LR308 Build

[James Moore]

Just a little LR308 I put together a while back.
Might get to the range soon to see if it will punch holes in paper targets.

Broken Armory 80 lower.

Strike industries enhanced lpk.

BA Melonite gas tube.


Superlative Arms Adjustable Bleed Off Gas Block.

CMC SS 3.5 lb trigger.

Strike industries ultimate dust cover.

Aero upper.

NBS dual ejector bcg.

Odin Works O2 Lite AR-10 M-LOK Forend - 15.5".

VG6 Epsilon 762 Muzzle Brake.

Armaspec smb.

Strike Industries Enhanced Pistol Grip.

Luth Ar MBA 1 rifle stock.

Faxon pencil 18" barrel.

Athlon Optics Argos BTR Gen II 6-24X50mm Rifle Scope

 

[USApat]

Nice build! All of yours typically are!

But, ha ha!
I'm building a 308 and not sure when it will be completed. It's the last one on the list, but I have a lot of the parts to build thhis same rifle. Same lower, same upper (however I'm looking for a raw version which is sold out everywhere), same stock, same trigger. I haven't decided on a hand guard, or barrel yet. Looking for a lightweight raw hand guard and if I find one, I will opt for a carbon and stainless barrel. No decision yet on optic.

Broken Armory's AR 15 lowers are very nice for anyone that's looking for a good lower with all the features. I wish their 308 was sculpted and cut like their smaller AR15.

 

[James Moore]

Nice build! All of yours typically are!

But, ha ha!
I'm building a 308 and not sure when it will be completed. It's the last one on the list, but I have a lot of the parts to build thhis same rifle. Same lower, same upper (however I'm looking for a raw version which is sold out everywhere), same stock, same trigger. I haven't decided on a hand guard, or barrel yet. Looking for a lightweight raw hand guard and if I find one, I will opt for a carbon and stainless barrel. No decision yet on optic.

Broken Armory's AR 15 lowers are very nice for anyone that's looking for a good lower with all the features. I wish their 308 was sculpted and cut like their smaller AR15.

Yes, Broken Armory makes a nice lower.
I tried to stay as light as I could without spending far more.
I know many people don't like the pencil barrels because they get hot faster, but I don't plan on using this for sustained fire. It should do nicely for what I want and it was the lightest without going with carbon fiber. Same thing with the handguard, the Odin Works O2 is as light as it gets in aluminum.
I may eventually get a JP Enterprises Low Mass BCG for it, because I've got another 308 planned with a Skeletonized lower from 80Lowers, so I may use this bcg for that. I've got a Tiger Rock low profile upper for it and another Odin Works handguard.

 

[Harold]

Aero upper. Faxon pencil 18" barrel.

What kind of fit do you have between the barrel extension index pin and the corresponding slot in the upper receiver? (In my upper build there's a little more slop there than I'd like to have).

BA Melonite gas tube.

Odin Works O2 Lite AR-10 M-LOK Forend - 15.5".

I looked at the Ballistic Advantage web site and the only melonite "rifle length" gas tube I see there is 15.125" long, so I'm assuming that this is the one you have, which is apparently intended for use in both an AR-15 and an LR-308.

I'll be interested to find out if you have any cycling issues using this gas tube, as I've seen comments on other forums where some people have apparently had problems which were attributed to the 15.125" gas tube being a little too short for an LR-308. (You may not have cycling issues with a Faxon barrel, as their gas port diameters may be a little bigger than those of most other .308 manufacturers' barrels, and this may compensate for the slightly shorter gas tube).

As of right now I may use an Anderson "AM-10" gas tube I have which is 15.5" long. What I don't like about the Anderson gas tube is that it is bent the same way that an AR-15 gas tube is bent, even though there are differences in the geometry between an AR-15 upper assembly and an LR-308 upper assembly. (See attached picture below).

In my experience, this may or may not be much of an issue, depending in part on the design of the barrel nut. What bothers me is that gas tube manufacturers generally don't tell you how their LR-308/AR-10 gas tubes are bent and many handguard manufacturers don't give much information on the barrel nut they're using; sometimes not even a picture.

I'm wondering: Does the barrel nut that comes with the Odin Works handguard that you're using play nice with the gas tube you've got? Does the barrel nut have to be timed? (As I understand it, some manufacturers' handguards come with barrel nuts that don't have to be timed. I would like to find one of these, but details are hard to come by).

 

[James Moore]

What kind of fit do you have between the barrel extension index pin and the corresponding slot in the upper receiver? (In my upper build there's a little more slop there than I'd like to have).



I looked at the Ballistic Advantage web site and the only melonite "rifle length" gas tube I see there is 15.125" long, so I'm assuming that this is the one you have, which is apparently intended for use in both an AR-15 and an LR-308.

I'll be interested to find out if you have any cycling issues using this gas tube, as I've seen comments on other forums where some people have apparently had problems which were attributed to the 15.125" gas tube being a little too short for an LR-308. (You may not have cycling issues with a Faxon barrel, as their gas port diameters may be a little bigger than those of most other .308 manufacturers' barrels, and this may compensate for the slightly shorter gas tube).

