View Full Version : problems with new .308 build
Hi, I went to the range today with my new ar 308 build and had nothing but problems. Looking for any input. Rifle upper is by redx arms, lower is psa, bolt carrier is by red barn armory, charging handle is bcm gunfighter 7.62. Mag is pmag and ammo is old brass surplus 7.62 x 51. I was not able to get multiple shots down range without a violent ftf, with the cartridges being bent, dented and scraped. I did not have any modern .308 to try so I could not verify if it was the ammo. I also noticed it was very difficult to pull back the charging handle at all times. Anyone have suggestions?2957029572
Did you function test before you went to the range?
Almost sounds like an incompatible upper / lower combination.
I used snap cap which would not cycle. I noticed that the caps were quite a bit shorter than live rounds so I cycled some live rounds successfully. I am at a loss, I thought only armalite was non compatible with other builds.
Did you buy a complete PSA lower? What stock and buffer/spring does it have? The CH is difficult to pull back related to what? Is it dragging or just heavy against the spring?
The cartridges just look like they're getting gashed by the bolt to me, as if it's short stroking. First I would ask how much lube and second, try one cartridge in mag, chamber, fire, see if it locks back open. Have you tried another mag?
The only upper I see sold from Red X Arms is a 20" upper with a .936 gas block, is this what you have? Is the gas block adjustable?
FWIW, all your parts look to be DPMS compatible. The only issue I know of with PSA lowers is when you try to use one particular model of Geissele trigger and it doesn't cause FTF's.
You're most likely seeing a tolerance stacking issue with parts from different manufacturers that theoretically are supposed to be compatible. Given that there are no real standards in the .308AR world (aside from really basic stuff like "uses Armalite steel mags vs SR25 mags") you're always taking a risk mixing and matching components; works great with AR15s, not so great with the .308 guns.
Can you move to a matched upper/lower set and a known BCG? Maybe also try a generic DPMS .308 charging handle; the Gunfighter .308 CH has been known to bind on some uppers.
You're most likely seeing a tolerance stacking issue with parts from different manufacturers that theoretically are supposed to be compatible. Given that there are no real standards in the .308AR world (aside from really basic stuff like "uses Armalite steel mags vs SR25 mags") you're always taking a risk mixing and matching components; works great with AR15s, not so great with the .308 guns.
Can you move to a matched upper/lower set and a known BCG? Maybe also try a generic DPMS .308 charging handle; the Gunfighter .308 CH has been known to bind on some uppers.
Thanks for all the input guys! A few more notes that maybe I failed to mention. The first round would always chamber, fire and eject and then the second would jam in spectacular fashion. I did not get the chance to only fire 1 round to see if the bolt would lock back. With the snap caps, the round would chamber and fire but it would bind up to the point I could not pull the charging handle back at all to eject the round. I went ahead and ordered a generic 308 charging handle so we shall see if that corrects anything. I can't link up to my upper but it is labelled as 20" RXA-308 SPIRAL FLUTED BULL UPPER HALF and as all my parts (according to their respective websites) dpms compatible.
I think you're on the right path. It sounds like that CH is binding. Let us know if it is smoother operating unloaded when you get the new one. The only other thing I would say is run it wetter than necessary the next time and try the one round out of the mag to see if it locks back or if there's a gas problem. Then, you won't be destroying ammo. Get a few rounds through it to see if it does or will start to lock open.
Two things I would check while you're waiting on the new CH. Make sure there aren't any weird marks inside the top of the upper receiver like the cam pin is dragging. I would also look and see if the bolts are staked on the gas key. You can find pictures on the web of what it should look like.
Just thought of this as well. With an empty chamber see if it will close if you ease the bolt down using the CH to check for a bent gas tube. It should be centered when you turn it over and visually inspect it.
New builds are funny sometimes. I built a 5.45 upper earlier this year and knew it was assembled correctly. However, the first round fired never even moved the BCA. The spent round was just sitting in the chamber like it had no gas system at all. It worked fine after that one shot.
Happy Veteran's Day
Need a more detailed build list, to include the buffer and recoil spring lengths, gas port alignment and troubleshooting of the gas system alignment, and basically every critical core component of the gun.
We're going to be seeing these types of threads indefinitely with the new wave of AR10 parts on the market.
AR10's have totally different buffer lengths, recoil springs, and fit issues from one maker to the next. There is no TDP for them that anyone will share, as they shouldn't. It's a monumental minefield to negotiate, especially since most of the target market has not been around to watch the developments and understand what has happened, and where these changes fall into place.
Conversely, I can take a bolt carrier group from the original Colt Model 601 AR15, and drop it into any of my AR15 uppers. I can take a Colt 601 upper made in the early 1960's, and slap it on any forged lower that I have. The FCG parts articulate properly with the BCG, and any AR15 barrel slips right into the upper as well.
Magazines work, and I even notice that Colt uppers made in the 1960s' or 70's have a square receiver face when I check them with a lapping tool-a great foundation for an accurate upper receiver when combined with a decent barrel.
With AR10's, you really are best advised to use a matching receiver set, and have someone that knows what they are doing assemble and troubleshoot the project. I've lost count on how many different AR15 builds I have done-all of which run extremely well in high volume, but the last two AR10 projects I did were custom jobs, and I just sent the parts off to GA Precision so they could work their magic. Since that time, I have gained a very good handle on what it takes to do one right, but I personally would want to start from a blank with the barrel, for the mere reason that I can't trust most of the industry to use the correct reamer, or line it up concentrically with the bore.
You're most likely seeing a tolerance stacking issue with parts from different manufacturers that theoretically are supposed to be compatible. Given that there are no real standards in the .308AR world (aside from really basic stuff like "uses Armalite steel mags vs SR25 mags") you're always taking a risk mixing and matching components; works great with AR15s, not so great with the .308 guns.
Can you move to a matched upper/lower set and a known BCG? Maybe also try a generic DPMS .308 charging handle; the Gunfighter .308 CH has been known to bind on some uppers.
Yeah, the tolerance stacking issue is a definite possibility.
You must be very careful about .308 AR builds and stick to compatible quality parts.
I have never even heard of RedX Arms or Red Barn Armory. I would stick to either a complete factory rifle or to parts from makers that offer a complete factory rifle.
^Exactly, that's why I bought my .308 rifles. I can build AR-15s all day long and in my sleep, and they will work first time every time as long as I pick decent parts. But the .308 world is just not to that level of standardization yet.
I wouldn't know where to start trouble shooting your rifle given that it is difficult to count on anything being right. But if you give more detail perhaps someone more skilled than I (and there are a lot of those on this forum) can help you.
First of all, thank you guys for your help. I have built many ar-15's without issue and did not research the build problems that could be associated with an ar-10. I did eventually get some snap caps to run and the action seem a bit smoother but when I exchanged the bcm charging handle with a generic ebay version, it was like night and day. No issues(at least with snap caps). Unfortunately(and for most of the country) taking it out to the range is out of the question with the weather we are having. Hopefully it will clear up one more time before winter sets in but I'm not counting on it.
thanks!!!
While you're at it, I'd also triple check that the gas key isn't slightly loose - it might be tacked down vertically, but if it has some yaw play in it, those can bind on stuff (and have the severity affected by what CH is in use). May not be the exact issue in question, but an odd one I've experienced that manifested similarly (but not in the same way).
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