Bolt effect on accuracy?

[kentuckyMarksman]

I've got an AR15 with a White Oak Armament 18" SPR barrel with a cheap no name BCG from AIM Surplus. I've tried several ladders with it, but haven't had luck getting any decent groups. I've done a Varget ladder with 69gr SMK bullets, and a AA2520 ladder with 77gr SMK bullets, and most groups end up in the 1.5-2" area. Optic is a 3-15x SWFA. Could the bolt be having an issue on accuracy?

I don't believe this is me misdriving the gun. I feel like these are good trigger pulls. I have a large AR in 6.5 Creedmoor, which I shoot .75-1" with, and several bolt guns which shoot well under 1". Anyone have any suggestions for me?

Edit - More info:
My particular barrel is 1 7" twist rate. It's a stainless barrel, no flutes. It has a Geissele gas block on it that was pinned on by a gunsmith (ADCO in Ohio). They also coated the exterior of the barrel with a black coating.

The upper receiver is a blem BCM upper, with a thin coat of Loctite 620 retaining compound on the barrel extension to take up any space between the upper and the barrel extension.

Trigger is a Rock River Arms 2 stage trigger.

I do have some 55gr handloads that it shoots 1.25", and it shoots Fiocchi 55gr ammo around 1.4". I'd like to shoot heavier bullets though, and I believe this rifle can do better.

I tried some Gorilla 77gr 223 ammo (smk bullet) in it and it was a 3" group. I then shot the same load from my 223 Tikka Varmint, and it produced a .5" group.

Edit 2:
I took a borescope picture of my gas port. Could this be the source of my problem?

 

[nn8734]

Id change your bolt carrier out of an abundance of caution regardless if it improves precision or not. Get a “MP” marked bolt (magnetic particle proof tested).

Plenty of reputable bcgs out there.

That barrel should be .75-1.0 moa with 24.6-25.3g AA2520 and 77 SMKs, all other things equal. Im getting 2830 fps out of my Douglas mk12 bbl in my Mod 1 w/ 25g of AA2520, 77smks and its consistent to 700m.

 

[Ledzep]

I doubt it very much. IME it's usually a barrel to upper fit or just a disagreeable barrel when it comes to AR accuracy. I'm by no means a subject matter expert, though. I usually fiddle with them a while, get fed up, and go back to using AR's for 2-3 MOA shit and bolt guns for precision. I like things to be simple, and my solution to the problem has been lowering my expectations

AR's for certain have a higher propensity to produce larger groups than what a guy would expect with nice bolt guns, even when feeding them top notch components.

 

[Halfnutz]

I put a 20 practical WOA barrel in an LMT flat top upper with LMT BCG and it was a hammer, switched it to a Spikes upper and BCG and it definitely had a detrimental effect on my groups.

Whether it was the bolt or the upper or both I don't know. I have yet to try the LMT BCG in the Spikes upper but that would be the tell all.

 

[ut755ln]

I've got an AR15 with a White Oak Armament 18" SPR barrel with a cheap no name BCG from AIM Surplus. I've tried several ladders with it, but haven't had luck getting any decent groups. I've done a Varget ladder with 69gr SMK bullets, and a AA2520 ladder with 77gr SMK bullets, and most groups end up in the 1.5-2" area. Optic is a 3-15x SWFA. Could the bolt be having an issue on accuracy?

I don't believe this is me misdriving the gun. I feel like these are good trigger pulls. I have a large AR in 6.5 Creedmoor, which I shoot .75-1" with, and several bolt guns which shoot well under 1". Anyone have any suggestions for me?

BCM currently have their BCG in inventory, they have never let me down.

 

[larryh128]

I've used a bunch of BCG's from Aim Surplus, never seen 1 yet that wasn't MPI and haven't had an issue with one either. I would suspect that barrel doesn't like heavy bullets. what twist is it?

 

[larryh128]

White Oak barrels typically shoot, I would try a 55 gr bullet with a known load or if you have some Benchmark, load 25 grs x 55 gr and try it. I've never seen a rifle that wouldn't shoot that load. Varget that you have as well at about 26 grs.

 

[nn8734]

I've used a bunch of BCG's from Aim Surplus, never seen 1 yet that wasn't MPI and haven't had an issue with one either. I would suspect that barrel doesn't like heavy bullets. what twist is it?

All WOA SPR barrels are 7 or 8 twist; both will stabilize the 77smk, no problem. My guess is its either shooter or perhaps inadequate clearance between rail and gas block or something similar. Or just a bad barrel.

