AR-Three O' Hate

arlaunch

arlaunch

Active member
This is my 3rd 308 barrel.

I have spent so much time and money trying to get this rifle to shoot. Some days it turns out good groups, the next time at the rifle range it shoots awful.

I took 204 AR's advice and ground more clearance on the hand-guard last night. It "seems" i have gone to the point where, when you flex the barrel down, it can no longer touch the hand guard.

I have spent hours fussing over the gas tube/BCG alignment. There is some movement on the gas tube to some degree. But not always, and when it touches a bit, it is minor. If you push the BCG home perfectly straight, it will not touch at all.

On the last barrel i had, i swapped scopes to a known good one. I did not see any difference.

I cleaned it prior to firing, and did 9, one shot/one cleans until no copper exists.

The barrel is a breeze to clean.

The gas tube clears the barrel nut w/o touching after i ground on the barrel nut.

I am using a Young Manufacturing chrome carrier, with a JP bolt that was head-spaced to the barrel extension.

I know what i am doing at the reloading bench. My rounds have minimal run out and the brass is bumped back .03-.05

I don't know what to do. I took it out shooting this morning... Poor performance!!!1

I have watched Johny's reloading bench a bit. It seemed he had the big change over in accuracy when he switched from Starline to Lapua.

I switched from Starline to Hornady. Hornady is definitely a step up. It sizes real consistently, and does not need and inch trimmed off after each firing. Groups are better, but obviously not better enough to solve the big picture problem.

It has a Surefire 3 prong flash hider that is not, and never has been put on too tight. Suppressor is on order.

Anybody have any ideas? I am a range trip or two from being done with the big platform. So much money, time and thought into this.

I suppose it is worth noting that a low flier is the culprit to what would have been a good group on many occasions. Not all though.
 
That would be frustrating. Just curious what barrel contour your using. I use heavy out to the gas block and .750 on out, don't have much barrel flex. My 6.5 gets a little jumpy with 140 RDF bullets but loves 95 and 100 grain bullets. My 308 does better with 175 RDF using TAC or 10X compared to 150 gr bullets. No easy answers but the money your spending there should be a winner in there somewhere.
 
Oh man, I feel your pain. What's odd is that 308 is one caliber I've never had success with group wise. I went through 3 barrels about 10 years ago and finally gave up also. My 243's are tack drivers, I have a 300 Saum that's very accurate also (all DPMS factory). I'm curious how it shoots without the flash hider.

Here's something to consider, my 243's were just kind of average until wrapped a couple wraps of teflon tape around the barrel threads before screwing the suppressor on. That made an unbelievable difference, sloppy thread fit must have been messing with the harmonics? It really sounds like you've done about everything you can. Sometimes I've wondered if it's a bad upper somehow, as I've had ar15 uppers never seem to shoot quite right with multiple barrels.
 
Thanks everybody for the good thoughts.

Tonight i had a good look at the gas block clearance again, and decided to remove the clamp on style block. My measurements where off somehow when i ordered it. I ground the gas block and the hand guard a LOT to get clearance. I thought i had plenty of clearance and could not flex it by hand to make contact. I could be wrong about that?

Where it is touching is in a peculiar place where you can't see it make contact.

Moral of the story is that the .936 SLR clamp on gas block does not work with the MI DPMS low, combat rail.

I am now back to the barrel manufactures set screw type. One can see immediately there is a ton of clearance now.

I ordered the gas block and the barrel at the same time. I hope this is the problem!!

My last build that was giving me even more fits, had a different rail and this low profile gas block.

I ended up buying another upper receiver, and trying that like 204AR said. No change.

It could be that the OEM DPMS upper and the spare Luth AR upper do have un desirable threads? I am not ready to blame those parts yet though.

It is a HBAR and the same gouged receiver as another post. Both my receivers are gouged like that now.

 
One thing on my last build that had me going round and round was the dang ejector spring. I have been running the JP High Pressure bolt. If you take a large round punch and push on the ejector spring it takes a TON of force to push it in flush!

With this set up it flings the brass back to the 3:30 at about 75 mph.

If i use a spare Brownells bolt, or the OEM bolt, their ejector springs are much, much weaker and cough the spent cases out the 1:00

I can only imagine the round is sitting in the chamber crooked under a high torque force. The last build i had, i could not see an accuracy difference when i swapped between them all. It was bad, and bad.

I will pull the flash hider also this next go round at the range.
 
AR builds(accuracy) is all about fitment,torque and a good barrel. True up the receiver face, properly torque barrel nut, general assembly procedures followed. Than at the range correct rest/shooting technique for best groups.
 
the gouge in your upper has - with near 100% certainty - zero to do with your accuracy issues.

period.

the bullet is long left the barrel *Before* your bolt even begins moving.





just out of curiosity, what bullets are you using/tried? what powder?

what do your ES/SD numbers look like?

have you checked when firing under recoil that your bullets arent moving/getting bumped out of concentricity when feeding? or if they're picking up a wild gouge from a burr on your receiver extension feed ramp area?

have you tried single loading (like hand feeding into the chamber, then letting the bolt drop) to see if that makes a difference on your accuracy?
 
