I took the 7mag to the range this morning, playing with some 140 TSX bullets. I loaded 3 different powders, checking for what max is in each: Re22, H1000, and Retumbo.

According to Barnes, their best powder with best velocity was Retumbo.

So, I loaded several bullets with each powder and never did hit a max in any and I was above Barnes' published charges.

Curiously, the Re22 never grouped over an inch with 9 bullets and was hitting 2" high from point of aim. The Retumbo charged rounds were about a 1/4" larger and also about 2" high. However, the H1000 was about 3.5" high for all test rounds and also grouped about an inch.

So, with the barrel whip, is this just a guess that the barrel was in the "up" position when the H1000 charged bullets left the barrel and in the down position with the other 2 powders? Or, is this possibly a much higher velocity, lower velocity? I couldn't take a chrono today as they had a pistol shoot going on.

Often, lower velocity rounds will shoot higher. This is simply due to longer barrel duration and more time for the barrel to lift in recoil. Another factor is powder burn rate. A powder that develops peak pressure slower but has the same mean pressure as another will also shoot higher for the same reason - longer barrel duration time. If I am not mistaken, H1000 is the slowest powder of the three you used. You did not give your charge weights, but did you require more H1000?

Of course, this is by no means the only possible explanation!

Retumbo is the slowest.

What I did was reference the Barnes load data that was emailed to me by them and loaded one round beginning at their minimum and adding half grain charges. Ultimately, my rifle took 75 gr of Retumbo easily but the case was getting very full. Same charge for H1000. Got up to 68.0 gr Re22 and in no case was there any pressure signs from.

I'll have to recheck their chart to see which one yielded the least velocity but I think it was H1000. Their bbl was also 24" long.

quote:

Often, lower velocity rounds will shoot higher

This is a little confusing b/c when I add powder, the bullets tend to string higher.

Any answer I could come up with based on the amount of factual data at this point would fall into the WAG category. I agree that the slower rounds might have a tendency to shoot higher at relatively short ranges, but barrel whip could also induce the rising stringing effect. The thing to consider is that the powder charge mass also has to exit the muzzle, and is a portion of the recoil calculation. Since this ain't rimfire you are talkin, perhaps the simple physics of the discharge is what you are witnessing.

Best guess, is still a guess.

I checked the tables - I was wrong about H1000. If adding powder is raising the POI then I am wrong on the other thing too. I should have said 'sometimes' to cover myself! Adding more powder can also cause more muzzle lift and hense higher POI. As you originally asked, "is this barrel harmonics?" Higher velocity could also result in less drop but at 100m is likely to be less significant. But to me, the fact that you are getting higher or lower POI is significant. (As opposed to horizontal changes). Of course, it 'could' be powder burn characteristics causing the difference from one powder to the other. Who knows really? All I can say for sure is that I have found that faster loads tend to shoot lower. More so with when changing to heavier and slower bullets. But not always.

Edited to add;

quote:

Best guess, is still a guess.