Range Report  is there an easy way to calculate this-help

inalabama

Gunny Sergeant
Minuteman
Feb 6, 2007
1,175
0
birmingham, al
i just moved my nightforce 8 x 32 nxs from my 6.5 x 47 to my sako trg 42 in 338LM. the scope was sighted in on the 6.5 x 47 with a 100 yard zero. the 6.5 x 47 has a 20 moa base on it. the ballistic table for the load i was using says at 100 yards there was 2.47 inches of bullet drop with the 6.5 x 47.

i want to adjust the 100 zero on the scope for the 338LM rounds. for now i am using the lapua 250 grain factory ammo and load [for starters before i start reloading]. i ran the ballistic table for the round as per the info from lapua and that table tells me that at 100 yards the 338LM round will have 2.03 inches of bullet drop.

here is my question, in order to adjust the scope solely for the 100 zero with the 338LM round [from the 6.5 x 47] is this as simple as reducing the dialed in MOA at the 100 zero by the difference in bullet drop at 100 yards, ie: -.43 inches, 1/2" [1/2 MOA less than now set?]. i am trying to avoid dumping lots of expensive 338LM ammo down range to figure this out.

one other question, does the MOA angle of the base effect this at all [the 100 yard zero setting on the scope] again as the base i am using with the 338LM has 15 MOA angle more [its a badgerwith 35 MOA] than the 20 MOA base on the 6.5 x 47.

all you math wizards out there, please help...

 

Lindy

Gunny Sergeant
Minuteman
Mar 26, 2003
4,006
6
Rifles Only
www.arcanamavens.com
Re: is there an easy way to calculate this-help

Yes, there is a way to calculate that, but not an easy way. You also need to know the sight height above bore for each rifle.

And I'm not going to do it. Take the f'ing thing to the range and shoot it. Generally speaking, I can zero a scope with about three rounds. If you can't, it's time to learn.

And it probably wouldn't work for windage, anyway, as the scope bases on each rifle are likely not aligned perfectly with the bore.


 

amc

Private
Minuteman
Jul 22, 2007
44
0
oklahoma
Re: is there an easy way to calculate this-help

The simple change of the bases will change the reticle palcement on the target at 100 yd 15 MOA. You will have to add that in to the equation. True MOA (1.047in at 100 yd)15x 1.047=15.7in. I did not see where you said anything about boresighting the 338LM??? Boresighting is a great way to save on ammo downrange. Not only will your elevation be different, but your windage will change between rifle to rifle depending on the relationship of how true to center of bore the holes for the scope bases are drilled.
 

inalabama

Gunny Sergeant
Minuteman
Feb 6, 2007
1,175
0
birmingham, al
Re: is there an easy way to calculate this-help

well hey lindy, nice of you to reply though it sounds like your having a bad hair day..., did i ask anyone [you] to figure it out? don't think so. last i heard this board was for sharing info/knowledge, that's what i asked for info/knowledge, if you have it and don't want to share it, that's fine, but no need to get grumpy with me...it's no magic to "zero a scope with about three rounds". with all that said:
1] i'd like to have the knowledge if some helpful shooter out there is willing to share it with me and [2] not waste the three rounds, if that troubles you then so be it, dont bother replying...
and cheer up you grump...
 

inalabama

Gunny Sergeant
Minuteman
Feb 6, 2007
1,175
0
birmingham, al
Re: is there an easy way to calculate this-help

thanks amc, i appreciate you taking the time to explain that to me and sharing your knowledge and suggesting bore sighting it, i'll try doing the math and see what happens when i bore sight it too
 

Lindy

Gunny Sergeant
Minuteman
Mar 26, 2003
4,006
6
Rifles Only
www.arcanamavens.com
Re: is there an easy way to calculate this-help

My hair is fine, thanks.

I have yet to encounter anyone who suffers from shooting too much. Given that, there are no rounds sent downrange which are wasted, except by people who aren't paying attention to what they are doing.

I have encountered people who suffer from overthinking stuff, though.
laugh.gif


 

inalabama

Gunny Sergeant
Minuteman
Feb 6, 2007
1,175
0
birmingham, al
Re: is there an easy way to calculate this-help

lindy glad to here all is well, i agree with you, practice does make perfect, it is pointless to shoot and not learn from it and yes paralysis by analysis is not good, i am just looking to continue to learn, have a good sunday and cya around...i think amc gave me the info i was looking for
 

desertHK

Gunny Sergeant
Minuteman
Feb 17, 2008
3,330
12
AZ
Re: is there an easy way to calculate this-help

you can also do it this way. Record on the scope (marking what have you) the zero for the 6 mm. mount it on the 338 LM. and zero it again. Record this marking also. Now this is assuming that you have a one piece mount. That way, you can just remove the mount and put the entire thing on the 338 LM. I have done that with my 300 win mag and 243 win. It works reasonably okay until enough money saved up for another scope.
 

marduk185

take my karma boom
Minuteman
Feb 3, 2009
1,056
9
tantric thrust
Re: is there an easy way to calculate this-help

think you got too many unknown variables in the equation inalabama. prolly just record your dope where its at now then bore sight on the other rifle. sorry thats less than math-tastic but k.i.s.s.
 

inalabama

Gunny Sergeant
Minuteman
Feb 6, 2007
1,175
0
birmingham, al
Re: is there an easy way to calculate this-help

well i took the new toy [trg-42] out to the range today, amc's advice to boresight first and marduk185's k.i.s.s plan worked out good, 3 shots and dead on with my 100 yd zero [Yo Lindy, nothin' like puttin some big ass bullets down the range on a warm sunny day to make ya feel good...], then the next 7 rounds at 440 yards were nicely together on the steel plate, only put 10 rounds through it, but they were a great 10 rounds...thanks for the advice gents.