Rifle Scopes Double Check my Math?

[joelinux]

So, I just purchased an RPR in 6.5 Creedmoor:

https://www.ruger.com/products/precisionRifle/specSheets/18029.html

I'm also going to get the ATACR 7-35x56mm scope:

https://nightforceoptics.com/atacr/7-35x56-f1

I'm evaluating these two scope mounts for suitability:

https://spuhrwebshop.com/en/isms/sp/34/6/sp-4603b.html
https://spuhrwebshop.com/en/isms/sp/34/6/sp-4602.html

If I'm reading this correctly:

https://www.snipershide.com/shooting/threads/ring-height-info-how-to-measure-correctly.20706/

We have a .5" clearance (Rail height), 1.5" height of the scope, and the bell diameter outside is 65mm, or .2.56, half of which is 1.27953".

Following the equation, we have:

.5+1.5-1.27953=.72047, meaning we have enough clearance.

The PRS has a 20MOA slant, which equals to 5.55mils, plus the 6mils on the scope mount, is 11.55 mills, is well within one half of the total internal adjustment range of the scope itself (14.5mils)

Now, the only appreciable difference between the two scope mounts is the distance between the rings.

The 4603b has a length of 5.79", which is within the ATACR's 6.5" Mounting Length.

The 4602 length is only 4.76", which I assume gives more of a chance for the scope to move?

As an aside, on the Scope Specifications, what does "Front/Rear Mounting Length"?

 

[Peter Laurvick]

So... not exactly the answer you’re looking for but, the ATACR will fit on both those Spuhr mounts. I think it’s easier to mount well with more room around the turret rather than less. But either way you’re not expecting the rings to clamp the turret but the tube, so that distance shouldn’t matter.

Next for your height equation. I’ve also gone that far in depth running math for clearance and such. But for that pair it’s simple because people have used those combos before and have matches. I’m running a 5-25x56 ATACR in spuhr on my RPR and it’s perfect. Just make sure it’s 1.5” high and you’re golden.

Sorry if that still doesn’t answer your question but hoping it helps

 

[joelinux]

So... not exactly the answer you’re looking for but, the ATACR will fit on both those Spuhr mounts. I think it’s easier to mount well with more room around the turret rather than less. But either way you’re not expecting the rings to clamp the turret but the tube, so that distance shouldn’t matter.

Next for your height equation. I’ve also gone that far in depth running math for clearance and such. But for that pair it’s simple because people have used those combos before and have matches. I’m running a 5-25x56 ATACR in spuhr on my RPR and it’s perfect. Just make sure it’s 1.5” high and you’re golden.

Sorry if that still doesn’t answer your question but hoping it helps

No, that helps out a whole lot. Is my math right on the mil travel distance for the scope?

 

[Peter Laurvick]

It’s easier with MOA but it looks solid. I’ve got the same slant in mine and I get 100MOA of vertical adjustment. The 7-35x is advertised as less than the 5-25x but everyone says it always has more than advertised. You should have around 80-90MOA of travel

 

[Near miss]

The PRS has a 20MOA slant, which equals to 5.55mils, plus the 6mils on the scope mount, is 11.55 mills, is well within one half of the total internal adjustment range of the scope itself (14.5mils)

Pardon me but I think 1 mil equals 3.44 moa, 20moa=5.8mil. Not crucial for you math but just to correct this.

I have 5.55+6 MIL SPUHR 4602 too and no issues on a scope with 25mil of internal adjustment. And I have not bottomed it, maybe around 3-4mil to go.

 

[lennyo3034]

Unless you’re consistently shooting ELR, I think that’s too much cant. Scopes perform best near the center of their travel and with 11 mils cant (6 from mount and 5.8 built in to RPR rail) you’re average engagement distance needs to be around 1200 yards. Meaning you will shoot beyond that just as often as below for those mounts to be ideal.

Personally I would go with the Spuhr 4002 with no built in cant.

 

[JohnsonKJ]

So if i have a 5-25x56 F1 MIL ON A 338 lapua magnum does anyone have Information for beyond 200 yards?

 

[JohnsonKJ]

Well if you had information on what grain bullets you’ve used and how many clicks for anything past 200 yards using 338 lm with the Nightforce 5-25x56

 

[JohnsonKJ]

I have several grain in 338 lm , its a TRG 42 with 5-5x 56 F1 Mil BEAST

 

[Slides]

I appreciate this is an old thread but for everyone reading, the scope centre to bore offset combined with bullet drop to 100 yards means even with a 20MOA base you are only about 1.5mil low of elevation centre on a scope. If you are regularly shooting 500-1500 yards, you are better off with 40MOA/12MIL cant on mount/ring combo or 60MOA/18ish MIL with a 34mm or larger scope body to actually make use of the internal elevation and best picture clarity at ranges where it matters.

 

[Near miss]

I appreciate this is an old thread but for everyone reading, the scope centre to bore offset combined with bullet drop to 100 yards means even with a 20MOA base you are only about 1.5mil low of elevation centre on a scope. If you are regularly shooting 500-1500 yards, you are better off with 40MOA/12MIL cant on mount/ring combo or 60MOA/18ish MIL with a 34mm or larger scope body to actually make use of the internal elevation and best picture clarity at ranges where it matters.

Yep, and even if the image would suffer at close distances, I would rather have slightly poorer image at close and the best image at farther distances.