scope base suggestion for a supressed big bore bolt action thumper


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R.W.Dale
February 27, 2010, 06:03 PM
I'm in the opening stages of building what I hope to be my first rifle with a can. It's a Stevens 200 that will be chambered for .45 win mag on a 17" bbl

My question is given the massive amounts of bullet drop I can expect out to 300m or even 200 would investing in a 20MOA base now be prudent?

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Ranb
February 28, 2010, 07:01 PM
It depends on what load you are using, range to the target, how much elevation adjustment is available and if you are able to hold over using mil-dots or other kinds of reticles. You will probably want to invest in a medium to high end scope like a Leupold which has plenty of elevation and will take the abuse of the heavier recoil.

Let’s say you were using a 500 grain bullet with a BC of .412 at 1050 fps with a zero of 200 yards. At 600 yards the bullet would drop 486 inches or 77 moa. If the same bullet is moving 2100 fps, then the drop is only 160 inches or 25 moa. http://www.jbmballistics.com/cgi-bin/jbmtraj-5.0.cgi

If you are planning on shooting out to 600 yards with subsonic ammo, then a tilt down mount will be a good idea. I have a 510 whisper with a 30 moa mount and a 140 " adjustable Leupold. I adjust the scope to 200 yards then use one of the 22 mil-dots for holdover. If you only want to get out to 200 yards, then any medium quality scope with a non tilt-down mount will do.

Ranb

PTK
February 28, 2010, 11:00 PM
For how long range that actually has, it's your call. Honestly, I'd have a hard time imagining a shot in AR over a 2-300 yards.

Zak Smith
March 1, 2010, 12:49 AM
With a subsonic 240-grain .300 Fireball load, the drop rate at 600 yards is approx 2.25 inches each yard. So if your range is off by five yards you'll miss your point of aim by a foot. This is something to think about with regard to very long shots with subsonic cartridges.

Ranb
March 1, 2010, 04:16 AM
One thing that I saw when first shooting subsonic at long range was that I always had the time to re-acquire my sight picture after pulling the trigger. So if the bullet landed somewhere that made it visible (like dirt) it was a simple matter to adjust the holdover then hit the target on the follow-up shots. This is how I am able to consistently hit a target at 500 yards with my 300 whisper in my AR-15, or other subsonic carbines.

I have them zeroed at 200 yards normally. I have to know my range very well and am not able to guess it very well either. This is where a ranger finder comes in handy. Past 200 yards, the subsonic bullet is headed downhill rather fast. Using the 458 cal 500 gain bullet above, from 200 to 250 yards it drops 21 inches; from 400 to 410 yards it drops 10 inches. The good thing is that you can expect very consistent velocities from a good subsonic load, especially one with a small case capacity. The whisper loads I shoot typically have a standard deviation of less than 15 fps.

Ranb

R.W.Dale
March 1, 2010, 11:11 AM
I think some of you are confusing .45 and .458 win mag.

The cartridge in question is 45win mag essentally a rimless 45LC if you will.

My max bullet weight will be no more than 300grs. With lots of 230grn ball being used in super and subsonic roles. BC's will be around .175

2 and 300m will strictly be for range fun. Any hunting will be with supersonic loads (1800 fps?) and be taken well inside 200m

so as you can see massive bullet drop will be the order of the day with this combo.

kludge
March 1, 2010, 01:18 PM
Just curious, what are you planning to use as the base for this build?

The .45 Win Mag is a curiosity for me (autoloader, IN deer legal).

R.W.Dale
March 1, 2010, 01:45 PM
Just curious, what are you planning to use as the base for this build?

The .45 Win Mag is a curiosity for me (autoloader, IN deer legal).
It's mentioned in the title and OP

This bbl is coming out of Indiana, Ya'lls wacky game laws are spawning off some really really neat innovations

Ranb
March 1, 2010, 05:38 PM
Opps, sorry. I read 458 mag when you actually said 45 mag. I would limit a pistol cartridge to 200 yards. I do not think you need a tilt down scope mount or a scope with lots of elevation to zero at 200 yards.

What twist are you going to get? I was thinking of a 45 win mag pistol in a savage, but after I got my 458 socom, I decided that the 45 mag pistol cartridge was not enough.

Ranb

R.W.Dale
March 1, 2010, 06:40 PM
But I'm not willing to limit myself to 200

some may concider it inhumane and unethical but I want to have the option of killing my steel gong at 300m

SharpsDressedMan
March 1, 2010, 07:47 PM
Having a scope modified with dots all the way down to bottom of the reticle wire is more important than a canted base. TK Lee custom reticles can modify a scope with dots. I recommend a distance of 12" between dots for maximum use of a 4-6X scope. Magnification is also LESS important than the bigger field of view needed to allow for such drop at 500-600 yards (about max for good supbsonics, like .300 Whisper or .510 Whisper (subsonics with good BC's). If you can see a target at 600 with the naked eye, you can certainly target and hit it with a 4-6X scope.

RyanM
March 1, 2010, 07:49 PM
According to my calcs, a 300 grain bullet with a .165 BC, will need to be adjusted 47 MOA to hit at 300 yards, 26 MOA for 200 yards. Dunno how many MOA adjustment the scope you'll use has, but I hope that helps.

R.W.Dale
March 1, 2010, 09:50 PM
Those numbers seem pretty close to my calculations. My problem is I don't know how much elevation you get with a typical scope.

I'm going to start with a leupold vari-xII 2x7x33 but intend to upgrade later to an optic that allows for quicker range compensation. Of course this is all very much in the air till I get the rifle built and determine my mv's

Ranb
March 1, 2010, 10:54 PM
Lets say a cheap scope has 80 inches of elevation available. Only half of this is available to raise impact above the direction of the bore. Using full elevation adjustment gives you 40" up at 100 yards, 60" at 150, 80" at 200, 100" at 250 and 120" at 300 yards.

If you use your BC and set the zero range to one yard and sight height to zero inches, you get the following bullet drop data.

50 yards 4"
100 yards 17"
150 yards 39"
200 yards 73"
250 yards 117"
300 yards 175"

This data says you will be able to adjust out to at least 200 yards with a scope that has at least 40" of elevation adjustment. But it is only worth the paper it is printed on.

Ranb

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