How many MOA do I need to reach out to 1000 yards?

[colbyshoots]

I'm looking to order up a base for my Ruger American and can't decide which size base (20 or 30 MOA) to get. Any help would be much appreciated!

If it matters, my scope will have 31 MRAD of elevation adjustment.

[tdbru]

That depends a lot on the bullet you're using and the muzzle velocity you are achieving.

if you go to some of the web ballistic calculators and fill in the data, they can help a lot. for example : https://www.hornady.com/team-hornady/bal...alculators

-tdbru

[Klem]

Colby,

With a high BC bullet in the Grendel velocity range you're going to need up to 15 Mils of elevation to get to 1K yds.

Your scope will be roughly half up and down, so at 0 cant you already have 15.5 Mils of available elevation. Add to that another 6 Mils for a 20MOA base (3.438 MOA = 1 Mil) and you have 21 Mils of dial-up elevation. A 20MOA base is more than enough.

[colbyshoots]

That depends a lot on the bullet you're using and the muzzle velocity you are achieving.

if you go to some of the web ballistic calculators and fill in the data, they can help a lot. for example : https://www.hornady.com/team-hornady/bal...alculators

-tdbru

I'm not well versed in those calculators but I'll give it a whirl.

[colbyshoots]

Colby,

With a high BC bullet in the Grendel velocity range you're going to need up to 15 Mils of elevation to get to 1K yds.

Your scope will be roughly half up and down, so at 0 cant you already have 15.5 Mils of available elevation. Add to that another 6 Mils for a 20MOA base (3.438 MOA = 1 Mil) and you have 21 Mils of dial-up elevation. A 20MOA base is more than enough.

Thanks Klem. Do you think there would be any reason to step up to a 30 MOA base? Is there any PRO to using a 30 MOA vs a 20 MOA?

[Klem]

Thanks Klem. Do you think there would be any reason to step up to a 30 MOA base? Is there any PRO to using a 30 MOA vs a 20 MOA?

Not in this calibre. Grendel is slower than a wet week thanks to its small case and so is not suited for long range shooting. Your bullet will get there but will be wobbling around the sky after 800yds as it crosses into transonic (1,350fps). As it slows the bullet's centre of gravity moves forward and in a pointy supersonic shaped bullet that means it starts to go unstable. Groups blow out, and by 1K it is subsonic.

With 20MOA cant you have enough to make 1K easily but with 30MOA it is useless elevation because the calibre is going to let you down if you want to use the extra elevation 15.5 (scope) + 9 (base) = 24.5Mil max elevation = roughly 1,400yds/900fps. Trying to be accurate at that range will be like driving jelly.

[VASCAR2]

It really boils down to the specifications of the specific scope on the amount of elevation travel. Many scopes have about 70 MOA of adjustment range which means if the reticle is centered you have about 35 MOA of elevation adjustments left. As an example with one Leupold 3-9 scope I had about 70 MOA of adjustment. I ran out of elevation at around 800 yards at 450 feet above sea level with factory Hornady A-Max at 2425 FPS. Going to a 20 MOA mount allows we enough elevation to shoot past 1000 yards with this scope.

The elevation where you shoot has a bearing on whether you need a canted mount because of the thinner atmosphere at higher elevation. If you shoot at 8000’ ASL you might not need a canted mount depending on barrel length/velocity and bullet BC. At sea level you’ll usually need a canted mount with a 6.5 Grendel to get enough elevation. I use 20 MOA mounts on my AR-15’s in 6.5 Grendel and a DIP 25 MOA mount on my Cz 527 24” barrel 6.5 Grendel.

There are scopes that have 50 MOA of elevation so I’m sure I’d use a 20 MOA mount with that scope. I have a couple of Warne one piece 20 MOA mounts that are gtg and are not to expensive.

[colbyshoots]

Not in this calibre. Grendel is slower than a wet week thanks to its small case and so is not suited for long range shooting. Your bullet will get there but will be wobbling around the sky after 800yds as it crosses into transonic (1,350fps). As it slows the bullet's centre of gravity moves forward and in a pointy supersonic shaped bullet that means it starts to go unstable. Groups blow out, and by 1K it is subsonic.

With 20MOA cant you have enough to make 1K easily but with 30MOA it is useless elevation because the calibre is going to let you down if you want to use the extra elevation 15.5 (scope) + 9 (base) = 24.5Mil max elevation = roughly 1,400yds/900fps. Trying to be accurate at that range will be like driving jelly.

