User Panel
Posted: 10/25/2023 11:11:04 PM EDT
So, I'm stumped on this. I have an upper that was assembled by D. Wilson which I shot about 600 or so rounds spread between 2 range days of PMC X-TAC through with no malfunctions. On a subsequent range trip I was about 2 or 3 magazines deep when I experienced my first failure to feed. I thought it was ammo, because I was shooting the last of some cheap Turkish ammo I had bought previously, and I've had issues with it in the past.
The next range trip, I experienced 2 failures to feed using AAC ammo, which I have heard is not the highest quality, but regardless, I decided to swap the buffer weight from a BCM T3 to a T2. On the next range day, I went back to the PMC ammunition and experienced 3 failures to feed, so now I'm confused. There are some things I had changed about the rifle in between the first two trips where I had no malfunctions, and the trip where I started experiencing the failures to eject, which were: I swapped the BCG to a Microbest chrome, the original being a phosphate, and swapping out lowers from a mil-spec Centurion lower to a Radian ADAC. My first assumption was the new BCG, because that seemed obvious, but I couldn't find anything wrong with it. I did the "gas ring test" where you set it on a flat surface to see if the weight of the carrier is enough to rotate the bolt, and it wasn't. So now I'm assuming the gas block might be out of alignment, but I'm not sure. I know D. Wilson aligns the gas block based off the gas port location, so even if the block is canted, I'm sure it's where it should be. Build details: Hodge 12.5" large port barrel BCM MK2 buffer (A5 style) with T2/T3 buffer Microbest BCG, chrome and phospate OCL Polonium Anybody have any input? |
|
|
[#1]
Have you tried one round in the mag to see if it locks back on empty every time?
Quickest way to see if it's a gas problem.. |
|
|
[#2]
You have a couple of choices. You could start swapping back parts, one by one, to the original configuration until it runs reliably again. I'm guessing BCG but just because guessing is fun.
Reality is, you don't have a previously reliable rifle. Once you change a major component for a complete different component you have a different rifle. This leads to option two... diagnose. Do you get bolt lock back? Is your gas efficiently? Is the extractor and spring in that new BCG to spec? You may now have a gun that's over or under buffered. Hard to say without more data. What prompted you to start changing parts? |
|
|
[#3]
Well, I built the rifle to SBR, and I already had one SBR lower, and I needed 2, so I was using the lower I already had as a placeholder while the form 1 for the new sbr was pending. And I was using a placeholder BCG as well, so that's why I put the new BCG in. I haven't noticed any issues with the bolt locking back on an empty mag, but I'll do some testing the next time I go to the range.
|
|
|
[#5]
That's what I was afraid of. Really don't want to eat that $200 tax stamp from an out of spec lower. Praying it isn't this that's the issue.
|
|
|
[#6]
Originally Posted By booger_hole: That's what I was afraid of. Really don't want to eat that $200 tax stamp from an out of spec lower. Praying it isn't this that's the issue. View Quote That was the same lower and magazine with two different uppers. |
|
|
[#7]
Oh, I see. I misunderstood. Definitely don't think it's the upper in my case. I'm just hoping it isn't something like an out of spec magazine catch or magwell.
|
|
|
[#8]
The BCGs could have different mass that is enough to effect function. It could have been on the edge of being over or under gassed and it was pushed over the edge if the BCG is different weight.
|
|
Let us never forget, government has no resources of its own. Government can only give to us what it has previously taken from us.
|
[#9]
On mag height in well, pull the mag catch, strip a mag down to body only, lock the bolt home, shove the mag body into the well until the mag lips are tight against the bottom of the carrier, then look inside the left mag release channel to see how high the lower side mag catch bottom edge, is above the bottom of the receiver mag catch bottom of slot. Should be only 1/8".
Also to point out, on non ejection side of receiver, bottom of mag catch slot to top of receiver, should be .9375" =/- .0035" . so if slot for catch is correct in lower receiver, then check the catch in play, since could be too small for the slot, with top of catch tab on it too low in the first place. If more than this 1/8" that the mag can be pushed up to bottom out against bottom of carrier that the mag catch should be holding the mag in the well, then grab another upper to put on the lower receiver and do it again. Hence is problem the lower receiver in play with multi uppers out of spec that it or the mag catch is holding the mag too low in the lower, or is the problem just the upper in play alone that its center of B/C channel is too high against top of receiver instead.. When reinstalling the mag catch, make sure that threaded end of mag catch is flush to outer face of button. To add, when installing the threaded side of the match catch, should be semi snug in side of catch slot to being with, if a lot of slop between the catch to slot, need to know the height of the catch, as well the height of the receiver slot. With this out of the way, can weed out if the problem is lower receiver out of spec, maybe mag catch out of spec, or upper receiver out of spec to being with to cause bolt over bolt over run strip problem, if the rifle is full stroking to get the bolt back past the mag to correctly strip a round in the first place. From here, need to check for leakage problems, such as bottom of key leaking to top of carrier, gas block to barrel or gas tube leakage and gas block correctly indexed with barrel gas port, and need to make sure that gas tube has been indexed correctly to key as well. |
|
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds... <---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind. |
[#10]
Originally Posted By Banditman: The BCGs could have different mass that is enough to effect function. It could have been on the edge of being over or under gassed and it was pushed over the edge if the BCG is different weight. View Quote I find this to be a stretch, but I guess it's not entirely outside of the realm of possibility. |
|
|
[#11]
If standard weight B/C, standard tension recoil spring for length of receiver extensiond depth in play, then normal weight buffer for depth of receiver in play (able to pull all the way back on charging handle, front of bolt stops 1/8"~ 1/4" in front of back edge of ejection window, and last 1" of CHH pull is same as middle of pull in tension), then rig should run fine.
