Why velocity?

U

unclebird

Guest
For paper punching, why do you need or want to know velocity? If it groups or shoots well, then why do you care how fast? The only reason I would want to know is when using my ballistic calculator to figure drop and scope adjustments.




:confused: Brad
 
Sometimes velocity comes into play because of wind drift comparison between cartiages. Also, for another reason I'll discuss. For example, one comparison, a 6ppc vs. a 22ppc-.xxx version. In order for the 22ppc-.xxx not to be at a disadvantage, you need to at least reach a velocity of 3500fps with competitive accuracy, if not, then just shoot the 6ppc. Sure, you can make a 22ppc-.xxx to be as accuarte at a lower velocity in good conditions but good conditions are not the normal during actual competition and thus a similar mistake on the wind will cost you more bullet drift with the 22 than the 6ppc, which ends up being a bigger group. Another example, which is one I really like to use, I was shooting groups one day at a friends house with a 22-250, my buddy said that he could shoot the same groups with his 220 swift so with the presumed increase in velocity, why wasn't I shooting a 220 swift he asked. I went over to the vehicle and got out the chronograph and set it up. He shot over it and in order for him to get the accuracy out of his swift, he was shooting, I believe, 5 grns more powder and was getting 200fps less than I was. So then, I asked him, why aren't you shooting a 22-250, in which he didn't have an answer. This is the second reason that can come into play. My friend just assumed, since he was shooting a swift, he was getting a greater velocity than a 22-250. Now, before I get flamed, this is gun dependant, if he had a swift that could shoot accurately in the higher velocity window, then his statement held more water. Just like in hunting rifles, if I can't get acceptable accuracy toward the top of a chamberings velocity, then why don't I just shoot a smaller cartriage.

Hope I kinda explained that well.

Hovis
 
Brad,

It depends on your discipline.

For example, I shoot to 1000 yards & beyond. Sometimes I'll load to the maximum velocity consistent with a good velocity spread & standard deviation, then use a tuner to wring the best accuracy out of it. Quite often I've found that loads with good accuracy at shorter distance testing have velocity spreads that suck & those loads have every liklihood of shooting bad elevation back of 1000 yards. I wouldn't expect that the barrel harmonics, or whatever you might like to call it would counter the stringing at every distance.

At other times, I've found that specific projectiles I use operate more efficiently within a limited velocity range & I chronograph loads on new barrels or with new powder batches to make sure I stay where it works.

Reading the benchrest forum, I've seen it said that there are specific nodes of accuracy for their favourite case. I imagine that they would load to those ranges.

John
 
I was told by a 600 yd shooter that the projectile "planes" differently at different velocitys. Therefore affecting it's BC. Again,,,if it's shootin' who cares how fast it's going!



Brad
 
Velocity

All I use velocity for is to tell me where I am with a particular combination.

For instance, I just had to switch over to 07-133. I did all of my initial testing overmy 35P Chrono so I could see how the powder compared in both weight and density to the 03 I have been using for the past 4 years.

I know that a certain weight of 03 gives me a specific velocity, so I can load the 07 tio were it hits the target fps, and tune from there.

It just so happens that by weight, it is very close to the 03. But, it is at least 1/2 grn denser. This is really a good thing, because it is easier to get it into the case when shooting in the upper load window.

the same can be said for using a different bullet. For instance, with all things being equal, the Barts Boattail will show about 75 fps more than the Bruno Boattail. So, when I started tuning in the Barts, I had a gut feeling that 3500+ fps was just too hot. Not particulailly unsafe, but if a load is too hot, you will get flyersin the form of popped shots. So, I adjusted things to where it shoots the same 3440 or so as the Bruno. And, they shoot quite well, and the load seems to be in the safe zone.

The culprit in this added pressure is the Barts is about .0003 fatter down toward the boattail junction, and it actually goes into the case about .025 more with the same bullet jam.

Contrary to what many think, we do not shoot at elevated pressures and upper end velocities in order to "buck the wind". I doubt anybody can read flags well enough to tell the difference in 3350 and 3450 as far as how much it moves the bullets.

Many of us shoot the upper window because we feel that is where the best agging capability is.......jackie
 
jackie

...with the PPC and 133.......it really does stuff the case, eh? My 27 gr/133 fireform loads are almost at the rim........
 
133 and 6PPC

When loading fireformed cases in 6PPC one can dump 28 gr of N-133 in without any fuss. The load will be up about in the middle of the neck. To be able to squeese in 2-3 gr more in the case as I belive some do, you need a long drop tube and carful metering and trickling the powder in. (Make a note I am NOT recomending exceeding 28 gr of N-133 without thourough testing and increasing weight very gradually)
 
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