determining base MOA..

1stmar · September 18, 2017, 07:56 PM

I have a Ruger MKII that I put Picatinny rail on top of it. It wasnt designed to be a 20 MOA rail but I figure it is sitting on top of the integral base so it must be adding something. Is there a way to calculate how much MOA lift I would get from the rail? Height of the rail from the top of the receiver to the top of the base maybe? My scope has 50 MOA of elevation (believe that means 25+/-) try to determine how much elevation in total I have. I need about 35 MOA I think to get to 1000 yds, so another 15 MOA or so.

Thanks

Mobuck · September 18, 2017, 08:33 PM

If properly designed and milled, you will get ZERO "MOA" from a dovetail to picka fanny rail adaptor. A true "20 MOA" rail is tapered and basically locates the scope on a plane not parallel to the boreline.
Raising the height of the scope above the boreline will affect point blank range but doesn't change the scope to bore axis alignment.

Stats Shooter · September 18, 2017, 08:48 PM

Like Mobuck said, height above bore has virtually no impact on maximum available moa down range. Only your maximum point blank range.

If, as you say, you need 35 moa to get to 1k yards, and have a 20 moa rail, you should be ok. A 20 moa rail (roughly) raises the rear base of the rail ten thousandths and lowers the front ten thousandths (again approximately depending on rail length). Back when, before the popularization of 20 moa rail, I would use a soda can shims to raise the base of a 1 piece rail. A soda can is 0.004" thick, this moved poi up about 4 moa +/- 1/2 moa or so. Took about 3 shims to get 10 MOA.

The other option is Burris XTR signature rings. With them you can build in up to 40 MOA

1stmar · September 18, 2017, 09:22 PM

Thanks guys.

tobnpr · September 19, 2017, 04:44 PM

Best to avoid shims under a scope base if possible. They angle the clearance hole in the base, and the mounting hole in the receiver is at precisely 90 degrees (natch). Assuming the clearance hole is minimal dimension, this can cause the screw shank and/or head to bind especially on deeper mounts. Best to replace with a 20 minute rail IMO.

1stmar · September 19, 2017, 05:11 PM

I need to look for a 20moa base that fits ruger integral mounts. They may be out there but I only found a couple of picatinny rails and don't recall stumbling onto any 20moa bases.

tango1niner · September 19, 2017, 06:50 PM

Mobuck, with a zero MOA base can you explain how height above the bore affects point blank range please. I'm not getting it.
thanks

Stats Shooter · September 19, 2017, 08:20 PM

The first thing height above bore affects is near and far zero. For higher velocity cartridges: The higher the scope is, the further out the near and far zero is. This is because the sight plane and bore center line are far apart such that the angle necessary to bring them together is steeper, and the muzzle does all the adjustment since line of sight cannot change.

Height above bore then affects maximum point blank range because the near zero is further out, as is the far zero. Also, not needing to be as high at 100 yards because the bullet already has to come up more inches just to reach line of sight at 100 yards.

In summary, steeper angle to reach LOS means more further Maximum point blank range .

Technically, the furthest maximum point blank range, assuming a 6" target, would be a scope 3" above bore.

Mobuck · September 20, 2017, 06:46 AM

Looks like Mississippi did a good job so I don't need to add more.

September 18, 2017, 07:56 PM	#1
1stmar Senior Member Join Date: March 21, 2012 Location: Connecticut Posts: 2,378	determining base MOA.. I have a Ruger MKII that I put Picatinny rail on top of it. It wasnt designed to be a 20 MOA rail but I figure it is sitting on top of the integral base so it must be adding something. Is there a way to calculate how much MOA lift I would get from the rail? Height of the rail from the top of the receiver to the top of the base maybe? My scope has 50 MOA of elevation (believe that means 25+/-) try to determine how much elevation in total I have. I need about 35 MOA I think to get to 1000 yds, so another 15 MOA or so. Thanks

September 19, 2017, 04:44 PM	#5
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 4,556	Best to avoid shims under a scope base if possible. They angle the clearance hole in the base, and the mounting hole in the receiver is at precisely 90 degrees (natch). Assuming the clearance hole is minimal dimension, this can cause the screw shank and/or head to bind especially on deeper mounts. Best to replace with a 20 minute rail IMO. __________________ Remington 700/Savage Rebarreling /Action Blueprinting 07 FFL /Mosin-Nagant Custom Shop/Bent Bolts Genuine Cerakote Applicator www.biggorillagunworks.com

September 18, 2017, 08:33 PM	#2
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	If properly designed and milled, you will get ZERO "MOA" from a dovetail to picka fanny rail adaptor. A true "20 MOA" rail is tapered and basically locates the scope on a plane not parallel to the boreline. Raising the height of the scope above the boreline will affect point blank range but doesn't change the scope to bore axis alignment.

September 18, 2017, 08:48 PM	#3
Stats Shooter Senior Member Join Date: August 26, 2016 Location: North Dakota Posts: 1,636	Like Mobuck said, height above bore has virtually no impact on maximum available moa down range. Only your maximum point blank range. If, as you say, you need 35 moa to get to 1k yards, and have a 20 moa rail, you should be ok. A 20 moa rail (roughly) raises the rear base of the rail ten thousandths and lowers the front ten thousandths (again approximately depending on rail length). Back when, before the popularization of 20 moa rail, I would use a soda can shims to raise the base of a 1 piece rail. A soda can is 0.004" thick, this moved poi up about 4 moa +/- 1/2 moa or so. Took about 3 shims to get 10 MOA. The other option is Burris XTR signature rings. With them you can build in up to 40 MOA

September 18, 2017, 09:22 PM	#4
1stmar Senior Member Join Date: March 21, 2012 Location: Connecticut Posts: 2,378	Thanks guys.

September 19, 2017, 05:11 PM	#6
1stmar Senior Member Join Date: March 21, 2012 Location: Connecticut Posts: 2,378	I need to look for a 20moa base that fits ruger integral mounts. They may be out there but I only found a couple of picatinny rails and don't recall stumbling onto any 20moa bases.

September 19, 2017, 06:50 PM	#7
tango1niner Senior Member Join Date: March 5, 2009 Location: NY Posts: 317	Mobuck, with a zero MOA base can you explain how height above the bore affects point blank range please. I'm not getting it. thanks

September 19, 2017, 08:20 PM	#8
Stats Shooter Senior Member Join Date: August 26, 2016 Location: North Dakota Posts: 1,636	The first thing height above bore affects is near and far zero. For higher velocity cartridges: The higher the scope is, the further out the near and far zero is. This is because the sight plane and bore center line are far apart such that the angle necessary to bring them together is steeper, and the muzzle does all the adjustment since line of sight cannot change. Height above bore then affects maximum point blank range because the near zero is further out, as is the far zero. Also, not needing to be as high at 100 yards because the bullet already has to come up more inches just to reach line of sight at 100 yards. In summary, steeper angle to reach LOS means more further Maximum point blank range . Technically, the furthest maximum point blank range, assuming a 6" target, would be a scope 3" above bore.

September 20, 2017, 06:46 AM	#9
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	Looks like Mississippi did a good job so I don't need to add more.