Baffled by 260 rem ballistics

[lordjackel]

First let me say I am in no way an expert in understanding ballistics, MOA, correct scope usage (first foray into precision shooting but starting to learn) but I do know how to sight in a scope. So I took my 260 Rem (AR10 platform) to the range yesterday to sight in my Vortex Viper PST 6-24 SFP. (Using 120gr Federal Fusion factory ammo)

Here are the results that make no sense to me what so ever (this is based on where I have to aim using the scope reticle). (3 shot groups)
At 50 yards - hits 3 MOA high (so holding on the # 3 subtension)
At 100 yards - hits 6 MOA high
At 150 yards - hits 9 MOA high
At 200 yards - hits 3 MOA low

Now looking at ballistic charts and such this shouldn't be happening this way (movement should only be 4 inches give or take across these ranges).

I am going to reload 140gr AMAX bullets today as I plan to use a heavier bullet but the above has me scratching my head.

Thanks for any insights

 

[Leo]

That is very strange results. The .260 Remington is a very flat shooter. For example, a 175 gr .308 needs to be about 37 inches high at 100 yards to be in the black at 1000 yards. A 142 gr from a .260 only needs to be 25 inches high at 100 yards to be in the black at 1000. There is no way there should be 12 MOA between 150 and 200 yards. I always use peep sights, so I cannot help you with the scope. I do know that some scopes are in MILS and some are in MOA.

 

[Twangbanger]

...(this is based on where I have to aim using the scope reticle)...

What does this mean? Are you putting the crosshairs in a different spot on target at each distance, using some kind of compensation, or...(not sure I understand)?

I'm not familiar with the reticle arrangements on Vortex scopes (yet), but those are weird results (a .260 shouldn't be dropping 12 minutes in 50 yards at this distance) so I'd take more data.

I'd recommend firing one 5-shot group at each distance:

1. at high enough magnification (and solid enough rest) that you can see and correct a half-inch of crosshair movement on the paper,
2. recording all shots on the same piece of paper,
3. making sure to hold the same crosshair in the same spot each time (I think this is different than what you did before).

Then you can post a photo and show us what the drops are with a ruler on paper, rather than by what the scope is "telling" you. (I expect the groups would be very close to overlapping in some cases).

Hope you get this figured out.

 

[42769vette]

I'm trying to understand what your saying, but I'm confused.

At what range is the rifle zeroed?


At 50 yards - hits 3 MOA high (so holding on the # 3 subtension So you are holding at the 3 above the main crosshair?
At 100 yards - hits 6 MOA high So your holding at the 6 above the main crosshair?
At 150 yards - hits 9 MOA high So your holding at the 9 above the main crosshair?
At 200 yards - hits 3 MOA low So your holding at the 3 below the main crosshair?

If you want call me at 765-580-0986. Somthing is off and I can figure it out talking alot faster than typing.

I'm guessing here, but you have the 6-24 SFP. Since its SFP the reticle does not compensate for changes in zoom. If you change the zoom for the different ranges then the reticle subtends diffidently. If you had the FFP version you would be able to change zoom's and it would keep the subtention's tensions consistent.

 

[lordjackel]

I'm trying to understand what your saying, but I'm confused.

At what range is the rifle zeroed?


At 50 yards - hits 3 MOA high (so holding on the # 3 subtension So you are holding at the 3 above the main crosshair?
At 100 yards - hits 6 MOA high So your holding at the 6 above the main crosshair?
At 150 yards - hits 9 MOA high So your holding at the 9 above the main crosshair?
At 200 yards - hits 3 MOA low So your holding at the 3 below the main crosshair?

If you want call me at 765-580-0986. Somthing is off and I can figure it out talking alot faster than typing.

I'm guessing here, but you have the 6-24 SFP. Since its SFP the reticle does not compensate for changes in zoom. If you change the zoom for the different ranges then the reticle subtends diffidently. If you had the FFP version you would be able to change zoom's and it would keep the subtention's tensions consistent.

Hey Allen. I will take you up on the offer to talk. Call you in a few. But yes holding as you note above. Not changing the zoom at all. It's a weird inconsistency in the flight path it seems. I use a 2' x 3' piece of poster board for the target with a big red dot in the middle to focus on. If I don't hold as indicated above i won't even hit the paper. ( unless I dial the scope down of course)

call you shortly. Thanks Sean