what choke is in it. i used improved cylinder and never had a problem
use an open choke for slugs, imp. cyl. or cyl.
The standard choke in the M4 is an IC, which is slug, lead shot, and steel shot compatible.
I am able to get 2" to 6" groups at 75 yards using Federal Tactical (reduced recoil) rifled slugs with the IC choke, depending on my sighting method (EOTech or Ghost-ring) and how I'm feeling that day.
*Do Not* fire the shotgun without the choke installed - you'll ruin the threads in the barrel.
You can verify the choke type by removal of the choke using the supplied tool:
Notches (muzzle end of choke) or Marks (exterior wall of choke tube), increasing order of restriction:
5 = Cylinder (open)
4 = Improved cylinder
3 = Modified
2 = Improved modified
1 = Full
The first two (5,4) chokes are rifled slug compatible, the first three (5,4,3) are steel shot compatible
I should also have added... a restrictive choke (i.e. anything other than a cylinder, or "C") has no significant beneficial effect on patterns produced by anything larger than and including #1 buck. This is especially true at defensive ranges. Chokes more restrictive than improved cylinder/IC cause lead fouling or worse, and potential accuracy problems with slugs.
The only reason to use a rifled choke is for sabot-style slugs, which are not generally useful for defensive situations.
The IC choke supplied in M4 barrels is a good compromise for defensive use - it won't create problems when used with buckshot or slugs, and it can still be used with benefit for smaller shot sizes to improve the pattern.