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Bubble level??

 
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  #29  
Old 03-26-2013, 05:50 PM
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Re: Bubble level??

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Originally Posted by aroshtr View Post
Elimination cant in the RIFLE isn't what is really important. Eliminating cant in the SCOPE is. One of these days I will film a demonstration showing this, as most people do not think it is possible to shoot at long range if the gun is not perfectly level. We do this all the time with archery equipment, and I have set up several rifles where the gun was not level (for shooter comfort), but the scope is, and they shoot true out to 1000 yards.

Joel
Your curved bullet path (drop) (minus wind) due to gravity is defined in a plain that is aligned with the pull of gravity. If your windage reticle (sight plain) is not parallel and aligned with bullets plain of flight there will be a divergence. if your scope is properly plumbed in relation to gravity and your rifle is canted right and you have zeroed to 100 yds in that condition, your bullet will have started it's path to the left of the vertical sight plain, traveling to the right to converge with that plain, and continuing to diverge to the right, away form the vertical sight plain. The farther down range your POA is the farther right your POI will be. This is a physical and geometrical fact.
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  #30  
Old 03-26-2013, 06:15 PM
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Re: Bubble level??

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Originally Posted by MontanaRifleman View Post
Your curved bullet path (drop) (minus wind) due to gravity is defined in a plain that is aligned with the pull of gravity. If your windage reticle (sight plain) is not parallel and aligned with bullets plain of flight there will be a divergence. if your scope is properly plumbed in relation to gravity and your rifle is canted right and you have zeroed to 100 yds in that condition, your bullet will have started it's path to the left of the vertical sight plain, traveling to the right to converge with that plain, and continuing to diverge to the right, away form the vertical sight plain. The farther down range your POA is the farther right your POI will be. This is a physical and geometrical fact.
So the rail mounted level, and the plum line trued reticle, will have you covered correct? I feel it does as I have not had an issue doing it this way.

Jeff
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  #31  
Old 03-26-2013, 06:23 PM
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Re: Bubble level??

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Originally Posted by Broz View Post
So the rail mounted level, and the plum line trued reticle, will have you covered correct? I feel it does as I have not had an issue doing it this way.

Jeff
As long as they both agree then both are aligned to the bullets plain of gravity.
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  #32  
Old 03-26-2013, 06:54 PM
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Re: Bubble level??

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Originally Posted by MontanaRifleman View Post
As long as they both agree then both are aligned to the bullets plain of gravity.
Yep, I just did one this afternoon. Checked the rail top with a small level as I mounted the level on the rail and they agreed. Then , watching the level, trued the reticle perfectly to the plumb line. Just like I always have done. After the barrel is broken in and load development, I will shoot the line as I posted earlier for the final check.

Thanks

Jeff
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  #33  
Old 03-26-2013, 07:34 PM
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Re: Bubble level??

Quote:
Originally Posted by Broz View Post
Yep, I just did one this afternoon. Checked the rail top with a small level as I mounted the level on the rail and they agreed. Then , watching the level, trued the reticle perfectly to the plumb line. Just like I always have done. After the barrel is broken in and load development, I will shoot the line as I posted earlier for the final check.

Thanks

Jeff
Yeah, as long as the reticule is lined up with the center of the bore and plumbed up and the levels reflect that you should be good to go.
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  #34  
Old 03-26-2013, 07:47 PM
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Re: Bubble level??

A hypothetical math example. Scope is plumbed and rifle is canted say about 10 degrees. Scope is mounted 2" above center line of chamber. At 10 degrees right cant let's say the center of chamber (and bullet) are 0.2" left of center of scope. Our zero is @ 100 yds. When fired, the bullet travels right in relation to the line (plain) of sight to converge on the zero point. At 200 yds, the bullet has now gone from 0.2" left of line of sight to 0.2" right of line of sight. At 300 yds the bullet is now 0.4" right of LOS. At 1000 yds, the bullet is 1.8" right of LOS. Not a huge deal.

If we move the zero out to 200 yds, the effect is smaller. At 1000 yds the bullet would be 0.8" right of LOS.
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  #35  
Old 03-26-2013, 08:33 PM
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Re: Bubble level??

Mark, you are exactly right, and I am in no way trying to argue, or disagree with your and science.

I was a little slow at doing my math by hand and compass drawings to get some actual figures. So, I guess since I did the math I will put what I came up with.

1.75" Sight Height, I actually came up with about .3" from center-line at 10 degrees.

If you were 10 degrees off with the rifle (Which would be blatantly obvious)
100yrd Zero = 2.7" off center at 1000 yards
200yrd Zero = 1.2" off center at 1000 yards
300yrd Zero = .7" off Center at 1000 yards

Most of my rifles have a 200 or 300 yard zero for my drop data/site tape, but I usually sight in and set my elevation and windage turrets at 500 yards. This helsp make up for any slight errors in my data. So in theroy If I set my windage at 500 then I will only be off .3" at 1000 yards from my gun being at some ridiculous 10 degree angle. Now when I set my guns up for a comfortable feel, I would bet that I am well within 5 degrees of square, and all these numbers would be about 1/2 their values.

I guess the point I am trying to make is that too many guys try and make this complicated and worry that if it isn't perfect then they won't be able to shoot accurately at long range. When the truth is, if you eyeball the gun, or use some other half ass method to get you close, it really is no big deal. Especially if you zero at 200. It is even better if you set the windage and elevation at your expected mid range shot distance. In this case the margin of error is much smaller than any gun or human being is capable of shooting.

The take away..... If it makes a guy feel better to spend your time and money on fancy gadgets and levels to get the gun perfectly level to the scope, that's fine. But for me and lots of other guys, my time is better spent shooting and confirming my drop data.

Joel
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