Desperate guy from Norway seeks help ! (new upper)

[olp73]

Hi everybody!

I have for some time gathered parts for a new upper. Being from Norway getting AR parts isn’t always so easy so when everything finally arrives you are like a child on x-mas eve.

This is the pars list:

· Troy Alfa rail 15”

· 18” Criterion hybrid couture barrel

· DPMS standard barrel nut (left over from a barrel I once bought)

· Aero stripped upper receiver

· Seekins low pro adjustable gas block

· Spike melonite gas tube

· JP, small Bennie Cooley brake

Since I don’t have a torque wrench I did not build the upper myself.

Basically I have two problems:

1. I suspect that the gas block is not perfectly sender over the gas hole in the barrel. To make the upper cycle I had to turn the adjustment screw almost all the way out. I noticed that the set screw was not perfectly lined up with the dimple in the barrel. The guy who built the upper said he measured the block and the barrel and that he had to set it a little bit away from the shoulder. I also found it to be a little sideways. Can I trust that the dimple is located where it needs to be on a Criterion barrel and use it to locate the gas block?
2. Second problem is not so easily fixed. I cannot get the Troy Alfa Rail to centre whatever I try it will not line up with the barrel. This should be easy right? I did what the manual say. Al 3 screws are evenly torqued down a little at the time. I even used blue Loctite. I am always careful not to overtight things, but I don’t think tighten them harder will fix anything. I might be wrong?

Yesterday at the range (where I noticed everything) I shot a couple of good groups before things started to open up terribly. (The groups had a strange string pattern) I suspect that the barrel is actually touching the handguard under fire, or not enough free floated if you like. The first thing I noticed was that the gas screw was really close to the handguard then I noticed that the barrel was of centre too. (To the opposite side of the gas screw) I could easily make the gas block touch the inside of the hand guard by bending the barrel by hand.

The big question is of course. Does anyone of you have an Idea what could be wrong? I am open for any kind of suggestions! Please help?

Thanks in advance!

Edited June 6, 2016 by olp73

[Glockinator]

The rear set screw is normally directly opposite the hole. You can take the gas block off and remove the gas tube. Remove the set screw and slide the block back on upside down. Center the set screw hole over the gas hole in the barrel and measure any gap needed. When you reinstall the gas block a feeler gauge can be used to get the same gap. If you lightly twist the block as you tighten the set screw you can feel the set screw as it centers into the dimple.

If a gas block is touching a hand guard you usually get some random flyers in odd directions. Stringing might be more related to the fit of the upper, barrel nut. and barrel.

[R112mercer]

Check to make sure the barrel nut is tight enough. I know you said you don't own a torque wrench but maybe you could borrow/rent one? Once you're sure the barrel nut is tight enough then tighten the handguard screws nice and snug.

For the gasblock what I usually do is block the barrel at one end, install the gasblock without tightening the set screws, then blow shop air down the open end of the barrel. You can then tune the gasblock by twisting/shifting it until the air flow sounds strongest. Then tighten down the set screws.

[olp73]

Thank you for the tips! I am learning every day.

I am pretty sure that I can fix the gas block issues. I bought the parts I did because I thought they were of high quality and with a good track record. Are there any known problems or compatibility issues with this part combination? For example between the barrel nut and the handguard?

How much space do I need from the gas block to the handguard to be sure that the barrel is free floated?

[R112mercer]

The Troy handguard is designed to clamp to a milspec barrel nut. You don't need much room between the handguard and the barrel to be considered free floated, so long as the barrel cannot make contact with the handguard while firing or if you pull/push the handguard with your support hand. I re-read your first post & saw you re-used a DPMS barrel nut, just do an image search & make sure it looks like a milspec nut.

[olp73]

At least it looks like a mil spec nut…….

[StealthyBlagga]

If you have a solid bench vice, an action block and a barrel wrench, I would recommend removing that handguard, gas block and barrel nut, and then reinstalling everything yourself so you can be sure it is done right.

For the barrel, you don't need a torque wrench; apply grease to the receiver threads, insert the barrel, tighten the nut firmly, loosen the nut again, tighten again, loosen again, then tighten one last time so that the next notch in the nut aligns perfectly with the gas tube hole of the upper (this may take substantial force). Looking from the muzzle, the gas tube hole in the upper receiver should look like Mickey Mouse, if that makes sense.

For the handguard, the Troy system is kind of a pain IMHO. I just installed one on a friend's JP barrel with Thermal Dissipator. Let me tell you, that was a HUGE challenge because of the limited clearances... the instructions as written were almost useless. I can imagine that if the barrel were a little too thick in front of the barrel nut, the handguard would not be very secure. You need to be sure all of the "collets" are in the proper place. There was also not as much clearance between the handguard and the bottom of the gas block (he was using a Midwest Industries non-adjustable low profile block with an adjustable gas key).

For the gas block, the hole in the block should be larger than the gas port in the barrel. Just remove the gas block, measure the distance from the edge of the block to the center of the gas hole, and measure the same distance on the barrel (shoulder to gas port center), and do your calculations... not rocket science. Either the gas block will go right up against the shoulder, or there will be a gap about the thickness of the GI handguard cap (~0.030" IIRC) - depends on the gas block design. As for side-to-side alignment, put pencil marks on both the barrel and gas block in line with the respective holes, then line up the marks during install.

I have assembled many many uppers over the years using the simple approach above, and haven't lost a patient yet

You can check the clearance between the handguard and gas block by flexing the barrel. More clearance is better. If you think it might be making contact during live fire, apply a thin layer of modeling clay (plasticine) in the suspected area and see if it gets indented. If so, either get grinding or get a new gas block and/or handguard.

Edited June 6, 2016 by StealthyBlagga

[olp73]

……..yesterday I measured absolutely everything 3 times from every thinkable angel. I cannot find any irregularities of any kind. Barrel is straight. Barrel nut seems to have even dimensions. I was also looking for burs. Could not find any.

I am heading towards a Troy rail out of spec.

[olp73]

I ended up with a JP XL MKIII handguard with a full top rail..............feels good, looks good.

[dauntedfuture]

I have a few HGs that mount the same and or are similar to the troy alpha. with several of them the barrel is not exactly centered inside of the handguard. The JP rails are very rugged and I think you will like them even if they are a little heavy. I hope you have solved your problem. You might want to buy a wrench when you can, like someone said, a wrench, vice and upper blocks are not expensive and swapping a barrel is easy.

[olp73]

I have a few HGs that mount the same and or are similar to the troy alpha. with several of them the barrel is not exactly centered inside of the handguard. The JP rails are very rugged and I think you will like them even if they are a little heavy. I hope you have solved your problem. You might want to buy a wrench when you can, like someone said, a wrench, vice and upper blocks are not expensive and swapping a barrel is easy.

Tanks, I think so too. On the JP barrel nut there are actually 4 set screws for centering the barrel in the hand guard. So, I guess this is a known issue.

[eddiegunks]

check your scope mount. make sure it is tight on the rail as well as on the scope itself.