Got a new Colt M4 for plinking, that is shooting paper plates up to 200 yards, can anyone tell me best weight ammo and what is the weakest power scope I can put on this rifle, any other modifications from your exp. would be appreciated, I do not shot competitively.

Thanks in advance.

what's your barrel twist?

if it's 1:9 then Lake City XM193 is your best choice

if it's 1:7 then Lake City is still good but you might want something with more weight, in the 60-70 grain area

It is the 16" version, I don't know the twist, any info on scope power? Thanks

I believe the MT6400 has a 1:7.  I use 62gr SS109 in my 1:7

There is no best weight to shoot.  You can shoot anything from 55 on up with wonderful results.  You wont notice worse accuracy with 55 grain as some people will try to tell you who have not tried both 1/9 and 1/7 versions of the same barrel.

The lowest power scope you can use would be a non magnified scope.  Then a 1.5x then a 2X then a 3X then a 3.5 then a 4X and so on.  I dont quite understand that question.  For 200 yards though Id just get an Aimpoint.  Its a non magnified dot sight.  If I wanted more Id get a 2X Compact ACOG then a 3X Compact ACOG and then a 4X TA31 ACOG.  It all depends on what you want but for a carbine Id be sure to get an ACOG for a magnified optic so I could use it like a dot sight up close BAC style.

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YEP !

ditto