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Thread: #&%@*%$!!!! Question on DPMS .308 upper rail height...

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    #&%@*%$!!!! Question on DPMS .308 upper rail height...

    So I bought a new DPMS assembled .308 upper with charging handle and FA from Midway a few months ago for my AR-.308 build. I have been buying pieces here and there and today found a screaming deal on a Troy .308 TRX battle rail (with "low" top rail). These are made in a "low height" rail and a "high height" top rail versions as appearently DPMS changed their rail height on the uppers some time in 2009. So I have assumed that I had a "new" version with the "low" top rail height since I just bought it. On the Troy website it shows how to measure and see if it is 1/8" thick (above the charging handle) or 3/16" thick. I figured I would measure it just to confirm before I ordered the Troy rail and WTF? It is not 1/8" or 3/16"! In fact it falls right between the two on my tape measure. So I got out my calipers and measured it and it is 0.168" which is a little more than half way between 1/8" (0.125") and 3/16" (0.1875"). So WTF rail height am I supposed to use or am I fucked either way?

    If someone has a Troy .308 TRX rail and knows if it is the high or low version top rail, can you please measure your upper (with calipers) as it shows in the troy website (link above) and tell me what I should use? How does your rail match up?

    Thanks!

    I also just noticed that the upper is stamped with a "DT" with a dot over the "D" and a dot over the "T" on the bottom of the rear lug (that would face into the lower receiver when assembled). The charging handle is also stamped "DT" on the flat up by the tip/gas tube opening (also facing the lower when installed). Is this really a DPMS upper? (or just DPMS compatible?)
    Last edited by Luky; 08-22-2013 at 03:11 PM.

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    If it is a CURRENT PRODUCTION model LR-308 upper (which it likely is because Midway buys direct from DPMS), then it has to be the lower profile model upper (unless its a blem or something that got outta QC when it shouldn't have). Every LR-308 flattop upper made by DPMS since ~08/09 has been the lower model. I don't have a lo-pro DPMS upper to measure for you, nor can I explain the difference in measurements you are getting, but I'm betting the lower version is what you'll want/need despite a slight discrepancy in the numbers.

    For anyone looking for the measurements and can't see the linked pic above too well, the rail height is measured using calipers or a mic (or a ruler if you are a cheap @$$ ) and determine the thickness of the material at the rearward-most portion of the receiver rail (just above where the CH rests when locked into the receiver). The "low" model should be 1/8" while the high model is 3/16". The other way to measure is from the centerline of the bore to the top of the rail (1.253" on the low and 1.313" on the high). I know we're only talking about a 0.0625" difference, but it makes a big difference!

    Good luck, Luky! Shoot me a PM if you need me.

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    Thank you Bryce. I tried measuring from the front (barrel side) from the center of the firing pin hole in the center of the bolt (in the BCG) to the top of the rail with my calipers and get around 1.258" or so. I believe you are correct that this is the "low rail" version...

    Thanks again for your help!

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    Quote Originally Posted by Luky View Post
    Thank you Bryce. I tried measuring from the front (barrel side) from the center of the firing pin hole in the center of the bolt (in the BCG) to the top of the rail with my calipers and get around 1.258" or so. I believe you are correct that this is the "low rail" version...

    Thanks again for your help!
    Glad that trick worked for you. At 1.258" (roughly 0.005" off the "ideal" 1.253"), I'd say its definitely the low version that you need. Hang in there, brother!

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    And I got the Troy 13.8" TRX .308 rail ordered for $175+$10 shipping/insurance. Found it on Valhalla Tactical Supply...

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    Quote Originally Posted by Luky View Post
    And I got the Troy 13.8" TRX .308 rail ordered for $175+$10 shipping/insurance. Found it on Valhalla Tactical Supply...
    Holy smokin' deals! Can't beat that...that's at least $40 cheaper than I have seen them in stock lately.

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    That's why I couldn't let it get away. Cheapest I saw before this was $209 delivered. I am a shopper!

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    The original LR-308 came out in 2004. They later released the AP4 and SASS, which had a lower profile upper, with the forward assist crammed in behind the brass deflector. The LR-308 never even had an ejection port door, so it was like a Lo-Pro Classic on steroids. The .223 Lo-Pro Classic was out at least as early as 2002, for about $630 retail at the time, with a bull barrel, .936" aluminum gas block, CLGS, carbine free-float tube, A2 stock, and soft receivers. The gas blocks burn out on them, just like any aluminum gas block will on a CLGS, leading to short-stroking.

    Anyway, when I got an LR-260 Panther, it had the lower AP4 upper on it, but all the other components were like the .308 LR-308, as far as handguard and gas block go, but the BCG was phosphated. My original LR-308 has a hard chrome BCG.

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    new member here, would like to try and verify this.....I just purchased a SunDevil nickel Teflon or Devil Coat NT upper/lower set . the guy that sold it to me says he just got it three weeks ago, and its a dpms pattern, so when I measure the tang at the charging handle I get basically the same measurements as Luky above.
    .140 in the center where theres a groove, .158 on the sides of the tang which is no where near the .1875 of the 3/16" version,.
    so unless the SunDevil people tell me different[waiting on an email to them to see if they can verify] I am going with a low profile rail version.

    thanks for helping a newb [though I have built a AR15] so looking forward to this ..........

    doug hunt

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    Hey stingray,

    Not sure about sundevil, but it seems most aftermarket manufacturers have stayed with the old "high" rail.

