Transonic range and pistol velocity?

[OlongJohnson]

Have been doing a bit of digging around the webs, and had some ideas I'd like to hear from people more experienced than I am. @Lost River, for one, knows who he is.

It's well known and generally accepted when shooting rifles at long range, and rimfires at 100 yards, that a bullet transitioning from above the speed of sound to below it tends to generate dispersion in groups. If you can keep your rifle bullet (centerfire or rimfire) above or below Mach 1 all the way to the target, you'll generally see better accuracy than if you don't.

We don't pay much attention to this with pistols, but I wonder how much of a factor it is. For example, 9mm 115gr factory ammo is typically advertised at ~1120 fps. If it actually launches at that speed from your gun, you're basically dumping it right into the transonic range at the muzzle. A 124 grain load, depending on your gun and loading, might get there, or it might be a little under. A 147 grain load will be reliably under. At 5-7 yards, it doesn't make any difference, but some do report significantly better accuracy at 25 yards and beyond with pistol bullets if they launch well below the speed of sound. I even saw a case where a guy reported his 9mm being able to match a .45 for accuracy out to ~15 yards, but the 9mm fell apart at 25 yards and beyond.

It's also empirically reported that many/most powders seem to burn most consistently when the pressure gets up toward the upper end of the allowed range, so simply loading down with a given powder to get the velocity with a lighter-for-caliber bullet down under the transonic range may not produce good results. We tend to like faster powders for such purposes.

It seems that there may be an optimization point around the heaviest bullet weight where higher-end loads of powders that give the best velocity will produce MV around 1050-1070 fps. That should give the flattest trajectory that won't have to pass through the transonic range, theoretically enabling the greatest accuracy at longer distances, while also delivering the greatest power factor consistent with that accuracy. Various of people's reported pet loads for a variety of cartridges seem to be right in that speed range, not 75 fps higher.

Just picking 9mm, load data suggests a 135 grain bullet should probably be maxing out around 1050-1070 fps. That doesn't land near any specific power factor threshold for competition, but it may be an optimization point for hunting, for example.

Not really sure where to go with this, other than it being one more thing to think about when working up general-purpose loads.

Any thoughts?

[Jim Watson]

I even saw a case where a guy reported his 9mm being able to match a .45 for accuracy out to ~15 yards, but the 9mm fell apart at 25 yards and beyond.

Any thoughts?

Not many, but the above item is arrant nonsense. What HIS 9mm did is not representative of a GOOD 9mm.
Unfortunately, David Sams doesn't say what load he uses in an accurized Beretta shooting 1.3" at 50 yards, an X ring gun.
My PPC Master friend hoards 9mm Hydra-Shok for the 50 yard line and shoots lesser ammo at 25 and in; but I don't remember what weight.

I think it would take a good deal of shooting to separate transonic effects from general bullet and barrel characteristics; as you say, it would be largely a choice between a fairly hot 115 and a standard 124.
Got a Ransom Rest and a really good gun?

Atlanta Arms makes great claims for their higher end ammo; whether 124 at 1055 fps or 115 at a rather mild 1100.

[Hambo]

Any thoughts?

Yes, two. First, don't worry about it. Second, if you can't stop worrying about it, buy subsonic ammo.

[Lost River]

Provided that you have a very accurate platform to use, what I have found that matters more than most in getting the utmost in accuracy is something that most don't consider. This is something that really matters more at extended distances than short ranges like 50 yards and in. What matters is a very uniform and heavy crimp.

In shooting handguns at targets hundreds of yards away, i noted that I was having wild variations in points of impact. A friend who is a very experienced handloader examined my ammo and told me that I needed to roll crimp it with a LEE roll crimp and that would reduce the variations we were seeing. Sure enough, as soon as I did, the difference was very significant.

We were shooting at (at the furthest) a target board at my cabin at 780 yards with 41s and 44s and with a heavy roll crimp, the size of the groups dropped by probably 1/4. The heavy crimp is allowing the powder to burn, and pressure to build more uniformly before the bullet is released into the bore. I noted with the chronograph that my extreme spreads were less with a heavy crimp.

[nycnoob]

The current goto for trans-sonic shooting is Bryan Litz.
Here are his books:
https://www.amazon.com/Bryan-Litz/e/B00J216MMI

About five years ago I went to a long range shooting seminar he taught.
He does experiments to uncover the truth about long range shooting
vs the myths that shooters believe (I was particularly struck by his
experiments on "bullets going to sleep"). In a breakout session I heard
him discuss powders for reloading.

