Ok so here goes. I recently started reloading a few months back and have developed a load that I've been tuning. Load is Retumbo and a 168 grain Berger classic hunter in 7mm Remington Mag. I'm averaging consistent 3/4" groups at 200 (consistent meaning I've replicated the performance several times over around 200 rounds down range) and happy thus far with it giving the fact that I'm relatively new to reloading and long range. I've can make first round cold bore hits out to 500 easily where I shoot and I want to trust this load everywhere. My question is...what will my group look like with changes in geographical location. For example I have a hunt planned in Montana next year that I'd really like to fill my tag with a load and rifle I've built. Should I expect it to open up or anything. I do believe velocity will differ some but not sure about other variables . I've been there before but didn't really think about the precision of shooting like I do now. My mind says group size will remain constant if I do my part but can't really test it until I'm there and Florida is a longe ways from Montana lol. Thanks.
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What to expect with POI changes with change in geographical locations/ altitude.
- Thread starter FlGunner
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Velocity will pick up and hence, bullet drop will decrease. Humidity and temp are still going to be scenario relative...yada yada yada. Your groups shouldn't change. I shoot Retumbo as well and don't ever have issues with temperatures, so I'd say your barrel harmonics should remain consistent with the gun still capable of doing its part.
Thank you. I just really wanted the confidence in knowing it would. I know conditions effect everything and I have no way of simulating that environment from home. Gonna have to trust my gun and equipment and practice a ton.
dfanonymous
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How do you dope your gun? That will determine how well you adapt to changing atmospherics and elevations.
FearNoWind
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[QUOTE="BigGrizz, post: ... Your groups shouldn't change.[/QUOTE]
I agree. Your groups shouldn't change but they will not strike the target at the same elevation relative to distance that you're seeing at the range. In your situation I'd collect as much dope as I could for the load you're shooting now, along with data for the area of the hunt. Plug that into a ballistics calculator and when everything on the calculator outputs matches todays real world results just change the atmospheric inputs to determine what allowance you may have to make in the field.
Thanks to dfanonymous for the telepathic assistance in preparing this missive.
We're all a team here.
I agree. Your groups shouldn't change but they will not strike the target at the same elevation relative to distance that you're seeing at the range. In your situation I'd collect as much dope as I could for the load you're shooting now, along with data for the area of the hunt. Plug that into a ballistics calculator and when everything on the calculator outputs matches todays real world results just change the atmospheric inputs to determine what allowance you may have to make in the field.
Thanks to dfanonymous for the telepathic assistance in preparing this missive.
We're all a team here.
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dfanonymous
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aww you stole my advise
Thanks guys. Yeah I'm collecting as much as possible and the outfitter said he has a 1000 yd range and will allow me to shoot and confirm anything. I know I'll need to get zeroed first and then hopefully with the atmospheric conditions and all in, will be able to make first round hits. I dope by using a ballistics app that I can enter variables in and then shoot the gun and verify everything is spot on. Out to 500 I've been dead on, but that's the fartherst I can shoot at my place.
As mentioned the concern is not the group size, but the impact of environmental conditions on point of impact. Over the long haul you would be better served changing to a 100yard zero since it will be unaffected by conditions, and when you check zero following travel it should be unchanged. Longer distance zeros mean conditions can cause a shift, and if you don't account for this exactly you could be misled into incorrectly making a zero adjustment; it's just more consistent. A basic ballistic app which you calibrate across as many different conditions as possible will get you there.
dfanonymous
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I really think the only benefit to a 200y zero is having a further PBR. Really only applies for hunters that dont shoot using turrets I reckon.
To be fair, i know you know you wont be losing much in terms of dope. You said you were shooting out to 500 and for a 7mm mag its probably something like .9 mils of hold or around there. So think of it as a fresh start. Zero, then shoot 200, miss, correct, shoot, hit, wright results in data book, move to 300, shoot, miss and so on. Wright down that DA for when you are shooting, light conditions/mirrage, relevant wind and W direction and go home. Then throw the data into your ballistic software and see if it aligns...and it wont. then tweak the MV and BC until the data matches what you wrote down on your electronic solver.
Easy day.
Then comes the wind.
To be fair, i know you know you wont be losing much in terms of dope. You said you were shooting out to 500 and for a 7mm mag its probably something like .9 mils of hold or around there. So think of it as a fresh start. Zero, then shoot 200, miss, correct, shoot, hit, wright results in data book, move to 300, shoot, miss and so on. Wright down that DA for when you are shooting, light conditions/mirrage, relevant wind and W direction and go home. Then throw the data into your ballistic software and see if it aligns...and it wont. then tweak the MV and BC until the data matches what you wrote down on your electronic solver.
Easy day.
Then comes the wind.
Thank you. Yeah it's not much in terms of correction. I am gonna go and re zero to 100 hopefully this weekend and keep my mv and BC figures in run everything with a 100 yd zero. Shouldn't take but a few shots to see if I'm on or a lil tweaking is needed. The good insight I find on here is y I come back. It's good to to talk to you guys and get good advice. I'll report back after I fire some shots down range.
WildRose
Well-Known Member
If you don't have a good ballistic calculator and environmental data to plug into it you will see a magnification of the errors as you move out.
It's really hard to measure a significant error difference at 100-200yds but the farther you go the more they come into play.
I agree with ya. I did rezero at 100 and plugged everything in to my app and re checked at 500 to see what would be. It may be luck or it might be coincidental but I held just under MOA roughly 4". My drop dope I got out of the app had me right on with my vertical dispersion being about 1.5"-2". The rest was probably wind or me. It was relatively calm and I did not make any corrections just held center. This was a good group for me at 500. I have done it multiple times with calm conditions but I know that the more wind I get it shortens my range until I prove I can do it more consistently. The gulf winds seem to always be shifting on me when I wanna squeeze the trigger lol.
WildRose
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Try living on the high plains sometime at 4000+ where the wind never stops and it may change on you three times before you get to the target!
Glad it worked out for you, that is great shooting. I like to practice on the rocks in my neighbor's fields. Good for him and very challenging for me even back down here at 1250'.
