factory load published data question?

[WillHunt]

Coming from a short to medium range hunting background here, so please bear with me. I am shooting a 7mm Rem Mag, Federal Premium 150 grain NBT factory loads and factory gun. The Federal website publishes the following trajectories: +1.4 @ 100yd; 0 @ 200yd; -6.4 @ 300 yd. I just shot the rifle 10 times (groups of 3 at 100 and 200 and 4 shots at 300). I was +2 @ 100, 0 @ 200, and -9.5 @ 300. Surely the reason for my lack of flatness isn't that I'm too high at 100 right? Or is it? If that were the case wouldn't I be high at 200? And if that were the case, I would need to click DOWN to move my 300 yard group UP?!! Help please. I thought my 300 yard group would be higher than the published data since my 100 yard group (+2) was higher than the published group (+1.4).

 

[FearNoWind]

The one piece of information that manufacturers often leave out of their data sheets is the statement "your results may vary". Based on the info. you posted both you and Federal are zeroed at 200 yards. Even though your rifles are zeroed at the same distance they are two very different rifles. In your case I'd want to run some MV samples and apply the results to a good ballistics calculator and see where the variable comes in to play.
In the interim, I'd recommend that you believe what your rifle is telling you and base your sight adjustments on what it tells you.

 

[gohring3006]

I don't read to much into the factory data two identical rifles will shoot them different I would reload for that rifle your probably paying out the *** for that premium stuff....

 

[LoneTraveler]

The big variables for plotting trajectory is, Scope height from the center of the bore. most are calculated at 1.5 inches above the bore. Change this height and it changes the trajectory. The rifle barrel itself. Some barrels are fast and some are slow. The one thing you should do is shoot the rifle over a Chronograph to see if you are getting the publicized velocity. Good Luck in finding the solution.

 

[snox801]

The big variables for plotting trajectory is, Scope height from the center of the bore. most are calculated at 1.5 inches above the bore. Change this height and it changes the trajectory. The rifle barrel itself. Some barrels are fast and some are slow. The one thing you should do is shoot the rifle over a Chronograph to see if you are getting the publicized velocity. Good Luck in finding the solution.

This is true, and on top of that muzzle velocity is also a big part. Now most of the time you cannot get the same speed as they publish. Like stated above different guns and barrel lengths have different speeds. For instance if you are shooting a 22 inch barrel and they tested there ammo on a 26 there can be a huge difference depending on what caliber.

 

[WillHunt]

Thanks for the help. Rifle's a Model 700 in 7mmRM so I guess it's a 26" barrel. Scope is a VariX III 50mm with the bell clearing the barrel by only a few millimeters; not sure what that makes my line of sight height from bore center. Regardless, I'll keep shooting and hold my shots while hunting according to the results I continue to see on paper. Just wish I was shooting as flat as the ammo manufacturer's claim. Yes, the ammo's expensive, but I'm really more of a hunter than a shooter; just shooting more right now to make sure I'm good out to 300+ in anticipation of traveling more to hunt the West. Here in SC, most of us would be just fine with a 30-30 and iron sights, but of course we all have flat-shooting rifles with huge scopes to take those 70 yard shots; its just how men are.

 

[roninflag]

WILL- you are probably not getting the velocity that the factory ammo is saying you should. for a flatter shooting round you could try a 140 or a 168. in the mean time i am suire those SC deer are in great danger with what you are using.

 

[WillHunt]

WILL- you are probably not getting the velocity that the factory ammo is saying you should. for a flatter shooting round you could try a 140 or a 168. in the mean time i am suire those SC deer are in great danger with what you are using.

Ron, forgive my ignorance, but would a 168 really be flatter than the 150? If so, why? BC?

 

[roninflag]

Will- at the shorter ranges the velocity of a 140 makes it flatter, still 168 because of its bc is still real flat. so it uis a combination of the bc and velocity. out to 300 yards the differences are small. besides flat also the affect of the wind comes into play ; BC really helps there. just shoot in a 500,600 or 1000 yard match sometime. it is an education.( my son-inlaw won the first 1000 yard match he fired in with a 7mm mag winchester laredo. it is a very capable round as you already know.)