What do we really know about the transonic zone?

[Distant Thunder]

Or think we know even?

The purpose of opening up this discussion is to lay out what is known or thought to be know on the subject and hopefully add to the understanding among BPCR and BPTR shooters with regards to the TRANSONIC ZONE (1346 to 897 fps) and bullet "flight".

I certainly hope I am not the only one but I do spend a fair mount of time about what happens to our plain lead bullets as they travel from the muzzle to the target. Now I am NOT a ballistic scientist or engineer or anything close, I'm a retired tool and die maker, so anything I say has to be seen in that light and I welcome other thoughts and corrections from those who have a better understanding of the subject.

I also welcome any information or thoughts from other shooters who like me have read or in some other way have come upon information that may be useful in any way. Please do be afraid to chime in and add to the discussion. Please.

Ok, so a few of the basics as I understand them. BPCR has two very limiting components, those being the plain lead bullets and black powder. I also think we can add to the mix the use of rather large caliber rifles, at least by todays standards. By large caliber I mean .38 to .50 caliber, though the lower end of the spectrum may be in less common use it still has a place and must be considered.

Even in the smaller calibers bullets of 400 or grains more are generally considered necessary to carry to 500 yards and beyond. With rifles in the 12 to 15 pound range launching bullets at over 1450 fps, while possible, will bring heavier recoil which can be detrimental over the number of shots required for most matches. Shooting 45 to 60+ rounds of 550 grain bullets over 120 grains of black powder and do it with accuracy is not something many of can do or would want to attempt.

Black powder is a very limiting propellent with the upper limit 1500 fps pretty much. I don't think there are many shooter using loads on a regular basis that reach the 1500 fps mark. There are always exceptions and for this discussion I would rather stay with that which is in common use and that I think would be bullets of 400 to 550 grains at velocities of 1200 to 1400 fps.

A couple of examples of velocities for two of the most commonly used calibers would be as follows:

A .45 caliber bullet weighing 550 grains launched at 1400 fps would enter the transonic zone at about 50 yards, would hit the speed of sound (1126 fps) at about 300 yards, and would drop below the transonic zone at about 800 yards.

A .40 caliber bullet weighing 410 grains launched at 1400 fps would enter the transonic zone at about 50 yards, would hit the speed of sound at about 300 yards, and would drop below the transonic zone at about 800 yards.

I know there will be some variations in velocity, weight and BC from bullet to bullet and cartridge to cartridge, but it's pretty clear that there isn't much difference in the two calibers at the same velocity. Both are spending the majority of their flight in the transonic zone.

Modern high power shooters do all they can to avoid transonic flight and with good reason, there are many unknow or at least not understood phenomena that lurk in the transonic zone and they can destroy bullet stability and with it any resemblance to accuracy.

The only reason the BPCR shooter plays within the transonic zone is because he has to, it can not be avoided with our BPCR sports.

It seems to be hard to find much "good" information about shooting in the transonic zone by searching the internet. What I have found in searching is information about transonic aircraft flight and that is certainly because more studies have been done on that. Unlike transonic shooting which everyone in the right mind avoids, transonic flight has to be dealt with if only briefly as an aircraft accelerates through it as quickly as it can.

The whole effort in transonic flight is to avoid the sonic shock wave produced by the aircraft. That sonic wave can cause destructive vibrations and unstable flight which apparently can be very negative for not just the aircraft but also the pilot and passengers. The problem with that information is that it always deals with an aircraft that is accelerating through the transonic zone whereas our bullets are decelerating through the zone. So the events are reversed.

The sonic wave, which can be photographed and videoed, actually is slower than our bullets at the muzzle and lags behind it, but unlike our bullets the sonic wave does not slow down. As a bullet does slow down the sonic wave catches up to it first coming in contact with it at the base. As a bullet slows even more the sonic wave, in relation to the bullet, moves forward and across the length of the bullet from the base toward the tip.

I'm guessing that while the sonic wave and the bullet are in contact with each other that the wave has some serious effect on the bullet just as it does with an aircraft and that is when it would have the most destabilizing effect.

