Rail to Rail adapters?
 

Are there any mount adaptors that would permit rail to rail mounting? Say, for example, mating a shotgun with rail to the underside of an M16 rail.
If so, what would be a source, and possible cost?
For that matter, what is the difference between a Weaver rail, a Picatinny rail, and a RIS? Are there differences?

Thanks for anyone's advice.

I looked into this a long time ago, I was unable to find a ready made product.

Most people just made their own.

Just need a vice, drill and bits, appropriately sized screws and some scrap metal.

Weaver = Picatinny = 1913

All are also known as "20mm" rail.

Technically, Picatinny is evenly spaced, while weaver can have random spacing (like on most sniper rifles or risers).

The term you are looking for is "masterkey". There is no really easy way to masterkey something that was not made for that.

However, you can take some cheap china scope rings that use a bent piece of steel as the "mobile" side of the mount. Take 4 like that, two screws (preferably cap screws) that are the same size as the knobs from theses mounts and you can clamp both rails together if you want.

http://www.brownells.com/.aspx/lid=1...he_Difference_

"Masterkey" is the Knights Armament (KAC) terminology of a shotgun mounted below a combat rifle, a "key to open any lock". Just for clarification, it is not for mounting rails together.

http://en.wikipedia.org/wiki/KAC_Masterkey

They are traditionally mounted via the same system as the M203, as their rail systems (like the RIS) couldn't handle the stress placed on it from a shotgun or m203 being fired.

Yup.

OP specifically mentioned mounting a shotgun under an M16.

I am suggesting he attempt the same as the real deal.

Rail to Rail, as he is suggesting, is a weak system and simply not done.

There's this site I found a couple months ago, but I can't speak for the reliability of the product:

http://www.zerooneairsoft.com/index....acturers_id=57

I want to test their stuff out, but UK shipping is always slow & expensive.

For something that simple, I don't think reliability will be an issue... Worst case would be the screw coming loose, just loctite it.
But I don't think it would worth $25-50 plus shipping... Lets find a Chinese company that will make them for $5. Actually, that's probably how the UK seller get them... :D

I remember seeing an M203 rail to rail mount somewhere but it was ages ago.

There is a masterkey set out there. Recently, by g&p I think.. Normally sold with an m4

We've been looking for a while, if you have better luck let us know!

It was about $200 I think, which is practicaly the price of a shotgun.

I made a mount using two M4/m16 carry handles.
I took the rails of both of them. took the two knobs off of one.
Then I used it to attach it to my gun, using the RIS on my M4, and the rail I had installed on top of my shotty. I'd take a pic, but, I left my shotty at buddies place...

Well, if there is demand for something like that, I might be able to run a batch (10-20 sets) in a week or two.

It's really two 5/16" bars cut in "U" to clamp the rails and two holes for screws. Nothing crazy there.

Let me make some calls when they get up...

Take two sets of scope rings and discard the top ring part. Bolt the bases together and you have a crude "Masterkey" rail.

SR25 sniper rifle w/ CQB protection:
http://i650.photobucket.com/albums/u...e/DSCN8494.jpg