Are 20 MOA tapered scope bases necessary?

[Fatelvis]

I'm still undecided what rifle and mounts to use, to put together a good, accurate long range rifle, using a Leupold M4 3.5-10 scope w/M3 knobs and in 308. I've never shot at 1000 yds., but I would like for this rifle to be capable, using the available elevation in the M4 scope. Is there enough adjustment, or do I have to use a 20 MOA tapered base when shooting out that far? Thanks-

 

[Dave P]

Yes

Well, total drop is around 48 moa. Can your scope adjust that far???

Tabular trajectory data at Std.ICAO Atmosphere
-------------------------------------------------------------------------------------
Gun / Ammunition : .308 Win RA60
Bullet : .308, 168, Sierra HPBT MK 2200
Bullet weight : 168 grains or 10.89 Grams
Muzzle velocity : 2581 fps
Crosswind speed : 10 Mph
Ballistic Coefficient(s) (G1):
C1=0.454@V>2600 fps;
C2=0.439@V>2100 fps;
C3=0.417@V>1600 fps;
C4=0.398@V>0 fps;


Optimum trajectory information :
Optimum sight-in range (X) = 86 Yds.
with max. ordinate above LOS at range (M)= 44 Yds.
and max. point blank range (P)= 102 Yds.
-------------------------------------------------------------------------------------
Sight-in clicks, 1 click = 1.0 cm/100 m or 0.394 in/100 m
Height of sight above bore axis = 0.0 cm or 0.00 inch
Gun is zeroed-in at 50 yds,
by sighting-in at level firing
-------------------------------------------------------------------------------------
Range Velo Time of Energy Path Deflection Total Sight correction Target
city flight to at crosswind drop for setting new lead
LOS of 10.0 Mph zero range 33 fps
-------------------------------------------------------------------------------------
·Yards fps s ft.lbs. in. in. MOA in. Clicks MOA yds ·
-------------------------------------------------------------------------------------
| 0 2581 0.0000 2485 0.0 0.0 ----- 0.0 ------ ----- 0.00
M 25 2531 0.0293 2389 +0.2 0.0 0.14 0.2 -1.8 -0.63 0.32
X 50 2481 0.0589 2297 0.0 0.1 0.27 0.7 0.0 0.00 0.64
P 74 2434 0.0879 2210 -0.5 0.3 0.43 1.5 +1.8 +0.63 0.96
| 100 2384 0.1202 2120 -1.4 0.7 0.67 2.7 +3.9 +1.33 1.31
| 200 2196 0.2518 1798 -9.0 3.4 1.63 11.6 +12.4 +4.28 2.75
| 300 2012 0.3942 1509 -23.7 8.0 2.55 27.6 +21.9 +7.54 4.31
| 400 1832 0.5495 1252 -46.9 14.9 3.55 52.2 +32.5 +11.19 6.01
| 500 1665 0.7233 1034 -81.2 25.0 4.78 87.7 +45.1 +15.50 7.91
| 600 1506 0.9122 846 -127.5 37.8 6.02 135.4 +59.0 +20.29 9.98
| 700 1361 1.1216 691 -189.6 54.2 7.39 198.8 +75.2 +25.86 12.27
| 800 1237 1.3529 570 -271.2 74.5 8.89 281.7 +94.1 +32.36 14.80
| 900 1136 1.6065 482 -376.5 98.6 10.46 388.3 +116.2 +39.94 17.57
| 1000 1060 1.8802 419 -509.4 126.3 12.07 522.6 +141.5 +48.63 20.56
-------------------------------------------------------------------------------------
M = Peak vs. L.O.S, X = Set Zero, P = Max. Point Blank Range
Elevation above Angle of Site (0.0 deg.) = 0.0210 deg.

 

[ocabj]

More like 38-40 MOA with a 175gr Sierra Match King. That 168 ballistic table you posted won't even work at 1000 yards. The bullet lost supersonic speed before 1000 yards.

Try the 175s. Most match loads shoot at 2650fps in a 24" barrel:

Manufacturer: Sierra Description: .308 dia. 175 gr. HPBT MatchKing™
Muzzle Velocity: 2650.0 ft/s Chronograph Distance: 10.0 ft
Sight Height: 1.50 in Sight Offset: 0.00 in
Zero Height: 0.00 in Zero Offset: 0.00 in
Azimuth: 0.00 MOA Elevation: 0.00 MOA
LOS Angle: 0.0 deg Cant Angle: 0.0 deg
Wind Speed: 10.0 mph Wind Angle: 90.0 deg
Target Speed: 10.0 mph Target Angle: 90.0 deg
Temperature: 59.0 °F Pressure: 29.92 in Hg
Relative Humidity: 0.0 % Altitude: 0 ft
Vital Zone Radius: 5.0 in Std. Atmosphere at Altitude: No
Corrected Pressure: Yes Target Relative Drops: Yes
Zero at Max. Point Blank Range: No
Calculated Parameters
Elevation: 3.90 MOA Azimuth: 0.00 MOA
Atmospheric Density: 0.07647 lbs/ft³ Speed of Sound: 1116.5 ft/s
Maximum PBR: 324 yds Maximum PBR Zero: 275 yds
Range at Max Height: 151 yds Energy at PBR: 1708.0 ft•lbs
Sectional Density: 0.264 lbs/in²
Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yds) (moa) (moa) (moa) (moa) (ft/s) (none) (ft•lbs) (s) (moa) (moa)
0 *** *** *** *** 2656.1 2.379 2741.0 0.000 *** ***
100 -0.0 -0.0 0.7 0.7 2475.6 2.217 2381.0 0.117 19.7 19.7
200 -2.0 -2.0 1.4 1.4 2302.2 2.062 2059.1 0.243 20.4 20.4
300 -4.8 -4.8 2.2 2.2 2135.7 1.913 1772.0 0.378 21.2 21.2
400 -8.0 -8.0 3.0 3.0 1976.2 1.770 1517.2 0.524 22.0 22.0
500 -11.6 -11.6 3.9 3.9 1824.2 1.634 1292.9 0.682 22.9 22.9
600 -15.7 -15.7 4.9 4.9 1677.9 1.503 1093.8 0.854 23.9 23.9
700 -20.3 -20.3 6.0 6.0 1540.9 1.380 922.5 1.040 25.0 25.0
800 -25.5 -25.5 7.1 7.1 1415.3 1.268 778.2 1.243 26.1 26.1
900 -31.4 -31.4 8.4 8.4 1302.9 1.167 659.5 1.465 27.3 27.3
1000 -38.0 -38.0 9.7 9.7 1205.8 1.080 564.8 1.704 28.6 28.6

