How to measure rings for a Picatinny Rail

[Alpha1]

I'm clue less when it comes to scopes and rings. I want to buy a picatinny rail for a project they advertise them as 20mm wide. I measured my scope rings and the dovetails look like about 18mm wide to me. How do you measure up for the correct rail.?

[bradaz11]

thats because they clamp, so if they were the same width, you wouldn't get them to be tight

[WelshShooter]

Wow you must have good eyes if you can tell they're 18mm by looking!

Yes, as bradaz has pointed out they will clamp on so they should fit. The main difference between picatinny and weaver is the space between the rails. This doesn't matter for single ring mounts but may be an issue with a single mount Base that occupies more than one slot. I've never had problems with any rings on any rail. I've just installed a single Base mount on a Tier one rail and had no issues.

[Alpha1]

How do you get a set of 18mm rings to clamp onto a 20mm rail or am I missing some thing

[WelshShooter]

Did you measure the internal width while they were closed or fully open? If the latter then you may have an issue...

[Alpha1]

I measured them open.

[WelshShooter]

I just re-read your original post. These are dovetail rings, and not weaver rings right? I suppose the 18mm dovetail rings would most likely be for a proprietary rail (such as those on Tikka's and CZ's) rather than for a picatinny/weaver rail then. What brand of rings do you have? Do they have the bar that goes across the gap or are they just clamps?

[Alpha1]

Like I said I know nothing about scopes or mounts. The mounts I measured came off a Steyr SSG 69.
I want to mount a scope rail on a rifle then obviously mount a scope on it. May be I'm looking at the wrong type of rail. I really have no idea.

[WelshShooter]

Ah OK I understand now. Picatinny rails and dovetail rails are different sizes. For example, rimfire rails are 11mm, the Steyr is 18mm, CZ dovetail size (i.e. 527) is 16mm and so on. The picatinny/weaver rail size is different from this and therefore you will need to buy rings that would fit onto picatinny/weaver rails. These are commonly sold by Leupold, Vortex, Warne etc.

Here's an example of rings suitable for a rail. Notice the bar across the clamping area? When mounting to a picatinny rail you would place this between a slot and pull the ring towards the rear of the rifle which causes the bar to engage the slot. You then tighten the clamp as you would a dovetail mount. The slots provide resistance against movement of the rings under recoil.

http://opticswarehouse.co.uk/product/le ... unt-rings/


As you already know you will have to decide on the height of rings needed and also what tube diameter you have. With regards to the rail, if you are shooting long range (~1,000m) I would recommend buying a sloped 20MOA rail. Conventional mounting of scopes will end up having a "mechanical zero" i.e. if your scope has 80moa of elevation then you will mostly likely have just 40moa as the scope would be zero'd at the mechnical nominal. If you had a 20moa base for example, you would gain an extra 20moa as you are zeroing below the "mechanical" nominal of the scope.

Hope this makes sense, I don't seem to be thinking in English very well this time of night

[Alpha1]

Thanks for that so I don't need to buy a picatinny or weaver rail I can just buy a dovetail rail and use a set off rings I all ready have.
Or if I do decide on a picatinny or weaver rail then I need to buy a suitable set of rings as well and as there is no chance of me ever shooting any further than 500 yards and realistically the distances are more likely to be 100 to 300 yards max I guess a standard rail will do. Does that make sense.