What I don't know is at what point during a bullet's flight and while it is near or in contact with the sonic wave does the wave has the greatest effect on the bullet's stability? Is there a specific velocity where the wave affects the bullet the most?

Is it at the point where the shock wave is affecting the bullet to a higher degree that we some times have trouble with and otherwise accurate load. I think we have all either heard of or have experienced problems at 900 yards with a load that seems to shoot better at 800 and 1000.

That is the discussion we had briefly at the end of the Wisconsin Rapids gong match yesterday. I know that for years I struggled at 900 yards but had very good scores at 800 and 1000 yards with the same load in my .45-70. I fixed that problem by switching over to paper patch bullets!

I don't believe for a minute that it was paper patch bullets that fixed the problem, well okay maybe a little I believe that, but rather that it was a change in the velocity with the .45-70 brought about by an increase in powder capacity using the shallow seated bore diameter paper patch bullets.

Could it be that with grease groove bullets seated necessarily deep in the case that my bullets were at the velocity that was most affected by the sonic wave at or just before hitting the 900 yard mark? Then by switching to paper patch bullets and upping my powder charge and velocity that I moved the specific velocity where the problem was to some place in the flight where the target wasn't?

Looking at the velocity charts it seems that most bullets are just nearing the bottom end of the transonic zone just after 600 yards to just before 1000 yards. At that time in flight the sonic wave would be either somewhere on the tip of the bullet or just in front of the bullet. That would be a destabilizing force on the nose of the bullet that could make a difference.

Any thoughts or idea on this subject?

[Kurt]

Jim,

I cant say much about the transonic zones but I think they have a play with our black powder loads because the 900 yards are my little gremlin also so maybe ???

But from what I under stand about this subject that is the altitude above sea level also has some effect where this zone is.

I know that I do better out west where the ground elevations are higher at 900 yards than I do at Lodi. Nine times out of them my 1000 yard score is better than the 900 yard around our location.

Kurt

[Distant Thunder]

Kurt,

Yes, you are correct and that is why I said there are some variables at play here. The speed of sound varies with altitude and that would also in effect move the transonic zone up or down. I used 1126 fps as the speed of sound and that is at sea level, at 70 degree F and probably at a specific humidity and moon phase. Change any of those and the speed of sound changes and so would the transonic zone, but not by that much if you're just trying to understand how this all works. Could it be enough to affect your scores out west, I think it maybe could be enough.

One of the things I'm thinking of trying is loading a lighter bullet and pushing it faster to see if the accuracy holds up better over the distance.

I suppose I should mention what prompted our discussion yesterday after the Rapids match. I haven't seen the scores yet so I only know what I shot and what Jim Ruch shot, a 32 and 35 respectively. I was shooting my .44-77 and I, like many others there yesterday, had trouble at 600 yards. I also have had some trouble at the Merrill matches at 500 yards. This has all been with my current load.

BACO 431520 seated .180" in the case
.060" LDPE wad
86.0 grains of 1 1/2 Swiss - lot 040313 - .100" compression
BACO brass
Remington 2 1/2 LP primers

The load has change a little since I first tried it last winter after getting the mold, but not anything real big. I also opened up the mold .0015" but that was just to improve the fit which made it shoot more consistently, eliminate the outliers.

At Rapids I started at 600 after the allowed 2 sighter shots with my BACO 441505EPP. I also have modified that mold to lengthen the base diameter from .200" to .300". That allows the same seating depth that has been working with my 431520 bullet.

We were to fire 4 shots at each of 3 gongs. Starting with the 441505 I shot 2 at each gong, switched to the 431520 and fired 2 more at each gong, no sighters after the switch of course. So I lost the first one with the 431520 to the elevation difference between the two bullets. When I was all done I had missed 5 of the 12 shot at 600. I was a bit disappointed!

The other 3 misses I had were two at 220 yards offhand, can't say too much about that and that little stinking 5" gong off the stix at 220 yards. I used the 431520 for everything other than those 6 shots at 600 with the 441505. It grouped very near 1 moa at 220 and 300 yards. On that 5" I was hitting just in to the gong at 3 to 5 o'clock and I slipped one that broke a touch right off the edge, so that was clearly spotter error!

