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Discussion Starter #1 (Edited)
1) When reattaching/mounting the barrel and tighening the barrel nut, is there any need to align the bbl's chamber with the receiver/bolt ? Any need to recheck headspace with a go/no gauge ?

Seems to be a couple of ?details?that no one mentions/ are left out of , AR 15 upper receiver/bbl/rail assembly/install videos on youtube? Seems to me like something needs to be closely aligned ? Or does close tolerances of upper receiver's bore and bbl/bbl nut already take care of this ? Because I haven't found anything telling me to the contrary, I presume is it "self aligning" ? Seems like a sorta loose fit to me..... To me this just seemed like a good "stupid question" to ask before attempting to fire the rifle.........
Safety 1st and all , ya know...

Now, I followed ALG Def.'s V-2 EMR , Ergonomic Modular Rail's supplied install instructions to the letter, and watched ALG's install video, both several times over. As far as I can tell, I followed them to a "Tee". Yet I have a 21.5 thousands gap between the end of the V-2 EMR rail and the AR556's upper receiver. I called Geissele, and their Rep. says that it IS within their accepted tolerances. I could live with it if I had to but.......it sure would suit me better for both ends to meet and be 100% flush.

2) My question is : Is there anything I can do to lessen, or completely make this "gap" dissappear?

3) Would doing the "accurrizing" step of lapping the end face of the receiver's 'threaded snout" where the bbl nut threads on , make this gap disappear ?
I saw a video where they use a specially machine tool that slides into the upper like the BCG, but has a "ledge" to enable one to lap the face of the upper's threaded snout as they usually are not machined 100% true but are often left at a very, very slight slant (/) I wondered if this lapping would close this gap?

FWIW, I installed the V-2 rail 1st, because it's held to bbl nut by 6 screws and it's easy to remove.No loosening of bbl nut required. Therefore I have NOT yet dimpled the bbl nor mounted the gas block and gas tube.

Pics below:





 
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The barrel/extension assembly and the bolt control headspace. The upper just lines them up.

Squaring up the upper receivers thread face would certainly help. Proper torque is critical as well.

I suspect Geisle has run into all kinds of uppers ranging from the premium Colt, FN, KAC, Daniel Defense to Fred's, garage variety - thus the gap.

AC
 

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The receiver extension fits into the upper receiver. The receiver extension to barrel fitment controls the headspace and is done when the vendor mates the two parts. You need to make sure it is fully seated into the upper receiver but that should be ok if you are torquing the nut the. Backinboff and torquing it again as is the proper procedure. The gap between the handguard and upper receiver has nothing to do with headspace and is likely just tolerance in their machining. I suppose you could remove some material off of the receiver or maybe even the barrel but if you can and there are no other instructions but you need to make sure any modifications do not prevent you from properly torquing the nut down.
 

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The torque on an AR barrel nut is between 30-50 ft lbs. The barrel extension has an alignment pin on it that fits into a mating notch on the upper receiver. I usually torque my barrels to 30 ft lbs and then see where I am as far as gas tube hole alignment. If it is just off but requires a little more torque to align then I apply a little more and align the gas tube hole. The alignment of the gas tube is critical and it must be perfect as the tube must be straight to line up with the gas key on the bolt carrier. Head space is best checked with the bolt in hand and the barrel not yet mounted. I just do this by hand using a go\no-go headspace gauge.
In your case by looking at the pictures it looks like your free float tube with the rail is mounted to the barrel nut with the 6 screws---instead of trying to shave a small amount off of the front of the upper receiver you could just slightly elongate the screw holes in the free float tube to allow it to set back .021 which would close your gap. I would not mess with shaving the receiver front. These receivers are pretty accurate with modern CNC machining and if it is a reputable brand it will follow Mil Spec.
 

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Discussion Starter #5 (Edited)
The torque on an AR barrel nut is between 30-50 ft lbs. The barrel extension has an alignment pin on it that fits into a mating notch on the upper receiver. I usually torque my barrels to 30 ft lbs and then see where I am as far as gas tube hole alignment. If it is just off but requires a little more torque to align then I apply a little more and align the gas tube hole. The alignment of the gas tube is critical and it must be perfect as the tube must be straight to line up with the gas key on the bolt carrier. Head space is best checked with the bolt in hand and the barrel not yet mounted. I just do this by hand using a go\no-go headspace gauge.
In your case by looking at the pictures it looks like your free float tube with the rail is mounted to the barrel nut with the 6 screws---instead of trying to shave a small amount off of the front of the upper receiver you could just slightly elongate the screw holes in the free float tube to allow it to set back .021 which would close your gap. I would not mess with shaving the receiver front. These receivers are pretty accurate with modern CNC machining and if it is a reputable brand it will follow Mil Spec.
FWIW valve lapping compund is used "to lap in" the edge to a special shoulder tool. haven't priced the tool yet though. Likely $100.00 or more easily. Works on same principle as Geissele Reaction Rod as in, it's machined to fit in the upper's bore and then the other large shouldered end butts against the edge of threaded snout. A video of it on youtube. Look to me to be a great idea. Looks like a thousandths or less of "lapping" is required to face it off 100% flat.

