Trying to understand 20 MOA rails.

[ctshooter]

My airgun came with a 20 MOA rail and I understand how that can help with elevation settings on longer ranges. But, how does that impact sighting in at shorter distances? Doesn't it create a higher angle on the scope that you than have to compensate by lowering the elevation settings even more than normal? I'm trying to visualize this in my head that the scope is now not parallel to the barrel but angled up at 20 MOA (which i guess calculates to 0.33333..... degrees?) so if you sight in at 25 yards does the holdover/under change when you go out to 50 or down to 10 from what a 0 MOA rail would give?

Sorry if this is a stupid question but I just can't get my head around it.

The reason that I am asking is that I sighted the scope in for 6 yards (indoor test shooting) and then went out to my longest indoor distance which is 17 yards and rather than the shot being about 4 inches high (which is what I expected) it was landing about 8 inches high (my wife hasn't seen the hole in the wall yet........).

[Roadworthy]

You never mentioned what type of gun you're shooting but if it's a break barrel there's a good chance it has some degree of barrel droop - many do.  I did not know scope mounts came with a stated MOA compensation, though.  I suspect the mount is tilting the scope a bit downward to have it more closely approximate where the pellet is actually hitting, in other words getting the scope closer to parallel with the barrel.  That should greatly reduce the required downward adjustment required with straight mounts.
If you sight in your scope at, say, twenty yards you would use a normal amount of hold over to then shoot at fifty yards - if I understand what's going on.  I've never shot a rifle at six yards so I'd have to look at Chairgun or something to find the appropriate hold under or over or whatever.

[Dairyboy]

Sean, I take it your talking about your Veteran? I'm trying to wrap my head around it at the time as well. It helps for longer range sighting in. My guns are all sighted in at 50yds with the  close zero at 20yds. However I've been trying to figure out a chairgun reticle chart and can't get it to work out. At 75yds I'm 1 Mil dot low but no matter what I enter in Chairgun it says it should be 1.5 Mil dots low but confirmed many times it's at 1 Mil. Not complaining as it extends my range but just trying to figure it out.

[rsterne]

Using a 20 MOA rail, which for many higher velocity airguns comes close to the drop at 90-100 yards.... does the same thing as if you simply cranked in elevation in the scope until it was sighted in at the same distance.... What DOES change is that your scope will be closer to optical center with the rail....

I don't know where the trade-off distance is (if any).... but 20 MOA is about 2" at 10 yards.... so if your scope is 2" above the bore it will be almost on optical center at that range as well.... You are likely to be closer to optical center at most if not all distances using the rail than without it....

Bob

[thwakk]

I use the diopter method of finding scope height for input into ChairgunPro on all my guns which have scope heights that range from .75" to 2.6" and results seem good in field use. I seldom get the opportunity to shoot off a bench with zero wind on the BLM land and would likely blame wind for small variances.

link to diopter method:
https://airgunaccuracy.wordpress.com/chairgun-and-scope-height/

[ctshooter]

I am using the Veteran that Dillon mentions which puts the sight 2.5" above the bore centerline. I'll have to get it out at further distances and see if the differences are as extreme at longer ranges - just haven't had the time on the weekends lately to go to the range. And the one range near me isn't ideal as last time I ended up to the right of someone who was just dumping mag after mag on his AR. Not very relaxing, but what ca ya do?

I know the distances are short for rifle shooting, but I live in a condo so anything outdoors would be a no-no. I just didn't expect that much of an extreme change.

Bob - so you're saying that technically a 20 MOA rail should really be no different than cranking 20 MOA on your sight?

[ctshooter]

I use the diopter method of finding scope height for input into ChairgunPro on all my guns which have scope heights that range from .75" to 2.6" and results seem good in field use. I seldom get the opportunity to shoot off a bench with zero wind on the BLM land and would likely blame wind for small variances.

link to diopter method:
https://airgunaccuracy.wordpress.com/chairgun-and-scope-height/

That's great information, thank you.

[rsterne]

Sean, that is correct.... Either way, you need to input the correct scope height into chairgun….

Bob