Can a 20mm attatchment fit on a 22mm rail?

[murshed2010]

I'm new to Airsoft and im buying my first airsoft gun (Shotgun) and the description of the gun says it has a 22mm rail but most attachments are for 20mm rails. Some say they will fit both 20m and 22mm and others say they can fit 11mm and 20mm rails. Is it possible to fit the 20mm attachments onto my gun and if not, is it possible to modify it (maybe extended bolt/pin or a modified riser idk) to make it fit? Also the description and customer service just say that it has "RIS" rails which is quite vague. It looks Picatinny to me but I could be wrong. Another question. Can I mount weaver attachments onto a Picatinny rail? Heres the link for the gun: https://gunfire.pl/product-eng-1152207123-GFG27-Tactical-shotgun-replica.html and link for an attachment I want to buy: http://www.ebay.co.uk/itm/302210403892 Also if anyone knows any shotguns that are for sale that's got rails on the forend slider and is under £50 please do tell me. Thanks

 

[Samurai]

They fit. 20mm rails are not 20mm wide on their widest point.

 

[murshed2010]

They fit. 20mm rails are not 20mm wide on their widest point.

I understand this but I am asking if it will be possible to modify it to fit? I had 2 ideas:
1. buying a 20mm riser and sanding the inside of the bottom part so it fits a 22mm rail and leaving the top so you cna mount 20mm attatchmens

2. replacing the bolt with a longer one

Would any of these work and has anyone done it before or would i be better off buying a 20mm rail?

 

[Tommikka]

They should fit,not only the tolerances to adjust but the original designs were American thus measured in inches and later popularised across the world in MM

RIS is a genric term - Rail Integration System

This type of 'tracked' rail began in the 70s with the Weaver mount.  The tracks allow for recoil but hold a sight in position better than a dovetail and allow the items to be removed and replaced consistently in the same position 

The Weaver dimensions are flexible and items can be inconsistent. The original definition used two separate mounts for one sight

Picatinny in the 90s was introduced as a US military standard with absolutely defined & consisten dimensions, followed by NATO standard

Any equipment designed for picatinny will fit Weaver, but equipment designed for weaver probably will but might not fit picatinny

Subsequent standards have been developed and legitimate open source standards have been defined which legitimises manufacturers without using trademarks or licencing