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Posted: 5/4/2016 5:25:04 PM EDT
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Hey guys, Im just looking for ideas to fix my short stroking problem. Here is my setup
16" barrel High powered armory billet upper and lower carbine gas system m16 bcg carbine buffer, tube, and spring Independence 5.56 ammo, also tried 2 different brands of 223 My ar short strokes nearly every shot and won't feed another round. Its basically a bolt action rifle at this point. The strange thing is I put my upper on my brothers bushmaster lower and I can run through a mag with no problems. His spring length and buffer weight are identical to mine. I ordered a couple different carbine springs and a carbine buffer to try. I also ordered a lower spring set to try changing the hammer spring. I just don't understand why it runs perfectly on one lower, and awful on another. Any ideas? |
| Only thing that it can possibly be is the buffer tube (receiver extension), or magazine placement in the lower. I would run his buffer and spring in your lower and see what happens. The only way this theory would work is if the rifle wasn't ejecting spent casings though. If it does eject fine, observe how deep the mag seats in each lower. Maybe, your mag is too low for the bolt to pick up a new round when cycling. |
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With the upper and lower together, the bolt locked home, and the mag catch assembly removed from the lower receiver, strip a mag down to the body alone, shove it all the way up into the mag well until the top of the feed lips of the mag body bind out against the bottom of the carrier, then look in the mag catch slot of the lower receiver to see how far up from the bottom of the catch slot that the mag's catch slot is up from the bottom (where the mag catch would normally lock into the mag side slot).
At most, the mag bodies side bottom of catch lock slot should be no more than about a 1/16" higher than the bottom ledge. 
Note, take a good look up the front inside surface of the mag well as well. Its the upper receiver edge at the top of the lower receivers well wall that you are making sure that the upper receivers edge is not protruding past (will not allow the mag to lock all the way up and home). If you are good so far (with either the mags or the lower receiver not out of spec), then when you install the mag catch back in the lower receiver, make sure that the end of the threaded section of the mag catch is flush with the face of the mag release button. Now with the rifle back together, pull all the way back on the charging handle, and make sure that the face of the bolt stops about 1/8" to 1/4" in front of the back edge of the ejection port window, and the last inch'ish of the charging handle pull all the way back is not harder in tension than the middle of the charging handle pull. Lastly, shotgun the upper open, unlock the hammer, and take a good look at the tail of the trigger and disco. Your looking white line/dents of the tail of the hammer making hard contact to the either the disco or trigger tail. If such is found, then post a photo so I can see if the problem is just that the tail of the hammer it too long, and not that the FCG pin channels where not milled incorrectly, and the hammer tail making contact with the rounded back side of the disco hook surface instead. As for seating a fully loaded mag, if the bolt is not locked back, then it may take a good palm slap to the bottom of the mag to get it to lock home on the mag catch. As for mags, even brand new, strip them down to give them a good CLP cleaning (to clean out all the assembly grit that may be in them). Also with the mags apart, good time to check the follower for casting burs that may need to be removed so the follower can glide cleanly in the inside of the mag. P.S, would help to know what is going in in great detail when it not feeding, since if the problem is something stupid like the hammer following the carrier back to lock the carrier about half way forward, could be that you did not install the disco spring large coil side down during the build, or install other spring incorrectly during the lower build. |
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Ok, I did all of the checks you described. I checked the mag catch, and it seems to be within the range you described. It goes in just enough to lock in and no further. loaded you do have to put it in like you mean it if the bolt is closed. When pulling the charging handle all the way back the bolt stops just in front of the back edge of the ejection port window. Close to 1/8" maybe a little less. Tension seems pretty consistent through the pull of the charging handle. It gets a little stiffer as the bcg comes over the hammer but stays consistent beyond that point. I also inspected the trigger assembly and saw no unusual marks anywhere.
I will try cleaning the mags like you suggested, I have never though to do that before. You asked for more detail when it fails to feed. This is what happens insert loaded mag pull charging handle to chamber first round safety off, pull trigger fires, ejects, and closes again without feeding another round. I have done the 1 round lock back test. It fails the test in my lower, but would lock back on the last round every time with my brothers lower. I didn't build it, I received it in a trade so I'm not sure exactly what spring is in it other than it is a carbine length spring. For all I know it could be an "extra power" spring. I am waiting on a new carbine buffer, and I ordered a colt carbine spring, and a cheap stoner spring to try also. Thanks for the help so far, I really cant wait until I figure this thing out. |
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Quoted:
Hey guys, Im just looking for ideas to fix my short stroking problem. Here is my setup 16" barrel High powered armory billet upper and lower carbine gas system m16 bcg carbine buffer, tube, and spring Independence 5.56 ammo, also tried 2 different brands of 223 My ar short strokes nearly every shot and won't feed another round. Its basically a bolt action rifle at this point. The strange thing is I put my upper on my brothers bushmaster lower and I can run through a mag with no problems. His spring length and buffer weight are identical to mine. I ordered a couple different carbine springs and a carbine buffer to try. I also ordered a lower spring set to try changing the hammer spring. I just don't understand why it runs perfectly on one lower, and awful on another. Any ideas? If you put his upper on your lower, does the problem occur? |
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With the short stroking/not locking the bolt back, either there is hammer wedging going on (check the tail of the hammer and disco, or other problems with the carrier coming back in the receiver extension.
I covered checking the hammer and disco tail, and the other thing to check is to pull the buffer and recoil spring out of the receiver extension so you can take a good look inside the tube for binding. Also, check the end of spring coils for burs, and even the buffer bumper roll pins to make sure it not hanging out one side to catch the spring. If needed, break out a file to either remove end of coil springs that may be binding on the inside of the tube, or to flush the buffer bumper roll pin if is handing out one side of the buffer and catching on the recoil spring. |
| I took another good look at the buffer. The bumper pin was out ever so slightly on one side and I could see where the pin was wearing from rubbing on the spring. I took a file and made it flush to the rest of the buffer. Im going to give that a shot and see if that was my problem. |
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Quoted:
I took another good look at the buffer. The bumper pin was out ever so slightly on one side and I could see where the pin was wearing from rubbing on the spring. I took a file and made it flush to the rest of the buffer. Im going to give that a shot and see if that was my problem. Let us know. Maybe I got one right...finally. |
Ok guys, just got back from another frustrating day at the range. The first mag with 10 rounds in it went good, then the problems came back just like before. Failures to feed, and a couple failures to extract. I tried two different buffers and springs with no change. I did notice these scuffs on the brass and I'm not sure its normal. I looked in the chamber with a flashlight and didn't notice any burs or anything. Im starting to get frustrated. At least my ak still works...
The reliability is just very in consistent. One mag it runs ok, the next it might have 5 malfunctions. I don't get it. |
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