I recently purchased a DPMS flatop upper, and a detachable carry handle.  I later decided to ditch the handle and go with an ARMS #40.  It arrived today (thanks gandrtactical) so of course, I did what everyone would do in my position, I tried to mount the sight to the upper.  

Much to my disappointment the sight does not fit.  Being relatively new to the ar 15 and switching from a 20" HBAR upper to the flatop, I thought, crap, I must be doing something wrong.  I got a brilliant idea and attempted to mount it to the rail where my vertical grip is mounted and it fits like a glove.  

My questions are: Are there different sizes of the flatop uppers as far as the area where I would mount a rear sightor? or is my upper just f'd up?

Thanks in advance

My ARMS #22 throw lever rings fit very tight on my DPMS upper.  You're not the only one.  

Had the same problem on my RRA upper but they replaced it cause it was out of spec. Call DPMS and see if they will switch it out because the uppers is out of spec.
           FREE

F'd up! DPMS in my opinion put out a lot of crap out of spec junk.
Jack

I've heard a couple of people mention this before.  Maybe I'm lucky but my CMMG/DPMS upper fit perfectly with all the ARMS products(SIR 50 and ARMS 40A) I put on it.

[img]http://a5.cpimg.com/image/CB/C4/19917515-fff9-02000180-.jpg[/img]

I had the same problem with my CMMG/DPMS flat top upper. I had to "beat" an ARMS #38 and or ARMS #40 on with a rubber dead blow hammer. I was too lazy to send it back, so once I got the mount on I just left it there for now.

DPMS upper seems to have a higher rail spec then normal. This can be very problematic.  

RRA have since fixed their rail spec on the upper and have not had any further latest std1991 rail spec claim. [;)]

I appreciate all the replies.  I should have specified it is a M4 16" upper, so I figured the standard stuff would fit.  I spoke w/DPMS at length about the problem.  They were friendly, and knowledgable.  However, we could not resolve the issue over the telephone, so they gave me a return # and I'll either ship it, or one of my buddies lives 20 minutes from their place, so I may get him to drop it off.  All in all rather frustrating, but I understand that sh!t like this happens from time to time.

It might be the mount, I got a 50 C a week ago and it had problems fitting to all my flat tops and tried a few in our armory.  The front of where it goes on the rail was just a little too large.

FWIW, mine was the standard run of the mill A3/A4 flattop just like everyone else makes. Granted the mounts went on, but only someone like ED Sr. could have put them on by hand [;)]. I do wonder if the teflon coating is not allowed for enough during the machining process, even though its thickness is probably less .0005 or whatever. Also I do not think it was the mounts, they both slid right on a bushy and RRA no problem.

I called DPMS and it took me a while to convince them that the ARMS#40 sight I had did not fit properly on the rail.  I was given a return # and I brought the upper to the factory.  

Nice people, and they even showed me which part of the detachable sight to file off so it would fit.  WOW!!  I explain that I may actually mount other stuff to that rail, so I'm still out of luck, so they admit that the rail is out of spec and say they will ship me a new one.  I ask if they can replace it on the spot, but they gotta test fire it, blah blah blah...  I don't claim to know anything about what kind of stuff they would keep around the factory, apparently complete uppers are not one of them, so I wait a week.  Get the upper back via speedy delivery service, well packed, nice box, and they even put the ARMS#40 on for me.  I am examining the new upper, yup, its the same, but this time the rail seems to be in spec.  Feels kinda light though....  Being the trained observer I am, I realize that they put the charging handle in, but forgot the bolt/carrier.  

I guess they somehow test fired my new upper, w/out a bolt/carrier in it, then bubble wrapped it, and shipped the thing to me.  

Needless to say I am just a little pissed off.  I understand mistakes happen, but this is getting to be a bit much.  I know others have had positive experiences w/dpms, but I for one will be extrememly reluctant to purchase any of their products in the future.

Almost forgot to mention, they did say they would send me the missing parts.

[%|] Crap man, sorry for your hard time.

ARMS #40A and #19S both fit fine on my DPMS upper. So did an Eotech and a Colt Carry Handle.