About elongating the holes...I thought about that as well. Only thing is the 6 holes in the rail are "relieved" in a somewhat countersunk way, into the rail, but not quite like "a normally countersunk hole" is. This is needed because ofthe raised ridges when metal is extruded/machined into the OD of rail which would not let the button head screws sit flat otherwise. The "raised stripes on the rail's metal act as a handgrip enhancer.. The holes have been "flatbottomed countersunked with no taper" and extends out to the outer diameter of the hole which matches OD of screw's flat-bottomed buttonhead screw.

This due to the stripes of "ridges" made into the aluminum of rail when extrudeding the stock and for screws's bottom to sit flush on the rails metal.. The screws are not countersink screws. And the "flat countersinks" will have to be recut in direction of movement, which then leaves a uncovered portion of theholeshowing. So, enlarging this type of hole will only make yet another "unsightly & unappealing appearance problem" via scratched up anodizing if "done by hand" , and I'd need a Bridgeport and an end mill to do it right. Neither of which I have....and it'd cost more to have it machined than the rail cost me, no doubt.

I think the gap would "look better" than U shaped holes with the anodizing scratched off in the unused portion of the elongated holes. ..so maybe only alternative is to face off the snout's face??

Also, these rails come with a "proprietary wrench". No torque wrench , nor ft/lb torque reading required. (see video below) .

The wrench has markings which determine/tell you which shim/shims are required and then when the nut's distance to align gas tube and rail's piccatny with upper's, arrives you're at the correct torque of @ 45 ft./lb. according to Mr. Geissele. Watch the ALG video on youtube. Using a 12" Adj. wrench or a 15/16th open end wrench works much better than "1" pipe" he uses.

Pics will help you understand why/better about the holes more than my description most likely. See what I'm referring to? I may just have to be satisfied with it "as is". EMR Install Video Link>:








 
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Question #1. The pin on the barrel slides into the receiver slot in the upper, this is properly aligned. Some barrels fit tight and others more loose. I've had some that dropped right into the upper like they were greased, and others I had to tap tap into the upper to get the barrel ring flush onto the upper.

Question #2. Honestly man, there isn't a dang thing wrong with what you have there. All AR's have a little gap in between the upper rail and the hand guard rail. Just line them up nice and even. Done. You can shim or remove shims from the barrel nut to get a perfect alignment if needed, I think I have only shimmed 1 AR barrel nut in all the ones I have built.

You really cant fit anything much until you get the gas block on and gas tube through your nut or holes or space and into your upper. Once you have all that tight and complete, then you can toy with the hand guard, all depending on the hand guard and nut style.

If that gap really annoys you, elongating the holes just a touch is likely the best answer. I don't think it would show much...but personally i would live with that tiny gap... that every AR has and roll on.

DR
 
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Discussion Starter #7 (Edited)
Question #1. The pin on the barrel slides into the receiver slot in the upper, this is properly aligned. Some barrels fit tight and others more loose. I've had some that dropped right into the upper like they were greased, and others I had to tap tap into the upper to get the barrel ring flush onto the upper.

Question #2. Honestly man, there isn't a dang thing wrong with what you have there. All AR's have a little gap in between the upper rail and the hand guard rail. Just line them up nice and even. Done. You can shim or remove shims from the barrel nut to get a perfect alignment if needed, I think I have only shimmed 1 AR barrel nut in all the ones I have built.

You really cant fit anything much until you get the gas block on and gas tube through your nut or holes or space and into your upper. Once you have all that tight and complete, then you can toy with the hand guard, all depending on the hand guard and nut style.

If that gap really annoys you, elongating the holes just a touch is likely the best answer. I don't think it would show much...but personally i would live with that tiny gap... that every AR has and roll on.

