ZERO adjustments

[jhumphrey]

I just came back from my range where the max distance that the target carrier can go is 62 feet (~ 18 M). I want to get a 25 M zero and I am having trouble with the math. what adjustments do I need to make to get the zero for 25 M? 14.5" BM with Magpul MBUS2 rear. I have the .040 taller front already.

Thank you all.

[zero7one]

Honestly, your range seems to be for pistol shooting, not rifle. I highly recommend that you try to find a rifle range or somewhere else that you can legally shoot at a longer distance. Zeroing at 25 is okay, but 50 would be more preferrable (IMHO). When zero'ed at 50 yards, you will also be zero'ed at approximately 250 yards. And realistically, between 50 and 250, the max apex above the 50/250 zero is only approximately 1.9" As for the exact math at 18m...that is beyond my mental ballistic calculator....but I will give it a shot, but it is just a theory, not written or tested fact, so please take the following with a very very large grain of salt...

18m is 28% closer to the target than 25m.

Given an approximate mechanical sight offset of 2.5 inches from center of barrel to sights.

With an upward trajectory as the round goes down range, if your point of aim is at center mass, your point of impact will be approximately .7 inches below center mass.

How I got there...25m minus 18m = a difference of 7m. 7m divided by 25m = a 28% change. 2.5 inches of mechanical offset x 0.28 = 0.7 inches low.

For a 50m zero - ...50m minus 18m = a difference of 32m. 32m divided by 50m = a 64% change. 2.5 inches of mechanical offset x 0.64 = 1.6 inches low.

If you want, give it a shot (no pun intended), and if you get the chance to confirm zero at 25 or 50, let us know how that worked out for you. Like I stated above, this is only a THEORY, so I cannot ensure that it will work or be extremely accurate, but if you are limited to an 18m range, it is what it is.

[Eric]

Why do you believe that you need a 25 M zero?

[jhumphrey]

I want to get the 25M zero because that's what I used in the Army to shoot expert. Unfortunately where I live (Denver) the only ranges that I can shoot at are the new centennial gun club (62' max for now) and cherry creek state park 50 yds / 100 yds.

Thanks for the suggestion for the zero adjustment. Is there any taller front sights than the .040? At 18 M I am already getting wobbly on the FSP. I really wish BM would have standard height FSB's...

[zero7one]

Download the Remington Shoot Ballistics Software program at:

http://www.remington.com/pages/news-and-resources/downloads/remington-shoot-software.aspx

I ran the numbers on this program and came pretty close to what I estimated. I think the difference from the 18m to 25m zero was .67 inches low using the software. I would take a look at the trajectory past 25m to see how much your round would go above the 25m mark.

Good luck.

[Vern1968]

Honestly, your range seems to be for pistol shooting, not rifle. I highly recommend that you try to find a rifle range or somewhere else that you can legally shoot at a longer distance. Zeroing at 25 is okay, but 50 would be more preferrable (IMHO). When zero'ed at 50 yards, you will also be zero'ed at approximately 250 yards. And realistically, between 50 and 250, the max apex above the 50/250 zero is only approximately 1.9" As for the exact math at 18m...that is beyond my mental ballistic calculator....but I will give it a shot, but it is just a theory, not written or tested fact, so please take the following with a very very large grain of salt...

18m is 28% closer to the target than 25m.

Given an approximate mechanical sight offset of 2.5 inches from center of barrel to sights.

With an upward trajectory as the round goes down range, if your point of aim is at center mass, your point of impact will be approximately .7 inches below center mass.

How I got there...25m minus 18m = a difference of 7m. 7m divided by 25m = a 28% change. 2.5 inches of mechanical offset x 0.28 = 0.7 inches low.

For a 50m zero - ...50m minus 18m = a difference of 32m. 32m divided by 50m = a 64% change. 2.5 inches of mechanical offset x 0.64 = 1.6 inches low.

If you want, give it a shot (no pun intended), and if you get the chance to confirm zero at 25 or 50, let us know how that worked out for you. Like I stated above, this is only a THEORY, so I cannot ensure that it will work or be extremely accurate, but if you are limited to an 18m range, it is what it is.

This is why I visit this forum. Knowledgeable people. Good stuff.