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Posted: 12/28/2013 8:08:30 PM EDT
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Okay, this is our first AR build for my son, so please bear with me as a noob.
Finished assembly and went to the range today. Everything went together nicely, and there were no apparent issues with the build. For the initial firing the Bolt was stopping with the shell end just coming out of the chamber, pulling the charging handle back another 1/2 inch would eject the shell. The bolt is snug, but not terrible. I have a good working M&P15 to compare to, and the difference in pull thru the stoke (no shells loaded) is maybe a couple pounds more pull force thru the full stroke. Not excessive, but definitely tighter. Assuming it just needed some work-in, we fired 4-5 more 10-round mags, cycling out the spent cartridges manually after each shot. Eventually is started ejecting, but was not cycling back far enough to pick up the next round from the magazine. Continued shooting, charging full stroke to get a round chambered. Started to notice that when we got a round chambered, the round (unfired) was jammed in the chamber. Had to bump the Charging Handle to break the shell loose. No real noticeable scratches or gouges on the brass. Started shooting better quality ammo, and began to get better ejection and enough stroke to pick up and load the next round, but the cycle was still not far enough to catch/hold the bolt open when the mag was empty. The shells continue to jamb in the chamber, and occasionally we get a no-fire, presumably because the bolt is not seated all the way. Since it's stuck, we can't tell if the shell is all the way in the chamber. Pushing the bolt assist doesn't seem to help, but I think it's just too tight. My assessment is probably not completely correct, but it seems that the chamber is too small. It's a 5.56x45 barrel, and the jamming happens with both 223 and 5.56 ammo. I think the tight chamber is taking the momentum out of the extraction cycle and there is not enough force left to make a full ejection stoke. My opinion is that the chamber needs to be polished or reamed, but I wanted some advise before I attempt any such modifications. The key build components are as follows... MEGA Arms GATOR Stripped Lower Forged
MEGA Arms Complete Forged Upper Receiver, M4 Feed Ramps AR-Stoner Bolt Carrier Assembly Mil-Spec AR-15 Parkerized DPMS Mid-Length Gas Tube Yankee Hill Machine Gas Block Low Profile 0.750" Inside Diameter Steel Matte Bergara Barrel AR-15 5.56x45mm NATO Mid-Length M4 Contour 1 in 9" Twist 16" Chrome-Moly Black Nitride Vltor BCM Gunfighter Mod 3 Large Charging Handle Assembly AR-15 Aluminum Black AR-Stoner Magazine AR-15 223 Remington 5-Round with Anti Tilt Follower Stainless Steel Black I do not have the Go, No-Go gauges. All the various ammo fires and cycles perfectly in my M&P15. The M&P15 Upper works perfectly attached to the MEGA lower assembly. I would appreciate any assistance you guys could offer.  </a>" />
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| I would first assume a gas problem if you are having short stroke/cycling issues. Are you sure the gas block is aligned correctly, and the gas tube is correct? I have heard bad things about the AR Stoner BCGs though as well so that could be the issue. I would start with the gas system first though. |
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What buffer and buffer spring are you running. I wouldn't be surprised if it too heavy. Take the buffer spring and buffer out of the m&p and try it in your new build.
Is gas tube properly aligned. You can check by plugging the barrel where the bolt locks into barrel. Use your small towel and finger to plug. Blow hard down muzzle feel the end of gas chamber for air. It should be a good amount of air and be unrestricted. |
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Quoted:
I would first assume a gas problem if you are having short stroke/cycling issues. Are you sure the gas block is aligned correctly, and the gas tube is correct? I have heard bad things about the AR Stoner BCGs though as well so that could be the issue. I would start with the gas system first though. I second this. Most of the time cycling problems are due to a bad gas system. If you have other AR's try mixing them around and see if it still works properly. As in the upper on another lower and the lower on a different upper. If one doesn't work then you can limit the problem to a more refined area. Also this may sound silly but make sure you're running it WET. I had some friends who were running their AR's more on the dry side with RemOil of all things. After a debate in which I was basically told I knew nothing, one of them took his RemOil and soaked it, little overkill imo, but it ran perfectly after that. Eventually they both switched to different oil and haven't had problems since. Anyways, its better to start off with the cheap to fix parts and figure out that's what is wrong, then it is to start with the most expensive part and find out you didn't fix it. It;s human nature to assume its the worse thing and completely ignore the simple fixes that could solve it. |
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Agree with checking the gas system first. Sure sounds like a lack of gas pressure to me. I happened to have this problem in my most recent build. If you can move your bolt carrier in and out of the chamber by hand without chambering a round, I would assume the bolt carrier is not the problem.