DR
Mine required the 2nd thinnest shim pack already. So I got kinda lucky there because it just worked out that way . The thinnest set is too thin to get any torque and the two pics rails, would go past their alignment. I tried them to see.....I tried all 3 sets just to see, but didn't do final torque thing. Wasn't needed to tell it wouldn't work. (I'm a curious,gotta see it for myself kinda guy)

Geuss it's either lap it or live with it...........the gap is hardly noticeable until you get right up on it to look closely.....acceting the gap is the cheapest way out right now. Maybe later on I can try lapping. I believe it'll work fine as it is now.
Actually the gap might be a "pro"or considered a "plus"....as the upper receiver and rail end aren't touching, so there will be just that much less bbl heat transfer to the upper, and also will allow the rail to cool slightly quicker/dissipate it's heat quicker , when hot....??
 

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Removing material from your threaded upper would likely close the gap.

Would I do that?

Never.

DR
 
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I see what you mean on the countersunk holes on the tube. Still looks okay with the small gap.
 
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I run the ALG rails on several of my guns. Some have a small gap and that is not an issue. I’ve never had on off by much when using the shim packs. Be careful not to strip out the mounting screws as it’s very easy to do if they Ste out of alignment. I’ve started to chase them with a tap just to clean up the flash.
 

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Discussion Starter #11
I run the ALG rails on several of my guns. Some have a small gap and that is not an issue. I’ve never had on off by much when using the shim packs. Be careful not to strip out the mounting screws as it’s very easy to do if they Ste out of alignment. I’ve started to chase them with a tap just to clean up the flash.
The rail screw holes in the bbl nut are a "close thread", and has less clearances than ordinary threaded holes.... And I haven't seen close threads in yeeeears on anything mechancal. I thought it'd become a lost art. LOL. I am thrilled to see they were used! No movement at all.

I wiggled the rail to where all screws started easily, and then once they all were started, threaded each in a few threads at a time and go to the next. Until all were snug, and then snugged them a tad more. I just hope the screw's coating/finish does not begin to rust after a few heat/cool cycles.
 
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The rail screw holes in the bbl nut are a "close thread", and has less clearances than ordinary threaded holes.... And I haven't seen close threads in yeeeears on anything mechancal. I thought it'd become a lost art. LOL. I am thrilled to see they were used! No movement at all.

I wiggled the rail to where all screws started easily, and then once they all were started, threaded each in a few threads at a time and go to the next. Until all were snug, and then snugged them a tad more. I just hope the screw's coating/finish does not begin to rust after a few heat/cool cycles.
They should not rust. If they do, pull them and take a torch and hot blue them. Very easy to do. Larry Potterfield (Midway USA) has a great video on it.

DR
 

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0051CF6F-D57C-40CF-A7D3-9633BCA2C31E.jpeg The screws may rust a touch, mine did after going in and out several times. I put high temp grill paint on a tiny brush to touch up. If your rail makes a ting noise, you can add a few of the rubber key mod rail covers and it will deaden this. The solid rails I wrap with camo hoof wrap from TSC. The Mlok rails I add 3 magpul type 1 for grip and sound deadening. I haven’t put all my screws back in since switching rails around.
 

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Discussion Starter #14 (Edited)
View attachment 760251 The screws may rust a touch, mine did after going in and out several times. I put high temp grill paint on a tiny brush to touch up. If your rail makes a ting noise, you can add a few of the rubber key mod rail covers and it will deaden this. The solid rails I wrap with camo hoof wrap from TSC. The Mlok rails I add 3 magpul type 1 for grip and sound deadening. I haven’t put all my screws back in since switching rails around.
I purchased a few of them thar "slot fillers" too..... Magpul M-Lok Rail Cover Type 1 in Black, and Type 2 in FDE, OD, BLK, & Grey so I can stagger them into a camo pattern/change colors at will.

But I haven't put 'em on yet as I'm playing with the mtg. location of the Magpul M-Lok AFG and Magpul AFG-2 (picatinny rail mounted". Also have a Knight's Armament "KA Forward Pistol Grip", because I got it on sale at Brownells a while back & price was so cheap I couldn't turn it down. Not sure if I'll like as I haven't installed it yet either. I figure the "redundant" items I don't use now, will work on another AR later , as I want a AR (LR?) in .308 WIN too later on..

I finally got time to assemble the rifle tonight. LPGB is mounted as is gas tube and slid rail back on tightened the 6 screws. Gap is a tight 21 thousandths of an inch now.... I lost a thou. LOL. OLIGHT light is on, AGF-1 is on for now. I'll fire it tomorrow some and see what works best for me....
 
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