Scope Bases
0 MOA Against 20 MOA Base
Quick answer
A 20 MOA base tilts the scope down at the front, turning unused down travel into usable up travel, which is why the Weaver Extended Multi-Slot Base, Remington 700 Short Action, 20 MOA exists. But on a rifle that will never shoot past about 300 yards, that same tilt can make it impossible to zero, because the erector runs out of down adjustment first.
Weaver Base Pair for Remington 700, Matte
$18.00Puts zero near mechanical centre with roughly equal elevation travel available above and below it, correct for a rifle that stays inside about 300 yards.
Best for: a hunting rifle inside 400 yards
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Weaver Extended Multi-Slot Base, Remington 700 Short Action, 20 MOA
$53.79Tilts the scope down at the front to convert unused down travel into usable up travel, correct for a rifle intended to dial come-ups well past 500 yards, and wrong for anything closer.
Best for: a Remington 700 short action shot past 600 yards
Check price on AmazonThis is the single most consequential decision in this whole comparison set, and it is also the one most often made by copying whatever the last rifle had rather than by actually working out the distance the current one needs to reach.
A scope's elevation adjustment moves the internal erector assembly up and down inside a fixed mechanical range, and roughly half of that total range sits above the point where the reticle starts, called mechanical centre. A base mounted perfectly flat, at 0 MOA, puts your zero somewhere near that centre point, which leaves roughly equal room to dial up or down from it.
A 20 MOA base changes the starting point, not the total range. It tilts the whole scope down at the front by 20 minutes of angle relative to the bore, so the erector has to dial up 20 MOA further than it otherwise would just to bring the point of impact back onto the point of aim at your zero distance. That consumes some of the lower half of the adjustment range to buy back an equal amount of the upper half, which is exactly the trade you want on a rifle being built to dial come-ups past 500 or 600 yards. On a rifle that will only ever be zeroed and shot inside 300 yards, that same trade can push the required zero adjustment past what the erector has left to give in the down direction, and the rifle simply cannot be zeroed at all with that base installed.
What does a 20 MOA base actually do to a scope's elevation travel?
Nothing changes about the scope itself. The base tilts the entire optic downward at the front relative to the bore centreline by 20 minutes of angle, so the line of sight and the bore are no longer parallel before you ever dial a click. To bring the two back into agreement at your zero distance, you now have to dial roughly 20 MOA of additional up adjustment compared to a flat base on the identical rifle.
That sounds like a cost, and at the zero distance it is: you spend elevation travel you would not otherwise have spent. The payoff comes at distance, past your zero, where the come-up you need continues to climb. Because your zero now sits lower in the erector's total range than it would on a flat base, there is more room left above it, and that extra room is what lets a scope reach a longer distance before the turret runs out of up adjustment entirely.
Why can a 20 MOA base make a short-range rifle impossible to zero?
The erector has a fixed amount of down adjustment as well as up. A flat base uses very little of that down travel just to get to zero, because the scope and bore start out roughly parallel already. A 20 MOA base starts the scope 20 minutes of angle tilted down relative to the bore, which means the point of impact starts out high relative to the point of aim at anything less than a fairly long distance, and bringing that back down to a proper zero consumes real down adjustment.
On a rifle and cartridge combination that only ever needs to be zeroed at 100 or 200 yards, that consumed down travel can exceed what the erector actually has, and the turret bottoms out before the point of impact and the point of aim ever agree. The result is not a rifle that shoots low, it is a rifle that cannot be zeroed with that base on it at all, full stop, regardless of how the turret is dialled.
0 MOA or 20 MOA: the blunt version
Rule-of-thumb guidance, because exact erector travel figures are frequently unpublished and vary by scope model.
A 20 MOA base is correct once come-ups past roughly 500 yards are the point of the build, and it is a real risk of an unzeroable rifle on anything meant to stay inside 300 yards.
Shooter convention
| Longest distance you will dial to | Recommended base | Why |
|---|---|---|
| Inside 300 yards | Flat, 0 MOA | A canted base risks running out of down travel before reaching zero |
| 300 to 500 yards | Flat, 0 MOA, check your margin | Most scopes have enough native travel; verify with your own come-up figure |
| 500 to 800 yards | 20 MOA canted | Converts unused down travel into the up travel this distance actually needs |
| Past 800 yards | 20 MOA or more, and a 34mm tube | Distance and tube diameter become a joint decision at this range |
Roughly half of a scope's total elevation travel sits above mechanical centre, but the exact split and the total figure both vary by model and are often unpublished. Work out your own required come-up before choosing a cant angle rather than copying another rifle's base.
Sources
- Manufacturer-published base cant angle specifications
- Owner-review consensus on erector travel and canted-base zeroing outcomes
Frequently asked questions
Do I need a 20 MOA base?
Only if you intend to dial come-ups past roughly 500 yards. A 20 MOA base converts unused down elevation travel into usable up travel, which is how a scope reaches distance. On a rifle shot inside 300 yards it does the opposite of helping, and it can make the rifle impossible to zero because the erector runs out of down adjustment first.
Can a 20 MOA base make my rifle impossible to zero?
Yes, and this is the real risk rather than a rare edge case. The base tilts the scope down at the front, which consumes down elevation travel just to reach a normal zero distance. On a rifle and cartridge combination that never needed much down adjustment in the first place, that consumption can exceed what the erector has available, and the turret bottoms out before impact and aim agree.
Will a 20 MOA base make my rifle shoot low at 100 yards?
It will require more up-dial than a flat base to reach the same zero, but once zeroed the rifle shoots to point of aim exactly like any other properly zeroed rifle at 100 yards. The base changes how much of the turret's travel gets consumed getting to zero, not where the rifle shoots once it is there.
How much elevation travel does a 20 MOA base actually add?
None. Total elevation travel is a fixed property of the scope's erector assembly and a base cannot add to it. What a 20 MOA base does is shift where your zero sits within that fixed total, moving it lower so more of the existing travel remains available above your zero for dialling come-ups at distance.
Is 0 MOA the same as a flat base?
Yes, those are two names for the identical thing: a base with no built-in tilt relative to the bore, so the scope's mechanical centre and your zero sit close together. Almost all factory-drilled bolt actions ship with an effectively flat, 0 MOA mounting surface unless a canted base is fitted afterward.
Should a hunting rifle ever use a 20 MOA base?
Only if that hunting rifle is genuinely built to dial come-ups well past 500 yards, which is not most hunting. For a rifle used inside 300 yards with a centre hold or simple holdover, a flat base is the correct and safer choice, because it leaves the erector's full range available in both directions from a normal zero.
Researched, not professional advice. This page is compiled from published manufacturer specifications, published optical and ballistic formulas, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are shooter convention rather than sourced numbers, and they are labelled that way wherever they appear. Ballistic figures come from a point mass model using the ballistic coefficient the maker publishes, so treat them as a starting point and confirm them on paper at a measured distance. Confirm your firearm is unloaded with the action open before you mount, level, torque or bore sight anything. Verify a zero only on a supervised range or a safe, legal backstop, know what lies beyond your target, and follow the law where you hunt and shoot, including rules on land access and permitted cartridges.