When do you need a sloped base?

Threemorewishes

Threemorewishes

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Hello all,
I am in the process of putting a scope on my new rifle and was wondering at which distance do you start needing a base with a built in slope. I know brand "a" scopes may have more adjustment than brand "b" and therefore require less angle but there must be some general distance that requires a sloped base no matter what brand you use. I am just beginning down the road to long distance shooting and will probably be served by a parallel base for some time yet, but would like to equip myself with the next distance base.
I am scoping for 308 Winchester and will be starting at 100yards.
Thanks for looking.
Greg
 
Threemorewishes said:
Hello all,
I am in the process of putting a scope on my new rifle and was wondering at which distance do you start needing a base with a built in slope. I know brand "a" scopes may have more adjustment than brand "b" and therefore require less angle but there must be some general distance that requires a sloped base no matter what brand you use. I am just beginning down the road to long distance shooting and will probably be served by a parallel base for some time yet, but would like to equip myself with the next distance base.
I am scoping for 308 Winchester and will be starting at 100yards.
Thanks for looking.
Greg
Click to expand...

Greg,

How much slope depends on how far you are shooting, available vertical adjustment in your scope, and bullet trajectory.

If you want to shoot 1000 yds with your .308, you may need around + 42 mins (up elevation) available in your shooting platform depends on mV and bullet BC.


Some 1 inch dia scopes will not have this much adjustment, many 30mm dia scopes do. Basically the erector tube in the scope tops out on the top dia of the scope tube and 30 mm tube has about 5mm, more room to adjust.

There is a problem working with high adjustment levels in the erector tube first the springs pushing the tube into position are max extension and are weakest there (could allow zero shift), also your available windage adjustment reduces as the erector tube tops out in the scope and finally you are not looking thru the centres on the lens.


By mounting the scope with tapered bases you can use the downward adjustment in your scope that really is seldom used, by pointing the objective lens somewhat down towards the barrel.

A rule of thumb for standard Rem/chester rifles is .001 rise in the rear base is worth aout 1" at 100yd or 1 min of angle. So, to gain 25 min. of elevation adjustment you could adjust your scope 25 min. up, or raise the rear mount by .025" . In this case and you would only need an additional 17 mins on your scope adjustment to hit at 1000yd.

The down side, and there is always a down side. To shoot close in, say at 100 yds, you are now well off centre.. and you may have taken too much and are shooting high at the lowest adjustment of your scope. Some thought and care are in order in picking the slope.

The flatter the trajectory your shooting platform is capable of the better.

A 6.5/284 with say 25 mins. elevation required to 1000 yds requires much less slope than your .308 with 42 mins required.

I hope this helped,

NormB
 
Hello NormB,
Thanks for the wealth of information, it helps alot. It looks like I will have to set myself up for a parallel base for now and stick to learning how to shoot at 100 yards before jumping up to true long range equipment. I was thinking about getting a 6X24-40mm Bushnell Elite Mildot and using it to learn at 100 yards and then changing bases for longer distances. I never even thought of the issue of shooting closer once the rifle is set up for longer distances.
Thanks again.
Greg
 
I was also looking at that scope for my savage fp10 le2b... But it only has 25 or so inches of adjustment.... If you have a 20moa base, and everything is perfect you will be shooting 7" or so above your target at 100yards. Wich would get you zero'ed right around 375yards. This is all dependant on everything being in perfect alinment... it may shoot higher... or lower.

I can't afford/decide on a high end target/tactical scope right now, so I purchaced a burris full feild2 3-9X40($350), with the Balistic plex reticle, it has 50" of adjustment. So thats 25 each side of zero. But it only required me to adjust it up 13" from center to get on target at 100yards with my 20moa base. In theory I should be able to make it out to 1000yards posibly with no holdover.
 
If I may, since you are getting a great scope with additional aiming points, you have a great advantage.

For now, use standard bases but get some Burris Sig rings w/ inserts. Allows for shimming the scope in the future.

Most actions will allow you to zero this scope with 10 plus mins before it tops out. This will allow you to go from 100yds to around 500yds. Probably keep you busy for a bit.

When you want to go further, you can 1) Use the lower mil dots as new aiming zeros, gaining up to 18min of elevation instantly. 2) Shim the scope so that you have the scope at full down at 100yds but still aim at the center 3) Shim the scope so that one of the upper mil dots is your new 100yd zero.

For very LR shooting, I set up one of my rifles so that at 100yds, using full down elevation, the top most mil dot was shooting 3" high - 300yd zero more of less. This means that the center of the reticle was approx a 1000yd zero and I still had the full elevation travel left in my scope to go further.

I could also use the lower mil dots to shoot further, upper mil dots with or without adjustments to shoot closer. I could use the turrent at any time to adjust for whatever distance I want by using different mil dots as the aiming points.

with this set up, I could take a standard 1" scope and go from 100yds to a mile using the mil dots and elevation adjustment. Don't need a 100min mega dollar scope. This is with one of the new flat shooting cals like 6.5 and 7mm.

The 4200 6X24 has about 26min of elevation . By using the mildots, I gain the 36 min that is part of the reticle. Then by shimming my scope for an extended zero, gain even more range.

My 7RM and 162gr Amax need 22min to go from 100yds to 1000yds. Set up the reticle so that the top most dot (the bar is even better) becomes a 300yd zero (flat enough that I can hold dead on a deer from 50ft to 300yds and hammer it). The center of the reticle is now 950/1000yd zero. I can use the turrents and/or dots to shoot anywhere in between.

I have 25/26 min of elevation which will allow me to go to approx 1500yds with turrent adjustment alone. If I use the lowest mil dot, I am at approx 1400yds, then with the turrent go beyond a mile. I would say that is pretty far by most people's standard and all with a min amount of elevation adjustment.

Most 1" scopes have 50min of adjustment which will give you more flexibility with a not so flat shooting 308.

The odds of you needing a canted base is slim. The Burris rings will do all you need until you want to go beyond 1000yds.

By the way, I have used several of these 6X24 scopes with full down elevation without a single problem either in optics or shifting zero. An awesome scope.

Jerry
 
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Threemorewishes - If you are in Ottawa, then it follows that your long range shooting will be at Connaught. Little 100m shooting there. Usually shoots are from 300 to 900 metres. The easiest and least expensive way to boost the elevation potential of your scope is to use the Burris insert rings as mysticplayer suggested. If you have not done so, have a look at www.dcra.ca, www.ontariorifleassociation.org. Through the DCRA website there may be a link to the NCRRA (National Capital Region Rifle Association), whose clubhouse is at Connaught. If you are interested in long range fullbore shooting, these could be your best contacts.
 
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