Struggling with 1 MOA at 100 yrds- range report

[Oldmauser]

1. Today a buddy of mine shot the rifle- see the targets below. We tried Hornady Match ELD 73gr, Hornady Black 75 gr and GGG SMK 77GR.
2. It seems that the gas block does touch the bottom of the handguard (in fact the piccatiny rail attached to it).

 

[Lawless]

The block touching the rail is something that needs addressing before you go any further.

 

[Eoddave27]

^^^^^^What Lawless said. That will totally screw up your accuracy. I had it happen on one of my rifles. It went from 1 1/2 moa gun to just over .5 moa after I fixed it.

 

[Precision Underground]

1. Today a buddy of mine shot the rifle- see the targets below. We tried Hornady Match ELD 73gr, Hornady Black 75 gr and GGG SMK 77GR.
2. It seems that the gas block does touch the bottom of the handguard (in fact the piccatiny rail attached to it).

How confident are you that the highlighted statement is not the problem? At 3moa my guess is that it is not your shooting and something is loose or something is touching something that it shouldn't.

 

[x_789]

The gas block is an issue. What are you measuring those groups to be? Is that at 100m or 100y?

 

[Oldmauser]

The gas block is an issue. What are you measuring those groups to be? Is that at 100m or 100y?

good question. these are the groups at 50 meters. So, my guess is that they would be twice as big at 100 m. They are measured in cm.

 

[davsco]

can you take your handguard off and take a pic at the gas block? is the pic above right side up? most of the gas blocks i've seen are thin at the bottom but taller at the top of course because that's where the gas tube goes and thus if it's touching the handguard i'd think your problem would be at the top of the gas block, not the bottom.

 

[CxAgent]

Had a similar similar issue with a AR Stoner 6.5 Grendel upper. Decided to tear the upper down to see what was going on. Best groups from factory ammo was 3" +-. Gas block in contact with hand guard, gas tube was tight to barrel nut. Lapped the upper, took the gas block to the grinding wheel, re-shaped the gas tube, and bedded the extension to the upper. Took it to the range and there was a noticable difference in the consistency of the groups. The rifle still does not shoot the Hornady black 6.5 Grendel approximately 3" groups. Hand loads are hovering around 1 moa. On my upper this made a pretty substantial difference.

 

[Oldmauser]

can you take your handguard off and take a pic at the gas block? is the pic above right side up? most of the gas blocks i've seen are thin at the bottom but taller at the top of course because that's where the gas tube goes and thus if it's touching the handguard i'd think your problem would be at the top of the gas block, not the bottom.

Nope. We checked this 3 times- the top is ok, it's the bottom of the gasblock that is touching the handguard.

 

[Austinjunks]

There is a video floating around were I took a handheld belt sander to the bottom of a gas block for a quickfix. Not proud of what I did to that rifle, but it fixed the issue.

 

[davsco]

take a pic showing the top of the gas block (and/or take off the handguard).

the handguard is on there straight (distance from the actual barrel is the same all the way around?).

what make and model is the gas block?

i just looked at a page of 96 gas blocks at brownells and for all, the tops stuck out more from the barrel than the bottoms again because the gas tube goes in the front of the top.

 

[kl3309]

2. It seems that the gas block does touch the bottom of the handguard (in fact the piccatiny rail attached to it).

So move the rail.

 

[mtrmn]

If that is the bottom of the gas block it won't hurt (at least if it was MY gun) to trim the bottom of the gas block if you don't want to move the rail.

Edit to add: I have no problem with using a grinder etc on my guns if I know it will improve performance.

 

[Oldmauser]

take a pic showing the top of the gas block (and/or take off the handguard).

the handguard is on there straight (distance from the actual barrel is the same all the way around?).

what make and model is the gas block?

i just looked at a page of 96 gas blocks at brownells and for all, the tops stuck out more from the barrel than the bottoms again because the gas tube goes in the front of the top.

100028069 brownells id
LUTH-AR LLC AR-15 LOW PROFILE GAS BLOCK

 

[R0CKETMAN]

Use a file/s

No need to replace gb

 

[x_789]

agreed I would grind that sucker down. Can you get a side photo with the rail removed?

 

[davsco]

100028069 brownells id
LUTH-AR LLC AR-15 LOW PROFILE GAS BLOCK

i don't know what's going on, but there is no way the bottom of that block is hitting your handguard, IF the top of that block isn't hitting your handguard. the top of the block is def higher off the centerline vs the bottom, again because it sticks up to accept the gas tube. is that handguard not on straight/true/whatever?

maybe the bottom of the block is hitting screws from a pic rail etc attached to your handguard?

