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Posted: 5/12/2016 6:28:31 PM EDT
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Finally finished my build. An SPR type build w/ an 18" barrel. I was extremely excited to take it to the range and test it. All parts are quality, mil-spec materials. Went to the range w/ a friend who had an older functioning, tried and true AR. Both are 5.56/223.
I kept having misfeeds and misfires. I only fired about 20-25 rounds. When I slid the magazine into place and released the bolt catch the first round always seats and fires properly. However, usually on the 2nd or 3rd round, the misfire would happen. Most of the time the cartridge wouldn't even get caught by the bolt - the chamber was just empty. A few other times, the bolt got stuck as it cycled b/c the cartridge would get stuck in the chamber at an odd angle. Again it seemed as thought the cartridge wasn't being fed & caught by the bolt properly. I switched my bolt into my friend's AR and used my mags and ammo in my friend's AR....and everything worked smoothly. I also used his bolt in my AR and the misfires continued to happen. Not sure where the problem is. Very frustrated. Any help/input would be greatly appreciated. |
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You just described a typical failure to feed, we need details about the rifle. What length gas system? What kind of receiver extension? Buffer weight? Buffer Spring? Quality parts all around (Or so I think. I put a lot of time & investment in this build): i. Rifle length gas system - .750 Gas block on an 18" Criterion Barrel (Hybrid) http://www.brownells.com/rifle-parts/barrel-parts/rifle-barrels/ar15-m16-criterion-barrels-prod54733.aspx ii. Mil-Spec 6 position Buffer Tube http://www.groundzeroprecision.com/collections/ar15-buffer-systems-recoil-management/products/6-position-mil-spec-carbine-buffer-tube-7075-t-7?variant=4546609985 iii. I'll be honest.... I'm not entirely sure exactly what the weight and spring are. It doesn't give those details in the product description. |
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Check your gas tube/gas block alignment.... I was extremely meticulous w/ the gas block installation & alignment. I even dimpled my barrel using a tool to ensure proper spacing and to hold it down tight. I can't imagine its the gas block. Plus, there are not ejection/extraction problems with the initial casing/firing....the bolt is moving backward and cycling. When it comes back forward appears to be the problem. I'm stumped/frustrated by this. |
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Couple of things off the top of my head .
New gun is likely to be a bit tight , I wouldn't get too worried just yet . New parts are not necessarily clean , clean the gun well , including the chamber . Try a different magazine , borrow a used proven one from your friend if possible . Start out with full power 5.56 ball ammo (I like federal 55gr XM193). Lube the bolt well. Check the gas key screws for tightness . If these things help some get a couple hundred rounds downrange to loossen things up . If trouble persists try swapping bolts with your friend and if still no joy start looking at the gas system |
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I was extremely meticulous w/ the gas block installation & alignment. I even dimpled my barrel using a tool to ensure proper spacing and to hold it down tight. Quoted:
Quoted:
Check your gas tube/gas block alignment.... I was extremely meticulous w/ the gas block installation & alignment. I even dimpled my barrel using a tool to ensure proper spacing and to hold it down tight. So the dimple is opposite the gas port, correct? IE, did not seat the gas block against the barrel shoulder (probably). What gas port diameter does the barrel have? You should have swapped the other lower into your upper to check function, just to exclude the lower as a source of the problem. |
| It's not the 'quality' of your parts, it's their compatibility with your system. Its not the gas block misaligned. It would have to be grossly misaligned to cause problems. So much so that it would be obvious to the naked eye. The hole in the gas block is substantially larger than the gas port hole. If you dimpled it 180 degrees to the gas port and made sure your allen screw lined up with that dimple, you are most certainly good to go there. I do not know why everyone suggest this first off, it is almost never the culprit. Your problem is likely the Rifle length gas system on the 18" barrel and your buffer system. This is the 2nd or 3rd thread this week with someone with a 18" rifle length gas gun that won't feed. If you are running an adjustable receiver extension make sure you have a carbine spring and 3.0oz (carbine weight) buffer. Try that and let us know what you find. |
