scope question please help

[GI44]

does the bullet cross the scope path twice or just ounce. i hear that people will sight their guns in at 100 yards and be dead nuts at 300 or 325. any thoughts?

 

[dstewart51]

Depending on many factors, yes it can. Its called primary zero and secondary zero. The bullet has to rise crossing the secondary 0 due to the scope being higher then the barrel and the fact the bullet is falling the moment it leaves the barrel. It will then hit the primary zero on its way back down.

That said, its not likely you can end up with zeros at 100 and 300 yards.

 

[bruce_ventura]

Depends on the bullet and caliber. For example, if I zero my 270 Win at 100 yds, the bullet trajectory touches line of of sight just once. If I zero at 200 yds, the bullet crosses line of sight twice, once at about 40 yds and then again at 200 yds.

 

[tulku]

I agree with the previous Posts . I'm guessing you would need something like a 22/284 , 220 Swift / Std. or AI , 257 Weatherby , 17 or 20 based on the PPC , 6BR , or 22/250 Case ( all of which exist and all with light Bullets ) to accomplish the 325 Yard figure .

 

[dstewart51]

Here is a good article explaining some basic optics and ballistics that covers this question,
PRACTICAL LONG-RANGE RIFLE SHOOTING - PART II: OPTICS

 

[brentc]

Short answer is yes. All rifles and calibers can use a dual zero. A 100 yard zero will never translate to a 325 yard zero as long as gravity has anything to say about it. I know several guys that run a dual zero by zeroing at 25 yards to get another zero in the mid 200 yard area. I've actually done this with several rifles, most recently a 375 Ruger when I was limited for range distance and shooting time. I zeroed at 25 yards and verified a 200 zero by popping milk jugs at 240 yards. For general hunting purposes it works quite well.

You have to realize that the POI at the in between zeros range will be high and depending on the size of target you may need to compensate. For instance on the same 375 Ruger mentioned above at the 25 yard zero will impact a target around 3" above my point of aim at 100 yards, if it's a small target you'll need to compensate, but if it's a bear or simlarly sized animal, hold on hair and squeeze the trigger.

 

[GI44]

so if i were to shoot a 300 WM and zero it at 100 yards it would not cross the line of sight again at further distances?

 

[brentc]

so if i were to shoot a 300 WM and zero it at 100 yards it would not cross the line of sight again at further distances?

No, it will not because your 100 yard zero is the second time the bullet crossed the line of sight. The first time it crossed was probably around 75 yards.

 

[brentc]

Depends on the bullet and caliber. For example, if I zero my 270 Win at 100 yds, the bullet trajectory touches line of of sight just once. If I zero at 200 yds, the bullet crosses line of sight twice, once at about 40 yds and then again at 200 yds.

It will always touch it twice not matter what your zero is, as long as your scope is mounted above your bore. At your 100 yard zero it would have hit around 75 yards the first time it crossed.

 

[dstewart51]

No, it will not because your 100 yard zero is the second time the bullet crossed the line of sight. The first time it crossed was probably around 75 yards.

Just ran a 155gr BTHP at 3300fps in Shooter, yep, about 75 and 100.

For the fun of it I tried a few light and fast and some heavy's at various and even impossible velocity. Never got anything close to 100 and 300 zeros. Maybe if your scope was a foot or more above your barrel?