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Bubble level??

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Old 02-12-2010, 12:30 PM
Junior Member
Join Date: Jul 2008
Posts: 22
Bubble level??

Ok, I am new to long range shooting. I have been hunting for years with a .270 bolt gun but never had a shot at more than 150yds. In the past year I purchased my first GAP rifle, the Rock model in .308Win. It will shoot under an inch at 200yds, even with me behind the trigger! What an amazing rifle.

My question is this, in the field, what does a bubble level do for you other than the obvious, keep your reticle level? Maybe the better question is what are the adverse effects of a canted reticle?

I am wanting to try long range hunting but even at that I can't see myself hunting beyond 400yds, I'm just not that good.

Thanks in advance.
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Old 02-12-2010, 12:42 PM
Platinum Member
Join Date: May 2008
Location: South of Canada and North of Wyoming
Posts: 5,954
Re: Bubble level??

Assuming your reticle is aligned with the center of your bore (many are not) canting your reticle would be the same as canting your bullet's fight path. Your bullet travels upward when it leaves the muzzle, to meat the zero point of your line of sight. If you cant the rilfe lets say to the left, the bullet leaves the bore, rising to the left and your POI will be left of your POA.

Bubble levels aren't perfect instruments but IMO they are a whole lot better than nothing. Since I started using one it has really opened my eyes to how much cant I would sometimes put into the rifle when trying to eyeball a level when there isn't a level horizon as a reference.

IMO, a bubble level is critical for LR hunting.

Welcome to LRH and good shooting,

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Old 02-12-2010, 12:45 PM
Junior Member
Join Date: Jul 2008
Posts: 22
Re: Bubble level??

Ah, very good. Thank you, that makes sense.

"I see said the blind man...."
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Old 02-12-2010, 12:55 PM
Platinum Member
Join Date: Dec 2005
Posts: 2,114
Re: Bubble level??

Bubble levels keep the sights elevation axis in the true vertical and the rifle's not canted. The amount a bullet will strike away from the aiming point horizontally is easy to calculate.

Multiply bullet drop in inches at target range by the sine of the cant angle.

For example, lets take a .321 Belted Magnum shooting 234 grain boattails out at 3210 fps. These bullets drop 300 inches at a thousand yards. If the rifle's canted just one degree, the sine of 1 degree is .1745. Multiplying 300 times .1745 we get 5.23 inches; five and a quarter inches in plain numbers. So the bullet will strike a bit over 5 inches to the right.

A .308 Winchester shooting a bullet that drops 450 inches at 1000, it would strike almost 8 inches to the side with a 1 degree cant.

There's virtually no change vertically as the cosine functions to show that end up with only a few inches difference for most situations. For the .321 Mag. example at 1000 yards above, a 10 degree cant will cause a 52 inch wide shot horizontally, but it would be only 5 inches lower.

Competitive rifle shooters have used bubble levels on their aperture front sights for years to ensure the rifle's not canted. There are some available for scopes, but they're hard to use as they stick up too far atop the tube. I'm not aware of any scope that has an internal one although such things have been suggested to scope makers.

Here's a picture of one on a .308 Win. match rifle and another showing what a bullseye target looks like through one. A small level's put on the rear sight's windage arm, leveled, then the muzzle band's loosened, turned to level the front sight bubble, then tightened. One can calibrate how much cant's needed to move impact one MOA at any range. I've done that in competition to make small windage corrections without coming out of position to turn the sight knobs.

Last edited by Bart B; 02-12-2010 at 01:11 PM.
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Old 02-12-2010, 01:08 PM
Junior Member
Join Date: Jul 2008
Posts: 22
Re: Bubble level??

Wow, a little goes a long way. Can you recommend a good bubble level? I am using Badger rings/bases and looking through a Leupold Mk 4 LR/T 65.x20.

Also, what is this angle cosine stuff I am seeing? Us rednecks just out in our stands shooitng whitetail don't know much about these here acoutrements. ;)

Thanks again!
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Old 02-12-2010, 01:10 PM
Silver Member
Join Date: Jan 2009
Location: Little Falls, MN
Posts: 251
Re: Bubble level??

The neatest scope ever was Springfield Armory with an internal level. I haven't seen any for quite some time. They must have been too costly to make.
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Old 02-12-2010, 01:17 PM
Platinum Member
Join Date: Dec 2005
Posts: 2,114
Re: Bubble level??

Here's some links to external ones.

Long-Shot MicroLevel - Precision Scope Level


It would be easy to put a small one at the bottom of the reticule plane in scopes. The bubble could easily be seen at the bottom of the field of view. It might be a bit out of focus, but who cares as long as it could be seen. And it would be totally internal; free from external bad stuff. Redfield, Weaver and Leupold liked the idea when I mentioned this to them years ago.

Last edited by Bart B; 02-12-2010 at 01:39 PM.
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