When your son is firing the rifle, stand to the side and observe if there is excessive smoke escaping from the area under your free float hand guard where the gas block is located. By the way, you dont want your off hand to be anywhere close to that area if you have a gas leak. When gas escapes from a leak there it is HOT and traveling at warp speed. If you do have a gas leak, you'll need to remove your free-float handguard and re-tighten the gas block allen screw, making sure the screw fits in the dimple in the bottom of the barrel. |
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Make sure your gas block is seated over the gas port. A lot of barrels gas ports are drilled assuming you're going to be using a handguard cap which will mean your gas block shouldn't sit directly against the small ridge right before the gas port.
Also I haven't heard very good things about the AR Stoner BCG's so maybe try using the BCG from the M&P and see what happens. |
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Spray gun cleaner into the gas tube from the inside with the barrel facing downward.. after a second or so the cleaner should DRIP out the end of the barrel..
I agree with most here.. sounds like your gas block is blocked and not alligned properly.. The easy way (for me) is picture a HALF of matchbook thickness between the gas block and the rear of the 'seat' on the barrel. Let us know what you find out.. |
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Second on running it WET. I would recommend some type of motor oil (Mobil1) and hit just about every joint or moving part on the BCG.
Also check the gas key screws while you have it out. Do the gas ring check also - stand the BCG with the bolt end down and it should remain extended so the weight doesn't make the bolt push back into the carrier. |
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You may have a gas problem, but it's not your main problem.
If you chamber a round and it's not just an easy pull but requires smacking or bumping the charging handle to free up you have a mechanical problem. If the bolt moves freely/easily in and out of battery empty and becomes difficult when a round is introduced the problem is in the chamber. Shine a light in there and make sure there's not rough machining or errant metal shavings if it looks good take a casting yourself and measure or have a smith do it, you have a dimension wrong somewhere. |
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Quoted:
You may have a gas problem, but it's not your main problem. If you chamber a round and it's not just an easy pull but requires smacking or bumping the charging handle to free up you have a mechanical problem. If the bolt moves freely/easily in and out of battery empty and becomes difficult when a round is introduced the problem is in the chamber. Shine a light in there and make sure there's not rough machining or errant metal shavings if it looks good take a casting yourself and measure or have a smith do it, you have a dimension wrong somewhere. This, may be something out of spec in the upper. |
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The AR Stoner BCG would give me pause. Take your M&P bolt carrier, put the Stoner bolt in it, and try that in your son's rifle. If the rifle runs, you probably have a gas key problem. If not, you may have a gas block problem.
Second the advice to run it wet, especially inside the carrier. Is the bolt especially difficult to move in the carrier? If so check the condition of the gas rings. |
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Quoted:
You may have a gas problem, but it's not your main problem. If you chamber a round and it's not just an easy pull but requires smacking or bumping the charging handle to free up you have a mechanical problem. If the bolt moves freely/easily in and out of battery empty and becomes difficult when a round is introduced the problem is in the chamber. Shine a light in there and make sure there's not rough machining or errant metal shavings if it looks good take a casting yourself and measure or have a smith do it, you have a dimension wrong somewhere. Yeah, live rounds that get stuck in the chamber are definitely not a gas problem. You may have to break everything down and check the torque on the barrel nut, but at a minimum you should have headspace gauges; you may have tight headspace. Swap BCGs with the M&P and see if it runs any better. The AR Stoner BCG makes me a little suspicious. Did I mention you should have headspace gauges if you are going to be in the habit of building you own? |
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Thanks for all the great responses guys.
