new gun ballistics question

[Cncjerry]

So I took my new 700 XCR Tactical Long Range in .300 win mag to the range today, bore sighted it at 50yds and then took a few shots. The group was good of course at that range. With all the screwing around with everyone wanting to shoot it, I quickly ran thru a box of 150gr Remington Core LoKt which shoot at 3290fps according to their ballistic tables. The BC is supposed to be .294. I then loaded-up some Winchester 180 gr with muzzle of 2960fps and BC of .438. The 180's hit 3" lower at 50yds, almost exactly. Same tight group. Can someone explain what is going on? According to all the software I have there might be a drop differential of .1" at 50yds between the two and I would have to move to 300yds before the delta hit 2.7".

So something happened along the way. The scope felt tight, I don't think anyone touched the turrets, etc. I only had 20 of each so I couldn't go back.

Assuming I have the time tomorrow, I'll pick some boxes up and move out to 100yds tomorrow, but for now I am puzzled.

Thanks

Jerry

 

[roggom]

You bore sighted at 50Y meaning your Reticle over the bore are a constant. You did not "zero" the individual loads @ 50Y. At that close of range the higher velocity load will generally hit higher on paper. If you were to zero the 150's at 100Y, shoot, and then zero the 180's at 100Y and shoot, the higher BC of the 180's will be recognized out at 600-900Y(or closer). The 150's will shoot flatter up front, but run out of gas farther down range. The 180's should have a consistant trajectory well past 1000Y and less wind deflection.

If you dont reload, then I would zero the load you will use the most, then record the dope for the other load. I/E zero the 180's at 100Y, then log the dope for the 150's as down .3mil or whatever it is.

Note:

I ran the numbers in G7 software and the trajectories will remain the same right to approx 700Y. The 180's will have sustained energy with a max terminal range of 1000 ft lbs at 600Y and the 150's hitting 1000 ft lbs at 480Y.

Now the 300WM is much more capable than those numbers, but you will need some better ammo. Factory ammo with Berger VLD's, or Nosler accubonds, or some are loading Amax will be devastating on deer much further than the core lokts and Winny white box.

The Hornady Superformance 180 Interbond extends the Terminal range out to 840Y (on deer sized game)

 

[Cncjerry]

roggom thanks for the reply. I got all that, what I can't figure is why the 180's were almost exactly 3" lower at 50 yrds vs the 150's. This was after I bore sighted and sighted the scope at 50 yards with anticipation of moving to 100yrds then 300yds. In a perfect world, the 180's according to my software should have been maybe .1" lower but not 3". The only thing I can think is either the scope or mount came loose or someone spun the turret on the scope and I don't see evidence of either.

 

[roggom]

If you were to plot both trajectories from muzzle to impact and slide both curves over each other, you would be able to see the scenario you describe. The point of which both of those loads cross the line of sight is far beyond 50 yards.

Reticle and line of sight is a straight line, the bullet leaves the muzzle, breaks the line of sight up and down again at the point of impact. Since you have two loads of different velocities you can not use the same Zero point in your software, because you have not zero'd both loads at 100Y.

If you were to zero the 150's at 100Y, then shoot a group at 50Y, then zero the 180 load at 100Y then move back to 50Y, then you may have a closer POI as predicted.

Make sense?


Honestly, I would not burn up too much ammo worrying about it.

 

[Cncjerry]

Roggom, just trying to understand what was going on, but I did shoot another box of 180's today so I guess I did burn some.

I shot a box of 180gr today without touching anything and the first 5-7 shots hit the 100yd zero line plus/minus a quarter inch. The wind was gusting too hard to stay with zero left/right, but assuming it was zeroed yesterday at 50yds, they should have been .9" high at 100yds as they are still rising from the scope being 2" above rifle bore zero. Conversely, since they are hitting zero at 100yds now, then at 50, they should be about 1" lower at 50yds, not the 3" I found. So the only conclusion I can make is that the box of 180s I had yesterday must have been bad, though I doubt it, I can't think of any other reason as the box I shot today performed as expected.

One of the 180s from yesterday had a big wrinkle in the case near the neck. I didn't shoot it, but I'm starting to wonder about Winchester Ammo.

Thanks for the input.

 

[Pappasniper]

Some ammo have POI SHIFTS. Especially cheap hunting ammo. It will damn sure kill a deer, but be real consistant , maybe -maybe not.

I wouldn't worry about. Zero at 100 then start to worry about shit out to 300-500 etc.

Good luck