Scope Rail, How many minutes?

[Jase PTRC]

Hello, im embarking on building a new rifle and hadnt given the scope rail much thought until now.
Just curious roughly what rail i should be running to get full use out of my scope.
I will be using a 8-32 NF BR in a 308 would like to set zero for 300 mtrs and have the scope at or close to the bottom of its travel.
is there an easy way to work this out or is it just an educated guess?

[saum2]

You need to consider shooting at 100yds or Metres for testing purposes. I have a 30MOA on my rifle with a NF Comp scope, at 300yds I have 8 minutes above zero so I can just get to 140yds. I chose a 30MOA rail as I'm thinking of long range shooting. On my other rifles I have 20MOA rails with NF. It may also depend on your scope choice for enough elevation.
Geoff

[Barry Davies]

Not a good idea to have your scope zero ( 300 mtrs or whatever ) close to the bottom of it's travel. As a general rule set zero around 8 to 10 MOA from bottom. Too close to the bottom and you will run out of windage adjustment.

How many MOA taper on the rail? Educated guess but usually 20 is sufficient to utilize available elevation adjustment of the scope. If you intend using a 308 you will need about 25 moa to reach 900 mtrs and you must leave sufficient over and above your setting for 900mtrs ( usually 10 moa or so ) or you will again run out of windage adjustment.
So, 10 moa at the bottom + 25 + 10 at the top = Min 45 moa. Not sure what the BR scope has available but it's less than the NXS.

Best way is to fit a 20 moa rail, zero at 300 mtrs and take it from there. IF the 20 moa is not correct --you may need more or less,--sometimes the scope rail can be remachined to give more or less taper.

[Jase PTRC]

Ok i did not know that being near the end of travel for elevation would affect how much windage i could have. On my current rifle with the BR i have a 20moa rail and im at roughly 4 moa above the bottom with a 100mtr zero

[Barry Davies]

You don't need much windage at say 300 mtrs but an added problem is if the scope does not zero in the centre of it's wind travel then you have lost that much as well ( on one side ) That's why it's good practice to have a 300 mtr /yard zero about 8 or 10 up. Windage adjustable rings would fix that problem though.

[AlanBT]

I reckon you want to have your shooting range be around the optical centre of your scope. For 300-800m ranges for a .308 this requires around 20 MOA travel. For 100m to 1000m you'll need about 36MOA travel and to reach out to 1200m you'll need about 53MOA travel.

A 20MOA rail on a NF will enable you to shoot out to 800m easily using a .308. I run out of scope elevation at about 900m with my NSX8-32 on a 20MOA rail and so need a 40MOA rail which will give me a setting of about 10 for 100m and a setting of 60 for 1200m (out of 65MOA total elevation).

Hope this helps somewhat..

Alan