As of right now I may use an Anderson "AM-10" gas tube I have which is 15.5" long. What I don't like about the Anderson gas tube is that it is bent the same way that an AR-15 gas tube is bent, even though there are differences in the geometry between an AR-15 upper assembly and an LR-308 upper assembly. (See attached picture below).

In my experience, this may or may not be much of an issue, depending in part on the design of the barrel nut. What bothers me is that gas tube manufacturers generally don't tell you how their LR-308/AR-10 gas tubes are bent and many handguard manufacturers don't give much information on the barrel nut they're using; sometimes not even a picture.

I'm wondering: Does the barrel nut that comes with the Odin Works handguard that you're using play nice with the gas tube you've got? Does the barrel nut have to be timed? (As I understand it, some manufacturers' handguards come with barrel nuts that don't have to be timed. I would like to find one of these, but details are hard to come by).

I got the gas tube from ar15discounts, but I imagine it's the same one you looked at.

I didn't measure it, but it fit fine and it has the same bend in it as other gas tubes. Cycled great after I realized that the Superlative gas block is closed to begin with, lol. Once I opened it up it was cycling fine.
They claim the Melonite is better for this and that reason, but honestly I got it simply for the black coating. Didn't want a shiny gas tube.

The barrel and upper fit good. The setup on the handguard is an adapter that screws onto the upper and the barrel nut into the adapter. The adapter covers the alignment pin, so can't see how much slop is there, but it felt tight and passed the go no go testing, so I'm sure it's gtg.

The handguard also comes with a pin to align the gas tube holes on the upper and adapter, so no timing involved, just crank it down to the 50lbs Odin Works recommends.
Everything on this build really fit together nicely. I am surprised that I didn't have any hiccups.

 

[Harold]

Good for you that your rifle had no issues.

About six years ago or so a friend of mine bought a new DPMS LR-308 variant from Gander Mountain, and I went with him to the range the first time he fired it. He had a box of Winchester M80 ammo and the rifle would not cycle properly with this ammo. IIRC it was acting like it was under-gassed.

I don't know whatever happened with that particular rifle but after that experience I put the idea of building an LR-308 type rifle on hold until recently. I thought that by now (about six years later), some of the issues underlying such problems would be worked out. But apparently not, as I'm finding out lately.

Not only have I encountered an unexpected amount of poor quality/improperly manufactured parts, but in many cases it's hard to find what you're looking for because manufacturers seem reluctant to provide basic information about their products, e.g., barrel gas port diameter, mechanical details of handguard barrel nut and associated hardware, gas tube specs. (is it bent for an AR-15 or an AR-10/LR-308?), etc.

I sent my defective gas block back to YHM (the roll pin hole was drilled off center by over 0.008," making it impossible to install the roll pin) and they replaced it with one which was much better (pin hole was within 0.002" of center), but then when I installed the Anderson gas tube, I found that the roll pin hole in the tube, while on center, was not perpendicular to the gas port but was off (rotated) by about five to seven degrees or something like that. And the Windham Weaponry gas tube had the same issue but was even a little worse. Also, neither of those two gas tubes was properly bent for an AR-10/LR-308.

Because of this I recently ordered yet another gas tube, but this time I got an actual AR-10 gas tube manufactured by Armalite, and when I installed it I found that not only was the roll pin hole properly oriented but the tube was actually bent properly for an AR-10/LR-308. So the moral of the story is this: for anyone putting together an AR-10/LR-308 upper assembly, consider using a gas tube manufactured by Armalite.

 

[USApat]

, consider using a gas tube manufactured by Armalite.

Thanks for your input. I've yet to tackle the LR-308, but mine is DPMS. Are you saying to use the Armalite gas tubes with the DPMS upper?

I realize the primary differences of the DPMS and Armalite uppers are the handguard rail heights and the sculpting and profile CNC cuts where the upper mates to the 308 lower. But, I'm curious if this will affect which gas tubes I use. Thanks for your input.

 

[Stephen G]

The gas tube length is either large frame caliber or small frame caliber.
From what I gathered is that while 10million gazillion proprietary parts in 308/large frame arena. There are (some resemblance of) A standard to gas lengths.

 

[Viking2721]

Yes, Broken Armory makes a nice lower.
I tried to stay as light as I could without spending far more.
I know many people don't like the pencil barrels because they get hot faster, but I don't plan on using this for sustained fire. It should do nicely for what I want and it was the lightest without going with carbon fiber. Same thing with the handguard, the Odin Works O2 is as light as it gets in aluminum.
I may eventually get a JP Enterprises Low Mass BCG for it, because I've got another 308 planned with a Skeletonized lower from 80Lowers, so I may use this bcg for that. I've got a Tiger Rock low profile upper for it and another Odin Works handguard.

Well Damn bro. After the load I received last week I told myself no more guns for a bit, but after looking at that skeletonized lower, and seeing its an 80% Im gunna hafta say no more guns for a while....after this one!

