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Post by mefunkymxw on Sept 16, 2013 17:45:23 GMT -8
took the FF tube, muzzle break, gas block and tube off... used caliper to verify that when pushed against the .936" shoulder the flash hole in the barrel and gas block line up (about 0.345" in from the shoulder to the back of the port) on that axis... reinstalled tube and block... i have taken off the rearmost gas block set screw and i can see the dimple in the barrel right smack dab, centered underneath, so should be good on that [rotational] axis as well.
wont have time to retest until Wednesday at the earliest, but will have the standard buffer with me at that time.
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Post by mefunkymxw on Sept 16, 2013 17:56:19 GMT -8
This is her without the muzzle brake..... second is my wifes AR, which as a 16" BHW middy in 5.56 on top of a S&W M&P lower... i got that one pre-assembled with an aero upper receiver from surplus arms and ammo i believe.
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Post by mefunkymxw on Sept 17, 2013 4:50:15 GMT -8
was thinking about my SMI bolt carrier yesterday, it was something i got in a relative hurry because there were some BCG supply issues a couple of months ago (couldnt get my hands on a WMD BCG)... i might swap out the SMI for my wifes BCM carrier for a test... i have a hunch that it might be acting undergassed if some of the gas rings arent fit tightly to the inside of the carrier... i did notice that the hammer had a bit more grime on it then i am used to seeing...
I am not sure if SMI does MPI testing or what spec they build their carriers to, so i guess i can't rule it out.
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Post by mefunkymxw on Sept 20, 2013 5:05:15 GMT -8
got a WMD carrier yesterday and am going to go to the range today to test. upon taking out the bolt from the SMI carrier i did notice that the splits in the gas rings were pretty well lined up. this might have added to the "undergassed" symptom, but probably not the complete cause of it.
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Post by GLSHOOTER on Sept 20, 2013 5:48:56 GMT -8
Are you going to shoot some non-S&B ammo?
Greg
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Post by mefunkymxw on Sept 20, 2013 14:58:06 GMT -8
Are you going to shoot some non-S&B ammo? Greg yea, i already posted the results of what i shot in the table on the last page.... i shot hornady, remington, and handloads (nosler projectile) anyway.... went back to the range today (another 15 bucks gone).... and shot some hornady 110 grains with the new WMD carrier.... still a no-go. extracted about 40-50% of the empties fine, still not enough steam to get the bolt back far enough to pick up the next round, on the ones that extracted. the other 50-60% didnt extract and i was manually pulling some cases. oh i did switch to the lighter standard buffer by the way.... It might not be undergassed, i watched the side of the carrier on a couple of rounds that didnt extract and there were a couple of nice little cones of expanding gas coming out. there is a lot of fouling on the outside of the carrier. FP is just crazy dirty as well... this leads me to believe that there is plenty of gas going through the carrier on the non-extracted rounds. really i think im down to three possible options now: 1. have a smith open up the gas port on the barrel (my least favorite option) 2. polish the piss out of the chamber 3. send it back to you all i know going with a full length gas system on a 18" barrel would reduce the dwell time of gas expanding into the tube, but like i said before, im not even sure that it is technically undergassed right now. ive checked the gas port alignment 3 times now and i am positive that is not it (as long as your barrel dimple is exactly 180 degrees around from your gas port and that it is on the length dimension) suggestions.... ??
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Post by mefunkymxw on Sept 20, 2013 14:59:14 GMT -8
ok, just got back from the range.... the news is better, but still not good tried 3 types of ammo AMMO Brand | Result | Hornady 110 gr V-Max | shot about 50 rounds, some ejected (50% ish), none with enough force to feed the next round | Handloads (115 gr nosler, 27 gr H322, LRP) | all ejected, i hand fed each of the 10 rounds i shot as the noslers were getting stuck on feed ramps | Remington 115 gr FMJ | shot 40 rounds, almost all ejected, none with enough force to feed the next round or lock the bolt open |
at this point i am beginning to think that it might be undergassed due to gas block misalignment, i am going to take off the the FF tube, gas block and remove the gas tube completely, reset the gas block and try to see exactly how the alignment is. i had to pin the gas tube first when assembling because the barrel nut i have is so deep so as to accommodate the FF tube. i will let you know the result. i did forget to bring my standard weight buffer, so i am going to put it in my range bag now so i dont forget for next time. quoting myself again for greg's benefit... apparently some folks are too good to go back to the first page....
