07-12-2012, 01:00 AM
michaelmew Wrote:Let me preface by saying that I am an amateur shooter with no formal training.
I want to re-establish all the zero distances on my rifles for various reasons and work up some type of dope chart for various distance and bullet combinations. I do not have access to a range past 100 yards at this time. Ideally, I would be able to shoot to each distance and see where I am on paper and then make a note in a dope chart, right? That is not a possibility, so I need to mathematically estimate to the best of my abilities what those results will be.
I have a couple of issues that are concerning me, so I'd like to float these questions out to you guys:
#1. Min & Max PBR is the distance that I can take a shot without the need to adjust POA (assuming a center mass or kill zone hold). Correct? I would think that +/- 5" would yield good results. Would you agree with that?
#2. If I zero my AR 5.56 at 50yds with 55gr M193 (3100fps), then POA=POI again around 245yds. Correct? If I do nothing other than load a 62gr M855 (3000fps) into the rifle and fire again, the 50yd zero is not the same, and the other POA=POI is different. Is there a way to calculate this difference? How much of a difference is that? What about if I am zero'd for the 77gr Mk 262, but decide to shoot the 55gr or 62gr… how much of a difference then?
This example is for a 5.56, but it could easily translate to the Grendel & other calibers, especially for someone who hand loads.
#3. Is it uncommon to use a different zero for your scope and your BUIS? I guess the assumption is that with BUIS you are engaging targets at a closer range, therefore your Min & Max PBR may shift?
I realize there are many unique factors that may come in to play, but try and give advice if you can. And, I would love to go out there and shoot and see what happens, but that just isn’t feasible right now. I need to have a calculated approximation of expected results before I get to the range. I appreciate your patience with an uninformed shooter trying to get started in the right direction for better marksmanship.
-michaelmew
MM:
1. You are correct.
2. Zero your blaster at 100 yards. I say 100 yards, not because it is the only way, but rather 100 yards is a distance where you can be sure your bullet has crossed your line of sight. Then you can look up the elevation from 100 that you need to get to your zero range. Given a 100 yard zero, if you want to get to 250 yards point of aim / impact, you will end up coming up about three minutes. And it probably won't matter in practical terms what load you are using. Note, however that your initial zero at 100 yards may well be different between different loads. Their come up to about 500 yards will be very close but initially they may zero differently. So, do not assume a hit if you change ammo and don't adjust your zero for the different ammo.
3. Depends on your conditions. One thing about a BUIS is that they are very crude devices and given the target somewhat blends into the background, your error becomes immense. Zero the BUIS for 200 yards and it will be fine on big targets with big kill zones.
LR1955