ARMS #40, ARMS #22 rings, EoTech and MADD sight all fit fine on my DPMS LoPro.  Sorry to hear about your problems.

Well, I just yesterday and today (11-8-03) went through the same problem.  DPMS Upper M4 16" and ARMS #40.  The site would only go on Half way.  Brought it to a local Gun store to try the site on one of his flat tops.  The site fit fine.  So, after talking with DPMS yesterday and them wanting me to send the upper and site back to them, waiting a few weeks... blah blah blah, We decided to file down the site a bit and tap it into place.  The site is on... seems ok now... just going to have to tap it off when My scope set up comes in.

The weird thing about this whole thing is that when I talked with DPMS yesterday, they said they had never heard of this happening, and then blamed it on Swan, the manufacturer of the ARMS equipment!  Total bs!

Did you need to get a taller front sight post because of the rail being a bit higher?

No I did not need a taller front sight post.  Of course, the gas block on mine is a DPMS quad rail gas block with a Bushmaster flip up front sight.
[img]http://members.cox.net/daphotoguy/DPMS_Q.jpg[/img]

I just bought a DPMS flat top upper at the funshow and mated it to a 16" DPMS H-Bar and RRA Quad rail FF HG.  

After reading this thread, I took my 6x VOMZ scope with ARMS #22 rings off my RRA upper and put it on this upper.  It is very tight, and I would have to say it feels like a slight dimensional difference, perhaps 1 or 2 thousandths.  I should be able to live with it, though.



Jim

I just mic'd three different AR flat top receivers across the rail, plus some FAL mounts, and here is what I came up with:

RRA flat upper w/keyhole stamp on side: .831
RRA flat upper w/no stamping on side:   .830
RRA quad rail freefloat handguard:      .832
RRA flat top gas block:                 .826
DPMS flat top upper w/h&triangle stamp: .834
DSA FAL rail mount:                     .834
ARMS FAL rail mount:                    .8355
TAPCO Gen 1 FAL mount:                  .818[:O]

Damn, I thought there was something f---ed up with that Tapco mount.  That pisses me off.  I never put it on a rifle.

Both the ARMS#5 mount and the #22 rings appear to lock down with a very slight cant as viewed looking down the DPMS rail, but not on any other mount or upper.  

Hmmmm..... It appears as though angle underneath the upper is slightly wider or dimensionally different on the DPMS, which may explain why the #22 rings lock down on the ARMS FAL mount (which is wider than the DPMS) and all the other rails with no problem.

Looks like RRA from here on out, as everything fit that with zero problem and the upper would've been $30 cheaper from ADCO, to boot.

I guess I'll find out which of my mounts held zero, since I removed all my optics for the measurements.  Tomorrow will tell.


Jim  

Man that stinks.
I can't knock DPMS because I've never owned one, but this makes me leary of them.

I have a lightweight-barreled A3 upper from CMMG that I feel it out of spec.  When I first got it, the front sight was off by a good deal.  I had to crank the carry handle sight way to the left to correct, and it still wasn't really on.  I called DPMS and they told me that they only warranty their uppers for 30 days, and when I finally figured out that the front sight was off, it was past the 30 days.  They also told me that if I wanted to send it back, they will be happy to quote me a price to repair it.  Eh...no thanks.  I followed the military armorer's manual to get it corrected.  Then, when I swapped out the handguards to an Oly FIRSH, the rail on the upper was higher than the FIRSH upper rail.  Well, no problem, I figure, since I'm not going to mount anything that "bridges" the upper and the FIRSH, but it still bugged me.  The final straw was when I put my ARMS #22M68 w/ Aimpoint on it.  The lever was so hard to tighten, I was afraid that it would break off.  I don't think I'll buy another DPMS product.  I'll stick to what worked for me in the past: Oly, Bushmaster, RRA.  

Ghost

Now that REALLY stinks!
I stick with Bushmaster. No problems.

I had to swap an Armalite upper onto my CMMG M4 to get my SIR to fit. Expensive.