DPMS Type High profile rail height

[guruofhotrod]

Ok, I bought an ODIN Works 15.5" 308 Kmod Forend : https://www.odinworks.com/308_KMod_Forends_p/f-15-km-308.htm

and specified that I have a high profile pattern upper (ares 308 billet DPMS type) upon receiving the rail I noticed it didn't

match the rail height on the receiver properly and the rail wouldn't "clock" correctly - so, I gave them a call and the young lady

that I spoke with confirmed to me that they had gotten a run of adapters that were machined incorrectly (the rail mounts to a

female threaded adapter that threads on to the upper receiver, has a hole drilled down the length of it for the gas tube and

above that hole there is a "key" that engages with the rail to align it to the receiver rail then the barrel nut (with male threads)

threads into the open end of the adapter and is torqued to retain the barrel) so she said they would send a replacement. 

The replacement arrived today and after installing it I'm seeing a rail height mismatch of approx .020"-.022" not much but

enough to create an annoyance! Their method of measuring for the height is making me wonder if they got their dimensions

 

wrong, using their method to measure the height I'm getting 2.0575" and they are expecting a height of 2.600"

however the handguard is about .020" too high and it's obviously not right - just for the hell of it I installed my newly acquired

Samson Star 10 that I put on my other upper on the one having the problem and the rail lined up perfectly(yea, I know the

Star 10 is advertised for the Armalite AR10 but with the optional Samson DPMS thread barrel nut it fit like a champ) it was

the only thing I had to compare it against - any chance any of you guys with high profile uppers could post a measurement

of their upper as specified in odin's instructions so I will have additional info to help identify the remedy to my mismatch.

 

Thanks

Edited February 8, 2015 by guruofhotrod

[survivalshop]

    The Armalite AR 10 rail height & one of the DPMS rail heights are close , but not the same , the two ,High & Low of the DPMS & AR10 are all different heights. I don't remember which of the DPMS rail heights are close . The was a video for a hand guard manufacturer that tells about it . I'll see if I can find it .

[guruofhotrod]

 

 using their method to measure the height I'm getting 2.0575" and they are expecting a height of 2.600"

 

 

That 2.600" expected height is supposed to be 2.060" .0025" higher than I'm measuring - two and one half thousandths of a inch 

obviously isn't much and shouldn't translate to a .020" mismatch in rail to receiver height - Odin has one rail and uses an adapter

with an offset bore to determine receiver height it will align with, I'm wondering if Samson may do something similar on their Star 10

to get it to fit the Armalite AR10 and the High DPMS both since their webpage shows it for an Armalite but I can assure you it fits

my High DPMS uppers perfectly

 

 http://www.samson-mfg.com/category/308AR_STAR_ARMALITE.html

[blue109]

DPMS high should be pretty close to AR10.

[guruofhotrod]

Here are some pics of the ODIN setup:

 

[guruofhotrod]

And the Samson setup:

 

 

 

[survivalshop]

DPMS high should be pretty close to AR10.

 

 

 

 Yes close , but not the same & its not much difference . The Samson rail height looks correct , what ever the Hanguard rail height was made for , but as said , the one DPMS rail height & the AR 10 are very close , so 0.005 ( example. ) may not be noticeable in the photo's .

[guruofhotrod]

The ODIN is the one giving me all the trouble and it's supposed to be made for the DPMS type receivers - I'm going to have to send the pics to them and speak with one of their engineers to try to resolve this. In the meantime if anyone has a high profile DPMS type upper and would be so kind as to take a measurement with a caliper at the location shown here I would really appreciate it :hail:

 

 

Edited February 8, 2015 by guruofhotrod

[blue109]

that Odin looks like its somewhere between DPMS high and low. I don't think its right for either just going by the pics.

[guruofhotrod]

I'm suspecting that the replacement adapter that they sent has the threaded mounting hole (that threads on to the barrel mount boss on

the upper) machined about .020" too low resulting in the rail being .020" too high? that's why I'm asking for some additional upper receiver 

height measurements from you guys that have DPMS type high pattern uppers so that when I get the ODIN guys on the phone there will be

no doubt as to what needs to be done for a fix.

