Why1504 Posted December 4, 2013 Share Posted December 4, 2013 I have an new rifle with an adjustable gas block (PRI low profile) running a standard BCG and rifle buffer. Barrel is 18 inches long. With the gas block wide open it will eject and lock back using XM193. With my reloads it won't lock back. On my other guns (all non adjustable gas system) barrels from 10-20 inches the reloads run flawlessly. I ran 100 plus rounds to get the gas block aligned and am reasonably certain the block is aligned to the barrel port. I have not measured the barrel gas port. I have run other uppers on the lower, no issues. Any suggestions? Thanks. Link to comment Share on other sites More sharing options...
Mark Gale Posted December 4, 2013 Share Posted December 4, 2013 The Federal cartridges are generating more pressure. I think it's that simple. Link to comment Share on other sites More sharing options...
woody2 Posted December 4, 2013 Share Posted December 4, 2013 It's like you said, "it's a new rifle". Either take time to break it in or use a little "Flitz" or bore paste & polish the chamber. They are all a little rough when they are new. Link to comment Share on other sites More sharing options...
Why1504 Posted December 4, 2013 Author Share Posted December 4, 2013 (edited) The Federal cartridges are generating more pressure. I think it's that simple. Yes, thats obvious. The reloads run in the other guns. They are ejected a normal distance. the problem is obviously with this gun and is related to inadequate gas energy for operation. I believe one of the following is where the problem lies: Barrel gas port is too small Gas block has an issue Gas tube has an issue. Brand new, it looks fine, so aside from some leakage around the block which again looks normal I dont think this is the problem. My question is, check the port and if too small, drill the port, replace the gas block, or is there something else I am missing? What is my best choice? I can mic the port when I get home. Polishing the port is no big deal either. I haven't had a chance to check the barrel port, but I think an 18 inch rifle gas barrel port shoud be .089 to .091 Edited December 4, 2013 by Why1504 Link to comment Share on other sites More sharing options...
Doug H. Posted December 4, 2013 Share Posted December 4, 2013 Could still be a misaligned gas block. I usually use a .025 feeler gauge to set the gas block slightly forward then test the gas by taking off the comp, droping the bolt and running compressed air into the muzzle. You can hear the change in gas as you move the block around. When you get the best air flow you have reached the sweet spot and that is the maximum air flow through that block. If that doen't work try a different gas block. I would try all those thing before I enlarged the hole in the barrel. Doug Link to comment Share on other sites More sharing options...
mpeltier Posted December 4, 2013 Share Posted December 4, 2013 Im pretty sure Doug nailed your problem. Go to the thread a couple lines down titled "Gas tube and pin leaking", I gave a few tips there that will help you. Sorry but my "link-fu" sucks and don't know how to do that from my phone. Link to comment Share on other sites More sharing options...
Why1504 Posted December 4, 2013 Author Share Posted December 4, 2013 Could still be a misaligned gas block. I usually use a .025 feeler gauge to set the gas block slightly forward then test the gas by taking off the comp, droping the bolt and running compressed air into the muzzle. You can hear the change in gas as you move the block around. When you get the best air flow you have reached the sweet spot and that is the maximum air flow through that block. If that doen't work try a different gas block. I would try all those thing before I enlarged the hole in the barrel. Doug Thats great. I was not excited about enlarging the hole to start. Link to comment Share on other sites More sharing options...
fastshooter03 Posted December 4, 2013 Share Posted December 4, 2013 what's your reload???? Link to comment Share on other sites More sharing options...
EkuJustice Posted December 5, 2013 Share Posted December 5, 2013 A lot if times the gas block had to get moved a touch forward to compensated for the fact that there isn't the front part of the factory handguard on there between has block and shoulder. Link to comment Share on other sites More sharing options...
Chuck Anderson Posted December 7, 2013 Share Posted December 7, 2013 Maybe I'm missing it because it's so early but have you adjusted the gas block? Sounds like you've got it tuned for the hottest ammo you have and it won't run the weakest. I tune for the weakest I have. Link to comment Share on other sites More sharing options...
