Is there a quick trick to estimate available scope adjustment?

[Nailedit]

I'm working on getting either a .308 or possibly a 6.5CM for my first long range project and in either case would likely use a 20MOA base. The more precise question would be: How would I go about approximating how much elevation adjustment (up) I would have with a given scope from a 100 yard zero?

The reason I ask is that I'm on a bit of a budget which has me looking at the Bushnell ET 6-24x50 with G2DMR reticle. It has something like 19 mils of total elevation (based on what I've read) and I want to be sure I can dial anything within mine or the cartridges capability. I have a feeling I'd be fine with a .308 but wouldn't have the adjustment to push my limits with a 6.5.

Does anyone know how many mils down they have had to come from optical center to zero either cartridge at 100 yards using a 20MOA base? For example the Bushy would have ~9.5mils from center and if a 100 yard zero typically requires coming down ~5mils then I'd have roughly 14.5mils available.

I hope my questions are stupid enough, lol.

 

[TOP PREDATOR]

Run a ballistics Calc for both for the load range you think you may be using with a 100 yRd zero.

see how many mils you need and bump it against the optic's adj range. Add in the Moa to mil conversion of the base.

that should give you an idea in the neighborhood of what you need.

 

[pinklbd]

^^^^. U will never truly know until u zero the scope. U should be fine though with a 20 moa base and 19 mils of adj.

 

[Bender]

That is a great scope! I would guess it would be more than plenty. Is it a 34mm tube? If for some reason it isn't enough elevation just go to a 30moa base. Quick fix.

 

[Blackjack988]

I'm thinking he is referring to the 30mm tube version of the scope. I have one sitting on my Tikka T3 back home. I'll take a look when I get out of work later tonight if need be. Its in .223 but it may give you a rough idea as to how much you'll have.

 

[Nailedit]

Run a ballistics Calc for both for the load range you think you may be using with a 100 yRd zero.

see how many mils you need and bump it against the optic's adj range. Add in the Moa to mil conversion of the base.

that should give you an idea in the neighborhood of what you need.

I've ran some numbers and come up with needing 12 mils of adjustment to push a .308 out to the transonic region, with the 6.5CM needing 16+, but I haven't figured out about what my starting point will be in terms of the scopes adjustment at a 100yd zero.

I guess I could look at the raw bullet drop at 100yds, factor in the base and get a decent idea of how much the scope would need to be adjusted down from optical center for the 100yz zero. Since we are talking about scope line of sight, I'm wondering if I should add the scope height to the overall bullet drop.

That is a great scope! I would guess it would be more than plenty. Is it a 34mm tube? If for some reason it isn't enough elevation just go to a 30moa base. Quick fix.

I'm actually referring to the 30mm tubed 6-24x, but I'm certainly working on possibly bumping up to the 34mm 3.5-21x. Both seem to be a great value in their price range, and the G2 reticle seems about perfect. I favor tracking/repeatability over superior glass quality when on a budget that doesn't allow both, so hopefully they both stand up in that regard.

As far as a 30MOA base...I wouldn't be against that unless I would have issues reaching a 100yd zero.

I'm thinking he is referring to the 30mm tube version of the scope. I have one sitting on my Tikka T3 back home. I'll take a look when I get out of work later tonight if need be. Its in .223 but it may give you a rough idea as to how much you'll have.

If you have a good idea of where your scope is optically centered, it would be great to know how far your 100yd zero is from that.

 

[Nailedit]

OK, for both .308 and 6.5CM, with a 1.8" sight height there is a drop of 1.2 mils at 100yds relative to the scopes center line. Basically saying that if I had the scope optically centered and parallel to the bore that I should hit 1.2 mils low at 100yds. Factor in 5.5 mils from the base and I should then hit 4.3 mils high. After dialing that in to zero at 100yds, and assuming the scope has 9.5 mils in each direction from center I should then have about 13.8 mils available.

Unless I'm missing something I should be good to go with .308, but if I end up with a 6.5CM and get a chance to really stretch things out I'll likely be using some holdover as well. If anyone sees a flaw in what I did, let me know.

 

[Boxcar]

The 6.5 should require far less elevation then the .308. It's a flatter shooting cartridge. What info are you using that requires 16 mils of elevation to take the 6.5 to 1k?

Federal .308 168gr gold medal match basic atomospherics 12.74 mils to get to 1k

Hornady factory 6.5 creed 140 Amax with basic atmospherics. 9.74 mils to 1k


Far less adjustment required to get 6.5 to 1k then the .308. If you're sure you can get there with the .308 you'll have plenty with the 6.5

 

[Blackjack988]

FYI. It looks like I have ~14 mils worth of elevation left when zeroed at 100 yards at .223. Not sure if it'll help.

 

[Nailedit]

The 6.5 should require far less elevation then the .308. It's a flatter shooting cartridge. What info are you using that requires 16 mils of elevation to take the 6.5 to 1k?

Federal .308 168gr gold medal match basic atomospherics 12.74 mils to get to 1k
View attachment 44015
Hornady factory 6.5 creed 140 Amax with basic atmospherics. 9.74 mils to 1k
View attachment 44016

Far less adjustment required to get 6.5 to 1k then the .308. If you're sure you can get there with the .308 you'll have plenty with the 6.5

Sorry, I should have specified that I would be interested in pushing to the transonic region with either cartridge. The 6.5 will require a bit more adjustment for that.

FYI. It looks like I have ~14 mils worth of elevation left when zeroed at 100 yards at .223. Not sure if it'll help.

Well, my math told me 13.8 mils, so that is reassuring. Thanks bud.