At what point does a 20 MOA base become necessary?

That depends on the adjustment range of the scope, the trajectory you're working with, and the distance to the intended target.

When you run out of adjustment in your scope for shooting at longer distance. A scope with a lot of adjustment range (like a 30mm tube for example) is less likely to need a 20 moa base than say a 1" tube with less adjustment range.

Any way to determine this before you build?

a lot of 30mm tube scope have less adjustment than 1" tubes do. most will out of adjustment between 600-700yds

Know the trajectory of the round you'll be shooting.

Know the distance you want to shoot.

Know the adjustment range of the scope you will use.

Take into account you may use up some of the available adjustment sighting in at your zero distance.

Reading and Research.....helps a lot!!

Beat me to it. What he said...

As an example - say your scope has 15 mils total vertical adjustment. If we assume for sake of discussion that your zero is in the middle of travel, that leaves about 7.5 mils you can dial up for distance shooting. A quick look at a ballistic chart for your 308 shows you can expect to run out of adjustment somewhere around 800-850 yards. If you want to dial for longer distance with that scope, you'll need more elevation built into the scope mount, via a 20 moa (or more) base.

On the other hand, if you're using a larger tubed scope with say 36 mils of adjustment, you'd be able to dial to 1100-1200 yards with a flat base.

If in doubt, there's not much downside to a 20 moa base.

Appreciate the input. I plan to limit my shooting to no more than 600 yards with my 280, 7 Wby, 308 or 300 WSM.

Everything below zero on the erector,is 100% fhuqking USELESS. Hint.

20MOA inclination,is a joke,at best.

Hint.................

With a 22LR You'll need one sooner than later.

For longer range 22LR, I started with a 30MOA, and probably should have gone with more. Oh well.

you can always addburris xtr sigs with inserts to get more slope

I shoot alotta 75 MOA 1913 extended rails for Anschutz 54 Rimfire Fun. KILLER setup. With all the inclination in the rail,one can use a lower ring height. Hint.




6BR assembled on Saturday,coughed up 39.6 Mils remaining on it's erector,after a 20yd 105 Hornie BTHP zero. Burris steel 25MOA 1913 rail base inclination and 'Horn's wearing all 40MOA,to secure the 6x MQ.




No zero-stop requisite,as less than a full revolution remains on the erector.

Hint..................

We don't need no 20MOA base!!

Dimick Caplock Rifle by .com/photos/61286670@N08/]Sharps Man, on [bleep]

At 1,000 yard many stock rifles run into the end of thier adjustments, which is never good for a scope (you want it to be more to the center).

Typically it starts at 800 yds so my rule of thumb - if it’s a 800 yard + rifle ... get 20 MOA rail, if it’s over 1,000.. think / research 30/40.. or more.
With 600 yards, and a 30mm tube you are typically OK... I’m sure there are exceptions.

I would focus on your typically target range, vs. the furthers range you’d shoot..

Meaning Easter woods hunting 600 yards is an exception (0 MOA is reasonable), Midwest / Western plains like West KS, anything under 300 is really rare - it’s more like 500yds is a common shot. (I’d think 20 MOA)

Built off Stith components? I like that rig, very cool.

If your shooting 1000y you need it. Remember if a scope has 60-70 total MOA, you divide by half and sometimes more just by the mounting system. This is just my 2 cent worth. The smaller the tube diameter the less travel you have as another poster mentioned. Large tube diameter usually give you more MOA adjustments at long distance, but not always.

Don't forget about vignetting. The outer 2-3 MOA are obscure on most scopes depending on quality.

Stick, do you keep the erector at the center and make elevation potential from the rail and ring insert combinations and hash marks? Does keeping the erector somewhat centered improve optical quality and maintain mechanical quality of the erector? I ask because of your statement of being below zero is a waste.
Thanks

How could you keep it centered and add more inclination without changing zero range?

I have a 20 MOA base on my 284 HB. It carries a sightron scope. That scope will not zero inside 200 yards. Even then it is bottomed out nearly. But that is a rifle intended for 1000 yards.

More than likely you would be better served by a 10 moa base.

Nah, you’d be better served by a scope better suited to the purpose of that rifle...

This is very dependent on scope design. A well-designed scope has optical quality and mechanical integrity that is affected little by the position of the erector. The SWFA SS, Bushnell LRHS, and several others, share this design commonality, and can be zero’d with enough inclination in the mounting system to bottom out the erector, with little to no negative impact. The Bushnell DMRII, for example, functions mechanically perfectly at all positions of the erector, but with that particular scope design the optical performance suffers significantly as the erector travels away from

With a well-designed scope, there’s no downside to adding inclination until the erector is about bottomed out after being zero’d.

