DPMS Receiver Heights

[Triggs75]

Sorry might of miss worded my question.  I the rail the same thickness where you would attach say a BUIS? 

I see the back "tongue" is thinner and the rail itself is lower.  However, where you would actually be placing your sights, is that part the same thickness?

Chad

[KellyTTE]

Yes, the 1913 rail specification is maintained, simply machined into the upper at a lower height.

[Benito]

I just bought an LR-308 AP4. I haven't measured the rail height yet, but I would like to know how the height change affects BUIS options. Mine comes with the detachable carry handle, but I'd like to go with either the Magpul MBUS rear, or possibly Troy. It seems to me that changing the rail height might result in misaligned BUIS. I may be wrong though.

Anybody know?

[survivalshop]

That's certainly a possability. I assume you are using or have a std AR front sight on the bbl. ?

Some say DPMS changed the upper receiver height to work better with the std AR front sight , not sure about that , but you would need to barrow a BUIS to see how it works out.

If you are using a complete BUIS set up on the rails( front & rear ) & both rails match in height , you should be OK .

[Benito]

That's certainly a possability. I assume you are using or have a std AR front sight on the bbl. ?

Some say DPMS changed the upper receiver height to work better with the std AR front sight , not sure about that , but you would need to barrow a BUIS to see how it works out.

If you are using a complete BUIS set up on the rails( front & rear ) & both rails match in height , you should be OK .

I am using what I believe is the standard AR barrel mounted front sight that came with the LR-308 AP4. I'll try out a BUIS and see how the height compares to the detachable carry handle that came stock. We will see.

[98Z5V]

I just bought an LR-308 AP4. I haven't measured the rail height yet, but I would like to know how the height change affects BUIS options. Mine comes with the detachable carry handle, but I'd like to go with either the Magpul MBUS rear, or possibly Troy. It seems to me that changing the rail height might result in misaligned BUIS. I may be wrong though.

Anybody know?

The new heights on the upper are 0.060" lower than previous versions.  For sight alignment alone, you can sink the front sight post that far and make up the difference.  Problem solved, as far as that goes.  Most front sights will adjust that far anyway, so it's not really a big deal as far as having the sighting "ability" to correct for this upper change.  Bottom line - it only matter for rail height alignment - aestetics - more than anything else.  It would screw you up if you've got a mount that bridges the gap between upper and rail, though.  Bad.

[Benito]

The new heights on the upper are 0.060" lower than previous versions.  For sight alignment alone, you can sink the front sight post that far and make up the difference.  Problem solved, as far as that goes.  Most front sights will adjust that far anyway, so it's not really a big deal as far as having the sighting "ability" to correct for this upper change.  Bottom line - it only matter for rail height alignment - aestetics - more than anything else.  It would screw you up if you've got a mount that bridges the gap between upper and rail, though.  Bad.

I see. Thanks. I'll slap some BUIS on there and see how the zeroing goes.

[imschur]

Here's a picture that summarises the height differences

[archangel]

i just measured my upper i have the old style dpms upper.  now the vtac jp free float with the rail will line up then?  does anyone know how tall that jp branded rail is?  i seen similar ones from yhm in 1/4" and 3/8" tall for a 1/4 of the price

[survivalshop]

The JP Vtac is a nice hand guard & its the way its attached to the upper that , at least to me, is a better platform . I used a 3/8 rail to match my rail height SI defence upper( same rail height as older DPMS). All the rails for the JP Vtac attach with screws & you can get 1/4 " height also ,as you Know.

Not sure if different manufacturers rails are interchangeable , but they could be . Mine for the Vtac, I got from Brownells , a little less expensive for me & they had slightly elongated holes for the screws on the rail for better alignment.

Is this the one you are talking about .

[archangel]

i have the middle height one.  the old one was way high then mine then the new lower one.  so if mine is a lil lower i maybe able to go with 1/4

[98Z5V]

i have the middle height one.  the old one was way high then mine then the new lower one.  so if mine is a lil lower i maybe able to go with 1/4

There was a Hi Rider, that was ridiculous, but there are currently only two versions of the flat-top upper.  Not quite sure what you're talking about here, with what you have.  Just hit the measurement links, find out what you have, and go from there - or post a side-shot pic of the back of your upper, without the charging handle in there.  We'll figure it out.  <thumbsup>

[Matt.Cross]

Monolithic receivers, the practical man's answer to receiver height issues! ;)

[archangel]

There was a Hi Rider, that was ridiculous, but there are currently only two versions of the flat-top upper.  Not quite sure what you're talking about here, with what you have.  Just hit the measurement links, find out what you have, and go from there - or post a side-shot pic of the back of your upper, without the charging handle in there.  We'll figure it out.  <thumbsup>

i have the thicker one.  i just measured

[98Z5V]

That one would be the "older-style" flat-top, then - before they "improved" something and made the lower one that didn't match anything on the market.  At the time, the only thing fitting the "new" one was their own tube. 

The way the market has responded, you have plenty of choices, either way.  Basically, anything that will fit the original flat-top upper is what you want to look for.  <thumbsup>

[jeffreyC]

PRI makes SPR rails for both DPMS receiver heights.

I think that is what my next upper will be wearing.

Wait a minute did I just say next upper ?

What's that noise ?

Oh, it's my wallet screaming.

[98Z5V]

PRI makes SPR rails for both DPMS receiver heights.

I think that is what my next upper will be wearing.

