Is there a difference between DPMS flattops and Colt or Smiths?

[oneyeopn]

I sold a person a Matech sight and he has sent me an email that said the sight is not compatible with his DPMS flattop receiver. For my own knowledge can anyone tell me what the difference between the DPMS's and the rest of the AR family of receivers is. I dont believe he tightened it down but because he is in PA and I am in Ks and dont have access to a DPMS I dont know. I have installed them on Colt AR's, M&P15's, Olympic's, PSA's, Bushmaster's and even the DPMS .308's. I am just wanting to be sure in my own mind because I thought that an AR flattop was an AR flattop. I am happily refunding his money but I want to make sure if they arent compatible that I dont make this mistake again.

 

[Dragon88]

All M1913 rails are suppose to be the same, but sadly they are not. Low end manufacturers such as DPMS sometimes use looser tolerances that cause problems when trying to mount true M1913 accessories.

Without having this person's rifle and the sight to mount yourself, there is no way to know. He might not be tightening it down correctly, or it's possible the DPMS railed receiver is so far out of spec the accessory can never be made tight.

 

[thndrchiken]

My upper is a a DPMS Oracle and have no issue with mounting any accessories.

 

[Plinker1962]

This is what I found on Wikipedia.

"Picatinny and Weaver rail systems both have slots machined into the rail as a whole. One difference between the Picatinny rail and the Weaver rail is the size of these slots, although many rail-grabber-mounted accessories can be used on either type of rail. Weaver rails have a slot width of 0.180 in (4.572 mm), but are not necessarily consistent in the spacing of slot centers. This is most true with the two piece system.

The Picatinny locking slot width is 0.206 in (5.232 mm) and the spacing of slot centers is 0.394 in (10.008 mm).[1] Because of this, with devices that use only one locking slot, Weaver devices will fit on Picatinny rails, but Picatinny devices will not always fit on Weaver rails.[1] The other difference is that Weaver rails are continuous, while Picatinny rails are cut by the slots (like a dotted line) to neutralize expansion caused by barrel heating."

 

[oneyeopn]

These sights are M4 takeoffs, so I would think that they would fit a "real" 1913 rail. Thats what they were designed for and I have installed 5 on different rifles including my own with no problems.

 

[Dragon88]

Yes, if there truly is a mismatch and they don't fit, the problem is almost certainly the receiver and not the sight.

 

[oneyeopn]

the guy sent me a message...he took his rifle back to the dealer and they measured his rail. It was way out of spec, so he got a new rifle because he hadnt fired it yet. The sight mounted correctly on the new Oracle. Learn something new everyday.