Ballistics question.

M

Mike38

New member
What would be the point of impact of a M855 round at 10 yards if the rifle is zeroed for 100 yards?

I tried to run some numbers in a ballistics program, but it would only go as short as 25 yards.

My less than educated guess would be 1 inch low.

Sound about right? :confused:
 
I would just guess that it is gonna be low slightly, itty-bitty bit less than the distance of the center of the scope to the center of the bore.

lets say your scope is 1.5" high then your shot will be 1.XX" low at ten yards. Thats if You are not having parallax issues that close...
 
Most AR's have scopes mounted higher than traditional rifles which makes for some unusual stuff if rifles are zeroed at close range but I'd think it would be less than 2". Probably closer to 1". Shoot it and see.
 
Take the point of impact in inches at 25 yards and the point of impact in inches at 0 yards . The number at 0 yards is the distance from the centerline of the bore to the sights (or centerline of the scope).

T = POI @ 25 yds
Z = POI @ 0 yds (This will be a negative number since the point of impact would be below the sights at 0 yards)

Both T and Z are in inches.

POI @ 10 yds = Z + ( ( (10 x 36) x (T-Z) ) / (25 x 36) )

So if T = 2 inches and Z = -1.5 inches then the POI @ 10 yards would be -0.1 inches.

That's a linear approximation and the trajectory isn't exactly linear, but it should be pretty accurate for the ranges involved.

You can get the point of impact at any distance between 0 and 25 yards if you plug the distance you're interested into the equation in place of the boldface '10' in the formula.
 
If this is for an AR-15 rifle, is it scoped? If so, is the scope mounted on a flat-top receiver, or on top of an M16-style carry handle? The answer will make a HUGE difference.
 
Sight offset is a bigger factor than bullet dynamics at close range. Figuring all the ballistics isn't the issue - it's that your sights will be on target, but the bullet impact will run under because that's where the barrel is pointing. The higher the sights are mounted, the more offset.

Common issue and teams have to train for it because of their precision shooting requirements in CQB.
 
A lot of ballistic calculators let you use 10 (or 5, or 1) yard increments.
At 10 yards you'd be about 2.5" low.
 
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