Why1504 Posted December 7, 2013 Author Share Posted December 7, 2013 (edited) Gas block was wide open, did the air test, it was aligned. Yes, the loads were light, but should XM193 require the block to be run wide open? I don't think so. I measured the gas port it was .091. I handed it back to the smith to sort out. He was embarrassed. I suspect the block has some kind of issue. My gun and the smiths gun are carbon copies. His runs great. One thing I can tell you, anytime you build things occasionally you have problems. I sent him the upper to put the adjustable gas block on it and it ran on his lower but not mine. Now he has the whole gun. Edited December 7, 2013 by Why1504 Link to comment Share on other sites More sharing options...
openclassterror Posted December 10, 2013 Share Posted December 10, 2013 On the subject that it runs on his lower, but not yours- I have about 15 different carbine length buffer springs at the shop right now from 4 different manufacturers. Free length varies by almost an inch, and number of coils varies by 3 full turns. All 4 makers claim "mil-spec" for their buffer components. I GUARANTEE you that if you were running on the ragged edge of cycling pressure some would function and others not. I don't ever guarantee functioning of rifle components unless customer brings me the whole rifle AND the ammo they intend to use. I comped an XDM 9mm for a customer, exact copy of the one I had been shooting. He told me he was shooting remanufactured 115gr 'factory spec' ammo. I test fired with factory ammo, and he trashed my work at the next pistol shoot because it wouldn't cycle. I found out from the guy he was buying the ammo from that he was shooting very light practice loads, as in like 950 fps range!?! Now I won't modify anything that effects cycling without the customer's ammo, and make it CLEAR that I can't guarantee function should he change the load. On another note, I have noticed that the gas passages on some of the adjustable blocks (Syrac in particular) are somewhat of a maze for the gas even when full open. Larger than the barrel port hole, but more restrictive than the .159 straight hole of a fixed block. Seems like as long as it exceeds the smallest restriction in the system ( barrel hole) it shouldn't matter, but I still wonder. Link to comment Share on other sites More sharing options...
kimberacp Posted December 10, 2013 Share Posted December 10, 2013 Could still be a misaligned gas block. I usually use a .025 feeler gauge to set the gas block slightly forward then test the gas by taking off the comp, droping the bolt and running compressed air into the muzzle. You can hear the change in gas as you move the block around. When you get the best air flow you have reached the sweet spot and that is the maximum air flow through that block. If that doen't work try a different gas block. I would try all those thing before I enlarged the hole in the barrel. Doug thats a good idea of running compressed air. how do you use the feeler gauge? between the back of the gas block and the step or shoulder on the barrel? also mpeltier did have some good tips on the other post about "gas block and pin leaking" thanks Link to comment Share on other sites More sharing options...
kimberacp Posted December 10, 2013 Share Posted December 10, 2013 On the subject that it runs on his lower, but not yours- I have about 15 different carbine length buffer springs at the shop right now from 4 different manufacturers. Free length varies by almost an inch, and number of coils varies by 3 full turns. All 4 makers claim "mil-spec" for their buffer components. I GUARANTEE you that if you were running on the ragged edge of cycling pressure some would function and others not. I don't ever guarantee functioning of rifle components unless customer brings me the whole rifle AND the ammo they intend to use. I comped an XDM 9mm for a customer, exact copy of the one I had been shooting. He told me he was shooting remanufactured 115gr 'factory spec' ammo. I test fired with factory ammo, and he trashed my work at the next pistol shoot because it wouldn't cycle. I found out from the guy he was buying the ammo from that he was shooting very light practice loads, as in like 950 fps range!?! Now I won't modify anything that effects cycling without the customer's ammo, and make it CLEAR that I can't guarantee function should he change the load. On another note, I have noticed that the gas passages on some of the adjustable blocks (Syrac in particular) are somewhat of a maze for the gas even when full open. Larger than the barrel port hole, but more restrictive than the .159 straight hole of a fixed block. Seems like as long as it exceeds the smallest restriction in the system ( barrel hole) it shouldn't matter, but I still wonder. I have also noticed two of the mil spec rifle springs are not the same length. I changed both rifles to the JP springs. JP spring both the same and consistant. period no guess to what it is. Link to comment Share on other sites More sharing options...
Doug H. Posted December 10, 2013 Share Posted December 10, 2013 Could still be a misaligned gas block. I usually use a .025 feeler gauge to set the gas block slightly forward then test the gas by taking off the comp, droping the bolt and running compressed air into the muzzle. You can hear the change in gas as you move the block around. When you get the best air flow you have reached the sweet spot and that is the maximum air flow through that block. If that doen't work try a different gas block. I would try all those thing before I enlarged the hole in the barrel. Doug thats a good idea of running compressed air. how do you use the feeler gauge? between the back of the gas block and the step or shoulder on the barrel? also mpeltier did have some good tips on the other post about "gas block and pin leaking" thanks Yes, between the back of the gas block and the step on the barrel to account for the missing piece of the standard handguard. Doug Link to comment Share on other sites More sharing options...
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