Is Faster or slower generally best?

[J.Murphy]

The slower bullet in these BPCR velocities will always have less wind drift. What I meant about vertical was that because the slower bullet's flight profile will always have a sharper angle of drop than a faster bullet, the same velocity deviation will produce a greater vertical impact variation than the faster bullet. What Bruce said is true. The only trade off is reduced recoil, which is not a small thing.

[mdeland]

I'll have to test for my self John to see if that is true at all times because Sierra says it isn't and logic agrees with what they say. Twelve inches difference is really hard for me to believe although I'm sure you are telling the truth as you witnessed it.
Another thought is that it may not be true across the board as there are so many variables that can influence the result. Bullet stability while transitioning the transonic for one. Some bullet designs handle it better than others.

[J.Murphy]

Most ballistic programs support my side, plug numbers in for drift at 1000 fps and then for 1400 fps, you'll be surprised. Drift is caused by drag causing a time of flight delay between a flight in a vacuum and the real flight, more drag, more delay. The problem is the really massive pressure wave generated at around the speed of sound, it doesn't even out until about 1900 fps, above that, it behaves as you think it should. The real proof is the fact that rimfire ammo, which approximates BPCR velocity, produces match ammo with an average velocity of 1080 fps. My Silhouette partner told me this when I started shooting, I was sure he was mistaken, I was wrong. You can easily test this, load 5 rounds minimum load, 5 rounds hotter, same bullet, wait until you can fire them long at a visible target, in a stiff crosswind, don't hold off, don't touch the sights, alternate the shots and prove me wrong!

[bruce m]

j murphy is correct.
go to the j b m ballistics site and see the calculations.
bruce.

[desert deuce]

Here is the $64,000.00 question.

So, what do we do when: We know exactly the BC of the bullet and the mv, then correctly calculate the ballistics by tables, fire the shot and it lands nowhere near where we calculated that it should ? Given a no wind, no mirage condition with a light overcast 12 O'Clock sun time.

[bruce m]

measure our sight radius to verify correct comeup?
check the barometer?
what else?
there will be a reason.
bruce.

[mdeland]

mdeland
Posts: 10728
Joined: Mon Nov 20, 2006 12:47 pm
Contact: Contact mdeland

Re: I need assistance on which barrel and twist rate to use

Post by mdeland » Wed Aug 19, 2020 1:55 am
I just looked up the difference in bullets weights between the target loads and high velocity stuff and found as I expected that the high velocity bullets are up to 25 percent lighter in some cases. Many of the low velocity target loads are 40 grains and many of the high speed bullets are in the 30-33 grain range which explains a lot of the difference in defection.
Another theory is that deflection is not caused by reduction of flight time as Sierra says but rather the percentage of velocity loss over the same distance. According to the article the low velocity stuff sheds it's speed at a lower rate than does the high velocity and this causes less deflection.
I don't think they have this nailed down yet across the board as there seems to be some different ideas about deflection cause with lead bullets.
Top

[rgchristensen]

All these wind phenomena are well-understood. Study a good book.

CHRIS

[desert deuce]

Well, the $64,000.00 question goes unanswered correctly, however, our great friends and diligent posters Bruce M. and M. Deland at least were bold enough to venture a guess. Yet they exactly illustrate the point I am trying to make. There are Theorists in BPTR and then there are Competitors.

So, what do we do when: We know exactly the BC of the bullet and the mv, then correctly calculate the ballistics by tables, fire the shot and it lands nowhere near where we calculated that it should ? Given a no wind, no mirage condition with a light overcast 12 O'Clock sun time.

The correct answer of course is, "adjust the sights on the rifle until the bullet lands where we want it to land."

Moreover, the contest between slower or faster is answered with the individual rifle, load, shooter, and results on the target be it steel or paper.

Reality trumps theory every time in competition. It is the Indian again.

[charlie young]

Exactly what Desert Deuce said. ^^^

[bruce m]

zack,
of course that is what you do.
but don't you ever wonder why?
there must be a reason.
he who grasps that will be a happy man.
bruce.

[Coltsmoke]

JM, I don't understand your test with a minimum load and a hot load. If I'm shooting my normal load in my Shiloh, a PJ money bullet loaded with 76grs. of powder I will have excellent accuracy. If I load it down to say 68grs. of powder with several wads to take up powder room now I have a minimum load to test. But the accuracy of the 68grs. is going to be crap right out of the barrel especially at long distances, it will be all over the place. So how is this even a test? I don't have a rifle with the same bullet where I have a hot load and minimum load to compare against each other. I have loads that will shoot at 83 and 82grs. I have loads that will shoot at 73gr. and 74gr. but not at 65gr. and then again at 73gr.

[mdeland]

Seems like the theories on deflection are similar to the same ideas on Greenhill formula for bullet spin stability requirements, in that it seems true under certain circumstances but needs tweaking under others. DT used to post about this if I remember correctly using a 1.25-1.50 factor in the equation rather than 1.
In .22 RF we find that to get the high speeds in the same case without over pressure we require a lighter bullet but I can't help wonder what the result would be if we could shoot the same 40 grain bullet from the low velocity match ammo at the velocity of the high speed stuff.

[mdeland]

I think wind reacts on the disrupted air cocoon and pressure wave around the spinning projectile in flight. The less signature that cocoon makes the less the wind has to react against and the faster it is the less time it has to do it. The more speed used the larger the cocoon but the less time wind has to work.
So it would seem that under certain circumstances there is less deflection because the cocoon is smaller for the wind to act on because the velocity is less and so is the resulting drag. On the other hand if it gets to the mark faster than that also cuts into the effect a cross wind can have on it.
It looks to me like in a lot of these scenarios of comparison we're mixing apples and kumquats and confuse the picture of what is actually happening.
At this point in my curiosity of how this all works it seems to me the drag is actually and indirect component of deflection and that the pressure envelope/cocoon is the elephant in the room being the primary driver of deflection. True, the larger the cocoon, the more drag but the wind is working against the cross section of the cocoon/envelope that drag is only a component of.
Higher BC's make smaller envelopes resulting in less cross section for wind to react to and speed makes less time for it to do so. Also, it looks like high BC's make smaller envelopes at higher speeds.
Now inter transonic influence and we find even more disruption of air flow around the bullet as it tends to oscillate, again increasing the envelope signature ie. more cross section area for wind to react on.
Poor ole bullets really take a beating in they're short active lives on the quick trip down range!

[desert deuce]

Dang Bruce, I really think you belong over here in the states my man. Your talent is wasted in OZ.
Beauty is in the eyes of the beholder and happiness is determined by the individual.
Yes, happiness is always a friendly warm playful puppy that doesn't nip too hard.
Happiness to me is when I watch my bullet into the backstop and wonder if it was on paper or not and it comes up a 6 at 1,000 yards, at the same time the shooters on either side have targets showing tail lights, or misses. I am 6 up and they are each ten down. No, it was not an X but it was otherwise a victory over the conditions that existed while that bullet was in flight.

And there in lies the key. The competitor is not competing against the other competitors or even themselves, rather, the conditions. That is considering the shooter arrived at the match with a balanced load.