What would you recommend and why. I would be just getting into long range shooting. Say 300 to 800 yards. I know what MOA is but can’t understand the 10 or 20 MOA on a rail mount. It seems like a lot.

https://www.spsroseville.com/o...0-short-action-matte

https://www.spsroseville.com/o...finish-0010710021-33

https://www.spsroseville.com/o...hort-action-matte-94

It is for this rifle.

https://www.bergara.online/us/rifles/b14/hmr-rifle/

Dang this stuff is confusing. My two hunting rifles were purchased used with good glass already on them. So I have never mounted a scope on a rifle. My two ARs have clamp on mounts that were already on the cheaper scopes and red dot.

Thanks

Someone else will give a better explanation, but its a system that gives your scope a greater range of elevation for longer distances.

It's basically to give you a head start on your elevation zero so you don't need to use up too much of your scope's internal adjustment for a long-range zero. If you have a ballistic chart for the load you are using and a good idea of the ranges you will be shooting, you can figure out what base makes the most sense. For 300-800 yards, I would guess either 10 or 20 MOA would be fine, depending on the scope you are using. But check to make sure you will have enough elevation adjustment to get back down to a shorter zero if you need it.

As bigwagon said, the fundamental purpose is to in effect make it possible to set the scopesight to a higher elevation for long range shooting. When we look at the specifications for sights, they will say something like they have 110 minutes of angle elevation adjustment. That usually means, though, it’s the total: i.e., 55 MOA up and 55 MOA down.

Depending on the rifle and some other variables, some adjustment down from the center may be necessary to shoot at a particular distance, but it is usually not much. On the other hand, shooting at long distances requires dialing the elevation up quite a bit, and sooner or later the scope will not be capable of being dialed up sufficiently. For example, one load I’m familiar with would require dialing up about 57 MOA at 1100 yards. If the scope has only 55 MOA of up elevation available, then there’s a problem. In addition, there can be other mechanical issues to consider when the scope’s elevation is dialed up near its maximum limit.

But if I have a +20 MOA base that the scope is mounted on, then I will need to dial up only 37 MOA, and that’s in the range of what it’s designed for.

Whether a extended elevation base is necessary or desirable depends on the individual factors that a shooter must consider. Many shooters believe, though, that even if we’re not going to be shooting at extremely long range, a base with a moderate amount of added elevation (e.g., +10 to 20 MOA) won’t hurt anything. Extreme elevation additions, though, can result in the opposite problem of not being able to dial down enough for short range shooting.

For your particular situation, I personally would probably just opt for a +20 MOA base without giving it too much thought. I have bases with about that much elevation on most of my rifles without its causing me any problems, and the extra elevation is there if it helps.

To be sure, though, it’s necessary to look at a ballistics table, such as the JBM (see below). When we enter all the data it requires for our particular scope and ammunition, it will tell us how much elevation we’ll need at something like 800 yards. For example, the load I mentioned above would require about 34 MOA elevation at that distance and we can then look at the scope’s specifications to see how close that would be to its maximum elevation limit.

http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

Added: I just looked at a Leupold scope that many hunters would use. It has a total elevation range of only 56 MOA, or 28 up or down. If I needed 34 MOA of up elevation to shoot at 800 yards, it wouldn’t be suitable without an elevated base. (Actually that scope wouldn’t be ideal for that purpose for other reasons as well, but that’s one definitive issue.)

I believe your Bergara is chambered in 308 win. Using a typical target ammo like Federal GMM 175, your bullet drop should be no more than 26-27 MOA at 800 yards, and no more than 12-13 MOA at 500 yards.

You should determine what scope you will buy. Let's assume it's a Vortex Viper PST Gen 2 5x25, which has 70 MOA of total vertical adjustment. With a flat base (0 MOA) rail mount, you have 35 MOA of elevation adjustment. Obtaining a zero at 100 yards will consume maybe 2-3 MOA of this 35 MOA, assuming your rifle's action is perfectly parallel to the barrel's bore. So...for 800 yard shots, you have consumed 28-30 MOA of this scope's 35 MOA of up elevation adjustment. Meaning that the scope will do it, but it won't be optimal.

Scopes produce their best optic quality when the elevation is set somewhere near the middle of the adjustment range. In the above scenario, you would be near the edge of the scopes elevation adjustment. The scope would perform better with a 10 MOA or 20 MOA base.

Regardless of what scope you purchase, if you truly will shoot at 800 yards, I recommend a 10 MOA or 20 MOA base.

You now need to consider the optics for this rifle.