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It's not the 'quality' of your parts, it's their compatibility with your system. Its not the gas block misaligned. It would have to be grossly misaligned to cause problems. So much so that it would be obvious to the naked eye. The hole in the gas block is substantially larger than the gas port hole. If you dimpled it 180 degrees to the gas port and made sure your allen screw lined up with that dimple, you are most certainly good to go there. I do not know why everyone suggest this first off, it is almost never the culprit. Your problem is likely the Rifle length gas system on the 18" barrel and your buffer system. This is the 2nd or 3rd thread this week with someone with a 18" rifle length gas gun that won't feed. If you are running an adjustable receiver extension make sure you have a carbine spring and 3.0oz (carbine weight) buffer. Try that and let us know what you find. I dug through my emails to find the actual order for my buffer tube, and, indeed it is a carbine spring and a 3.0oz buffer weight. Here is the link to the complete kit and the vendor. Do I need a heavier weight? http://www.groundzeroprecision.com/collections/ar15-buffer-systems-recoil-management/products/6-position-mil-spec-carbine-buffer-tube-7075-t-7?variant=4546609985 I agree w/ you that the gas block is not the most likely cause. The barrel actually had one dimple already done by the manufacturer directly beneath the gas port hole (and Criterion Barrels are top notch). So not having the gas port and gas block properly aligned is highly unlikely. I went the extra mile to put the 2nd dimple in the barrel just to further ensure that the gas block wouldn't move. But, all these posts about the gas block have me 2nd guessing. Thanks for all the input. I appreciate the feedback. |
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So the dimple is opposite the gas port, correct? IE, did not seat the gas block against the barrel shoulder (probably). What gas port diameter does the barrel have? You should have swapped the other lower into your upper to check function, just to exclude the lower as a source of the problem. Quoted:
Quoted:
Quoted:
Check your gas tube/gas block alignment.... I was extremely meticulous w/ the gas block installation & alignment. I even dimpled my barrel using a tool to ensure proper spacing and to hold it down tight. So the dimple is opposite the gas port, correct? IE, did not seat the gas block against the barrel shoulder (probably). What gas port diameter does the barrel have? You should have swapped the other lower into your upper to check function, just to exclude the lower as a source of the problem. I didn't think of changing the lowers, but this seems like a solid idea. I'm assuming my lower is functioning properly. I've never really heard/read of a magazine well being defective out of the box. My lower is a mil-spec Anderson Manufacturing lower. And my lower parts kit was CMMG mil-spec as well. Haven't heard/read of a problem with Anderson's mag wells and/or feeding issues....but eliminating all potential problems at this point is necessary. http://www.primaryarms.com/anderson-manufacturing-stripped-lower-7075-t6-multi-cal/p/kt-ar-15-a3/ Thanks again everyone for the input. |
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OP,
You are describing what is referred to as short stroking, which is usually either gas system (undergassed for some reason), ammunition related (low power) or underlubed, dirty or not broken in gun. If you have not really cleaned your gun, including with a bore brush, then do so. And run your weapon wet at least to start. Lots of new weapons have debris in the chamber and lube is your friend. If you are sure the gas block is not the problem, then take the bolt out of the carrier and see if the BCG slides smoothly over the gas tube. If it does, then good. If it does not, then the gas tube alignment is off. Check that the gas key is staked and that one of the hex head machine screws is not broken. Use new brass cased US manufacture ammo to start, many short strokeing problems can be traced back to steel cased underpowered ammo. Good Luck |
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Break-in. <-- my vote.
My first build, also an 18" rifle-length gun, had short-stroking issues at first. After couple hundred rounds of 55 gr. Wolf Gold down the barrel, the FTF's went away. Before you change anything on the rifle, run it until you know whether you actually have a problem that requires parts changes. |
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Your assumption that the lowest cost generic parts on the market are "mil spec" is somewhat humorous.