 

[Black max]

Check the gas key. The gas key came loose on the last 2 AIM carriers I had. Both rifles still cycled but accuracy went to shit.

 

[larryh128]

BCM currently have their BCG in inventory, they have never let me down.

It isn't a nitrided barrel is it?

 

[kentuckyMarksman]

My particular barrel is 1 7" twist rate. It's a stainless barrel, no flutes. It has a Geissele gas block on it that was pinned on by a gunsmith (ADCO in Ohio). They also coated the exterior of the barrel with a black coating.

The upper receiver is a blem BCM upper, with a thin coat of Loctite 620 retaining compound on the barrel extension to take up any space between the upper and the barrel extension.

I do have some 55gr handloads that it shoots 1.25", and it shoots Fiocchi 55gr ammo around 1.4". I'd like to shoot heavier bullets though, and I believe this rifle can do better.

I tried some Gorilla 77gr 223 ammo (smk bullet) in it and it was a 3" group. I then shot the same load from my 223 Tikka Varmint, and it produced a .5" group.

 

[larryh128]

My particular barrel is 1 7" twist rate. It's a stainless barrel, no flutes. It has a Geissele gas block on it that was pinned on by a gunsmith (ADCO in Ohio). They also coated the exterior of the barrel with a black coating.

The upper receiver is a blem BCM upper, with a thin coat of Loctite 620 retaining compound on the barrel extension to take up any space between the upper and the barrel extension.

I do have some 55gr handloads that it shoots 1.25", and it shoots Fiocchi 55gr ammo around 1.4". I'd like to shoot heavier bullets though, and I believe this rifle can do better.

I tried some Gorilla 77gr 223 ammo (smk bullet) in it and it was a 3" group. I then shot the same load from my 223 Tikka Varmint, and it produced a .5" group.

Standard trigger?

 

[kentuckyMarksman]

Standard trigger?

Rock River Arms 2 stage trigger.

 

[Rocketvapor]

Find someone with a similar AR.
You shoot his, he shoots yours.

EDIT I see you also have a "AR in 6.5 Creedmoor".

 

[larryh128]

Rock River Arms 2 stage trigger.

That eliminates the trigger issue.

 

[nn8734]

My particular barrel is 1 7" twist rate. It's a stainless barrel, no flutes. It has a Geissele gas block on it that was pinned on by a gunsmith (ADCO in Ohio). They also coated the exterior of the barrel with a black coating.

The upper receiver is a blem BCM upper, with a thin coat of Loctite 620 retaining compound on the barrel extension to take up any space between the upper and the barrel extension.

I do have some 55gr handloads that it shoots 1.25", and it shoots Fiocchi 55gr ammo around 1.4". I'd like to shoot heavier bullets though, and I believe this rifle can do better.

I tried some Gorilla 77gr 223 ammo (smk bullet) in it and it was a 3" group. I then shot the same load from my 223 Tikka Varmint, and it produced a .5" group.

Rule everything else out (scope, mount/rings, you, parts on rifle like gas block-rail contact, gas key as suggested above, etc) and if still no cause, call WOA for an RMA return/replacement barrel. No sense in beating your head against the wall (not saying you are but these problems can be a pain and time consuming)

 

[Shawn1492]

BCM uppers are very tight. And I believe white oak uses large barrel extensions. It should have been a very tight fit with no need for sleeve retaining compound.
Have you checked you scope, rings and muzzle device?

 

[kentuckyMarksman]

BCM uppers are very tight. And I believe white oak uses large barrel extensions. It should have been a very tight fit with no need for sleeve retaining compound.
Have you checked you scope, rings and muzzle device?

There was just the slightest amount of clearance when the barrel was in the upper, hence the compound.

Muzzle device is tight. Scope and mount seem tight, as well, but plan on investigating further. Rifle has spray paint on the optic rail. Wondering if that may be an issue.

I intend on taking the scope mount off and mounting on another rifle just to confirm the scope is good.

 

[Black max]

There was just the slightest amount of clearance when the barrel was in the upper, hence the compound.

Muzzle device is tight. Scope and mount seem tight, as well, but plan on investigating further. Rifle has spray paint on the optic rail. Wondering if that may be an issue.

I intend on taking the scope mount off and mounting on another rifle just to confirm the scope is good.

Did you check the gas key???

 

[bill_van]

Every BCM upper I've ever used required a heat gun to expand the bore enough to slide it on the extension. If yours was loose, something is mis- dimension-ed. Removing one that fits is tough...... with locking compound, you will need to use heat to remove.