Add a oppressor in play, which does increase the bore back pressure/ port pressure that will cause the bolt to unlock sooner, then there is where a heavy buffer is needed, to bring the bolt unlock timing back to normal, so the residual bores pressure does drop back down to normal, so the spent case is not pressure welded to the chamber at unlock/which can cause the B/C to loose a lot of momentum at back stroke to cause short stroking. As for the positive note, easy to tell when the bolt is unlocking too soon/ rifle is over functioning, since with the spent case too pressure welded to the chamber, extractor is going to bend the hell out of the spent case rim backwards during the pull. So best way to tell if bolt unlocking timing is correct, simple load a round in to the mag, insert mag/charge round, fire for effect and go police the spent case to check it. Hence correct effect will be bolt locked back on catch (catch in front of bolt face, not just on the bottom of carrier), and spent case rim will not be bend back to hell from the extractor on chamber pull/spent case primer will not be completely flattened to sides of case primer pocket from ammo going over pressure. And the lovely, the shorter the barrel, the more ammo sensitive the rig will be to start with. Hence this has to do with the over all working pressure that the ammo is generating to begin with, and the burn rate of the gun power is play, and the slower the burn rate of the powder, the closer the powders max dwell spike will be to the gas port. Hence ammo with faster burning powder, and ammo will slower burning powder can both be loaded to the same working pressure, but the slower the power burn rate, the higher the gas port pressure will be. So with commercial 223 ammo, its working pressure is lower that 5.56 Nato loaded ammo, and then your still back to the burn rate of the powder in play, that changes the amount of port pressure. And to throw a curve ball, Nato 55gr ammo loaded to 62Kpsi working pressure, while say 223 69 grain ammo that is loaded to 55Kpsi working pressure, since the power used in the 69 gr ammo has a much slower burn rate, the 69 gr ammo can produce more gas port pressure at is lower over all working pressure, then higher working pressure nato ammo isntead. |
|
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds... <---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind. |
[Last Edit: emandude]
[#12]
Best to mess with one variable at a time while maintaining constants elsewhere.
I ran into a feed ramp issue on a gun and had to have the ramps machined. It was confusing the hell out of me because there was one or two brands of magazine that oriented the round in such a way that it would skip over the imperfection and chamber every time. The rest on my collection would not. I had them mixed together and On some magazines I'd get repeated failures and on others I'd get 30 shots off malfunction free. I eventually had to sort by brand and run them that way to begin to understand what was going on. Look for lockback on a single round to check for a gas/timing issue as opposed to a tolerance issue. If you run magazine brands mixed sort them out and try each brand to see if there's a tolerance or geometry issue some magazines overcome and others don''t. |
|
|
[#13]
swap your OG BCG back into it and see if your problem stops.
New parts sometimes need time/rounds for wear surfaces to smooth out. Just because it passes the gas ring test, doesn't mean the new BCG isn't your problem. but when you start swapping in new parts, and malfunctions start happening, its the new parts. |
|
www.newnanarmscompany.com
|
[#14]
Swapped back to the old BCG, problem is still occurring. It only seems to happen with Okay Surefeed magazines, though. My Magpuls are 100% reliable so far.
|
|
|
[Last Edit: emandude]
[#15]
Delete
|
|
|
[#16]
Sounds like those magazines don't play well with your chosen configuration. It would appear you've solved the problem.
|
|
|
Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!
You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.
AR15.COM is the world's largest firearm community and is a gathering place for firearm enthusiasts of all types.
From hunters and military members, to competition shooters and general firearm enthusiasts, we welcome anyone who values and respects the way of the firearm.
Subscribe to our monthly Newsletter to receive firearm news, product discounts from your favorite Industry Partners, and more.
Copyright © 1996-2024 AR15.COM LLC. All Rights Reserved.
Any use of this content without express written consent is prohibited.
AR15.Com reserves the right to overwrite or replace any affiliate, commercial, or monetizable links, posted by users, with our own.