Rifle Scopes Rails: 0 MOA or 20 MOA or 30 MOA

[REX27]

Greetings fellow shooters.

While the benefits of mounting a rail with some MOA are clear and can be summirized in giving a margin on top of what your scope turret gives in terms of elevation corrections at long distances. I have not clear what the disadvantages are.
Can you give more insights?

 

[ormandj]

What distance are you shooting and what cartridge/barrel length? You should aim to have enough elevation to keep the scope erector near center point at the distances you shoot most frequently, if possible. The scope will perform best, optically, at this position. That’s the advantage aside from the obvious having more elevation as you shoot further out. Pick the elevation you need in the mount to get you there based on the ballistics in your rifle/cartridge combo.

 

[gnochi]

Greetings fellow shooters.

While the benefits of mounting a rail with some MOA are clear and can be summirized in giving a margin on top of what your scope turret gives in terms of elevation corrections at long distances. I have not clear what the disadvantages are.
Can you give more insights?

If you do your homework, you avoid the biggest disadvantage - which is that sometimes you can’t zero at your preferred zeroing distance. You avoid this by keeping rail cant well below half of your scope travel - like, ~15moa below unless you know exactly what you’re doing.

The other main disadvantage is that every scope - from a 50 year old Weaver to a brand new Tangent Theta - has better optical properties at the centers of the lenses, which corresponds exactly with the true mechanical centerline of the scope. Erector travel almost always tries to be centered on this as well, but tolerances happen and such is life.

If you’re using a not-great scope, and you’re at the edge of travel, chromatic and spherical aberration can get really bad really quickly, and maximum resolution drops considerably. Even using a great scope that allows ridiculous erector travel - like the new March 5-42 - it’s noticeably poorer quality at the extremes.

 

[longshot2000]

What distance are you shooting and what cartridge/barrel length? You should aim to have enough elevation to keep the scope erector near center point at the distances you shoot most frequently, if possible. The scope will perform best, optically, at this position. That’s the advantage aside from the obvious having more elevation as you shoot further out. Pick the elevation you need in the mount to get you there based on the ballistics in your rifle/cartridge combo.

I think that is the real question. If you are shooting 300 to 1,000 yards, a 20 MOA rail is nice, but probably you can do without cant, or get it in your mount sas well. If you going out to 2 miles, 40 MOA begins to feel more comfortable.

 

[Steel head]

Depends on how much elevation you need.
0-500 a 0 rail is perfect

A mile plus a 30, 40 or more is nice.
My 260 currently has a 20 moa.
My 7 saum has a 45 moa.

 

[REX27]

Ok thank you for the answers, much appreciated. Mine was more of a generic question but let's talk real numbers.
Hypothetically we can say that I shot 6.5 creedmoor out of a 22''barrel with a scope that has 35mil/84 MOA adjustments. Use will go regularly from 100 to 800 meters occasionally up to 1000 mt and as close as 50 meters. I will zero at 300 meters.

 

[gnochi]

Ok thank you for the answers, much appreciated. Mine was more of a generic question but let's talk real numbers.
Hypothetically we can say that I shot 6.5 creedmoor out of a 22''barrel with a scope that has 35mil/84 MOA adjustments. Use will go regularly from 100 to 800 meters occasionally up to 1000 mt and as close as 50 meters. I will zero at 300 meters.

You would be okay at 0moa and 100yd zero to easily dial to 1000m. Also, 35mrad is 120moa, but even with 84moa adjustment you would be fine with 100yd zero and 0moa rail at 1000m dialing - you’d need to dial 27-30moa depending on bullet and load.

Edit: for clarity, in your position I would just get a 20moa mount and stop thinking about it. Also, zero at 100yd so getting the wind call right matters less (read: doesn’t matter) for your zero condition.

 

[ormandj]

Ok thank you for the answers, much appreciated. Mine was more of a generic question but let's talk real numbers.
Hypothetically we can say that I shot 6.5 creedmoor out of a 22''barrel with a scope that has 35mil/84 MOA adjustments. Use will go regularly from 100 to 800 meters occasionally up to 1000 mt and as close as 50 meters. I will zero at 300 meters.

I'd do a 20MOA mount with 6.5CM. Go use a ballistic calculator, figure out how many MRAD you need at the 'average' distance you'll shoot. You want the scope centered in elevation travel at that distance. 20MOA tends to be about right for most 6.5CMs shooting at longer ranges.

300 yard zero is interesting, any reason for that? I'm just curious!

 

[BikePilot]

20 on my AX with a 26" barrel in 6.5 Creed seems to be perfect.

 

[REX27]

I'd do a 20MOA mount with 6.5CM. Go use a ballistic calculator, figure out how many MRAD you need at the 'average' distance you'll shoot. You want the scope centered in elevation travel at that distance. 20MOA tends to be about right for most 6.5CMs shooting at longer ranges.

300 yard zero is interesting, any reason for that? I'm just curious!

Just for practical reasons, I live in Switzerland and I am literally sourranded by ranges that allows to shoot just and only at 300 meters and just on particular days of the year. So if I need to check zero quickly or check out a different ammo, 300 meters is what I have easy at hand. But I have limited experience so far, I never used a ballistic calculator, or a high quality scope, or a flat shooting caliber. My current set up is a K31 with GP11 ammo and an affordable Chinese 10x scope. So the 6.5 is going to be next year and I may discover that what worked for my old gun will work differently for the new one.

 

[BLJ]

Probably a dumb question, but what is the relationship between the base and the scope? Meaning if I have 85 MOA of adjustment available in the scope and add a 20 MOA base, do I end up with 62.5 MOA for dialing up?

Not meant to hijack, but seemed relevant here. Thanks.

 

[chevy_man]

Probably a dumb question, but what is the relationship between the base and the scope? Meaning if I have 85 MOA of adjustment available in the scope and add a 20 MOA base, do I end up with 62.5 MOA for dialing up?

Not meant to hijack, but seemed relevant here. Thanks.

85 moa total travel. This may have 42.5 from center, depending on where your zero is at. Theoretically it gives you 62.5, but could be anywhere from 40 to 80 in reality. Can't guarantee anything as nothing is ever quite perfect.

 

[BLJ]

That's what I was understanding. More of a general total MOA instead of definitive. Relative to zero and scope. Thanks.

 

[Gleedus]

If you equipment is all quality stuff. Take center of scope travel add amount to zero amount of travel from bottom is the base you can run. E.g.
Minox has 28 mil of elevation. So middle is 14 mil from bottom. Scope is 2.2 inch above center of bore so at a 50 yard zero 1.2 mil. To zero my 22lr my bullet drop from bore is 4" at 50 yards so 2.2 mil.
14+1.2+2.2=16.4 mil or 55.7 moa total cant you can run in theory. My experience has been that this is generally safe figuring and i normally can run more. With a centerfire you would be more like 14+0.6+1.