Strange day at the range today

KnotRight

KnotRight

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Barbara was out of town for the weekend so I decided to head down to the range. Took the CCMG 5.56 out (does not get shot much) and started at the 100 meter range. Could not get any grouping under 2". Then went to the 500 yard range to shoot some steel.
The benches are about 35 to 40 feet above the steel and the first 40 or so yards is a down hill to the steel level. The first set of steel is at 300 yards then 400 and 500. I was shooting 55 grn FMJ @ 2900 feet per second. Usually I can hit the 300 yard steel 95% of the time. Today was complete different. First of all, we had maybe a 10 to 15 knot wind blowing from around 300 degrees (10:30 on the clock).
I was hitting the 300 yard steel maybe 60% of the time but all over the 24" gong. Per Bullet Flight I should adjust the scope 4.3 clicks (MOA). At 400 it changes to 8.1 and at 500 13.0 MOA. The 500 yard steel was straight down a dirt road and with the 13.0 dope adjustment. With that adjustment I was 20 to 25 feet short. Need to go to around 16+. Maybe hitting 20% of the time.
I know that head wind does effect the flight but do you think that the ramp going down to the steel level would effect the flight as much as the wind out 400+ yards. If so, how do you adjust for different wind pressures? It was like the scope was loose on the rifle but everything was solid.
 
Handloads or factory ammo?
 
The down hill angle at 500 yards probably has a negligible affect on the shot as the angle will not be very great. It is the change in distance due to angle (cosine) that causes the bullet to hit high. Not so intuitively, the same applies when shooting uphill.

The 10 to 15 knot wind at 10:30 will definitely require some upward adjustment on the sight picture, but how much on a 55 gn bullet will depend on the BC of the bullet. What bullet were you shooting and I can plug it into Ballistic AE and see what the result is.

According to Pythagoras, of theorum fame (a2+b2=c2), shooting at 30 ft elevation over a distance of 500 yards, gives a horizontal distance of 499.9 yards. That 0.1 yard equates to 3.6 inches of vertical distance, or 0.69 MOA (1 MOA @ 500 yd = 5.235 inchs). But you would have to subtract that as the actual distance (horizontal) is shorter than 500.

Strange indeed.

Are you sure of your muzzle velocity?
 
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Just checked the wind call on 10:30. At 10 mph, that is a 3/4 MOA call, so it is worth 3 clicks on a 1/4 MOA scope, 10 to 15 knots, may get you a full MOA, but that is almost compensated for by the angle, so again strange, but in the ballpark. I again wonder about muzzle velocity.
 
I was using a Hornady 55 FMJ (BC .243), 22.0 grns of Tactical Rifle, WSR primers, OAL 2.25 which should produce right at 2,950' second per manual. Next trip I will bring the chrono.
Past range trips produced much better hits at the 300 and 400 steels. I agree with the wind coming up that hill should raise the bullet and not make it hit lower. I am not sure if the effect of the wind 400 yards down range would have that much more effect on then the wind @ 50 yards.
I guess it is the loose nut behind the rifle.
 
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KnotRight said:
I agree with the wind coming up that hill should raise the bullet and not make it hit lower.
Click to expand...

I believe it is the other way around. A 10:30 wind has a headwind component, in addition to the lateral component. It will have the effect of slowing the bullet some, equivalent to reducing muzzle velocity, but my bet is the muzzle velocity is something lower than 2900.

So many variables here. It was a warm day, so probably not temperature sensitivity of the powder from prior engagements on which your initial dope is based, but crimping, neck tension, barrel length, different primer, can all change muzzle velocity enough to cause the discrepancy you are seeing.

I am betting on muzzle velocity or scope shifted. Like they say, "believe the bullet".
 
Considering you’re going off what the manual says, and without knowing much else, I think you’re MV is way slower than you think.

Also, that bullet is getting close to unstable at 550-600 yds, depending on the conditions you’re shooting in. You’d be happier with a better bullet.
 
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Tim I agree with the heavier bullet. I loaded some 68 grn but they did not find their way into the range bag. The twist is 1:9 and thinking that 75/77 might be too heavy.
 
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