Rifle Scopes Ring size question after sticky

[flynlow3]

I just read the sticky on ring height and curious before I order. I have an AR I will be mounting a NF with a 56mm bell. The tube is 30mm. Since this is an AR platform with a quad rail, What size rings would you need? According to the sticky, you take (rail height+Ring height)-(Bell diameter X .5) My rail height is 0 (correct) + TPS Med 1.075 =1.075

Bell diameter is 56x.5=28

1.075-28=-26.925


OK what it boils down to, I think this is wrong and I need to know what size TPS rings I should get to clear the quad rail without hoisting it way above it. I would like to get it as close to the rails as I can.

Thanks

 

[okiefired]

No rail height is 0, that would mean it does not exist. Measure the thickness of the front of your rail and add it to the equation.

okie

 

[flynlow3]

But on an AR with a quad rail, there is no dip from the receiver to the barrel. It is a flush straight line from the rail. That is why I thought the rail was 0.

 

[BobinNC]

Your mixing inches and mm in your calculations. Use one or the other linear measurment.

Nightforce 56mm scope has an objective measuring 2.575" on the OUTSIDE. Half of that is 1.2875". Add back 0.10" if your running BC covers. Total to be cleared 1.3875". In this case your rail height is indeed zero, you need rings at least 1.3875" inches high. By my calculations you'll need Xtra-High TPS 30mm rings that run 1.400" .

 

[flynlow3]

Thank you BobinNC. That is where I was confused. I was using 2 different measuring systems! However when i converted the 56mm to inches, I came up with 2.20472" so times that by .5 or in reality divide it in half and I came up with 1.10236". If this is correct, (And Please call me out if I am wrong) I can get by with TPS high's measuring in at 1.225"

 

[BobinNC]

Which Nightforce scope/model then are you using?? If your NF scope has a 56mm objective bell (like found on the NSX 3.5-15x56mm or 5.5-22x56mm) then 56mm is your lens size.... You need the outside measurement of the entire objective end, which will be a bit greater than 56mm.

Posts like this are always easier to evaluate and translate into good information for you when you provide all the information. That way we aren't guessing or making assumptions based on incomplete data.

Though not really related to ring size, just curious what are you going to be doing with an AR that it's application requires a scope so large (56mm lens)? It's a real headache to mount one with that fat a lens on the AR platform, BTW. Steel Ultra High 30mm rings run just over 3/4 of a pound (12.5 oz), alloy ones are about 5 oz.

And 1.400" height is about as high as you can go, and your clearance still will be only paper thin. I guess what I'm saying is unless you really, really need a 56mm objective, 50mm is a lot easier to mount, 44 mm is better yet. An AR is not the best platform for fat lensed scopes..

Another way to get more height is to use a riser rail. Badger Ordnance makes one with 22 MOA of cant and is .430" high. Then you might could use TPS medium rings.

 

[flynlow3]

The scope is a nightforce nxs 5.5-22x56. It is going on a custom sass ar for prairie doggin. The scope is used and had all the features desired so that is why I picked it. I understand 56mm is a bit much on an ar platform but it is a noveske and if it shoots like my .308 noveske, this scope will help do it justice on the longer shots.

 

[flynlow3]

Just to give a follow up. I ended up going with TPS 1.400 x-high rings. On the NF 56mm bell they work great. There is a very slight gap between the quad rail and the scope bell. Needless to say, I am happy and thank you for the advice. I hope this helps someone else in my similar predicament. Hope you all like how it came out. I DO!