MOA slope in scope bases

danny1444

danny1444

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im considering purchasing a scope base in either 20 or 25 MOA. it will be for a rem700 in .308. at what point would it be too much slope? would this pose a problem for zeroing a scope? what range do most of you guys zero your 20MOA scope bases at, 200yards?

danny
 
For a 308 20 or 25 moa is more than enough to get to the 1000 yard mark, yet with any decent scope will still let you zero at 100.
I make rails with as much as 80 moa for my 50s, but then zero is not possible until 500 yards
 
The 20moa is about the limit without sighting issues for the rig you mentioned.

TPS are true picatinney spec bases and in steel are $95.00. al7075 is less money and lighter! Farrell makes wonderful bases as well at any moa you want. They are nice bases as well, however you must order them to 1913 spec since they are not supplied as such.
 
One thing to consider about raised bases is this - the position of the rings on the rail determines the height of the scope relative to the bore. Therefore, if the dimensions of your scope limit where you can put the rings on the base you could loose some of the benefit of the sloped base. I had to shim my 20 minute base because to use the rear most mounting point on the base brought the scope too far back. Mounting the scope just 2 positions further forward on the rail meant that I lost height above the bore - and I consequently ran out of vertical adjustment despite the fact that the rail has 20 minutes of slope.

The same situation applies to the front mounting position. If the front ring is set back one or two positions from the front mounting position to allow the bell to clear the barrel, it is now higher - relative to the bore - and once again some of the advantage of the rail's built in slope is lost.
 
yes but your scope will still be slanted at 20MOA, how does this change anything? can anybody tell me how much of a difference moving your scope back 2 notches on the base will make? im looking for a measurement not a guess
 
Moving the scope and rings back or forth on a plus 20 rail will not alter the plus 20 moa , the rail top where the rings mount to is a straight line.
You will very slightly alter the distance between the center of the scope to the center of bore, which will slightly alter where the line of sight crosses the bullet path, but I don't think significantly.
Each rifle/scope/rail combination will have its own equation in this regard.
 
danny1444 said:
yes but your scope will still be slanted at 20MOA, how does this change anything? can anybody tell me how much of a difference moving your scope back 2 notches on the base will make? im looking for a measurement not a guess
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Kind of tough to get your head around - that's what I thought too - the actual angle is unchanged. What matters though is that by using the full length of the base the reticle is higher above the bore's centerline by 20 minutes, just as it is when you moved it 20 minutes higher with your vertical adjustment. Measure a 20 minute base with a caliper and you will see a significant increase in thickness between the mounting slots at the rear of the base compared to the second slot from the end. When I get home tonight I'll measure the thickness of my base at each mounting point if no one else has posted by then.
 
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So here I have a Near 25 minute base for a long action Remington (R7L) which is not mounted on a rifle - this will be easier to measure than the 20 minute Badger which is on my .308. From thr rear of the rail - moving forward on each mounting shoulder, the heights are as follows:
.500"
.497"
.493"
.490"

The height of the front mounting point is .380", so the difference in height front to back is .500-.380"=.120" Because this is a 25 minute base we can conclude that every .01" change in height equals roughly 2 minutes of elevation. Therefore to move the rear scope ring ahead by 2 spaces - to the third mounting point drops the base height from .500" to .490" or from 25 minutes to 23 minutes. Two minutes at 800 yards equals 16".
 
My scope is limited in elavation b&l 3200 5-15x50mm, with my large 50mm bell, will i have to go to a base with more of an angle. I'm going to purchase from near mfg. and for a newbie $250 is expensive so I need some help so i don't have to buy twice.
 
Richard makes a nice product. Personally, given the application...I couldn't justify spending the extra cash when you can buy TPS or Farrell or significantly less. I think the money would be better spent on a barrel, stock or improved scope...

I don't see how the 50mm objective is going to make you go to a higher MOA base. Physically it would be make things worse and you may need to go to a higher ring. The internal adjustment limit of the scope is one reason you might want to go to a tapered base.

