I was getting 4 inch groups out of my carbine at 100 yards with xm193 and attributed it to iron sights, short sight radius, and old eyes. Maybe I can do better with better ammo, but a carbine is not a target rifle.
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You might find the results of this little test interesting. Using a free-floated 20 Colt A1 barrel, I fired three 10-shot groups from a bench-rest (using a Leupold scope) using hand-loaded 52 grain Sierra MatchKings. The groups had extreme spreads of:
1.39
1.26
1.40
Those three, 10-shot groups had an average extreme spread of 1.35.
http://www.box.net/shared/static/u6legb6eft.jpg
In 1964, during testing for report number DPS-1471, the US Military conducted accuracy testing of production M16 rifles (which had the same barrel as the M16A1.) With the rifles secured in a machine rest, three 10-shot groups were fired (hmm . . . where have I heard that before) from 100 yards using M193 ammunition. The average extreme spread of the groups ranged from 2.6 to 3.6 inches.
For nostalgia sake, I fired three, 10-shot groups of IMI M193 off the bench at 100 yards from my A1 barreled upper. The average extreme spread of the three groups was 3.00.
http://www.box.net/shared/static/sviaxupx5u.jpg
http://www.box.net/shared/static/u8vt9v6jge.jpg
What's a good group size at 100 yards with irons? And what's the best target to use?
Well, I feel better now, or at least average!
1/7 16" C/L CMMG LW barrel with either Fed XM193 or Win Q3131 at 100 yds =
right around 3" using open sights off the bench.
I have done five shot groups, ten shot groups, and even 30 round groups - all about the same.
It seems to be the first manually chambered round that mucks things up the most.
You misunderstand.
The difference in trajectories at 100yds between 55gr and 69gr bullets is negligible.
The heavier bullets typically impact higher because they're slower out of the barrel. The muzzle is already flipping upwards more as they leave, so they hit higher.
Bimmer