How to use bore-sighter?

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Potashminer

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I have mounted many scopes, using levels, plumb bobs, etc. and the Mark 1 eye-ball gauging device to get the vertical crosshair in the scope dead centre on the center of the firing pin (Mauser actions). I believe that gets the scope square and plumb to the rifle. I have been "bore sighting" by looking down the bore - getting a mark 20 or 30 yards away centered as close as I can through the bore, then adjusting the scope turrets so cross hair is on that mark as well. Seems to work for me. Can level the rifle action (with a level) with barrel held in soft jaws in a vise, then hang a plumb bob on far wall of shop, then crank on the vertical turret and get the cross hairs to follow the string up and down. The scope must therefore be square to the receiver.

So, a friend convinced me that my process was too "old fashioned" and I needed to use a proper bore scope to "bore sight" a rifle. I purchased a "Bushnell Standard Bore Sighter" - the kind with 15 different arbors. Trying to make sense about how to work it.

How do I know that the bore sighter is vertically plumb to the rifle? Does this thing rely on the scope crosshairs to be square to the rifle? Looking through the scope, I can tip the bore sighter left or right. But I can also cant the scope left or right if I have the mounting screws loose, and can then adjust the turrets to match the grid in the bore scope, while tilted. So, only two parts - the scope and the bore sighter. To get the bore sighter properly set up, can someone confirm that I must rely on the scope installation to be plumb in the first place?? In other words, the bore sighter can not verify that the scope is indeed plumb? Or am I overlooking something, obvious or not?
 
I’m a fan of simple things that work, sounds like your old fashion way worked well enough. For me, bore sighting is to get you on paper and generally looking down the barrel does this nicely for no extra cost. For semi autos I will use a laser sighter as pulling the bolt takes more time. I like the old fashion methods most of the time, they usually work!
 
Mount scope.
Get it as close to plumb on the shooter as possible.
Install bore sight and make the two + hairs vertically/horizontally equal
in spacings.
Crank turrets until the +hairs become one.

I remove and reinstall the bore sight.
If the results are the same as before removing it, I'm content.
If not, I repeat step one.

Never had much of a problem pounding a round very near to bulleye at 25 yards.
Usually it's an elevation thing.
Best to have the round under the eyebawl on the target as it could turn out poi at
the 100 yard mark be high.

Iff'in yer blind, all bets are off.
 
Thanks, guys. Sort of as I thought. These bore sighters rely on the scope mounting to be correct in the first place. And they are no aid to getting that done.

My buddy was proud as all get out that his new scope on his 22-250 had been "bore sighted" by the gunsmith who installed the scope, in the city about 3 hours away, and was therefore good to go. I didn't think so - I'm thinking he actually needs to shoot targets to "sight it in" but he is convinced that since he paid good money to have that scope "bore sighted", I needed to change from my old-fashioned ways, since my way requires burning up cartridges at paper targets ... And, to his credit, he has taken a couple coyotes with that 22-250 and that scope.
 
I've not found using a commercial bore sighter to be any more accurate than just resting the rifle securely and looking through the bore at a mark. More convenient, though.
I donn't trust either without firing shots to confirm zero.
 
Many years ago I used a rifle with a scope mounted that was as square as it could be to set up level on the bore scope.

First I levelled the rifle in a padded vise... and then I inserted the bore scope in the muzzle... looking through the scope I rotated the bore sight so the grid appeared square to the cross hairs... then I took a blob of AcraGlas Gel and epoxied a level on top of the bore sighter with the level being level. I check it a few times while it was curing to make sure the level was still level and the sighter grid still square with the cross hairs.

It has worked very well for a long time in mounting scopes with the cross hairs square with the rifle...

As to bore sighting... I compared rifles that were sighted in to the grid and recorded the results... I found with this bore sighter the majority of scopes needed to be sighted 4 squares left and 2 squares high... when the medium adjustable spud was used. Over the years I ended up making a reference chart for where the various calibers needed to be.
 
This is my own experience with a bore-sighting tool so do with it what you wish.

This tool was a common spud-mounted offering from Bushnell. I have a .223 bolt gun that from out of the box with the scope that came with it in the box, would shoot hole-in-hole groups with most any slug fro 40 gr up to 55 gr. I shot a lot of these groups over the first few month's I owned the gun.

After a bit of shooting these 100 yrd groups I convinced myself that maybe I should install a 6-24 on her and stretch it out a bit. The promotional offering of that scope came with a bore-sighter included, mounted the scope and decided to use the tool to see how it did....so inserted the spud as per directions.

That gun never shot another hole-in-hole group ever...the tool did put the impact point close to aim point but I think that inserting that spring loaded metal spud changed something in the last 3 inches of the bore enough to degrade accuracy a small noticeable amount. The gun will still shoot "almost cloverleaf groups" but it is disappointing when you are used to much better.

The "almost cloverleaf groups" are still somewhat adequate and if I didn't have the previous benchmarks of hole-in-hole groups, I wouldn't probably know or suspect any damage was done.
 
fingers284 said:
I shot a lot of these groups
Click to expand...

Ed Shilen stated he can see considerable bore wear and a loss of the fine accuracy in as little as 400 rounds with small and medium cases.

Often crowns are refreshed for better accuracy as well.

I think your shooting a lot of groups most likely took some of the edge off your accuracy and possibly your new scope had something to do with it as well.
 
Before mounting a scope I use a Wheeler reticle level which works well on rifles with a flat surface for the first level to sit.

For rifles without a flat surface the EXD reticle level works on all rifles.
 
Jaylegger said:
I do a 360 degree spin of the bore sight then adjust sight to the middle of these errors. Works well.
Click to expand...

That is the correct way to use a bore sight or laser boresighter but I think they are talking about a bore mounted collimator used for bore sighting if you are being really technical.

A true boresight is a sight that fits down the bore of a weapon and looks at a distant target slowing sights to be aligned to it. It's usually found attached to the end of larger guns and cannons especially tank cannons. It also commonly found with a gunner or sight technician hanging off the end of the boresight.
 
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