LOL, driving jelly. I've never heard of that but that pretty much sums it up. Sounds like a 20MOA base will be plenty for what I'll be doing.

[VASCAR2]

Here is a link to the Diversified Products 25 MOA mount I use on my Cz527. They have canted mounts for other brands of rifles.


https://www.diproductsinc.com/Detail.asp...2&CAT=4268

[colbyshoots]

It really boils down to the specifications of the specific scope on the amount of elevation travel. Many scopes have about 70 MOA of adjustment range which means if the reticle is centered you have about 35 MOA of elevation adjustments left. As an example with one Leupold 3-9 scope I had about 70 MOA of adjustment. I ran out of elevation at around 800 yards at 450 feet above sea level with factory Hornady A-Max at 2425 FPS. Going to a 20 MOA mount allows we enough elevation to shoot past 1000 yards with this scope.

The elevation where you shoot has a bearing on whether you need a canted mount because of the thinner atmosphere at higher elevation. If you shoot at 8000’ ASL you might not need a canted mount depending on barrel length/velocity and bullet BC. At sea level you’ll usually need a canted mount with a 6.5 Grendel to get enough elevation. I use 20 MOA mounts on my AR-15’s in 6.5 Grendel and a DIP 25 MOA mount on my Cz 527 24” barrel 6.5 Grendel.

There are scopes that have 50 MOA of elevation so I’m sure I’d use a 20 MOA mount with that scope. I have a couple of Warne one piece 20 MOA mounts that are gtg and are not to expensive.

I had to look it up as mine is in MRAD but this scope has 110 MOA of adjustment!

I'm in southern WI so I think we are pretty close in elevation.

[lazyengineer]

Not in this calibre. Grendel is slower than a wet week thanks to its small case and so is not suited for long range shooting. Your bullet will get there but will be wobbling around the sky after 800yds as it crosses into transonic (1,350fps). As it slows the bullet's centre of gravity moves forward and in a pointy supersonic shaped bullet that means it starts to go unstable. Groups blow out, and by 1K it is subsonic.

With 20MOA cant you have enough to make 1K easily but with 30MOA it is useless elevation because the calibre is going to let you down if you want to use the extra elevation 15.5 (scope) + 9 (base) = 24.5Mil max elevation = roughly 1,400yds/900fps. Trying to be accurate at that range will be like driving jelly.

This is a great reply.

I tried running mine at 1000. It didn't work because E-targets needed it to be good supersonic still to work.

I tried it at 1000 on a gong range. It did work pretty decent, but I definately needed a friend on strong glass to see and call the impacts. It's quite mild at that distance, so not a lot of noise or plate movement on impact.

Grendel is a damned fine round, and can make it to 1000 yards, but where it shines and dominates is more on an NRA or CMP 600 yard midrange match. (IMHO)

[lazyengineer]

To the OP, I found 20 MOA offset to just barely leave enough room to still fit a 100 yard zero. 30 MOA and in my case I wouldn't have.

[colbyshoots]

To the OP, I found 20 MOA offset to just barely leave enough room to still fit a 100 yard zero. 30 MOA and in my case I wouldn't have.

Thank you for that. I was wondering how close the 30 MOA would be.

[lazyengineer]

Thank you for that. I was wondering how close the 30 MOA would be.

YMMV of course, but 6.5 Grendel just isn't the round for a 30 MOA offset, IMHO.

I Just wish someone made a cost effective offset mount

[tdbru]

Klem,
did you mean to say that the center of pressure moves forward, rather than the center of gravity? I would think the center of gravity for an object like a bullet that is a solid shape remains the same. It's my understanding, perhaps wrong, that the further forward of the CG the CP is, the faster you have to spin the bullet to keep the pointy end headed down range first. i.e. short bullets take less spin than long bullets. My understanding is that the spin will still keep the bullet going pointy end first, but as you transition the sound barrier the CP does move which causes a random dispersion to the trajectory which is why the groups open up as the bullet goes from supersonic to subsonic.
please clarify if I have it wrong.
thanks,
-tdbru

[Klem]

tdbru,

Correct, Centre-of-Pressure - my bad.