 

[Harold]

Thanks for your input. I've yet to tackle the LR-308, but mine is DPMS. Are you saying to use the Armalite gas tubes with the DPMS upper?

Yes, the gas tubes are the same - or at least they should be the same if the DPMS LR-308 is to be built properly IMO. What I mean by "properly" has to do with what I believe is the optimal engagement of the gas tube with the bolt carrier key (but take everything I say with some salt because my OCD is raging when I do projects like this).

In the above picture (on the top) is shown an AR-15 upper with an AR-15 gas tube; underneath is an Aero M5 upper with a Faxon 20" barrel with an AR-15 "rifle length" (15.125") gas tube installed (not that it matters but I think it is an "AR-Stoner" tube from Midway). Note the position of the end of the gas tube in each case relative to the bolt cam pin cutout area.

In this picture, an Armalite AR-10 15.5" gas tube has replaced the AR-15 15.125" gas tube on the Aero M5 upper with Faxon barrel. Note that the end on the gas tube is now approximately in the center of the bolt cam pin cutout area, just like the AR-15.

In this (poorly focused) picture, the Armalite AR-10 gas tube is on top and the AR-Stoner AR-15 rifle length gas tube is on the bottom. It's kind of hard to see in this lousy picture, but on the right hand side of the bent area the tubes are touching all along the length, whereas on the left hand side of the bend there is a small parallel gap between the tubes; a gap which apparently corresponds to the approximate 0.062" (or whatever it is) greater distance between the barrel and gas tube bores on the M5 upper receiver. (I believe the AR-Stoner gas tube would be representative of all AR-15-bent gas tubes in this comparison).

So the Armalite tube enters the M5 upper parallel or very nearly parallel to the barrel and carrier key compared to the AR-15-bent tube, which enters at a slight upward angle. This may not be a big deal in practice but because of my OCD and because I want to use a Magpul or an A2 type handguard on this rifle instead of an aluminum free floating handguard (which means I have to use the DPMS type barrel nut), I believe the Armalite AR-10 gas tube may be the way to go.

 

[Harold]

BTW here's a link to the Armalite AR-10 gas tube if anyone is interested in this part:

Armalite AR10 Rifle Length Gas Tube 10007010 Armalite Parts | EveryGunPart.com

AR10 Rifle Length Gas Tube MPN: 10007010 UPC: 651984106587 Specifications: Caliber: .308 Overall Length: 15 – ½”

everygunpart.com

 

[USApat]

Yes, the gas tubes are the same - or at least they should be the same if the DPMS LR-308 is to be built properly IMO. What I mean by "properly" has to do with what I believe is the optimal engagement of the gas tube with the bolt carrier key (but take everything I say with some salt because my OCD is raging when I do projects like this).

View attachment 12628

In the above picture (on the top) is shown an AR-15 upper with an AR-15 gas tube; underneath is an Aero M5 upper with a Faxon 20" barrel with an AR-15 "rifle length" (15.125") gas tube installed (not that it matters but I think it is an "AR-Stoner" tube from Midway). Note the position of the end of the gas tube in each case relative to the bolt cam pin cutout area.

View attachment 12629

In this picture, an Armalite AR-10 15.5" gas tube has replaced the AR-15 15.125" gas tube on the Aero M5 upper with Faxon barrel. Note that the end on the gas tube is now approximately in the center of the bolt cam pin cutout area, just like the AR-15.

View attachment 12631

In this (poorly focused) picture, the Armalite AR-10 gas tube is on top and the AR-Stoner AR-15 rifle length gas tube is on the bottom. It's kind of hard to see in this lousy picture, but on the right hand side of the bent area the tubes are touching all along the length, whereas on the left hand side of the bend there is a small parallel gap between the tubes; a gap which apparently corresponds to the approximate 0.062" (or whatever it is) greater distance between the barrel and gas tube bores on the M5 upper receiver. (I believe the AR-Stoner gas tube would be representative of all AR-15-bent gas tubes in this comparison).

So the Armalite tube enters the M5 upper parallel or very nearly parallel to the barrel and carrier key compared to the AR-15-bent tube, which enters at a slight upward angle. This may not be a big deal in practice but because of my OCD and because I want to use a Magpul or an A2 type handguard on this rifle instead of an aluminum free floating handguard (which means I have to use the DPMS type barrel nut), I believe the Armalite AR-10 gas tube may be the way to go.

@Harold
Thanks for showing this detail. For me, the cost for the Armalite gas tube is so cheap, it won't matter to me if it doesn't work. It's worth trying just to rule out some potential issues and save some unnecessary grief. I don't know when I'll finish the 308, but I'll try and add that tube to the equation.

I just wish Aero Precision would replenish their raw, bare aluminum 308 upper. They have been out of stock for almost two years or more now. I called them and they were mum and not really forthcoming if they would ever release them again in raw form. It would appear it would be an easy thing to do if they actually make their own uppers and coat them in house. Just leave ten or twenty on a run for raw inventory and I bet they would disappear.

Thanks again for the post and follow-up!