Wait a minute did I just say next upper ?

What's that noise ?

Oh, it's my wallet screaming.

PRI SPR parts are SWEEEEEET!!!  <thumbsup>

You will love that stuff.  (Get their forearm wrench...)

[ball turret]

A NEWBIE HERE, AS FAR AS AR’S GO ANYWAY. DOING MY FIRST BUILD TO BOOT. THIS HIGH LOW THING HAS ME BUFFALOED.

I HAVE THESE 3 COMPONENTS THAT I’M TRYING TO VERIFY WILL LINE UP CORRECTLY

SI DEFENSE GEN 4 308 SET (IN MY POSSESSION)

JPHG-1D VTAC FREE-FLOATING MODULAR HAND GUARD. DPMS LR-308 OR SIMILAR. RIFLE. (ORDERED)

JPGS-3 JP ADJUSTABLE GAS BLOCK, .936 BORE, WITH RAIL. (ORDERED)

SI IS ADAMENT THAT THE UPPER IS LOW PROFILE. I’VE MEASURED IT IN 3 PLACES THAT I FEEL ARE IMPORTANT. THE OVERALL HEIGHT IS 2.06, THE BORE TO RAIL IS 1.31 AND THE TANG ABOVE THE CHARGING HANDLE SLOT IS .210

ACORDING TO AN EARLY POST IN THIS THREAD THE LR308 OLD VERSIONS ARE 2.063. I THINK I READ THAT THE OLD VERISIONS WERE HIGH PROFILE AND THE TANG MEASURED 3/16. THE NEW, LOW PROFILE WAS SUPPOSED TO HAVE A TANG THAT MEASURED 1/8, THAT WOULD CORRELATE WITH THE 2.003 OVERALL HEIGHT DIMENSION IN THE PREVIOUSLY MENTIONED EARLY POST. SO, I’M FEELING THAT THIS IS A HIGH PROFILE RECEIVER, BUT I DON’T HAVE A CLUE WHERE THE .210 TANG DIMENSION COMES INTO PLAY???? EVERY TIME I THINK I HAVE A HANDLE ON THIS BEAST I GET DELT ANOTHER CARD. THE DESCRIPTION ON THE TROY SITE HAS POOR VIEWS AND DOESN’T COVER THE .210 SIZE. I WOULD LOVE IT IF MY RAILS WOULD LINE UP LIKE SURVIVALSHOP’S DID (REPLY #34), NOT LIKE THE EXAMPLE BELOW. CAN ANYBODY HELP? OR AM I DOOMED TO BE  :(

[survivalshop]

Since I just installed another JP hand guard on an AR 15 , the instructions read if you mate the hand guard as I did on my SI defense 308 upper , meaning tight fit to the upper , "that under sustained rapid fire , there will be a derogation of accuracy , in there testing. "

The one I just installed is close ,but there is a very slight gap between them.

I also can't say my 308 has any accuracy problems under sustains fire ,because it has only MBUS on it since day one , but to me , shoots fine .

I will post a photo of the newest install when I get on my PC to pull one up.

If they haven't changed , the SI defense uppers rails are the org. DPMS height .

If you haven't got a rail for the JP hand guard yet , be prepared for sticker shock , because the rails a propitiatory to there hand guards & they must really like them, but they fit good , that's for sure .

[ball turret]

thanks, i really like the jp rail. fully aware of the add on rail prices, but also like the fact that i'm not going to have rail that i never use. i need to have the tops line up for future iron site use. right now i want to just have a free float for grip and to add a bipod later. it's not a big deal for the gas block to line up, but it would be nice to be able to have options down the road. sustained fire isn't in the program. if anyone can confirm the jp block will line up i'd appreciate it. i can always switch it for a conventional block if it wont. since jp hasn't shipped yet i'm looking for this info now. i'd rather do the trade before than after.

[washguy]

So my first dpms build last week was a weird deal... Had the lower thanks to Spectrascott!

got in the upper and then proceeded to measure the rail height with my dig caliper....so went to the dpms site and looked at the pdf explaining the different upper heights....if its this number its the low if its this number its the high....so, what did i come up with? the numbers indicated its neither high nor low...its inbetween! just great :unsure:

so I decided to go with a gator grip and gave them a call....the nice gal that answered transferred me to the tech who was in the machine shop...I could hear all the machines running...so I tell him what i came up with. he then gives me instructions while on the phone to measure a different way....guess what? he sez mines in between! they sent me a high picatinny rail that bolts on....so all I have to do is remove material on the picatinny.....the scope is mounted on the upper so no big deal :) Wash

[gnatshooter]

Hi folks, I just joined!

 

Anyhow, if you want to see what kind of response I got from DPMS asking about rail heights on the LR-308, go to https://www.dpmsinc.com/crm.asp?mk=cfcrw5t6ev-22725

 

It's really excruciating. If you want to know rail heights, you're "over-thinking"!

 

I wasn't real happy with him making up numbers, either.

[unforgiven]

Welcome from Indiana brother gnatshooter.

[blue109]

While I agree that the factory should be able to give you measurements when you want them...I also agree you might be working a little to hard at this. Pull upper....look down bore...line it up on a target...check sights...adjust as needed. I just did this with 2 Scopes and an eotech last weekend and first Shots were on the paper.

Edited June 18, 2013 by blue109

[EasyEJL]

well, I think particularly with DPMS having the 2 different receiver heights, this should be something they should be able to answer definitively and quickly.