I am trying to train up for a competition. The competition suppose to be shoots no longer than 800 yards. I am shooting sub MOA at 100 yards right now. But I have never shoot over 400 yards before. I have a range finder on the way to help with accurate ranging. I am also using JBM calculator. I am running a 308 SPS tactical with a USO 3x17, a flat base, and a Harris bipod. Any other suggestions beside shooting and correcting the JBM calculations?
- Thread starter GillJr
- Start date
Re: Suggestions
I'm pretty new here, but I'll take a shot at some suggestions for you.
To be sure of accurate DOPE for the distance ranges you mentioned you have two choices. Shoot at those ranges to see what your bullet does (then adjust your MV in the ballistics calculator to match the actual vertical drop as best you can - this is assuming you have a good BC for your bullet). Or, chronograph your ammo to get a good estimate of your muzzle velocity (MV)and plug that into the ballistics program to get a good first cut at drops for your distances. It's way better to do both and refine as needed.
Others, please chime in and correct me if this is wrong. Thanks.
I'm pretty new here, but I'll take a shot at some suggestions for you.
To be sure of accurate DOPE for the distance ranges you mentioned you have two choices. Shoot at those ranges to see what your bullet does (then adjust your MV in the ballistics calculator to match the actual vertical drop as best you can - this is assuming you have a good BC for your bullet). Or, chronograph your ammo to get a good estimate of your muzzle velocity (MV)and plug that into the ballistics program to get a good first cut at drops for your distances. It's way better to do both and refine as needed.
Others, please chime in and correct me if this is wrong. Thanks.
Re: Suggestions
Best thing for you to do is shoot out to those ranges and tweak your muzzle velocity to match what your rifle is doing. That's what I've done without a chronograph.
Best thing for you to do is shoot out to those ranges and tweak your muzzle velocity to match what your rifle is doing. That's what I've done without a chronograph.
Re: Suggestions
Guys I went out shooting yesterday. I got to close up my grouping a little bit. But the wind really started messing with my shoots at 300 yards. I went from a closed area (trees blocked wind) to an open field. Got to get better at calling the wind.
100
200
300
400
Guys I went out shooting yesterday. I got to close up my grouping a little bit. But the wind really started messing with my shoots at 300 yards. I went from a closed area (trees blocked wind) to an open field. Got to get better at calling the wind.
100
200
300
400
Re: Suggestions
Assuming you kept track of your elevation adjustments at all those ranges (100-500 yards), and are confident of consistent solid shooting on your part, you should have enough information from those targets to refine your dope using JBM. (It would be better to have 5 shot groups on each target, but just take what you have.)
My estimates based on eyeballing your targets: At 100 yd your shots average 0.25 in (1/4MOA) low, at 200 your elevation is spot on (are you zeroed at 100?, 200?), at 300 your shots average just 0.5 in (1/6MOA) high, at 400 your shots average 2 in (1/2MOA) high, at 500? - add same info yourself.
I suggest you make a table of all that, including your actual elevation adjustments at each range, play around with the MV in JBM and see if you can get drops to match up at all distances.
Have fun and let us know how it goes.
Assuming you kept track of your elevation adjustments at all those ranges (100-500 yards), and are confident of consistent solid shooting on your part, you should have enough information from those targets to refine your dope using JBM. (It would be better to have 5 shot groups on each target, but just take what you have.)
My estimates based on eyeballing your targets: At 100 yd your shots average 0.25 in (1/4MOA) low, at 200 your elevation is spot on (are you zeroed at 100?, 200?), at 300 your shots average just 0.5 in (1/6MOA) high, at 400 your shots average 2 in (1/2MOA) high, at 500? - add same info yourself.
I suggest you make a table of all that, including your actual elevation adjustments at each range, play around with the MV in JBM and see if you can get drops to match up at all distances.
Have fun and let us know how it goes.
Re: Suggestions
Great. So at 500yd you're 8in (~1.6 MOA) high. (Post a pic of your 500yd target if you get a chance.) That's a consistent pattern - the average of your shots is a bit higher than your actual elevation adjustments at each distance (300-500yd). That suggests tweaking your MV up a bit (trial & error) in JBM to better match your actual drops. (You are already close; it's just that the actual MV from your gun is a bit different from the MV on the ammo box.)
Bet you've already got it figured out, so I'll shut up - soon. Remember, you're not looking for perfection. Match the drops as best you can (and recheck that all the info you've put into JBM is good - especially temperature, BC and bullet length !).
Once you get a good match, I suggest that you then shoot again at those distances to <span style="font-weight: bold">confirm your refined DOPE </span>- again I suggest 5 shot groups. You may have to tweek again slightly, but you should be really, really close.
Have fun shooting!
Great. So at 500yd you're 8in (~1.6 MOA) high. (Post a pic of your 500yd target if you get a chance.) That's a consistent pattern - the average of your shots is a bit higher than your actual elevation adjustments at each distance (300-500yd). That suggests tweaking your MV up a bit (trial & error) in JBM to better match your actual drops. (You are already close; it's just that the actual MV from your gun is a bit different from the MV on the ammo box.)
Bet you've already got it figured out, so I'll shut up - soon. Remember, you're not looking for perfection. Match the drops as best you can (and recheck that all the info you've put into JBM is good - especially temperature, BC and bullet length !).
Once you get a good match, I suggest that you then shoot again at those distances to <span style="font-weight: bold">confirm your refined DOPE </span>- again I suggest 5 shot groups. You may have to tweek again slightly, but you should be really, really close.
Have fun shooting!
