friend and I took M1A  "loaded" to the range and shot 60 rounds.    It "double tapped" with him 8 times and none with me.    Benchrest off sandbags.   Shot ammo from battlepack purchased last weekend with label reading   FNM76-29  (was told it was Portugese).    Any help??  suggestions???
thanks,
John

Eight times?  After twice, I wouldn't be shooting it any more.  I had an AR do this once upon a time.  "Neat!" I thought, being young and dumb.  Then when the damn thing blew up, I realized I was lucky to still have my face.

Let someone who knows what they are doing look at it.  Probably the hammer is following the bolt forward and hitting the primer hard enough to set the round off, but that's just my .02.  If this is the case, a new disconnector and/or hammer ought to fix it.  YMMV.

I had this problem and it was the ammo but your  sear can need roughing up as its to light .CALL SPRINGFIELD if the and try remington ammo or some good brand.

I shot my first 100 rounds of Portugese through my M1-A last Friday with no problems, and have heard nothing but good about the stuff.

I would suspect the rifle.   I usually test brands of ammo by loading 2 rounds, firing the first round, then manually eject the second and look at the primer to see if there's a ding in it.  There should be no more than a pinpoint sized scratch. If there's more, and it happens with a couple brands of ammo, something is amiss.  I'd suspect crud build up in the chamber or bolt face, but I'm no expert.

I shoot American Eagle, Winchester, and Portugese, and found the Winchester primers have the biggest dings, but still haven't had a slamfire.  Though some people poo-poo American Eagle, the primers are harder than Winchester in my experiments, and it's plenty accurate.

A double tap doesn't necessarily mean a slamfire.  Given that it double-tapped only for him and not for you, the gun could have a bad trigger group.  I had a Springfield NM gun that had a cast repro trigger group, and after a few thousand rounds the hammer/sear engagements had worn down to almost nothing.  Trigger pull dropped to less than 2 lbs, and it started double tapping.  Turned out the trigger was so worn and so light that under recoil it would reset and fire again if I didn't really hold that trigger back. The difference in the way you and your buddy hold the rifle could be making the difference.  My suggestion would be to first have a 'smith who knows M1A's take a look at that trigger group.

My rifle(M14-S) has also double-tapped on me.  I found that it only did this when:
1. I focused on pulling the trigger slowly and deliberately.
2. Was shooting from a benchrest.
What I theorize was happening was I wasn't pulling the trigger fully to the rear.  The recoil allowed the trigger to move just enough to reset and then would go off again from the position of my finger.  
Of course I could be wrong.  But, since it only happened with your friend and not you and he was shooting from a bench it sounds like a possibility.

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Sounds like a problem for the folks at the fulton armory. This is THE place for advice on your M14/M1A/M1 issues.
http://www.fultonarmory.com

Pull the triger group and check the disconector and hammer hook.  Sounds like either it as your friend flincking, of the disconector is bouncing.  Check for a bur, weak spring,or bad contact.

Also, pull the bolt and check the firing pin for fouling, or burs.   I have a hard time beleaving that the rifle is slam firing, unless you haven't clean the rifle and bolt before you shot it.  If the firing pin shaft is fouled or sticking, this would case a slam fire.  
P.S. when cleaning the bolt, try not to wipe the grease out of the bolt bearing.

You say it didn't happen wehn you fired the rifle?  Teach your friend proper shooting technique.

i have a national match garand that did double taps. I set it into fulton armory to be looked at.Turned  every thing was in workiking order.

I Was informed that many of the slam fires in M1 rifles are infact unintentional bump fires by he operator caused by the operator.

But by all means spec out you ammo im willing to bet your ammo is oversized. If thats not the case then its time to have your rifle checked out.

Before sending it anywhere, I would first clean the crap out of the chamber, bolt face and lugs and see what happens.