My understanding is that there is a most efficient shape for supersonic, and subsonic flight, and they are different to each other. For supersonic flight it is the Sears-Haack, and for subsonic it is a Teardrop. If your bullet impacts the target fully supersonic then the bullet should be similar to a Sears-Haack, pointy front and bulk to the rear. For subsonic the bulk is the opposite, CoG more to the front, a stubbier bullet like the Lapua 200gn 30cal for subsonic loads with a lock base. Same with aircraft; jet fighters vs. passenger planes.

As the bullet slows down it wants to reverse, weight forward, and spin stops it from doing that. But as I understand it, too much spin and it resists pointing down to the target after reaching the top of the curve or apogee 2/3 distance downrange. It wants to keep pointing at the sky and so it presents a yaw to the target as it approaches. Again, bullets that are still fully supersonic, above 1,350fps when they impact the target are easier to keep stable.

For F-Class anyone shooting .223 in our State had groups starting to blow out at about 800-900yds, and by 1,000 it was like they were drunk. Against the 308 guys we were fine until 800-900, and even had an edge with less windage needed, but it turns to custard after 800. Not many bullets to choose from in the 80-90gn range 223, maybe three: Berger, Hornady, Sierra. I understand there are other bullets in other calibres that are fine transitioning from supersonic to subsonic, retaining their accuracy as they do. It would just be a matter of testing different bullets and loads and that would be interesting.

[BowChamp]

There's some really good info posted here...want to thank everyone for posting it up.

To the OP...I have several ar 6.5 grendels with 20 MOA bases, I've had no problem getting a 100yd zero so far. My scopes have been Trijicon Credo's and Vortex PST's with LaRue Tactical 20 MOA bases.

[imaguy3]

Also don't forget you can add in elevation adjustment with your reticle too. So for example you need 20 mil of adjustment but can only get 15 out of the scope before it bottoms out, with the proper reticle you can hold 5 more above it, giving you 20 total.

FYI, according to strelok and my 16" setup with 123gr SST at 2400 and a 50 yrd zero... It says I need 41moa or 12mil to get to 1000.

[grayfox]

tdbru,

Correct, Centre-of-Pressure - my bad.

My understanding is that there is a most efficient shape for supersonic, and subsonic flight, and they are different to each other. For supersonic flight it is the Sears-Haack, and for subsonic it is a Teardrop. If your bullet impacts the target fully supersonic then the bullet should be similar to a Sears-Haack, pointy front and bulk to the rear. For subsonic the bulk is the opposite, CoG more to the front, a stubbier bullet like the Lapua 200gn 30cal for subsonic loads with a lock base. Same with aircraft; jet fighters vs. passenger planes.

As the bullet slows down it wants to reverse, weight forward, and spin stops it from doing that. But as I understand it, too much spin and it resists pointing down to the target after reaching the top of the curve or apogee 2/3 distance downrange. It wants to keep pointing at the sky and so it presents a yaw to the target as it approaches. Again, bullets that are still fully supersonic, above 1,350fps when they impact the target are easier to keep stable.

For F-Class anyone shooting .223 in our State had groups starting to blow out at about 800-900yds, and by 1,000 it was like they were drunk. Against the 308 guys we were fine until 800-900, and even had an edge with less windage needed, but it turns to custard after 800. Not many bullets to choose from in the 80-90gn range 223, maybe three: Berger, Hornady, Sierra. I understand there are other bullets in other calibres that are fine transitioning from supersonic to subsonic, retaining their accuracy as they do. It would just be a matter of testing different bullets and loads and that would be interesting.

Klem,
not to hijack the thread, but this is good stuff. Can you add some more on your statement "too much spin" - ie, spin/twist rates like 1:7, 1"7.5, 1:8, etc... I know for most cartridges there are standard recommendations but it would be instructive to see how this factors in to the yaw effect you mention.
thanks.

[SCJim]

20 MOA assuming your scope is capable of 30 MOA come up from a 100 yard zero. Using a high BC 130 gn Berger, and a powder capable of getting you 2450 FPS at the muzzle you need 41.6 MOA come up for 1000 yards according to JBM calculations. You would be just above supersonic at 1173 FPS. I think it is easily doable with a 24 inch barrel and the right powder/bullet/barrel combo. I am just now starting to experiment with long range Grendel shooting and will probably start looking for a 24 inch barrel soon. The farthest I have shot is 835 and my velocity was just above supersonic at the target. I am confident can do a lot better than that with a bit of tweaking on my gear and load