Either way, you won't be disappointed with one of Richards bases....now Richard makes a very interesting brake........
 
Richard does make a nice product, when he gets around to making it or sending it.
I would agree with Joe that a Warne, TPS or Farrel at 1/2 the cost does the same job.
Typically with installing a rail the scope is raised up from the action, and you get more clearance at the bell
You don't mention what rifle or caliber, but you may be better off investing in a scope with more elevation. The 3200s are pretty good for clarity, but lack in elevation. For long range you may find 15x not enough magnification. I don't know what distances you intend to shoot, but if you are needing a plus 20 rail , that tells me you want to go long.
 
Why not just get a set of high or very high Burris Sig rings w/inserts? About $70.

You can then adjust the amount of 'shimming' you ACTUALLY need. Going to a canted base can be useful if you know where your load is hitting at 100yds and need the adjustment. If you haven't shot the rifle yet, shoot it first then decide the amount of adjustment you need. Might surprise you.

Although the 308 is not the worlds flattest shooting rd, it should only take 35 to 40 mins of elevation to make the trip from 100 to 1000. Almost all 1" scope have that much internal adjustment so why the need for a canted base?

Find a load that works well at 200yds. Get a 100yd zero and see how much elevation is left in the scope. Let's say you have 25min of UP left. The most you need to shim this scope is 15min so the inserts can easily accomplish that. You can shim 30min using the inserts.

Big bonus - the bell will still clear the barrel. I have an Elite 4000 with a 50mm bell on my 7Mystic. I use a Farrell 20MOA base AND Burris rings shimmed. I enjoy LR shooting so don't care about a zero much inside 500yds (right now it hits 16" high at 180yds).

There is precious little room between the bell and base and barrel when the scope is canted that much. What you might need are taller flat weaver bases and Burris rings so that you elevate that bell to clear your barrel.

Jerry
 
Boomer: There is no change in angle on your mount, regardless of ring position, unless it's bent.
There is (has to be) a difference in the the mount-to-bore distance at different ring positions, because the bore and scope plane are intersecting, not parallel.
If you were to mount the scope using only the front ring, and then mounted that ring in all the different positions on the mount your point of impact should only shift 0.003" or 0.004" independant of distance, not some 16" at 800 yds.
 
Proof is in the shooting - the doubters are free to experiment as I have. Raising the rear of scope to a higher position above the center of the bore, with all other adjustments unchanged raises the point of impact at the target.

Of coarse when you move the rings back and forth along the rail nothing changes unless they are fastened to the scope and the scope and rings are moved as a unit along the rail - and this is what causes the point of impact to rise and fall.
 
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Splatter said:
Then something isn't straight.
Click to expand...

Wrong - As the scope moves along the rail it climbs and decends along the rails length. What you are saying is only true if the rings move to different positions along the rail while the scope remains in the same position.
 
Have to agree with Boomer in this debate. But Jerry has the best/cheapest solution with the Burris rings and off set inserts.
For Danny1444, " can anybody tell me how much of a difference moving your scope back 2 notches on the base will make" Tan of 20 minutes X distance between slots. Thats how much difference the center or bore and scope will be by moving it back of forth.
 
alberta tactical rifle said:
Richard does make a nice product, when he gets around to making it or sending it.
I would agree with Joe that a Warne, TPS or Farrel at 1/2 the cost does the same job.
Typically with installing a rail the scope is raised up from the action, and you get more clearance at the bell
You don't mention what rifle or caliber, but you may be better off investing in a scope with more elevation. The 3200s are pretty good for clarity, but lack in elevation. For long range you may find 15x not enough magnification. I don't know what distances you intend to shoot, but if you are needing a plus 20 rail , that tells me you want to go long.
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Yes indeed i want to go long, I wanted to try f-class in the next year with my 308 winchester stealth 2. I know this platform is far from ideal but i just want to start particapating in matches and meet some people that i can learn from. Someday(next 2 years) i hope to start commonwealth style shooting so I'm staying with 308 so I will have lots of ammunition data and experience when it is time to switch to Irons. thanks for the advice
 
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