Now one thing leds to another;
I ramped up my M4 with screwed on silencer.
How ?
Well, I got myself a same bolt and nut set; except they are 6 mm.
Yes, these bolt and nut dimension comes in even number, no odd ones.

Coupler, 12.7mm (small end) / 15mm (large end)

Use washer and goop / glue it to the smaller end, align it to the center.

Take the flash hider out of the M4 and put in the 6mm nut. ( the joke; 5.56mm round off is 6mm)

I scavenged a tube to double as silencer.

This screw will be used to insert into the washer

Goop / Glue the screw into the washer.

End result
Note: Goop needs 24 hrs or overnight to set maximum strength.
I used a rubber bung, found in my tool box and stuffed into the space to prevent the screw from shaking like Tower of Pisa.
Can use super glue to stiffen the base of the screw if possible.
Full view of the M4 Silencer

The nut end, I used super glue to harden/stiffen the glue joints. Worry due to gravity may sag......

Upon screwing back the silencer, the completed one.
( Need to do some touch-up later)