The carbine I built still isn’t giving me the accuracy I’m expecting. I’m looking for 2-3 MOA but actual results are much worse. I initially thought the problem was a 16" Del-Ton barrel, standard hand guards, and the DPMS BCG that came with the upper, but that has been replaced with a 16" Daniel Defense barrel with LaRue rails and a BCM BCG–still on the DPMS upper.
I’m shooting my all factory ArmaLite rifle beside it as a control to make sure it isn’t me. I get much better results out of the rifle. Both are being shot sandbagged from a bench with the same magnified optic (QD mount switching back and forth, paying attention to the group size and ignoring the shift in POA/POI between different ARs). Unfortunately, there are too many differences between the rifle and the carbine for me to say it’s one thing or the other; examples, 1/9" vs 1/7" rifling, clamped gas block vs pinned front sight post, barrel profile, one all factory vs one built by me (this is probably the culprit heh), etc… At 25 yards, which should be very manageable, the control rifle is turning out < 1" groups (fine) and the custom build carbine is spreading them out to 2-3" groups. Remember: this is sandbagged from a bench.
I fully recognize Federal XM193 and XM855 isn’t the most accurate ammunition in the world, but it should be tighter than 2-3" at 25 yards. I get the same results from both the rifle and the carbine whether I use XM193 or XM855.
I’ve reviewed the barrel installation procedure and I think I got it right. Zero loc-tite was applied during installation and the barrel nut took about 65 ft-lbs to get everything lined up, which I believe shouldn’t be under nor over-torqued.
[ul]
[li]Could there be something funky with the dimensions of the DPMS upper, especially as it pertains to how loosely the barrel fits into the receiver (I thought torquing the barrel nut would make that not matter a bit)?
[/li][li]Is the Daniel Defense barrel, as tough and reliable as it is, just not going to give me the desired results?
[/li][li]Am I just expecting something that is not reasonable from the carbine even though the ArmaLite rifle is yielding satisfaction?
[/li][li]Something else I’m just not thinking of?
[/li][/ul]
Will be happy to share any further details, but I think I brain-shat the right info… Thanks in advance!
Even with 193/855 at 25yds and a magnified optic there should be a 1 hole group happening. What optic are you using? Are you getting the same results with irons? I have shot a buddies Delton barreled carbine before and it would shoot fine.
Post a pic of your group and internal components and exterior. Make sure nothing is lose. Federal m193 I’m getting rounds right next to each other with the mp15. Make sure the receiver is straight. I have know people torquing down the barrel nut and put a slight bend in the receiver. Also make sure the scope you have on is secured and the sight pics is the same. I have also seen ppl bend barrels installing them.
Using a TA11F on an LT100. No noticeable difference between it and irons.
Then the receiver should be “suspect”, along with installation… I don’t see any noticeable defects. . I hope I got the important angles here. Let me know if I’m not giving you hands and eyes on what you’re looking for and I’ll shoot some more. Unfortunately, I did not keep the target.
Although I haven’t had my booger hooks calibrated, I don’t feel any catches or resistance when I separate the upper and lower receivers then slide the BCG back and forth through the upper. It just feels like one smooth, unimpeded, EWL-coated back and forth motion.
I do remember there being a very loose fit between barrel and upper receiver, but I figure the barrel nut should take care of any issue there.
Looks like I’ll have to break the pics up into 3 segments…
If your receiver is loose it will effect accuracy and will not keep a stable sight pic. The barrel nut is use to hold the barrel so you don’t shoot it down range. I would get a thing to stabilize the upper and lower. I don’t remember what is called . A little loose is fine.
Has anyone else fired the rifle with the same results? Grab the upper in one hand and grab the barrel in the other and twist, there should be no movement, just the barrel itself not the rail.
When I hold the upper receiver in one hand while separated from the lower and the barrel forward of the rails in the other and twist, there is no movement. Thanks.
Sharp eye, sir. I do think that is copper. I did spend some time with Hoppes Elite so it may be leftover from that wash-out. Is it reasonable that <500 rounds through this barrel would justify that much copper removal if bullets are not dinging the muzzle device on the way out?
I do not actually see any signs of contact when looking closer at the edge of the muzzle and inside the FH. I do see what I believe should be adequate clearance. I will certainly take her to the range with FH removed to observe results. Thank you.
I had an FAL that came new with a non-concentric flash hider. The rounds hit it on the way out and I was getting four inch groups at 25 FEET. A new flash hider fixed it.
I’m not a guru when it comes to AR accuracy. Of all those I’ve assembled, I only test fired them at short range for function and basic targeting. Nobody ever complained. OTOH, if I was building an AR for accuracy, I’d wonder how square the front of the upper was to its bore, and take steps to correct it if it was found to be lacking. Brownells and a few other companies make squaring tools and fixtures for that. I’d be very careful to make sure the barrel was not a sloppy fit in the upper and also that the barrels bore was concentric with the upper’s bore. Finally, I’d worry about the bolt carriers bore being square and concentric with the rifles bore (centered and not tilted).
The bolt gun boys shake their heads and wonder how the AR can do so well. I dunno either. But taking pains with things is not a bad thing. You’ve swapped barrels and BCG’s. You might wanna make sure the front of the upper is square, and that the barrel nut is also good. The idea is to have that barrel un-tilted in any way, and even pressure on its shoulder.
Some smart guru of the AR accuracy will probably come correct me. I’m open to tweakage in the thought train.
I do remember there being a very loose fit between barrel and upper receiver, but I figure the barrel nut should take care of any issue there.
This is the common thing between the two barrels. It is most likely your issue.
Let me restate what i meant. The barrel nut is to hold the barrel on to the upper receiver. It will not shoot the barrel off. With the barrel aligned with the upper receiver and proper torque their should be no movement. If there is movement you have to look at the alignment pin on the barrel ext or the slot on the upper receiver to see if it’s worn. If that checks out fine, look at the threads of the upper receiver and barrel nut. Also over torquing will damage the upper, barrel nut or barrel ext.
The is no affect to cause inaccuracies when the upper and lower has movement, but depending how you position yourself and the rifle will determine the out of your group. I myself hold the upper loose and a looser lower will cause me to take a longer time to acquire my sight picture. But that’s just me.
I also agree if the round is hitting the muzzle device it will cause the round to tumble
I hope this explain it more clear then my previous comment.
I’m going to second the notion that the muzzle device has a high probability of causing your issue. Put a standard A2 on it (being sure to torque it properly) and test it out. You’ll likely see your problem fixed. This also happens to be the least expensive fix if your going to throw parts at it.
Much thanks for all the advice. cjb brings up a really good point about concentricity of barrel extension, upper receiver, and bolt even though everything may be tightened down and to proper numbers and AKDoug correctly points out it is one of the last common parts… E-Man reminds me of the reputation the manufacturer of the current upper has…
In the name of good troubleshooting, I’ll definitely get it out without the muzzle device to see what happens. Meanwhile, if it does happen to come down to replacing the upper, would this upper from BCM be a decent choice? While BCM is a trusted vendor, the name of the manufacturer of this upper is not mentioned for reputation checks. No offense to BCM here; please understand.
