Not really.
I do this all the time.
Are there adverse effects?
Minor ones, mostly not noticeable unless you are shooting very long range.
Also make sure there is no contact with bb and the Muzzle as the bb exits the Muzzle of the Mock Suppressor.

You can always use pvc and pvx pipe cut to size and make a makeshift Inner Barrel Extension. This will essentially fit by going over the Inner Barrel and through the Mock Suppressor Flash Hider opening.
Usually, the Flash Hider opening is larger than the Muzzle opening.
So, you can get a nice tight fit for your bridge.
Can also make for some cool sound effects.

 

My kjw m700 had problems with this sorta...

I had a working suppressor when my gun was still gas and it decreases my range by like 80 ft and fps by like 200... Never knew why. Nothing was disrupted.

 

Depending on the Mock Suppressor, the expelled gas and then air pressure turbulence was most likely disrupting your shots.

 

So long as it's not hitting the inside you're golden