    I know for a fact my two Mega uppers need a high rail to match the receiver rail.

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    Sting...

    The problem is that there is NO universally accepted, "mil-spec" for .308 uppers/lowers/etc. While I'm betting that your Sun Devil is a low profile based on the numbers you provided above, it may actually fall somewhere in between the higher and lower DPMS spec which will make sourcing a handguard/rail a royal PITA if you are wanting same height or something akin to a "monolithic" type top rail. I haven't gotten one in hand yet, but from the pics I have seen all over, the portion of the receiver just above where the charging handle rests when locked into place appears "different" to me than other designs/mfgs, including both the low and high DPMS specs.

    You might try making the alternative measurement that I recommended in one of my first posts above which is from the centerline of the bore to the top of the rail (should be 1.253" on the low and 1.313" on the high).

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    As a late follow up... The Troy "low" rail matches the DPMS upper almost perfectly. However I found that the bottom rail retainer block inside the front of the tube was touching my gas block (I chose Wilson combat as I needed a .936" with the adjustment screw in the front and this was the only thing I could find that met my needs). I wound up getting a PRI carbon fiber handguard that is an excellent piece of kit. I still needed to trim one of the rail retainer pieces under the top rail (shaped like a capitol "I" and I just cut it in half) and just leave 3 screws holding the rail but not a big deal to me. Also this PRI tube does have a top rail, but it is only on the front 1/2 so you don't have to worry about it lining up with the upper receiver.

    308 upper pic.jpgFranken-SASS.jpg
    Last edited by Luky; 01-19-2014 at 12:17 PM.

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    followup to my initial post, thanks for the help guys:

    well, I received the following reply from SunDevil [they are very fast at responding to emails] the "trouble" referenced was my question concerning a post I found online where there was interference with the bolt catch when the upper and lower were pinned together, but due to the age of my upper/lower manufacture I am in the clear "hopefully"

    from SunDevil email: Yes, we originally had trouble with a few .308 uppers but they have since
    been replaced. That was 3 years ago and the receiver set you were sold is a
    recent model. All of the uppers we make now have the 'new low' dpms
    profile.
    Hope this helps.

    Anita Beaty
    Phone: 480-833-9876
    Fax: 480-833-9509
    sales@sundevilmfg.com
    SunDevil Manufacturing - Custom AR-15 lower receivers, AR-15 parts and accessories
    Follow us on Facebook for current updates - www.facebook.com/SUNDEVILMFG

    as a follow up. I now have everything in hand except the rear stock/buffer/buffer tube/ and spring [its ordered and shipped, just not in my hands, and of course I am still on the fence as to what handguard to buy...

    here is my parts list:
    SunDevil "devilcoat" nickle boron upper/lower receiver set
    Anderson mfg BCG
    Rainier Arms Raptor AXTS ambidextrous charge handle
    DPMS lower parts kit
    Rainier Arms select 20" stainless steel barrel
    Wilson Combat adjustable low profile gas block
    PRI 308 muzzle brake [from Rainier Arms]
    5/8" x 24 accu washer alignment system [from Brownells]
    308 GO gage
    308 NO GO gage
    Magpul PRS stock
    A1 buffer tube
    308 rifle buffer
    308 rifle buffer spring
    kns anti rotating trigger/hammer pin set [if they will fit]

    I have a dpms 308 claw / a dpms 308 lower magwell vice block and I purchased the steel tool that engages the barrel extension[from Brownells] [when I built my 556 I was very uneasy trying to index the compensator with the crush washer]
    so I bought the accu washers to make it less stressful completing the muzzle brake install.

    I plan on changing my Daniel Defense M4 midlength rail on my 556[going to a 13.5 diamondhead VRS-T] so I bought the geissele tool for the 556 [better than the Brownells version] but out of stock for the 308 version

    I am right now leaning toward the Apex handguard......but I am on handguard #3 for the 556 build so I am agonizing over which one,[only want to buy one, haha] I contacted diamondhead as I read they were coming out with a 308 handguard but they responded quickly saying it would be at least three months before it was on the market
    Last edited by stingray230sx; 02-16-2014 at 08:38 PM. Reason: forgot something

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    here is the finished rifle.....I still got to get some optics, and also remove the extractor and check the headspace, but these poor iphone pics were taken last nite and this afternoon real quick............AR308 right side view 2.JPGAR308 roght side view on the vise 1.JPG
    AERO PRECISION AR15 [first AR build-DD M4 midlength quad rail/16" no name Douglas Barrels blank/LMT BCG/Battlelink stock]
    SUNDEVIL 308 NICKLE BORON UPPER/LOWER / Anderson mfg BCG/Rainier Arms 20" select barrel/Rainier Arms AXTS charging handle/Wilson Combat adjustable low profile gas block/Magpul PRS stock [waiting on me to decide on a handguard] [want a Diamondhead but they say 3 months, prob get a Apex ??]

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    I must have a real basturd then dpms upper .540 rail height.

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    measure the thickness of the part above the charge handle ... DPMS 308 A3 RECEIVER HEIGHT - 762AR.com

    troy & Midwest industries make both heights in a few styles
    savage MA-10 ruger kimber ford
    http://www.supermotors.net/registry/1445