It takes a pretty poor scope to not handle a 20 moa cant and still zero at 100 yards. More likely your mounting system is not true to the barrel and has more cant built in than you think. Either that, or your windage adjustment is way off to one side (again because of an out of true mount), which reduces available vertical adjustment in the scope.

For reference, 20 moa is roughly equal to 6 mils. That's not very much, and most scopes intended for dialing can handle it easily with plenty to spare.

Maybe I'm wrong. Truth is I haven't tried it in a good number of years. The sightron SII 6-24, love it.

If you aren't running out of adjustment you don't need one. Not needing something but having it anyway isn't a big deal, but like most things there is pluses and minuses. Pluses are more elevation adjustment, some flexibility in mounting and scope interchange ability. Both are good if you need them and useless if you don't.

Minuses are obstructing the loading port, potential higher than optimum mounting, they cost sometime, and weigh something. I see rifles that are harder to load than they have to, with adjustable stocks that they wouldn't have needed otherwise, all at at cost in dollars, just to solve a problem they didn't even have.

I'm guilty to, having many rifles that have slanted rails that they don't need and will never need. Just a pain in the butt that I had to pay for.

Rule of thumb for me is if 600 yds or less then I can use standard mounts with 0 cant. More than 600 yds it's a 20 MOA rail. BUT if I'm going to use a rail it'll be a 20 MOA because there's no real reason to go for a 0 MOA rail over a 20. On rifles I'm carrying a lot I prefer two piece bases and rings just because I like to carry them with my thumb hooked between the scope & rifle and a rail interferes with that.

The rail is a superior system though and if you are going to use one then make it a 20 MOA, there's no real reason to buy a 0 MOA rail that I can see.

Can't quite reach 600 with a Swaro z5 1 incher and a 200 yard zero on a 308 or '06.....

I run a 20 minute rail on most of my custom rifles. My Nightforce scopes will still adjust up close. But NF has a ton of adjustment.

The LAST fhuqking thing I want,is an erector centered at zero. You just threw halfa your scope in the dumpster.

I want a glass that'll cough up all of it's erector travel,less concession(s). Have lotsa platforms,that yield 40 Mils or better on the erectors alone,at their zero range.

Hint......................

https://youtu.be/RJOrwjj44Yc

Sugartits it’s you and then some. Crying laughing

I've used the follow rough rule of thumb when considering how much base cant to use on a rifle. Much of course depends on your rifle and load. It's silly to use a 40 MOA base on a rifle that's meant to shoot 200 yds or less, even if the scope has enough the elevation adjustment to use a canted base. At the same time it's also silly to have a rifle, cartridge and scope capable of shooting 1,000 yds. and choking it down with a base and scope that won't let you utilize it's inherent range.

All this is to say, the rifle, it's cartridge, it's scope and it's bases and rings are all part of a package. And each part must complement the other.

Now on to canted bases. Any decent scope maker will now tell you the total elevation travel in the scope specifications. Those numbers are expressed in MOA or MILS.

Any Scope that has a Elevation travel of less than 50 MOA (14 Mils) gets a 0 MOA Base
Any Scope that has a Elevation travel of Less than 70 MOA (20 MILS) gets a 10 MOA Base (3 Mils)
Any Scope that has a Elevation travel of Less than 85 MOA (24 MILS) gets a 20 MOA Base (6 Mils)
Any Scope that has a Elevation travel of Less than 100 MOA (29 MILS) gets a 30 MOA Base (9 Mils)
Any Scope that has a Elevation travel of greater than 110 MOA (32 Mils) get a 40 MOA Base (12 MILS) or more.

I use rounded numbers in the above. And yes there are exceptions, and special purpose applications where deviating is necessary, but generally unless you know what your doing, the above works well and will not get you into trouble.

Some of the dumbest fhuqking schit I've ever seen. Hint. Congratulations?!?

Someone who "knows" and "does" as "much" as you,will always be best served by asking questions,rather than giving "answers". Hint.

Glass with the least erector travel,needs the most help.

Bless your heart for trying though.

Hint.

Laughing!.........................

Sugar tits poor poor sugar tits.
Better off beating off ! If ever a song fit sugar tits that one nails your shît show center mass. 🤣🤣🤣🤣🤣🤣https://youtu.be/RJOrwjj44Yc

Them that cain't break trail,simply must follow and relate their Melting Snowflake Routine...which is assuredly no "Act". Congratulations?!?

Only ordered (1) 40MOA rail yesterday and I reckon it'll do nice thangs for a 6x MQ aboard a SALAMI 22-250 and it's 3K fps+ 88gr Smooches.

Google it all.

Hint.

Bless your heart.

Laughing!..................

Your still number 1 in my heart Larry......

Well you did get it completely backwards lol.

Don't pick on her,because she's doing her BEST. Hint. Laughing!

Oooooopsie!..............