 

[Yondering]

i don't know what's going on, but there is no way the bottom of that block is hitting your handguard, IF the top of that block isn't hitting your handguard. the top of the block is def higher off the centerline vs the bottom, again because it sticks up to accept the gas tube. is that handguard not on straight/true/whatever?

maybe the bottom of the block is hitting screws from a pic rail etc attached to your handguard?

Maybe you're forgetting about the relief in the top of the handguard for the gas tube & block?

Of course the top of the gas block is taller - and that's why handguards have extra clearance at the top, unless they're the large diameter type which is not what the OP's picture shows.

 

[Oldmauser]

This is exactly was I was writing before- the bottom of the gasblock is hitting the picattiny rail attached to the handguard. There is little space between top of the gasblock and the handguard. Little patience- I am taking the rifle back to gunsmith next week.

I need however your advice as to whether he should deattach the receiver from the barrel and put it back together. Do you think that putting loctite 620 before reassembling the barrel and the receiver is a good idea?
I am thinking about polishing the trigger. It's a hyperfire enhanced duty trigger which is not a competition trigger.

 

[bfoosh006]

This is exactly was I was writing before- the bottom of the gasblock is hitting the picattiny rail attached to the handguard. There is little space between top of the gasblock and the handguard. Little patience- I am taking the rifle back to gunsmith next week.

I need however your advice as to whether he should deattach the receiver from the barrel and put it back together. Do you think that putting loctite 620 before reassembling the barrel and the receiver is a good idea?
I am thinking about polishing the trigger. It's a hyperfire enhanced duty trigger which is not a competition trigger.

If he is going to Loctite it in... I would lap the upper receiver face first. Use a quality brand / respected tool.

And no contact between the handguard and gas block is mandatory. Fix that first.

Where are you located ? I ask because of the GGG 77gr ammo... IE where did you buy it ?

 

[ShooterwithNoName]

This is something I've ran into several times with M-Lok rails especially...

I've had the attachment screws hit as well as the little M-Lok nut itself. If your using a bipod and loading it much, it can touch even if it has clearance while shooting.

Anytime I assemble an upper nowadays I check for gas block clearance. If you can shave down the M-Lok/Keymod rail hardware, screw/nut, I would go there first. I like to have at least 1/16th of an inch clearance under that gas block. It's definitely an easy fix, hopefully that will set you right.

I've never "bedded" an upper before with Loctite. I know a lot of folks do with good results. I pretty much religiously use Aeroshell anti-seize on every barrel extension/upper. Only way to find out is to try it? Hopefully the barrel won't get stuck too bad if you ever need to disassemble.

 

[Oldmauser]

You can buy GGG ammo in Europe. As you saw my goups with GGG were better than the ones with Hornady Match ELD. Quite funny.

 

[Precision Underground]

- I am taking the rifle back to gunsmith next week.

Was this assembled by a gunsmith or by you?

I built an AR

If a gunsmith assembled it and sent it out with the Gb touching I’m not sure I would trust that gunsmith.

 

[hlee]

Do you really need a gunsmith to remove the pic rail that is hitting the gas block? Remove the rail. Test fire the rifle to confirm it shoots better without the interference. (Re)Install it so that the fasteners don’t touch the gas block. This is a 10 minute fix, tops.

 

[Oldmauser]

Technically you are right. But it's not only about gas block. I will request the upper to be disassembled and reassembled according to the rules. If a gunsmith was paid to to do it, he's obliged to correct his own mistakes.

 

[Oldmauser]

The rifle was disassembled and reassembled by the gunsmith. I was shooting at 100 yrds using 77gr SMKs. A group of 5 shots was within 1 MOA. Hallelujah.

 

[mark5pt56]

The pitfalls of these slim rails. With some, you can grind down the MLOK screw so it won't hit, even with barrel whip. Others you will need to move which dependent on weapon set up is a pain. While not desirable, you can use a longer rail to have whatever accessory attached where you need it and not have an issue with GB contact.

 

[davsco]

Hallelujah.

NICE! so what did he do or move, that made the diff?

 

[Oldmauser]

NICE! so what did he do or move, that made the diff?

1. unscrew the barrel
2. cut off the part of the handguard which was touching the gasblock
3. Polished the receiver (the thread) with the lapping tool.
4. Put Loctite on the barrel before reinstalling it
5. Torqued the barrel nut according to the specs.
6. Polished the trigger.
7. checked the scope mount.

 

[davsco]

nice, guessing #2 was the culprit.

 

[bfoosh006]

"2. cut off the part of the handguard which was touching the gasblock "

I'm curious... pics ?

 

[Oldmauser]

I believe it was the combination of things. With match ammo it's capable of going below 1 moa.

 

[Oldmauser]

100m, 77gr SMKs.

 

[Oldmauser]

measured in cm.