I guess this would be my first post on the site.  Thank you in advance for your help.

I having an issue with scope rings not fitting my Mega Arms recievers tightly. I built a rifle on a Mega slick side, side charger upper. I put 800 rounds down range so far using a GG&G QD 1198 mount. I noticed it was difficult to achieve consistent groups shooting factory match loads. Naturally I thought it was me not the rifle. However I checked over the rifle to rule it out considering this is my first build. What I found was slight side to side play between my GG&G QD 1198 mount and flat top. I thought ok an adjustment is in order to take up the slack no problem. No matter how much I tightened the lever it would not fully tighten to the reciever. I had to fully close the lever and tighten the cross bolt like it was a non QD mount. Still it had a slight amount of play that could be felt and seen if looking very closely.  I called GG&G thinking the mount maybe at fault. I didnt get to far with them but thats another story for another day. I decided to order a set of Badger Ordnance rings part# 306-18 for AR flat tops which arrived today. Excited, I quickly began to mount the rings up to discover the Badgers will not tighten either. The clamp bottoms on the ring body. I have another Mega side charge upper and a Mega Ma-Ten waiting to finish building so I tried the rings on those recievers, still loose. Tried mounting the rings on my D and L accessory rails and  two JP railed gas block to see if they would tighten. Sure enough they did. Finger tight was rock solid before even being torqued. All parts involved are quailty, and I cannot find a single case of a Mega rail being out of spec nevermind three of them. I have heard of other manufacturers with undersized rails. Im on my way after posting this to buy a digital caliper help me figure this out. Has anyone experienced this? Am I being stupid and missing something? Thanks again!

I think i have it figured out.

From where the bottom 45 degree angle begins to top of the flat top is .200" on the Mega. JD rail is .217". D and L rail is .226"

From where the bottom 45 degree angle begins to bottom of recoil groove is .085" on the Mega. JD rail is .095". D and L rail is .115"

Depth of the recoil groove is .117" on the Mega and .123" on the JD and D and L rails

These are the only dimensions that varied between the rails. I looked up the 1913 mil spec standard dimensions and it does not list these dimensions I gave except for recoil groove depth. I believe the shorter dimension on the Mega rail is allowing the ring to sit lower over the bottom 45 angle. The further down the 45 the narrower it gets and the crossbolt is bottoming before it can reach it to contact and clamp down. Hope this makes sense.

http://www.biggerhammer.net/picatinny/1913_specs.pdf

Thats odd.  I have never had any issue with my mega GTR-3H or my Carbine Length Mono upper.  I would call mega with your dimensions and see what they have to say.