2 bullets touching might actually have the group centres crossing, or diverging, or one shoot above the other. More shooting is necessary to 'prove' points of impact - from any gun.

If each barrel was capable of shooting a 1" group, and 5 shots were fired from each barrel, the groups would not only touch from a .50 cal. rifle but the holes would also overlapp - this being from a gun that was perfectly regulated to shoot groups that were exactly bore centrelines apart, ie: perfect regulation as I understand it.

A 1", centre to centre group with a .50, can comprise a hole that, if the group is perfectly round (few are) that is 2" in diameter. Each barrel's 'group' will comprise a hole that is 2", although it might be a slot, oval or round.

2 shots on a target only gives a very rough indication of what the gun is shooting.