The Leupold Mark 4 you have should have over 100 minutes of adjustment (cut that in half from factory center). So yes, it's possible. But there's a chance that your regular base and ring combination will place the scope too high above bore line, thus cutting the effectiveness of the internal scope adjustments. So while a 20MOA base may not be needed. It won't hurt to get one.

A simple way to test at 100 yards is to fire a shot. Then go all the way up on the elevation and fire another shot. Measure the distance between the shots. This should give you an idea of how much elevation you have on your scope (@100 yards, 1.047" = 1MOA)

 

[Fatelvis]

Leupold states that this scope has 65MOA adjustment for elevation. Since the reticle comes centered in the tube when new, that means I only really have 32.5 MOA actual "usable " MOA elevation, right?

 

[ocabj]

Leupold states that this scope has 65MOA adjustment for elevation. Since the reticle comes centered in the tube when new, that means I only really have 32.5 MOA actual "usable" MOA elevation, right?

That's how I have always interpreted it. You can verify by running the elevation all the way to the top or bottom and then go back all the way to the other end counting the number of clicks.

 

[adobewalls]

If you are shooting long, then the 20MOA base is helpful as it keeps more of your field of view in the sweet spot of the scope. If you do not use a 20MOA base, then at the longer distances the scope may have sufficient travel, but you may also begin to experience some wierd distortions due to being at the extreme edge of the optics - it ain't supposed to happen, but sometimes does.

 

[rockstar.esq]

You might also consider buyinga scope with a 30mm tube. My IOR 2.5-10X42 can handle the needed dope for a .308Win. The 20MOA bases certainly aren't going to cause any problems at shorter ranges and you'll need bases anyway so the added cost is negligable. I appreciated the added light that the larger tube allows. I've also noted that mirage seems like less of an issue with a max magnification of 10X whereas nearly every higher magnification scope I've ever looked through magnified mirage to the extent that I was having greater difficulty defining my target.

 

[Fatelvis]

Rockstar, the Leupold Mark4 is a 30mm scope, but I agree, I'll take all the light transmission and elevation travel I can get!

 

[USSR]

Fatelvis,

As a user of the Leupie M3 on a .308, you do need a 20MOA base.

Rockstar.esq,

Scope tube diameter has zero to do with light transmission. Light transmission is dependant upon objective lense diameter. All a larger tube does is allow for more elevation and windage adjustment.

Don

 

[oldfart]

There is another, even better way to get that elusive 20 MOA. Buy a set of Burris signature rings and a set of 20 MOA "inserts" for them.
In past years it has occasionally been neccesary to "lap" the rings to keep them from binding the scope tube unevenly. Burris developed a system of rings with fiber inserts that grip the tube solidly but allow it to settle into the rings without binding. They also sell inserts that allow the shooter to elevate the rear of the scope (or lower the front) enough to accommodate long-distance shooters. They're easy to use and not terribly expensive. The rings, with neutral inserts, cost about the same as any other quality rings and the extra inserts can be had for less than $20 shipped.
I use them on two of my rifles and have never had a problem.

 

[ctdonath]

Without a sloped base, my .308 maxed out around 600m.
With a good scope, I don't see a reason to _not_ have a 20MOA base - more options.

Buy a set of Burris signature rings and a set of 20 MOA "inserts" for them.

I did. Used 'em at Storm Mountain's Long Range Rifle courses. Sold 'em as soon as I got back, couldn't get rid of 'em fast enough.

They'll do in a fix, but if you're working at long ranges you want a rock-solid base, which you won't get from plastic inserts. I had reason to believe mine spent the week trying to "settle", which messed up some shots (glad Rod was in a good mood...).

 

[USSR]

Yeah, the Burris Signature rings are alright for a range queen, but they will never hold up on a tactical rifle. Most of my rifles have Badger rings, but I've got a pair of TPS and Leupold MK4's as well, all mounted on Badger 20MOA bases.

Don

 

[ctdonath]

That said, I understand Barrett (as in the M82 .50BMG) has a set of sloped rings that are reputably reliable. Haven't put my hands on 'em yet, but they're out there.

 

[Falconeer]

I built up a Savage 10FP for long range and used Ken Farrell 20MOA base and rings. Great quality and cheaper than the Badger stuff.

Also, unless you're wedded to the Leupold you might want to look at the SWFA Super Sniper (ok, goofy name, but ignore it). There's nothing better at the price point (plus it's not a variable so you don't lose the mil-dot capability).

Oh, and buy a Mildot Master.