I am presently considering to buy one of these in 5.56mm, I love the quality of these swiss rifles and I cannot for the life of me like the AR-15/Bushmaster family.
The rifle will be used for shooting military programs..

Do any of you have experience with these rifles...?

Pondoro, well, no one has answered so let me try. I am NOT familiar with the 550. I do however have the Sig 556 which, if you read the reviews is very accurate. I am not sure what you mean by "shooting military programs". NRA matches all use the standard military rifle, the AR 15, which in Colt HBAR (or in other match) iterations, are extremely accurate. My HBAR with a scope will shoot sub 1" at 100 yards, and sub 2" at 200 yards. The Sig 556 is very heavy, and while accurate, has a 16" barrel, so the sight radius will let you down. If however you just want to shoot 3 gun IPSC matches, then just about any light weight AR15 clone will do as the accuracy standards are not that high. Again, watch the weight of the gun and balance it against the accuracy requirements and sight requirements ie. open, red dot, scope. Just FWIW
Peter.

never shot one, but i sure have looked them over with accumulating one. They do seem very well thought out and made. i love the charging handle on the side etc. come to think of it i don't know why i don't have one yet. oh yea $$