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Post by GLSHOOTER on Sept 20, 2013 15:06:39 GMT -8
got a WMD carrier yesterday and am going to go to the range today to test. upon taking out the bolt from the SMI carrier i did notice that the splits in the gas rings were pretty well lined up. this might have added to the "undergassed" symptom, but probably not the complete cause of it. I meant were you going to shoot other stuff TODAY. I know you did before. If the cases are not scratching and getting marks from the chamber I don't think polishing will do much. How big is the port diameter now? You should be able to determine if the dimple is placed at the proper place. How does the inner surface of the GB look? Is the gas marking centered in the port? Greg
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Post by mefunkymxw on Sept 20, 2013 15:16:49 GMT -8
cases aren't really scratched, they have some normal surface marks around the whole circumference.
not sure what the gas port size it now, but it is whatever came from BH, havent changed anything.... ill take it apart and check.
last time i took it apart, yes the gas markings were pretty well symmetric and the gas tube definitely had some build up on it.
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Post by GLSHOOTER on Sept 20, 2013 15:26:49 GMT -8
cases aren't really scratched, they have some normal surface marks around the whole circumference. not sure what the gas port size it now, but it is whatever came from BH, havent changed anything.... ill take it apart and check. It is not unusual to have to redrill a port. I have never seen rhyme nor reason in it but it is quite common. Each supplier picks a size that works most of the time but the combination of various GB's and tolerances of the entire upper come into play. I do know that a rifle length gas system on an 18" can be a tad problematic at times. Greg
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Post by GLSHOOTER on Sept 20, 2013 16:35:00 GMT -8
PM sent.
Greg
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Post by mefunkymxw on Sept 20, 2013 19:05:12 GMT -8
the current flash hole diameter is just under 1/10 of an inch coming in at 0.096" the gas block opening is larger at 0.160" almost (about 5/32nds of an inch)... given the pics i am about certain that the holes are lining up... i could move the gas block just a hair off the shoulder if i want to go center to center, but i think the larger hole in the gas block more then makes up for it. i set the caliper to 0.159 and set the front blade to the tip of the fouling circle closes to the shoulder and it looks like i have plenty of room on the GB to cover teh whole flash hole.
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Deleted
Deleted Member
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Post by Deleted on Sept 21, 2013 4:13:41 GMT -8
the current flash hole diameter is just under 1/10 of an inch coming in at 0.096" the gas block opening is larger at 0.160" almost (about 5/32nds of an inch)... given the pics i am about certain that the holes are lining up... i could move the gas block just a hair off the shoulder if i want to go center to center, but i think the larger hole in the gas block more then makes up for it. i set the caliper to 0.159 and set the front blade to the tip of the fouling circle closes to the shoulder and it looks like i have plenty of room on the GB to cover teh whole flash hole. View Attachment View AttachmentView AttachmentYour gas block needs to be centered over the port!!!! Move it forward. With an 18 inch barrel and a rifle length gas system the dwell time is very short. Look closely at your picture, you are closing off the front of the gas port. Use the dimple to center the set screws. If this doesn't work, drill it out to .100. But you will still need to be centered over the port. Your gas block was never intended to butt up against the shoulder of the barrel. The manufacturer made room for the handguard cap which can be as much as .035 thick.
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Post by mefunkymxw on Sept 21, 2013 5:56:06 GMT -8
the hole in the block is larger then the hole in the barrel, by 0.063", no part of the block is covering the flash in the bbl... all of the gas that is coming out of the barrel is making it down the tube!!!!
i can try to get it center to center, but i dont think thats going to change the result.
update... ok moved GB up a little over 0.032" off the shoulder to get center to center... going to range now... shooting remington fmj, ill take 40 rounds. ill let you know the result.
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Post by mefunkymxw on Sept 21, 2013 16:11:02 GMT -8
ok, 20 more rounds of remington fmj, not doing well.... even with gas block moved back over 3/100ths and matching center to center with the gas port had issues with undergassing.
have it with a smith now who will enlarge the gas port incrementally until we get it extracting and feeding reliably. reflecting on this i suppose i should have gone with a mid length gas system, but you live, you learn.
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