We did get it real wet with RemOil, but that's all we had with us at the time. It didn't seem to help. My boy has the gun with him, so I can't check all the things you suggest first hand, but he read this thread and we just talked. Blowing thru the barrel with the chamber plugged produces a free flow of air out of the gas tube. The Gas Block seated into the dimple opposite the Gas Port and pulled away from the shoulder a little. Obviously we didn't measure the offset, but the block is not hard against the shoulder. When he pulled it apart, he noted that the chamber surfaces are fouled with fine brass shavings and some thick residue. He is going to clean it out good and see if that is the source of the jamming issue. Frankly, we didn't clean the barrel before the assembly, so there could be some Cosmolene or other such greasy rust inhibitor in there that we didn't notice. Noob mistake I guess. We were getting close to closing time and it was getting dark, so we were rushed and not taking time to think things thru at the range. Cleaning should have been an obvious thing to try. We had a boresnake right there with us. He doesn't have any ammo or dummy rounds with him, so he can't check the operation after cleaning. We may get together tomorrow afternoon to do a few of the things suggested here and test fire it again. Swapping BCGs, cleaning, checking for looses screws, checking/swapping recoil springs, etc. I think we have lots of good things to check here. I'm ordering the headspace gauges today. Thanks again for all the feedback. I'll report our findings when we get another chance to fire... |
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Quoted:
Thanks for all the great responses guys. We did get it real wet with RemOil, but that's all we had with us at the time. It didn't seem to help. My boy has the gun with him, so I can't check all the things you suggest first hand, but he read this thread and we just talked. Blowing thru the barrel with the chamber plugged produces a free flow of air out of the gas tube. The Gas Block seated into the dimple opposite the Gas Port and pulled away from the shoulder a little. Obviously we didn't measure the offset, but the block is not hard against the shoulder. When he pulled it apart, he noted that the chamber surfaces are fouled with fine brass shavings and some thick residue. He is going to clean it out good and see if that is the source of the jamming issue. Frankly, we didn't clean the barrel before the assembly, so there could be some Cosmolene or other such greasy rust inhibitor in there that we didn't notice. Noob mistake I guess. We were getting close to closing time and it was getting dark, so we were rushed and not taking time to think things thru at the range. Cleaning should have been an obvious thing to try. We had a boresnake right there with us. He doesn't have any ammo or dummy rounds with him, so he can't check the operation after cleaning. We may get together tomorrow afternoon to do a few of the things suggested here and test fire it again. Swapping BCGs, cleaning, checking for looses screws, checking/swapping recoil springs, etc. I think we have lots of good things to check here. I'm ordering the headspace gauges today. Thanks again for all the feedback. I'll report our findings when we get another chance to fire... That was a potentially disastrous mistake. Savvy shooters even dry-patch a barrel that they know is clean before leaving for the range or sometimes at the range before firing. Our guns will try to tell us there's a problem - next time listen to it before you have to pick shrapnel out of your face. |
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Nice looking rifle by the way. I remember earlier this year when bolts were in very short supply, Midway got some of the AR-Stoner bcg's in. Sold the piss out of them, my buddy bought one as well. I saw several complaints with them doing the same thing as yours. They were bone dry and tight fitting. Make sure you strip the bolt, clean and lube, hand cycle. Some guys went as far as taking an emory cloth to them. My friend just did as I recommended above and his was fine.
AR-Stoner Magazine AR-15 223 Remington 5-Round with Anti Tilt Follower Stainless Steel Black Also, did you try any other magazines? |
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UPDATE
So, we went thru the gun and cleaned it up real well. I used a brass bore brush on a drill and gave the chamber a good scrubbing so it's very clean. We checked gas delivery airflow and all seems well. Got out to the range and loaded up some Fiocchi 55 grain 223 ammo, everything worked perfectly. It even latched open on the empty mag. We shot 2-3 mags this way, perfect. Then we went back to the Battle-Bag re-manufactured ammo I was shooting before. My gun cycles that stuff all day without incident, except when I get a badly dented shell case now and then. At 39 cents per round delivered, it's nice if you can cycle it. When we loaded up a clip with that ammo, it jammed on the first round. We checked the chamber again, clean as it can be. Tried again, same thing. UGH! Then we started studying the ammo careful, and noticed there was a mix of 223 and 5.56 in the bulk pile of ammo. Wow, I had never noticed that. The barrel of the new gun is clearly stamped 5.56x45. We sorted out a pile of 223 rounds from the bulk ammo loaded that up in a few mags. It cycles fine, but occasionally short cycles and fails to pick up the next round. It seems that there are two problems. One is now obvious, the chamber is not able to load a 5.56 round without jamming, and the other is there seems to be a lack of gas pressure or flow to fully cycle the bolt with the low-quality ammo. We went back to the Fiocchi 223 ammo, and it works perfectly again without any issues at all. Full cycle, no jamming and complete full stroke cycles every time. We swapped the lower with my M&P15, loaded the cheap 223 ammo again, and it still short strokes and FTF. We put my M&P15 buffer spring in the new gun too, same result. I will be contracting Bergara about the barrel chamber depth and see what they have to say. It seems clear there is a chamber sizing issue. So, now the cycle issue still presents a problem. I know, you will say "don't use cheap ammo", but what fun is that? Does anyone here have any additional advice? Is there a possibility that the mid-length gas system is the problem? (affordable Carbine length barrels were not available when I bought that part before Christmas, so I went to the mid-length because of availability) Any ideas would be appreciated... |
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Shoot nothing but factory load ammo in it until you get it figured out, broken in, loosened up, ect. From what I have read it fires those fine. You are having problems with reloads.
You are only saving a couple bucks on the reloads, your firing them through a new tight rifle, the problem is obvious. Shoot about a 1,000 rounds of XM855 through it, I bet you don't have any more issues. Well maybe a 1,000 rounds is excessive, but you get the point. |
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