Use a Boresighter BEFORE Changing Scopes???

[BruceB]

Looking up and down the list of forums here, it seems this one's the most-logical place for a thread about rifle sights.

I have a substantial number of rifles and likewise quite a few scopes, and in the past few weeks I've been really shuffling the deck by switching scopes around from rifle-to-rifle (for what seemed to be good reasons at the time).

My old Bushnell boresighter has a grid pattern in the field of view. It occurred to me that if I recorded a boresighter reading BEFORE removing a scope from a given rifle, then I MIGHT save some hassle and re-zeroing time and ammunition by adjusting the "new" scope to the same boresight reading as the removed scope.

In short, for the four rifles involved, it worked quite well. The WORST result was with my #1 Tropical in .416 Rigby. I swapped off a Bushnell Trophy 3-9x and installed a Leupold fixed 4x. The first group at 100 yards was about 5.5" high and left, but very nicely on-paper, which meant that the final zero was a snap. The other three were better, and my wife's M77 .270 (Leupold 2-7x installed in place of a Tasco 6-24x varmint model) was just about perfectly zeroed on test-firing.

Seems like this is a useful shortcut, as long as one's boresighter has some kind of calibration which allows adjusting to the same reading.

[carpetman]

BruceB--That was an interesting experiment with the bore sighter. I have never had a bore sighter. For guns I can look through the bore, I do so and sometimes I use a deprimed case installed which has the effect of a smaller aperture. Fire one shot and then sight on that and move crosshairs to center of target. Then fine tune from there. My gunsmith friend has a Sweeny collimator he swears by. In his case it's justified as mounting scopes is a frequent deal.

[Ranch Dog]

BruceB...

I use RSI Shooters Lab software and they have a "Boresight" entry for each load. It works when changing things and returning to a given load. I've attached a screen-shot of all the windows related to the bore sight info.

[NVcurmudgeon]

I seldom switch scopes around and do not own a collimator. Bruce's idea has merit for those of us who switch wildly varying loads around, too. There can be a radical point of impact shift (especially when dealing with rifles of substantial recoil) between LV cast boolits and HV jacketed bullets. For example, when my .35 Whelen is sighted in @ 100 yd. with cast, full power jacketed loads shoot about eight inches high and four inches left. I keep this information for all of my dual purpose rifles in the notebok that lives in the range box. Such rifles are likely to be re-sighted twice a year. When changing sight-in loads it is convenient to first dial in a "ballpark" adjustment. Saves wasting too many of Mr. Nosler's bullets at 75 cents each. Sometimes it isn't convenient to change sight settings for a few rounds, so I will then use my POI list to tell me where to put a false aiming point on the target, enabling center hits without adjustment.

[fourarmed]

Fire one shot and then sight on that and move crosshairs to center of target.

Don't you mean "Fire one shot, sight on the center of the target, then move the crosshairs to the bullet hole"?

[Scrounger]

Don't you mean "Fire one shot, sight on the center of the target, then move the crosshairs to the bullet hole"?

You put the crosshairs on the center of the target, fire one shot. Then stabilize the rifle on sandbags or whatever with the crosshairs in the center of the target. Then, without moving the rifle, use your scope adjustments to move the crosshairs to the center of the bullethole you just made. Your rifle is now sighted in for that distance. Always remember it this way: You cannot change where the rifle and barrel place the bullet; you must always move the sights or crosshair to coincide with that point.

[felix]

Yeah, that's the problem. You can't move the gun while changing the crosshairs. Else, you got to start over again, with one shot at a center target somewhere, and now move the crosshairs again. ... felix