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Bubble level for rifle

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Unread 03-06-2004, 02:01 PM
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Join Date: Jun 2001
Location: Palmer, Alaska
Posts: 2,539
Re: Bubble level for rifle

I looked at that last night myself, and I see what you're saying.

The extra elevation needed to account for 100 yards worth of drop would no longer be needed at 90 degrees cant, and the deflection would be equal to this amount drop at 100 yards if it were left dialed in.

So, if this amounts to x.x MOA, it would be that at all distances and the calcs would be off by that much, right?

I've got to go pick up some steel plates and may call Jim on the drive to Anchorage about this to see what he has to say.
Brent Moffitt
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Unread 03-06-2004, 02:15 PM
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Join Date: May 2001
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Re: Bubble level for rifle


The 6 degree figure comes from a post in this thread by *WyoWhisper* and a subsequent reply. Numbers were stated and that's why I used the 6 degree figure, no other reason. (Keep in mind that as always, any number selected is going to piss someone off so any number can be used as long as we're consistent.)

You're correct, the number are good to know if you're a sniper or shooting in that type of competition. The level is a essentially a binary device, on (level) or off (non-level) and I intend to use it in that fashion. For LR shooting I'd like to check level. I have only one shot to get it correct and every little thing helps. Cant is particulary unfriendly to shooting vertical targets, we shoot tall and skinny targets, if they were short and wide cant wouldn't be so much of a consideration. For example, we shoot a mover (nominally 3 mph) that's 12 inches wide and 48 inches tall at a distance of 600 yards, pre shoot prep dictates removing cant as much as possible.

On using a 180 degree "cant"... we've shot in this position too an it's fairly humbling without considerable forethought. Just tipping the rifle over at 100 yards you'll be about (don't hold me to this as I've not run the numbers) 6 or 7 MOA low (below POA). I don't care to argue this point, it's just for fun. [img]images/icons/smile.gif[/img]


Thanks, let's see what the RSI folks have to say, I'm curious (as always).
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Unread 03-06-2004, 02:58 PM
CAM CAM is offline
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Join Date: Jan 2002
Location: Utah
Posts: 385
Re: Bubble level for rifle

I agree it affects vertical moving targets more than horizontal targets,

Any idea about the nightforce NP2 sighted at 600 and not dialing dope? would this roughly reduce error by half at 1200? But increase error at 100?

That's what I use the level for also "to check level" and it works for that.

No arguement on the 180 deg. I was kidding you a little.

Have a nice week end
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Unread 03-06-2004, 06:32 PM
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Re: Bubble level for rifle


I know you were kidding on the 180 thing but we've actually shot in that manner, just wanted you to know folks are trying all kinds of stuff.

Sighted at 600..reduce error by 50% at 1200 but increase error at 100... ??? I'm not sure exactly what you're asking but I'll give it a whirl.

I'll assume you're asking about cant error. Damn, I'm getting a little leery of talking about cant and stating values (my ass is beginning to look like that of a Mandrill).

Cant error is increased by the amount of offset/trajectory correction in the sighting system. This means that if you're sighted (zeroed) at a greater distance the deflection error is greater than if you were sighted (zeroed) for a somewhat shorter distance. The size of the base (the distant end) of the "cone" that projects from the center of the rifle bore to the line of sight "zero" distance determines the magnitude of the deflection cant could cause. For example, a 100 yard zero on an imaginary rifle would allow for about 3 MOA of correction (TOF "drop" for 100 yards ~ 2MOA and sighting system height ~1 MOA). This would make a "cone" with a base of 6 MOA. If you rotated the rifle in 1 degree increments and fired a round onto the same target using the same POA at each interval when you had completed a 360 degree rotation you'd have a circle 6 MOA in diameter. At 12 o'clock on that circle would be the round fired in the Zero -0- degree cant position, at six (6) o'clock would be the round fired at 180 degrees of cant (it'd be 6 MOA low).

Not let's figure the same for a zero of 600 yards. I'll guess you use a magnum and that your 600 yard zero is about 11 MOA (sea level) ON TOP of your 100 yard zero (a hidden ~3 MOA). You can see that if you perform the 100 yard "round robin" test again your "cone base" circle is going to be at least ~22 MOA plus the "hidden" 100 yard zero correction of ~3 MOA (but 6 MOA of "cone base"). Overall I'd say you would have a circle of about 28 MOA.

Of course if you had used a 1200 yard "zero" data set the cone base would be much larger but that's not the other part of the question. The other part of the question if whether or not the 1200 yard cant error would be decreased by 1/2 by using a 600 yard zero.

Then you say "nightforce NP2 sighted at 600 and not dialing dope? would this roughly reduce error by half at 1200?" I take it to mean that you would use hold overs to get to 1200 yards. By doing so you effectively raise the muzzle of the rifle as you use a lower aiming point in then scope, this is no different in my eyes that if you were to "dial on" the additional data, the "cone base" gets larger. So I guess the answer to the 600 yards zero, 1200 yard shot only 1/2 the error would

Anyone have thought on this?? Does this sound correct?

My out: I'm not a rocket scientist, ballistic expert, or college graduate. All this data is pure speculation on my part, it's based on things I've read, pondered on and "worked out" on my own. I could be wrong and if I am I'd like to know the correct method(s) and answer(s), so speak up, I'd appreciate it.
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Unread 03-06-2004, 10:13 PM
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Join Date: May 2001
Location: Lock Haven P.A.
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Re: Bubble level for rifle

Dave,WHAT THE H#&& DID YOU JUST SAY [img]images/icons/confused.gif[/img] [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img]
Boyd Heaton...
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Unread 03-07-2004, 06:26 AM
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Join Date: May 2001
Posts: 2,369
Re: Bubble level for rifle


I don't know?? I was possessed by a demon of some sort and all the stuff just came flying out. Sort of like Linda Blair (Regan(?)) in the Exorcist. Yaaackkkk, and there it was! [img]images/icons/smile.gif[/img]
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Unread 03-07-2004, 08:07 AM
Posts: n/a
Re: Bubble level for rifle


Believe it or not I do understand what you are saying and you are basically correct.. ( can you believe I just said to Dave he is correct and I even understand it )

maybe in laymans terms...

your scope when mounted on a 20 MOA base is basically pointed down.... your barrel is basically pointed straight or flat... if you would draw a line from you line of sight ( scope ) or point of aim.. and a line from you barrels trajectory those two lines would intersect at some point...
now here's where it gets tough to explain...
If you cant your rifle.. ( given you movemnet is perfectly pivoted around your rifle barrel ) you barrels trajectory is still pointed at the same place but your line of sight or point of aim is now actually looking at another point ( away from your original target )and now you move your entire rifle so that you're aiming at your original target... hence this is how cant will cause you to have bigger groups.. However slight at 100 yards but it becomes greater as the distances grow!..

keep in mind I did not factory in trajectory of the bullet or ballistics as I tried to keep it simple..

did that make any sense to anyone other than me... I am not the best teacher thats for sure....
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