How do I figure out if I have too much cant on my mount/base combination?

[TacosGigante]

I know there are a lot of threads asking if X scope will be able to zero at 100 yards with a 40 MOA base. I have a similar question and was wondering how one figures that out. I know I could ask the hide-mind and get the right answer, and I will below, but I would like to know how to do the math myself for next time.

Thanks

Ok - my specific set up would be a 20MOA rail married to a 20MOA mount on a TT 5-25 with 28 MRAD of working elevation. Calibers include 308, 6.5cm, maybe 6cm and something like 338 Lapua or 300PRC. I would like to be able to zero at 100 yards without issue.

 

[TheOE800]

40 MOA = ~ 12 MIL. 28/2 = 14. Stay under 14 additional mils in added inclination to get most of the 28 mils of travel in the TT turret while still being able to zero your rifle at 100 yards (as long as your gun isn’t curved ).

 

[Dogtown]

Beat me to it.

 

[UpSideDown]

Your elevation travel is your total adjustability up and down. If you have 28 MRAD of elevation adjustment, that means you can go up 14 MRAD or down 14 MRAD from scope center. 40 MOA equals 11.6 MRAD, and you have 14 MRAD to play with according to the spec sheet.

A 100 yard zero will have your scope adjusting downward some from parallel to the bore. So if your scope actually has a true 28 MRAD of adjustability, and your rounds are hitting reasonable close to inline with the center of the barrel at rest, then you could use a 40 MOA base assembly with your 28 MRAD adjustable scope and zero at 100 yards.

 

[TacosGigante]

40 MOA = ~ 12 MIL. 28/2 = 14. Stay under 14 additional mils in added inclination to get most of the 28 mils of travel in the TT turret while still being able to zero your rifle at 100 yards (as long as your gun isn’t curved ).

Thanks!

 

[TheOE800]

On a lesser scope system you may have image degradation or windage limitations at the extremes of elevation erector travel/adjustment, but on top tier stuff like ZCO, S&B, and TT those issues shouldn’t occur.

 

[b6graham]

a good general rule i've found is 33-40% is non issue

so 9.3-11.2mil

40moa total should be safe in most scenarios with a 28mil travel TT without having image issues

 

[Dogtown]

Threads like this give me brief flashbacks to my old USO SN-9 - 230MOA external adjustment, baby!

 

[TheOE800]

Why you need 40 MOA out in Falls Church? Shooooot.

 

[TacosGigante]

Why you need 40 MOA out in Falls Church? Shooooot.

HAHA, mostly I want to see if I need to order a new mount or if I can use an existing one.

 

[UpSideDown]

Threads like this give me brief flashbacks to my old USO SN-9 - 230MOA external adjustment, baby!
View attachment 7852867

Wot in tarnation!?

 

[Dogtown]

It was for a .408CT Windrunner, but I put it on the AR as a joke. Back in the early 2000s a lot of scopes had issues as you approached the limit of the erector cell (some still do), especially at high magnification. The SN-9 was designed to mitigate that by having the elevation and windage be external, so you were always looking through the center of the lenses.

 

[Lonely Raven]

The SN-9 was designed to mitigate that by having the elevation and windage be external, so you were always looking through the center of the lenses.

That makes a lot of sense, assuming they can have it track accurately...you'd always been looking through the best part of the glass!

I just sighted in my .375 CT this Saturday. 70 MOA on the Rail, and 30 MOA on the Spuhr mount(!)...even with the new Zeiss LRP, 100 yard zero has me with 25.5" of offset. I'm unsure what my "true zero" would be...probably something like 1300 yards.

 

[Longman]

That makes a lot of sense, assuming they can have it track accurately...you'd always been looking through the best part of the glass!

I just sighted in my .375 CT this Saturday. 70 MOA on the Rail, and 30 MOA on the Spuhr mount(!)...even with the new Zeiss LRP, 100 yard zero has me with 25.5" of offset. I'm unsure what my "true zero" would be...probably something like 1300 yards.

Hello, can i have a question? what you think about zeroing .375CT on 500m+???

 

[b6graham]

Hello, can i have a question? what you think about zeroing .375CT on 500m+???

lots of variables in that

i'd figure out what the mil offset is at 100y to match a 500m "zero" and then confirm at 500m

 

[Longman]

And what about accurate and precise on that 500m? Distance between hits. It should be in the 2MOA circle? Or more?
Thanks

 

[b6graham]

i was gonna say 2" group at 500m or whatever YOU as a shooter are capable of. doable with a dasher. should be no problem with a 375

really you want to make sure your 500m offset at 100m matches POI and isn't like 1-2mil off

but at the end of the day. it what really matters is knowing what your dope is at distance and how to make that work

offset 10mil into your 100m zero and ballistic apps can easily account for that now a days