I picked up a Mossberg SSI-One from my father-in-law last summer.  Two barrels, one in .30-06, and one in .223.  I took it to the range finally last Sunday to try it out.

For the .30-06, I took several boxes of Greek Prykal M2 ball (of course!) and a little Lake City National Match.  For the .223, all I had was the 55 grain 5.56 I bought from OGC recently, Federal XM193.  (I know, 5.56 in a .223.  Get over it.)

First off, I just could NOT get over how CUTE the 5.56 round looked!  So tiny and shiny, lying there on the table next to .30-06 rounds, like a little boy trying to play grown up!  Like a toy cartridge!  I can't believe they shoot these at people and expect it to hurt!!!   

Anyway, I started the day with the 5.56.  It was also my first day out with a rifle since my surgery, and I wanted to take it easy.  Got the scope zeroed in just a few shots, and worked my way through a box doing 3-shot groups.  Gotta say, I was disappointed.  3" groups at 100 yards.  But I understand that with these rounds, matching the bullet weight to the barrel rifling is pretty important, so maybe I'll have better luck with a different load.

I moved to the .30-06 barrel next.  Now that rifle kicked like a respectable gun!  It took me a while to get the scope remotely sighted in because that thing was throwing my M2 ball all over the place.  6" groups at 100 yards!  Well, if you can call 6" a group.  I call it buckshot.  I stubbornly stuck at it for about a box and a half, long enough to get my shoulder good and tender, then grudgingly swapped ammo for the national match stuff.  Wouldn't you know it?  My groups instantly tightened up to 2" at 100 yards.  Probably they would have done better, but I was already good and tenderized, and was fighting the flinch.

Oh, I got my first ever taste of scope bite, too! 

Yeah, I dunno.... I don't generally like to own guns that don't like to shoot the cheap stuff.  I may give it another go, or it may show up in the classifieds real soon. 

Anyway, I started the day with the 5.56.  It was also my first day out with a rifle since my surgery, and I wanted to take it easy.  Got the scope zeroed in just a few shots, and worked my way through a box doing 3-shot groups.  Gotta say, I was disappointed.  3" groups at 100 yards.  But I understand that with these rounds, matching the bullet weight to the barrel rifling is pretty important, so maybe I'll have better luck with a different load.

isnt 5.56 supposed to be not as accurate in a gun chambered for .223 anyways?

i thought the point of the .223 wylde chamber was to alleviate the tendencies of each chamber to favor its own ammo.

I wouldn't discount the rifle yet. Try some "match" loads.
for 30/06 even the NM loads were not optimum. The old 173 grain bullets weren't really accurate and was nothing more than a FMJBT.
SIerra Match Kings may give you better accuracy.

Hey Tom,

Have you tried reading through some of the Mossberg forums? It may help you to find out what other people are buying to get better accuracy? It may be that there is nothing out there. Or it could be there is a pet load/brand that it likes. Could just be ammo sensitivity like a .22 has.

Anyway, I started the day with the 5.56.  It was also my first day out with a rifle since my surgery, and I wanted to take it easy.  Got the scope zeroed in just a few shots, and worked my way through a box doing 3-shot groups.  Gotta say, I was disappointed.  3" groups at 100 yards.  But I understand that with these rounds, matching the bullet weight to the barrel rifling is pretty important, so maybe I'll have better luck with a different load.

6" groups at 100 yards!  Well, if you can call 6" a group.  I call it buckshot.  I stubbornly stuck at it for about a box and a half, long enough to get my shoulder good and tender, then grudgingly swapped ammo for the national match stuff.  Wouldn't you know it?  My groups instantly tightened up to 2" at 100 yards.  Probably they would have done better, but I was already good and tenderized, and was fighting the flinch.

IMO 3" groups with bulk 55gr ammo is respectable at 100 yards.  I'm not sure I understand what there is to be disappointed about.  If people are consistently getting better than 3" groups with BULK ammo, then I need some help because that's about my average.  If you were getting that type of groups with MATCH ammo I would be like .  So, I bet if you used match ammo your groups would tighten up just like the 30-06 did.