Hi, i got a jp 9mm gmr which im going to SBR (about 5-8") and add a suppressor inside the handguard for the cool integral look.

My question is if the space between the suppressor and handguard is too small and will interfere and disturb accuracy due to barrel "sway" when fired?

The JP handguard has a 45 mm inside diameter and the suppressor i want has a 42 mm diameter.

Thanks, and sorry for my poor english i'm from europe!

My experience is with a Samson Evolution Keymod handguard which has a 1.56 inch inside diameter (39.6 mm) and a AAC TiRant 9 suppressor which has a 1.38 inch outside diameter (35.1 mm).  This is a bit more room than your setup.  I have a 4.5" barrel and the rail length is 7.6", so the suppressor is nested well inside the handguard.  I have had no issues with clearance when shooting.  The short barrel, I think, provides less barrel whip, even when the heavy suppressor is installed on the end of it.  When shooting non-suppressed, I replace the TiRant 9 with a 5.5 inch flash hider to allow the muzzle to extend outside the handguard.  I see very little POI shift when shooting the same ammo type between suppressed and non-suppressed, but the groups are a little better when suppressed.  I don't know if this helps you or not, but I think you'll be ok, even with such a small clearance.

ETA: hard to see, but this is an attempt to show the clearance of the suppressor inside the handguard:
Attached File

and your English is better than mine.