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Different MOA bases

 
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  #1  
Old 07-18-2008, 07:01 PM
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Different MOA bases

Can anybody tell me why there are different bases like 20moa and others?

Is picatanny (sp?) the only way to go for long range shooting or are other style bases alright?
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  #2  
Old 07-18-2008, 09:31 PM
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The reason for different sized bases is that scopes often don't allow enough elevation to reach out long range. If you are using a scope that has 35 MOA adjustment (which isn't uncommon) that means you have approximately 17.5 moa up and 17.5 moa down. We are only conserned with the up because we want to reach farther right? So if you are shooting a 308 at 600 yards you will need to increase your elevation about 16 MOA from a 100 yard sight in. If you want 700 yards then you would need something like 21 MOA - about 4 MOA more than you have adjustment. SO if you put in a 10 MOA rail, you will have started with your scope adjusted down allowing you to use more of your scopes internal adjustment to go up when shooting at long range. If your scope has 40 or 50 MOA adjustment, then you may want to use a 20 MOA rail because you would be able to use almost all of you adjustment to increase your range. However, if you only have 35 MOA of adjustment, you might not want a full 20 MOA rail because you wouldn't be able to sight in for less than, say 350 yards.

The Picatinny rail is a very strong reliable system that is very popular. It is the system that the military uses.
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  #3  
Old 07-19-2008, 12:12 AM
KRP KRP is offline
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I think saying that you have 17.5 MOA up and 17.5MOA down adjustment is a good way to confuse people and only applies if your original zero coincides with the center of adjustment range of the scope(how often does that happen). The scope has 35MOA of total adjustment, the amount of available upward adjustment depends on the original zero. The sloped base allows you to use less of the scopes total available adjustment for your original zero.

Let's say for example with a 0MOA base and a 100 yard zero you have 20MOA of upward adjustment left in the scope. Now swap the 0MOA base for a 10MOA base and rezero at 100 and you now have 30MOA of available upward adjustment.
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  #4  
Old 07-19-2008, 03:27 AM
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The whole thing itís easy to figure out. Let's say we're shooting a 308 with 155 gr. Palma Sierra Bullets at 2950 ft/sec, 5000 ft of Altitude. The Drop at 100 yards would be about 2", not the bullet path, the Drop, meaning if the barrel is completely horizontal, at 100 yards the bullet would drop about 2". If the scope height is 2" from center of the bore to center of the scope then that would make a total of 4 inches. 2" for the scope height and 2" for the bullet drop. That would mean that when the barrel and scope are in the horizontal and the scope turret has been centered exactly at 17.5 moa, then we know the bullet will strike 4" low at 100 yards. You could say that in zeroing in you would be using 4 moa. That would leave 17.5 - 4 = 13.5 moa left to be used. From 35 moa to 13.5 there is a difference of 21.5 MOA that are basically wasted and can no be used. Here is where the tapered bases come in. If you get a 20 moa base it would be putting it you too close to the scope's adjusting limit. A 15 MOA would be nice because it would let you have a total of 13.5 + 15 = 28.5 MOA for long range shooting and it would not be that close to the end of the scope's adjustment since there would still be 6.5 moa left. Hopefully I did not get confused. :confused: ;) If you need to be more accurate, which I don't think you need, you can always take 4" / 1.047 = 3.82 MOA. I would just call it 4 MOA.
17.5 middle value is very important and it should be used.
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Last edited by Eaglet; 07-19-2008 at 04:47 PM.
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  #5  
Old 07-19-2008, 11:18 AM
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Naw..guys this is exactly what I was trying to figure out just getting started here.

So my real question is this now....what scopes have the most adjustment for elevation, what MOA bases would be required or wanted for shooting to 1200-1500 yds, and would picatinny style be the "only" way to go?

My apologies for being a new guy. I'm sure there are a bunch, I just wish I knew as much about this as dogs.
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  #6  
Old 07-19-2008, 11:52 AM
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Need more information, what cal, load are you shooting?? Big difference between a 338 Allen Mag and a 45-70 and a 17 hmr. Scopes vary from brand to brand and modle to model for how much adjustment they have. Your Lupy's Mark IV and Long range target scopes will give you lots of adjustment. Nightforce will too, but these are all in the 1000 to 1700 dollar mark (I think they all have someware between 80 and 120 MOA). On the other hand, Nikon Buckmaster 3-9 has 80 MOA, but the 6-18 has only 40 (generally speaking, as the power goes up, the adjustment goes down - or you have to pay big bucks to get the adjustment increased by upgrading brands). Most Optics manufacuters will list the specs of their products on their webpages. So you can do some picking and choosing. No offense, but if you are new to it, maybe try focusing on something like 500 to 800 yards first. It really takes a lot of tallent and years of practice to make reliable 1000 yard shots. Try JBM - Calculations when you are figuring out what your drop will be for a load.
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  #7  
Old 07-22-2008, 12:32 PM
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Join Date: Jul 2008
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NO OFFENSE TAKEN!!! You gotta learn to walk before you can run, especially if you want to run fast over long distances......You are absolutely correct about starting at shorter distances. That's what I plan on starting with 500-700yds.

As far as the caliber I will go with, that's still up in the air, but likely a .338 (Lapua, Ultra Mag, Edge, or other long ranger). I don't think my 6.5-20 x44mm Nikon will hold up for these big bangers for real long so I'll keep it on my 223 or 25-06. But I was thinking Nightforce to put on the rig so I can keep the same rifle for starting out 500-700 yds, then move out when I learn how to shoot properly at those distance, handload myself, and the game in general.
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