 

[smoothy8500]

Two BCM (blem) uppers I built with WOA barrels, including one recently, took heat to insert extension. Odd that it took sleeve compound.

 

[6.5SH]

Same as last two posters, with a blem BCM upper it required heat to put the barrel in, no green loctite needed. I have the same model WOA barrel as you OP.

With the ADI 69 gr SMK ammo it is .75 MOA. That ammo is on the slow side (2700 out of an 18") so perhaps something to compare with your loads.

 

[kentuckyMarksman]

Did you check the gas key???

I will check the gas key tonight.

I did stick a borescope down the bore and noticed this. Could this be my problem?

 

[Black max]

I will check the gas key tonight.

I did stick a borescope down the bore and noticed this. Could this be my problem?

Most definitely, that is a hefty burr!

 

[kentuckyMarksman]

Most definitely, that is a hefty burr!

Does it look like the gas port is partially blocked by the gas block? That's my concern.

 

[Ledzep]

Most definitely, that is a hefty burr!

I don't think it's a burr. I think that's the baby beginnings of the flame cut that happens on the front side of the gas port on all... gas ported.. barrels.

 

[Black max]

Appears to be catching a ton of copper, like a burr.

 

[kentuckyMarksman]

I pulled the BCG today. No MPI markings or any markings at all. Appears to be a phosphate finish though. I've had this in a parts bin for probably 9 years.

The gas key is staked on, good and tight

Does the gas port look partially blocked by the gas block?

Is the consensus that it's probably my upper receiver? If that's the case, wouldn't the loctite 620 take out any of the play?

 

[Black max]

Have you taken the bolt out of the carrier and slid it in and out of your upper to see if it’s free floating on your gas tube?

 

[ssc45]

Just some thoughts: You have not reported any gas issues. Does the bolt lock back on an empty chamber? Load one round and shoot. If the bolt locks back then it would appear that you do not have a gas issue. That doesn't mean that you have 100% gas efficiency, but at least you do not have a major gas issue.

Respecting the bolt, there have been a couple of thoughts on accuracy. First, the bolt affects the headspace. One theory is that with excessive HS, the bullet makes a jump to the barrel which could affect accuracy. Hence, checking HS might be a good first step. Second you could try a different bolt to see if your results change for the better. Third, you could have a competent AR15 smith "fit" a bolt to the barrel.

In addition to the above, I would send a copy of the gas port picture to WOA. It is hard to tell if there is a burr and/or if the bullet is being disrupted by the "burr" as it travels down the barrel. Frankly, I would have already sent the picture with your concerns. They may RMA the barrel as the gas port looks to be problematic. I would also ask them to fit a bolt to the barrel if it is sent back.

There is also the theory that a bolt doesn't affect accuracy. I don't know, but HS is a factor. As far as fit of the barrel to the upper, I have seen many uppers shoot MOA where the barrel slipped into the upper without heat, shims or bedding. Perhaps it is the archer not the arrow. I have had uppers built by well known folks that shoot MOA or less. I know they do because I have friends who are into shooting groups and have developed great skills. I hand them the gun and watch them shoot sub MOA. I can take the same gun, with the same ammo and am lucky to shoot sub 2MOA groups. I just don't have the patience nor skill. Perhaps have a friend who is a known ar15 MOA shooter put a few rounds downrange.

YMMV.
Cheers, Steve

 

[r.tenorio671]

I've got an AR15 with a White Oak Armament 18" SPR barrel with a cheap no name BCG from AIM Surplus. I've tried several ladders with it, but haven't had luck getting any decent groups. I've done a Varget ladder with 69gr SMK bullets, and a AA2520 ladder with 77gr SMK bullets, and most groups end up in the 1.5-2" area. Optic is a 3-15x SWFA. Could the bolt be having an issue on accuracy?

I don't believe this is me misdriving the gun. I feel like these are good trigger pulls. I have a large AR in 6.5 Creedmoor, which I shoot .75-1" with, and several bolt guns which shoot well under 1". Anyone have any suggestions for me?

Edit - More info:
My particular barrel is 1 7" twist rate. It's a stainless barrel, no flutes. It has a Geissele gas block on it that was pinned on by a gunsmith (ADCO in Ohio). They also coated the exterior of the barrel with a black coating.

The upper receiver is a blem BCM upper, with a thin coat of Loctite 620 retaining compound on the barrel extension to take up any space between the upper and the barrel extension.

Trigger is a Rock River Arms 2 stage trigger.

I do have some 55gr handloads that it shoots 1.25", and it shoots Fiocchi 55gr ammo around 1.4". I'd like to shoot heavier bullets though, and I believe this rifle can do better.

