with commercial ammo, but have never gotten the bolt to lock back with CFE 223 reloads up to 69gr. I've double checked the GB port alignment and the rings are good. GB is wide open and I still got nothing. With commercial ammo I was in the middle of the GB adjustment range. I ran a lighter spring in mine temporarily. I found out that for my bolt to open, I had to have the gas open the same exact amount no matter what my spring weight is. So I decided to put the spring rate back to standard so that the carrier moves as slowly as possible... Link to comment Share on other sites More sharing options...
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