DD Lite Rail 12 (AR-10) for DPMS LR-308

[federalist22]

Has anyone tried to remove a DPMS free float tube and replace it with a DD Lite Rail on a LR-308 (AR-10)?

I have a DPMS LR-308 24" heavy SS barrel with a DPMS free float tube (polycarbon or something) and plan to remove the standard DPMS tube and replace it with the DD Lite Rail 12. I bought the DD AR10 Lite Rail Barrel Nut Wrench, the LR-308/AR-10 Free Float Wrench, and the DD Lite Rail 12 (AR-10 for DPMS).

First, am I missing any relevant tools or parts?

Second, is this a gunsmith job or a DIY?

I can do most things, like install a piston retrofit kit, etc., but a barrel nut job might be more than I want to mess with to get it right.

[John Hwang]

Looks like you have everything you need. You have an upper block to lock the upper in place I assume? Let me know if you have any questions during the install and we can walk you through it. It's also nice to have a torque wrench to torque the DD LITE barrel nut. Since the DD nut doesn't have to align to the next gas tube hole like most barrel nuts, you can be exact with the proper torque. I like running 50lbs of torqu on my DD barrel nuts. You actually only need about 35lbs but I find 50 to be secure but not over tighted.

[Stickman]

I can do most things, like install a piston retrofit kit, etc., but a barrel nut job might be more than I want to mess with to get it right.

If you can play around with pistons, you can swap out the rail without any trouble. If you haven't taken a look at the DD Lite rail install guide, you might want to check it out.

Once you start it, if you have any questions, you can always post them here. I'll help out however I can, and I know other people will as well.


DD LITE RAIL INSTALL GUIDE

[federalist22]

Thanks guys. My DD rail is in shipment right now. I do not have an upper block, but I can probably find and order one.

I assume you are talking about this one: http://www.dpmsinc.com/store/products/?prod=600



Do you think it's an at-home job? I have never removed a free-float rail or a barrel nut for that matter. I assume the DD rail comes with instructions, but I would need advice on how to remove the DPMS tube. I assume I need to remove the gas block/tube too.

Here's a pic before I get started.

[federalist22]

I have removed the gas block/tube on my rifle (last post). To get the DPMS tube in the pic above off, I know I have to secure it in a receiver claw/block, and I have a LR-308 free-float tube wench, but how do I go about getting that wrench in there. I mean, do I first apply heat (to loosen any loc-tite equiv) and then use a strap wrench to loosen the tube first to get the tube wrench in there to unthread it? I assume the tube is secured to a barrel nut of some sort, right? Any assistance is greatly appreciated. Thanks.

I don't think I'll have any problem installing the DD rail.

[federalist22]

Alright, so everything was going good on this modification until I installed the DD Lite Rail.

The DD Lite Rail 12 is too long for the picatinny gas block seen in the picture above. The gas block is fixed to the bull barrel with two allen-head screws that secure into two corresponding dimples in the underside of the barrel. The lite rail prevents the gas block from being positioned by about 1/4", which blocks the gas tube/gas escape hole on the barrel from lining up. Ouch. Guess I need a new gas block that doesn't impede the rail.

Any thoughts?

[Stickman]

Is the Lite rail secured all the way? Check to see if there is a difference in length between your old and new rail. The Lite rail should fit without any problem.

[federalist22]

Unfortunately, I had to fly to Denver on business today, so I don't have the rail with me.

Yes, I secured the rail completely and went to slide the gas block w/ tube back in and ran into the problem.

My .308 DPMS bull barrel has a rim on it just aft of the set screw dimples that the gas block rests against and the rail caused it to be about 1/8th of an inch (not a 1/4 like I said earlier--error). The rail is hitting the picatinny top of the block. I will match the sizes up, old tube and new rail, when I get home at the end of the week. Wondering if a low-pro block would solve it. I am not tied to the factory gas block and was going to call Rainier tomorrow about this Stage piece: http://www.rainierarms.com/?page=sho...roduct_id=1307.

[Stickman]

If you are bored, you could also chop the rails down off your existing gasblock and save a little money. If you go that route, spray it with high heat/ ceramic header paint and drop it in the oven to cure for a good looking and durable finish.

[federalist22]

I saw a thread on that in another forum site--I would have to buy tools to do that, so I think I should just get a low-pro block. I'll see what Rainier says for suggestions. Thanks for the help though. Other than an ill-fitting gas block, the DD Lite install is easy--just a lot of small allen wrench turns--patience.

[Stickman]

There certainly is a lot of twists with the allen wrench to get it locked down. The shops I know use a long bit to get them tightened, then wrench the final turns by hand.

[federalist22]

Stick,

After calling Rainier last week and talking to a rep, it was suggested that I examine the shoulder on the barrel at the gas port to see how the rail rides (lined up or out over it). The DD Lite Rail 12 (AR-10) extends out over the shoulder of the DPMS 24" bull barrel by about 1/8", which prevents the standard DPMS picatinny railed gas block (.936" inner diameter for bull barrel) from seating properly. Rainier suggested that if the rail does go out over the shoulder then to look at a low-pro gas block like a PRI that would fit inside of the DD rail.

To get around this problem, I ordered a PRI low-pro gas block in .936" and will migrate the gas tube to it, hoping to complete this modification. I hope the PRI block fits. I will post notes and pics upon completion once the new gas block arrives from Midway USA. Thanks for the tips (Stick and Rainier reps).

[gotm4]

It's been awhile since I've looked at the directions for the Lite Rail but IIRC the torque they specify was 55-75ft lbs. I torque 5.56mm Lite Rail nuts to 70ft lbs and .308 Lite Rail nuts to 75ft lbs.

[federalist22]

I torqued it, but it didn't make up for the 1/8" overhang of the rail over the shoulder on the barrel aft of the gas port. The rail is solid on the rifle now and I am planning to install the PRI block when it arrives on the 26th. Hopefully it works, or I will be a very unhappy DD Lite Rail owner--nothing else to put it on, so I will have to eat it.

[Stickman]

In an absolute worst case scenario, you could mod the rail and grind/ cut it back the small amount needed. A little Alumablack, and you would be good to go.

You could also chop the block back a bit in the needed area.