I tried some Gorilla 77gr 223 ammo (smk bullet) in it and it was a 3" group. I then shot the same load from my 223 Tikka Varmint, and it produced a .5" group.

Edit 2:
I took a borescope picture of my gas port. Could this be the source of my problem?

....that's common on gas ports of new barrels, which eventually will "smooth over" any downward projecting burrs created during the gas port drilling. That one actually looks like it chipped a bit when the drill/milling bit broke thru. Looking to the left of the picture where the actual port is, it doesn't appear that the rough spot is above the surface of the groove, Over time it probably will "fill in" with copper, along with further gas erosion of the ports edges. Aggressive copper cleaning will remove it, which may or may not affect attainable accuracy if the erosion is below the leading/following edges of the port.

 

[kentuckyMarksman]

I pulled the BCG again, took the bolt out, yes it's free floating on the gas tube.

Funny that you mention lockback. I shoot this rifle from a bench, Atlas bipod in the front, sand bag in the rear, and as such, I have 2 20 round magazines I use with it. 1 locks back, the other does not. I assumed it was a bad magazine. Maybe I should try it in another AR.

Headspace has been checked with the current bolt and tested fine. Sounds like I may try another bolt though.

 

[Mike_in_FL]

What rail? How much clearance around the gas block?

Have you shot it without the muzzle device and what is it?

What scope mount? IS the paint affecting it? Known good scope?

Got any 8208XBR? If 23.2-ish grains of that won't shoot with a 77 SMK you've got a problem unrelated to ammo.

 

[kentuckyMarksman]

What rail? How much clearance around the gas block?

Have you shot it without the muzzle device and what is it?

What scope mount? IS the paint affecting it? Known good scope?

Got any 8208XBR? If 23.2-ish grains of that won't shoot with a 77 SMK you've got a problem unrelated to ammo.

It's an ALG V1 rail. there's plenty of clearance around the gas block. Can try to measure later, but I've got several uppers with this same rail and haven't had any clearance issues.

It's an A2 flash hider. No, I haven't shot it without it.

SWFA 30mm scope mount. You might be onto something here. The mount and scope is unpainted, but the rail on top of the upper receiver is. I think that might be the culprit.

I do have some of that powder. Sure, will give that a try.

 

[Mike_in_FL]

SWFA 30mm scope mount. You might be onto something here. The mount and scope is unpainted, but the rail on top of the upper receiver is. I think that might be the culprit.

I do have some of that powder. Sure, will give that a try.

I have had an extended type mount apply pressure to the barrel nut and rail and affect accuracy. Now, I prefer to see some daylight in between mount and rail. Seat those 77s at 2.245, you can probably go anywhere between 23.2 and 23.5 but watch pressure and don't blow your gun up, for the lawyers.

 

[kentuckyMarksman]

Thanks. This rail doesn't have the picatinny on top, so it sits slightly below the top of the upper receiver, so no contact between the rail and the scope mount. Will clean off the paint on the upper receiver rail and see if that changes anything.

 

[Evintos]

The upper receiver is a blem BCM upper, with a thin coat of Loctite 620 retaining compound on the barrel extension to take up any space between the upper and the barrel extension.

Try removing the paint off the upper receiver rail first and if that doesn't solve it, remove the bedding compound and retorque. On the rare occasions, properly bedded barrels can be detrimental to the performance. Assuming the extension was properly bedded to the upper.

Also as others have mentioned, the picture is gas port erosion. It's common in gas operated semi-atuomatic firearms and the more you shoot, the longer the erosion (erodes forward towards the muzzle) becomes. It also appears in the very first round you fire.

 

[Molon]

Most definitely, that is a hefty burr!

That’s not a burr, it’s gas port erosion. This is a burr.

Also, that gas port appears to have been beveled, which removes any burr that may have been there. The pic below shows a beveled gas port in a virgin Krieger AR-15 barrel.

Gas port erosion in an AR-15 barrel can become readily visible after just one hundred rounds have been fired through the barrel. There are a variety of variables involved, but generally speaking, the shorter the gas system, the more pronounced the gas port erosion. The next pic shown below is a from a chrome-lined 14.5” barrel with a carbine gas system after firing 500 rounds.

The following picture is from a 20” match-grade stainless steel barrel with a rifle length gas system that has had 1,000 rounds fired through it. (Note the gas port is perfectly centered in a groove.)

….

 

[Molon]

Appears to be catching a ton of copper, like a burr.

That's not "a ton of copper". That's not unusual for a semi-automatic AR-15.

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