You do risk to damage the valve and because I hate fixing those here is the spacer :
http://www.airsoftbuddy.com/index_ep...roducts_id=226
Airsoft Buddy has loads of stuff for WE 
For polishing yeah it does but if you don't do it right it will lower the piston O-ring lifetime from a bit to a few games.
My advice : leave it like this until the open bolt kit comes out.
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Tous les jours nous nous endormons plus instruits mais pas forcément moins bêtes...
I can do a CTRL+ATL+DEL on your gun !
Gun doc in Montreal on AEG, GBB, GBBR and Bolt rifle (gaz and spring)
Heavy custom builder (including painting)
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