 

Thanks Again

 

 

Here's a pic of the adapter and barrel nut that they provide with their rail system:

 

 

Edited February 8, 2015 by guruofhotrod

[survivalshop]

  That could be , it was wrong once . <dontknow>   I'll go in & measure my DPMS pre-2009 Upper receiver .Took some trying to get that reading , I think its easier just to measure the thickness of the tab above the Charging handle . I don't have a AR 10 to measure , some here do .

 

 DPMS, High ( pre-2009 ) Upper receiver ----2.060 "

 Tactical Machining, Low ( post 2009  height ) 2.000"

 SI Defense , Billet Gen. II , Upper Receiver -- 2.060 "

[guruofhotrod]

Thanks for the measurements  <thumbsup> Looks like my receivers are within .0025" of the expected dimension so I'm seeing this as 

a screwup on their end - I'll followup tomorrow with an update on how this turns out.

[FaRKle!]

Measured my PWS (SI-Defense) upper receiver and it was 2.061"

[guruofhotrod]

Thanks FaRKle!  Looks like we're all within around +/- .002" of what's expected - not bad!  I spoke with Katie @ ODIN Works and sent her an email

with the pics and an explanation of the problem, hopefully I get a timely response. Also I mentioned that it is important to get the nomenclature right

with the 308 AR platforms - they have references to AR10 on their product page but their forearms (handguards) are made for DPMS type 308's

obviously if it were for an Armalite AR10 the barrel nut threads wouldn't mach up.

 

I'll post back as soon as I get a response from ODIN Works

[FaRKle!]

Also I mentioned that it is important to get the nomenclature right

with the 308 AR platforms - they have references to AR10 on their product page but their forearms (handguards) are made for DPMS type 308's

obviously if it were for an Armalite AR10 the barrel nut threads wouldn't mach up.

Keep fighting the good fight! Lol, this worse than people using "magazine" and "clip" interchangeably.

[blue109]

my 4yr old knows its a magazine, but she always points out its "not the kind you read". proud papa lol.

[guruofhotrod]

Just spoke with a guy named Tom that handles the manufacturing at Odin Works, He has requested a measurement from the bore center to the top of the picatinny rail on my upper. Had an interesting discussion about the lack of standardization with the 308AR stuff and all the difficulties that arise because of it.  As a side note he mentioned that the location of the gas tube in relation to the bore centerline is not consistent with the various manufacturers of the DPMS type 308 stuff requiring them to slot the gas tube hole in the forearm adapter. Got me wondering how they are pulling that off since the gas keys are pretty well standardized and bolt carriers are for the most part interchangeable and furthermore, you can't move the centerline of the BCG in relation to the barrel centerline so how the hell do you move the gas tube position?

 

Hmmmmmm <dontknow>

Edited February 11, 2015 by guruofhotrod

[mrmackc]

maybe he is talking about the height of the gas tube at the gas port block, and the same gas tube would be able to be inserted in the receiver extension hole because the tube is kind of flexable at the rear end, so you could use a couple of different gas port blocks with the slotted forearm adapter and have the tube still line up with the key on top of the bolt carrier. Just guessing.  I have been told that here are two different heights on DPMS uppers.

FYI: from Troy Industries;

How to tell what type of DPMS LR-308 receiver you have:

IMPORTANT: DPMS, BUSHMASTER & REMINGTON may have two different height upper receivers. Please reference Rifle Technology Page for more information.

• The new “Low Profile” upper receiver has a 1/8″ wide top portion where the charging handle is installed.
• The older “High Profile” upper receiver has a 3/16″ wide top portion where the charging handle is installed.

 

Edited February 11, 2015 by mrmackc

[survivalshop]

  Gas blocks are all the same as far as gas tube position , other wise you couldn't use them for both the 308AR & the AR 15 platforms .There should be no flexing of the tube for fitment, if there is , somethings not right .

   That's another way of measuring for the two different heights of Upper Receiver rails for a DPMS. Odin asked to measure it in a different way , as above measurements.

 

Just spoke with a guy named Tom that handles the manufacturing at Odin Works, He has requested a measurement from the bore center to the top of the picatinny rail on my upper. Had an interesting discussion about the lack of standardization with the 308AR stuff and all the difficulties that arise because of it.  As a side note he mentioned that the location of the gas tube in relation to the bore centerline is not consistent with the various manufacturers of the DPMS type 308 stuff requiring them to slot the gas tube hole in the forearm adapter. Got me wondering how they are pulling that off since the gas keys are pretty well standardized and bolt carriers are for the most part interchangeable and furthermore, you can't move the centerline of the BCG in relation to the barrel centerline so how the hell do you move the gas tube position?

