it is possible or likely to give you feeding issues if you keep existing hop unit that paired with 20.5mm nozzle
"most" M4 setups tend to use a 21.4mm nozzle which is compatible with "most" M4 hop units
(sometimes it is a smidge under 21.4mm or maybe 21.45mm on SHS red nozzles, but there abouts)
Now there are some M4's than use smaller nozzles, like some ICS M4's especially split v2 box
they seem to use a 21mm or just under nozzles
You can use a SHS M4 nozzle but struggle to feed unless you change hop unit
which then becomes a real PITA coz you have to hack off material from reg M4 hop
as ICS is thinner where feed tube of hop unit is
Also odd Force-Core M4's used a 20.7mm nozzle with a normal looking M4 hop unit
but the nozzle had no "shoulder" to it and the SHS or other M4 nozzle with "shoulder" won't fit fully into hop unit
so yet another time if you change nozzle you likely might need to change hop unit too
(you could use the long AK nozzle @ 20.7mm (not short 19.7mm nozzle), but again had a shoulder so won't fit inside hop)
**** hold up a sec ****
before I wander off on a War & Peace meets Gone With The Wind sequel....
You can try it but prepare yourself for potential problems perahps
you could keep the std nozzle, which might seal a little better on new cylinder head
(most compression is lost by a shit o-ring on piston head, then maybe loose leaking cylinder head
the nozzle is not such a massive problem in fps drop & should never be so snug it struggles to move at speed)
The other alternative is maybe use the LONG 20.7mm AK nozzle that "should" give you less issues with feeding
PS - congrats on taking the time to measure shit BEFOREHAND, than just chuck stuff in without bothering to compare etc...