Originally Posted By: spotstalkshoot Than at the range correct rest/shooting technique for best groups. The thing that affected accuracy the most for me when I went to big gassers was cheek pressure on the buffer tube or stock. I use a half inch riser but if I put any cheek pressure on the buffer tube I had flyers. Corrected that and I’m getting 3 and 4 inch groups at 500.
 
I read most of this thread and may have missed a detail or two but did you try any different bullets? I generally let the barrel pick the bullet that it prefers. All that gas tube alignment stuff is not worth worrying about imo. Handguard to gasblock is a big deal though. The Troy .936 low profile is the lowest profile I've found.
 
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I got the rifle out to the range yesterday. I removed the clamp on gas block and installed my old low profile gas block. I was certain this was going to fix the problem. The rifle did not shoot horrible. But i would not call it good either.

I really wish i would have removed the flash hider.

I also was reading an article the other morning about how some custom barrel makers have smaller chamber dimensions. And sometimes bullets get pinched a little which reduces accuracy. I never have let my cases get long. But i am going to try trimming them way back to see if that helps.

Also.... I need to follow DM63's advice and get the cheek pressure off the butt stock. I load the back with my cheek very heavy.

V2223,

I have tried Nosler 165gr BT's, Sierra 168gr MK's and Barnes 150gr TSX.

This thing starts harming brass at 2475 fps or so with 165+ grain bullets. All my other rifles shoot best with a full case of powder. This one, will wreck brass if i do that. 4064 does a good job with case fill and low speeds. Kind of.
 
If 168 Sierra's won't shoot, that's a bad sign lol. Actually factory GMM 168 ammo is a good litmus test for any 308, that stuff should shoot very respectable to outstanding in most any 308.

I feel bad that nothing has worked so far. Is that gas block adjustable? It shouldn't be trashing brass with full power loads. It makes me think it's overgassed.
 
V223,

I shoot for around 0.03 - 0.04.

204AR,

This gas block is non adjustable. If i can get this rifle shooting i will cough up some more money and buy the Bootleg adjustable key bolt carrier. At this point i am done putting any more money into this rifle.

Though in time i may have to.

I am tracking:

SpotStalkShoot's advice on truing up the receiver face. I will look into this.
Trimming the brass way back.
Removing the suppressor adapter
Buying a box of FGMM
Different shooting method to reduce pressure off the buffer tube
Screwing around with different bolts that i have on hand.
Single loading and checking ejected rounds before firing as P1 suggested.

Plant 1,

I have mostly been working with IMR 4064, H4895, AR-Comp, W748, N135 and PP2000 MR

I have tried CCI BR2's, 34's and 200's for the most part. Those three primers show very little difference over my Lab Radar. There is a myth out there that the 34's are a mag primer. B.S.!!

My plan is to work on this check list and get back to the range in a week or so.

Thank you everybody. Will report back after that range trip.
 
Your posts suggest inconsistency of groups, if that is the case. What are you changing? Are range conditions changing? Scope problems and torque/contact points are change issues. Loads that are the same, normally perform the same. Barrels usually are consistent, until fouling or wear occur. I have seen some odd bench bag/rest setups cause major group problems.
 
Originally Posted By: arlaunch
I have tried Nosler 165gr BT's, Sierra 168gr MK's and Barnes 150gr TSX.

[/quote]
Plant 1,

I have mostly been working with IMR 4064, H4895, AR-Comp, W748, N135 and PP2000 MR

I have tried CCI BR2's, 34's and 200's for the most part. Those three primers show very little difference over my Lab Radar. There is a myth out there that the 34's are a mag primer. B.S.!!

[/quote]

holy cr@p... it wont shoot 168 MK's over H4895?

somethings reeeeeeeeely wrong here.

be interesting to see your follow up after the range report.
 
Made it to the range yesterday. I trimmed all the cases a bit shorter than normal, pulled the suppressor adapter and did an experiment with shooting a group with an entirely different BCG.

No luck.

My dad gave me an old 16 inch barrel DPMS barrel a long time ago. I did not believe it was worth the trouble of even putting on a rifle. It has a carbine length gas system and took me 2 days to get what seems like 2lbs of copper out of.

I put it on the 2nd upper receiver i bought trying to solve the accuracy problem with this rifle. HA!!!

It ended up shooting decent. It does less damage to the brass than the rifle length 20 custom barrel does.

I actually shot MOA groups with it with 168's with both IMR 4895 and H4895.

At this point i am putting the high dollar crap away and just going to shoot this junker 16 inch DPMS barrel with the DPMS BCG.

When i can get a control group with it, if i can???

I will start adding and removing parts and components from the old rifle to see where the problem is.

The SAGA continues!!

Somewhat of a side note, with the DPMS re-build.

I did not grind on the barrel nut to ensure the gas tube was not touching. I also did not fret over the somewhat restrictive feel of the gas tube going into the gas key.

I also need to see decent results the next 2 range trips at least to believe this shoots ok.

Too many times have i had a good session, only to return for disappointment.

 
Over the years, I've had quite a pile of DPMS barrels, and only 1 or 2 could be considered duds, and several were amazing, including a couple I have now.

One of my regrets is not buying a few of their 204 barrels when Midway had them for $200 for years.

Sounds like you're on the right track. I'm reluctant to offer any more advice since everything has been a dead end so far, but it's worth noting that I have noticeably shrunk groups by tuning gas blocks down to barely function. It sounds like the custom barrel has a much too large port.
 
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