 

Hmmmmmm <dontknow>

 

  Wouldn't or shouldn't they already know that , for the different platforms they are making Handguards for ?

Edited February 12, 2015 by survivalshop

[blue109]

one would think. I've never heard of the gas tube hole being in a different spot for any of these guns. only reason for a "slot" (assuming he means horizontal?) would be to give you a little wiggle room to line the rails up.

[guruofhotrod]

He was pretty clear about the position of the hole for the gas tube on the front of the upper being inconsistent between manufacturers (vertically) relative to the barrel centerline thus the vertical slot in their adapter. (see pic in previous post) As to the height mismatch we've completely ruled out any possibility of a mixup between high and low profile receivers and handguards/forearms/adapters everything is DPMS high pattern (pre 2009) style - at this point we're looking for a machining or manufacturing discrepancy. 

Edited February 12, 2015 by guruofhotrod

[blue109]

I could certainly be.wrong, and my only hands on experience is with DPMS pattern uppers, but in all my time on this forum and all the troubleshooting I've seen across various brands I havnt seen anyone mention gas tube height being an issue. I know larue and RRA do their own thing with rail height, but they are still able to use standard gas blocks and tubes so id assume the hole in the upper is in the same spot. can any of you gurus confirm this?

[survivalshop]

    It looks like their rail height is wrong for your platform or the rail height is machined incorrectly .

    That adaptor nuts channel for the gas tube is odd , not sure how its made , but I don't think there would be much off center as they say . If there was as much as they suspect  ( to cut or make room in their adaptor ,for out of Spec Gas tube opening in the Upper Receiver ), we would see problems with Gas Tubes binding or hitting the Carrier Key . There's not much room for error there .

  Maybe they cut that channel in adaptor nut that way to remove some weight . <dontknow>

[guruofhotrod]

 If there was as much as they suspect  ( to cut or make room in their adaptor ,for out of Spec Gas tube opening in the Upper Receiver ), we would see problems with Gas Tubes binding or hitting the Carrier Key . There's not much room for error there .

 

My exact thoughts on this! To move the position of the gas key, you'd have to move the BCG inside of the upper and then the bolt face would be out of alignment with the barrel extension - I'll have to pick this guy's brain a little more on this one   <dontknow>

Edited February 13, 2015 by guruofhotrod

[guruofhotrod]

Update: The mismatch is caused by the barrel centerline being around .020" too high causing the handguard top rail to be .020" higher than the upper receiver rail. On top of that, I have 2 different uppers, 1 from Ares Armor (the one with the Samson rail mounted to) and the other one, bought together with another of it's kind by my employer - He needed an upper for his rifle and I showed him the listing on ares' site and asked him to order 2 cause I needed a second. Well, turns out he went hunting around on the internet and came across this: https://www.armsunlimited.com/AU-AR10-DPMS-LR-308-Stripped-Upper-Receiver-p/au-ar10-sur.htm

Now, I know about their shady counterfeit parts reputation but, at first glance it looked to be a decent high profile upper, hmmmm - to make a long story short the ares upper also is a little high on the barrel centerline (around .008"-.012")  but, the arms unlimited is far worse at around .020" - after quite a few phone calls to Odin Works I made the decision to fabricate an adapter at work on one of our Haas mills - to expect Odin to make me a one-off adapter to me seemed like asking a bit much! Tom up at Odin offered to send me a PDF print of the adapter so I could draw it up in Mastercam with the necessary modifications but, much to my surprise, instead of the print an email turned up in my inbox indicating that they were making a run of adapters and would make a special one for me with the threaded barrel nut hole and gas tube hole raised .020" the only  condition was that he would have to send it to me "in the white" or as raw aluminum without anodizing. Well anodizing is no problem as I have a company I deal with on a daily basis that does plating for my employer and I can get miscellaneous stuff done as a favor! So, should finally have this thing functional in another couple of weeks!! :banana:  Can't say enough good things about the great people over at Odin Works! <thumbsup> They really went the extra mile!

Edited March 8, 2015 by guruofhotrod