strange range Data.

[triggernick]

I was able to get membership to a local range that has a 600 yard line! I went out this morning to get some data for my come ups, and came up with some interesting data:

After I verified my 300 zero i clicked in 10 clicks (1/10 mil adjustments) to measure what 1 mil of adjustment would do to my POI on the target at 300 yards. I assumed it would be 10.8 inches (3.6 inches per 100 yards = 1 mil from every piece of liturature I've seen) however I found that my POI moved 14 inches. I then reset my 300 zero and moved to 400 yards, and made no adjustments and no hold overs simply to measure the amount of drop. I shot 5 rounds that were 13.5-14 inches below center. I again dialed in 10 clicks up to measure what 1 mil of adjustment would be at 400...it put me dead center...so 1 mil of adjustment = 14 inches at 300, and at 400? at racine...doesnt seem to add up.

I compared this to the data I got from another shooting trip at a different range. The drop from 300-400 didn't add up from either trip. At this range (bowler wi) the adjustment to get on target from 300 zero to the 400 target was 1/3 of a mil holdover where it was a full mill of scope adjustment at the range I am now a member of. is it posible that the distance from Bowler's 300 range to 400 and My range could be that different? (Bowler's shorter than 100 yards from 300-400, or this one longer?)

1 mil worth of clicks on the scope should be = to 1 mil holdover right? (at Bowler I was using hold overs, at My new range I dialed them in for easier calcualtions.)

Just some observations, curious about your thoughts.

groups are fantastic, just learing about the come ups for different ranges, I know how to adjust for different ranges.

The round in question is Federal Gold Medal Match 175g
shot from USGI parts M14 clone with LRB receiver 22 inch barrel
Sadly no Chrono data, but estimates are 2600 FPS muzzle velosity, i think.

 

[jerkface11]

My ballistic calculator shows 13.88 inches of drop from 300 to 400 yards.

 

[Robert101]

My calcuator shows 14.68 drop with 300 yard zero. That is with a .42 BC and 150 grain BT.

 

[triggernick]

The 14 inch drop from 300 to 400 is normal, that isnt what is in question here. the strange thing (to me) is that 10 clicks (one mil) moved my Point of Impact 14 inches at 300 yards... 1 mil at 300 yards should be 10.8 inches... right?

then I moved back to 400 yards, and 10 clicks (one mil) moved my POI 14 inches. (that is normal)

1 mil of adjustment should not be the same at 300 as it is at 400 yards, right?

 

[rcmodel]

I've shoot on more then one range that has the yardage off.

One I know of for instance, the 200 yard targets are lasering 227 yards from the line.
The 300's are lasering nearly 350.

Might check on that.

rc.

 

[MCMXI]

the strange thing (to me) is that 10 clicks (one mil) moved my Point of Impact 14 inches at 300 yards... 1 mil at 300 yards should be 10.8 inches... right?

Yes ... +1.00 milrad at 300 yards should move the POI up 10.8".

What scope are you using? It's not uncommon to find adjustments that are off by some percentage but you hope that the error is consistent over the entire adjustment range so that you can account for it. If you dialed in +1.00 milrad at 300 yards but the group moved up 14", then you actually dialed in +1.30 milrad ... kind of a large error at 0.13 milrad per click. You can secure your scope in a vice by clamping the mount, then use a vertical tape measure at a suitable distance to see if the adjustments are accurate and linear over the vertical range. My guess is that they're not.

1 mil of adjustment should not be the same at 300 as it is at 400 yards, right?

+1.0 milrad at 300 yards from a 300 yard zero should move the POI up 10.8". +1.0 milrad from a 300 yard zero at 400 yards (with FGMM 175gr) should move the POI up about 13.9".