The above posters nailed it. Get the 20 MOA mount.

The scope mount should be selected when you take into consideration the scope, barrel length, caliber, range, and bullet you intend to shoot.

For example, shooting a 308 at 300 yards, a flat scope base will be find, assuming your scope has ~10 MOA (+/-) adjustment. A 167 gr Lapua Scenar zeroed at 200 yards from a 26 inch barrel traveling at 2700 fps, will be down 8.4 inches at 300 yards. Henceforth, a flat scope base would require your scope to have 3.8 MOA in elevation (below line of sight), but this is in addition to zero at 200 yards *which may already be -4 MOA. Keep in mind, the scope will always be working with negative line of sight when you have a flat scope base. At Zero, the scope LOS and path of the bullet will never cross, which is why many shooters immediately reach for a canted scope mount, where the rear is higher than the front, and allows for greater movement.

Getting back to the 308, let's say you want to take your gun hunting. If you were to drop in a lighter hunting bullet, say a Swift A Frame 165 gr, because it has worse ballistics, it is expected to drop 9.7 inches when zeroed at 200 yards - problem is the drop from muzzle to 200 yards is another 0.9 inches more than the 167 Scenar, meaning you would need to aim 2.3" over the same 300 yard distance for what is essentially the same weigh bullet.

Take 4" off that 26" barrel, and the velocity drops, and ballistics are even worse.

As Fritz mentioned above, a 175 GMM that is zeroed at 200 yards will fall an additional 205" from 200 to 800 yards. Meaning you will need an additional 26 MOA in addition to what you have already used to zero at 200 yards. Because most scopes only have 40-60 MOA (20-30 in single direction), 800 yards will likely be very dicy (with a zero MOA base).

As an aside, and to prove the point I made earlier about caliber, the same bullet from a 300 win mag, traveling at 3050 fps from a 26" barrel would drop just 151" at 800 yards, assuming zero at 200 yards, and would require just 18 additional MOA from the scope.

Lastly, know that your scope is not meant to work at it's best at the extremes. IF you have 60 MOA , and take your scope to 28, and then back to zero it stresses the movement. Just because it says it has 30MOA of single direction movement, I never use more than 75% of stated travel. I have broke a few and had to send them back because I expected too much travel. If you have 20, 15 should be considered usable, if you have 30, 22 would likely be the most I'd go. 34MM main tube scopes usually allow more travel than 30MM, and 30mm more than 1".

This gets back to why I say, it needs to be considered in conjunction with distance, caliber, bullet, barrel length, scope, and mount.

FWIW, if you ever want to try 1000 yards with that 308 and the 175 GMM ammo, my back of the envelope calculation suggests a 20MOA scope base would be very tight. It would need another 40 MOA in addition to the 4 to zero at 200, subtract the 20, leaving you will 24 within the scope, which depending on the scope may or may not work.

I realized I never answered your question.

A 10 MOA canted mount means your scope will be pointing down wards by 10 minutes of angle. At 500 yards it provides 50" of additional latitude that is not required by your scope. Whatever the distance, divide by 100 and multiply by the MOA to get the drop benefit from the scope mount (which makes your scope work less). A 20 MOA base at 300 yards yields 60" (all approximates because actual MOA is 1.047").

I personally Start with a 10 MOA for all guns, move to a 20 based on caliber, etc around 400 yards, and 30 MOA (again caliber and situation specific) at 700 yards. Consider how you plan to shoot, your ballistics, and try to pick a mount where 70% of your shots fall within 50% of your MOA from the scope.

Long story short, it gives you more adjustment range and keeps the image centered in the optic, longer.

One other benefit to a 20 MOA (or 10, or 30) mount is that as you crank in more elevation, the turret assembly moves further and further away from the vertical center of the main scope tube. As it gets closer to the vertical limit, you start to lose horizontal (windage) adjustment range because the main tube becomes effectively narrower. So if you're shooting at 800 or 1000 yards on a windy day you risk running out of windage adjustment (unless you prefer to hold off for windage instead of dialing it, and have a reticle that supports holding off). Keeping the turret as close as possible to vertical center maximizes the amount of windage adjustment that you have.

Thanks everyone.
As always many members help others.
This is a learning curve for me.

Thanks Again Everyone

Roy

A canted rail does not give you more adjustment range, it only shifts the range in one direction or another. The riflescope still has the same range as before.

I have 20MOA rails on several of my rifles and my F-TR Match rifle has a 30MOA cant; I like to keep my scope centered as much as possible for the 1000 yard range to get the best IQ.