I have recently purchased a "scout" M1A and have read all the literature provided by Springfield. They harp about "slam firing" & using only "GI" spec. ammo (NATO). They warn not to use commercial ammo as the primers may be to sensitive for the floating firing pin.

My question is... I want to accurately sight in my rifle. I have purchased a battle pack of Portuguese 7.62x51mm made in the late 70's-early 80's, but is there anything of "NEW" manufacture that is to "GI" specs that will work "SAFELY" in this gun? Springfield mentioned something about Federal or PMC, what flavor is the "GI" spec. ammo called?

What kind of grouping will I get out of the surplus ammo vs "New". Is there really a difference?

Thanks
Shane

Blue, the NATO recommendation is for the lawyers and reloaders.  I have never had a problem with good quality commercial ammunition, nor do I know anyone who has.  NATO ammunition is typically made with a harder primer and so there is very little risk of slam fire.

The Portuguese is good ammo and should give you between 1 - 2 MOA.  Hirtenberger or British Radway-Green are also excellent.  Hirtenberger is highly desired because it is Boxer primed and reloadable.  Federal Match is probably the best commercial product and will give you 1 MOA or less as long as you and the rifle can do your part.

Reloads are the best of all, but a lot of time and care needs to be taken to prepare cases, especially primer pockets, to prevent slam fires.

Should I expect to see the NATO ammo group way off the bullseye if I sight my rifle with a quality commercial ammo?

I would hate to burn expensive commercial ammo if I'm not accurate with my plinking ammo! I would hope both ammo's group about the bullseye. Anyone out there gone through the comparison test?

dito what fox says.  the warning is BS.  but I load in a safe direction anyway.  
between lots of the same brands ammo I have have noticed 6" @ 100 yd dia differences.  you may see as much as a foot or two difference.