He does not have much patience for the tuning of powder in hand loads,
and thinks most of this effect is due to small sample size issues.

but I have no first hand experience in any of this. I found the whole seminar
not to be relevant to the shooting that I do.

[JCN]

Pretty cool thought experiment!

[TicTacticalTimmy]

Provided that you have a very accurate platform to use, what I have found that matters more than most in getting the utmost in accuracy is something that most don't consider. This is something that really matters more at extended distances than short ranges like 50 yards and in. What matters is a very uniform and heavy crimp.

In shooting handguns at targets hundreds of yards away, i noted that I was having wild variations in points of impact. A friend who is a very experienced handloader examined my ammo and told me that I needed to roll crimp it with a LEE roll crimp and that would reduce the variations we were seeing. Sure enough, as soon as I did, the difference was very significant.

We were shooting at (at the furthest) a target board at my cabin at 780 yards with 41s and 44s and with a heavy roll crimp, the size of the groups dropped by probably 1/4. The heavy crimp is allowing the powder to burn, and pressure to build more uniformly before the bullet is released into the bore. I noted with the chronograph that my extreme spreads were less with a heavy crimp.

Do you know if this also applies to autopistol cartridges?

One of my interests is shooting 9mm 100-150yds (or was before ammo was so expensive), and I have found it does seem to be dramatically harder to hit a 12" target as you go up each 25yd increment.

What I don't know is if this is because of the greater marksmanship challenge (smaller target in terms of angular measurement and more drop and wind drift) or because the ammo is spreading out disproportionately or getting fliers at those distances. I never have tried any type of 'rested' shooting at these distances with 9mm so I am not sure, I pretty much always use 115 or 124 FMJ for this shooting, although at the 25yd line I have found 147HST's to be the most accurate load in my 'long range pistols'.

Not really apples to applies, but with my 22/45 I can shoot 1"-1.5" groups at 25yds and the one time I put it on paper at 100yds it was about a 7" group. This was with CCI Mini Mags, and I would say that is basically a proportionate increase in dispersion given that my aim with a red dot at 100yds is not perfect.

[Lost River]

It absolutely applies to auto pistols.

A heavier crimp allows a more uniform pressure build up. My experience in shooting ammo with heavier crimps (such as 9mm, 10mm and .45) has shown that it is consistently across the board more accurate.

Not being a scientist or even all that bright, my thoughts are that it is similar to neck turning rifle brass. You are getting a consistent release of the projectile that is more directly in line with the bore. Much like throwing a perfect spiral football, it is not wobbling (or minimally)when it enters or exits the barrel due to that and it is more accurate.

Accuracy results at longer ranges seem to bear this out.

Sorry I don't have any longer range auto pistol groups at the moment, though I probably should shoot some with my Baer just for giggles.



These are all 3 shots, except the last one which was 5 shots. The range was slightly over 100 yards.

The pistol is a 7.5" Redhawk and a 300 grain XTP pushed by 22.5 grains of H110.

It is pretty consistent shooter at 100 yards with a rest.

You can see how heavy the crimp is in the last pic.








5 shots:

[Velo Dog]

As a practical matter, 9x19mm can have equally excellent accuracy at 50 yards with subsonic 147 grain bullets or faster offerings such as 124 +P.
https://pistol-forum.com/showthread....-duty-calibers

However, 800-900 feet per second is a sweet spot for handgun cartridges to resist wind drift.

Bullets leaving the muzzle much slower than 800 fps or faster than about 900 fps will tend to have worst wind drift at typical handgun velocities. Flatter trajectory comes at the expense of greater wind drift until rifle velocities are achieved.

Full Wadcutter bullets are more deflected by wind than projectiles with higher ballistic coefficients, but wadcutters still perform best at around 850-875 fps in wind.
https://www.federalpremium.com/ballistics-calculator

[pyrotechnic]

Bullets leaving the muzzle much slower than 800 fps or faster than about 900 fps will tend to have worst wind drift at typical handgun velocities. Flatter trajectory comes at the expense of greater wind drift until rifle velocities are achieved.

Thanks for sharing that.
So this had me in full WTF mode, as it didn't make sense at face value, and I've written a rudimentary, but successful, point mass solver using MATLAB so I thought I had a pretty good grasp of external Ballistics.

However after further investigation I beleive this is due to the massive increase in drag coefficient around the transonic range and the corresponding increased drag forces. Since wind drift is actually a component of your drag and is essentially governed by the difference between time of flight in a vacuum and real life, the added velocity cannot compensate for the increase in drag over that velocity range.

If anyone has a better explanation I'd be interested in hearing it.
This is a graph of drift of a .308 110gr Vmax at the listed velocities. Wind is 20 mph at 90 degrees