There have been occasional issues with out of spec Anderson lowers IIRC. Pin holes being out of position could create extra drag on the BCG. You can also have assembly issues / parts mixups that can create excessive drag on the BCG from the hammer. Could also have a (relatively rare) buffer misalignment causing drag. |
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Your assumption that the lowest cost generic parts on the market are "mil spec" is somewhat humorous. There have been occasional issues with out of spec Anderson lowers IIRC. Pin holes being out of position could create extra drag on the BCG. You can also have assembly issues / parts mixups that can create excessive drag on the BCG from the hammer. Could also have a (relatively rare) buffer misalignment causing drag. Gamma, I always appreciate your comments. Isn't it interesting that in this era of readily available quality parts, we can still find so many things that can go wrong or be not quite right on a build? The act of assembling one of these forces us to get into the weeds and really learn how these things work. That's a big part of the fun for me. |
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I was skeptical of the low cost Anderson lower at first. But, hundreds of positive reviews (on multiple sites) and mil-spec 7075-T6 forged aluminum and MIL-STD hard coat anodized construction made me reconsider. Did I make a mistake? I made my decision to save money and spend more for a quality barrel and the Anderson lower seemed decent quality/functional....despite the price point.
My ammo was 55 grn American Eagle FMJ and 69 grn Privi Partizan Hollow Pt -- both are brass, no steel cases. If my barrel is 18" and the gas system is rifle length, what should the weight and spring on my buffer tube be...?? Someone on here said it should be a carbine spring and a 3.0 oz weight. Do I need a different weight or spring? I gave the specs once before but here they are again.... http://www.groundzeroprecision.com/collections/ar15-buffer-systems-recoil-management/products/6-position-complete-mil-spec-ar-15-buffer-extension-assembly-carbine?variant=1205799617 Again, I appreciate the advice men. Trying to learn here..... going through the details and building from the ground up has definitely helped me learn the ins and outs of my rifle. |
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In theory that gas combo should be fine pending the gas port is large enough. But your rifle is telling you something is keeping it from cycling all the way. Whether it's drag on the BCG or too heavy of a buffer system is a matter of experimenting. If it's drag on the BCG it will likely loosen up with use. Sometimes you can have tolerance stacking between parts causing them to be on the tight side. Try lubing the BCG liberally and if that doesn't work try swapping BCGs with a friend. If you eliminate the BCG as the culprit then it is likely your buffer system is too heavy. You can remove a weight from the buffer (it will have 3 steel weights and 3 bumpers inside) to see if a lighter buffer system helps. I feel like the rifle may just be tight since it is new made from parts from varying manufacturers. If the light buffer system works run it for 100 rounds or so and then put the buffer back together and see if it runs. If it still doesn't, you can cut a couple coils off your buffer spring to make it lighter and able to run the 3.0oz buffer as a "permanent fix" (you could always get a new spring to return it to normal for $4ish). Another thing you could do if the rifle still doesn't run and you don't want to alter the buffer system is use a linear compensators that creates backpressure like a KX3 or KX5.
Also, as for the Anderson lower, do not fret over it. They put out a quality product at a fair price. The only thing I have seen 'problematic' with them is the rare very slight tight mag well that will not drop a magazine freely, which will not affect shooting function. Every manufacturer has the ability to have a bad lower slip through the cracks once in awhile. No one bats 1000. Anderson puts out a decent product at a more than fair price. I just wish the finish was a little nicer and they would run a batch of no logo lowers, that'd be a game changer for them. Lastly, do you know the gas port hole diameter for your barrel, and was the ammo you were using .223 or 5.56? See if you can get your hands on some XM193 or M855 to try out. |
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Alright. It looks like all that was needed was to break in the rifle. After shooting about 100 rounds the short cycling stopped and the rifle ran smoothly. Put about 150 total rounds down range and was able to zero in my scope as well.
Thank you everyone for the input. Trying to post some pics for everyone but can't figure out how to attach a photo here.... |
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