So the thing that has me puzzled, not an unfamiliar state for me, is that this rifle shoots incredibly well out to 300 and even 400 yards but I am not doing well with it at 500 and even more so at 600. I really don't know why.

The only longer shooting I've done with this rifle and load was at Lodi back in May at 800 yards. I ended that relay with an 83 with one miss, the last shot. Toward the end of my string I was hitting a bit high on the target and I asked my spotter if he thought we should drop the sight a half minute? No, he said we're good. I figured he has to learn sooner or later about were the last 3 shots are on the target and always trying to work toward the center, so I went with his advise. The last one slipped just over the target. Again, spotter error. So it looks like it will shoot at 800. The question remains, what's up with 500 and 600 yards?

[Kurt]

Those round plates are on the small side Jim. I had a hard time seeing the two smaller plates last year. I developed more problems with my eyes at the Q. I had two heavy floaters tear loose that are bad enough that they completely block out the sky light in the camper during the early morning dawn IO mean completely gone with a red ring around the outside that I can see when slowly moving my eyes away.
I wanted to make the Rapids match but I just came home from Gettysburg Pa yesterday. Took the 12 and 14 year old Granddaughters there for a history lesson.

As far as the lighter bullets.

I been working with an alloy that will take a 520 gr down to 485 gr out of the same mould. I shot them at the Q at 805 yards during the week to see if they will hit that mark but they get pretty wind sensitive. I haven't shot them over the chronograph to see what the velocity difference is yet, but the snow bank bullets look very good as far as obturation filling the grooves and staying under the paper.
They proved to show 5 shot test ladder loads sub MOA at 200 yards using the .44-77 and the .45-90.

But it's hard to say if they make any difference going transonic.
The light bullet might get bumped worse.

[JKR]

So I now realize my one missed shot yesterday at 600 was spotter error! I’m startin’ to get it! I feel a heck of a lot better suddenly!
JKR

[Distant Thunder]

Jim,

Actually I think you pulled that last shot at 600, I had you dialed in there good. What more can a spotter do?

I don't blame you for any of my misses at 600, that was all caused by something I haven't figured out yet. The miss I had at 220 was because you kept me on the edge of a 5 inch diameter gong when a good spotter could easily have moved me over a 1/2 inch toward center.

I shouldn't even have to explain the miss at 800!

Oh, and incase I forgot to say it, good shooting!

[Don McDowell]

Not quite sure how a fella could pull it off, but a real test on whether the so called trans zone and shock waves are the culprit for good at 8, bad at 9, and good back at 1000, would be to shoot all 3 targets with the very same conditions. That would help to understand if it's a matter or stick placement, bullet length, or unseen wind/mirage shifts/vortexs, sun height/anlge and temperature humidity variations at the various ranges.
I have seen that bullet length/velocity plays a huge part in good shooting, same with stick height and body position behind the gun.
There's also a good deal of difference in a bullets flight between slick sided patched bullets , and the noble grease groove.

[Distant Thunder]

Don,

You touched on one thing I need to work on and that is stick/barrel placement. When I was rebuilding my .40-65 several years back that was one of the last things that I found that was causing me problems, where the barrel rested on the sticks. It also turned out that that barrel did not like a hard surface to rest on.

Rested over a sand bag it shot 1 moa groups consistently, rested on my sticks with a worn out old, thin piece of felt I was lucky if I could cover the groups with a dinner plate no matter were I rested the barrel on the sticks. Once I figured that part out and put a new thick felt on my sticks it settled in nice. At the first mid range match I learned how much difference exactly were I placed that barrel on the sticks made one hell of a difference in the elevation, 3 to 4 minutes! I had to learn to be consistent in my placement on the sticks. No other rifle I have is as fussy about the sticks as that one.

I have not worked with my .44 to see what it likes and what difference it makes.

I'm still going to give a 480-ish grain bullet a try and see how that shoots out to 600. I should be pushing a lighter bullet along at 1350 +/- fps and maybe the velocity will make a difference.

The other thing I can try is Kurt's Sagebrush bullet. That bullet shot very well at 600 early on and I have enough to test them again with this lot of Swiss. Which is were my troubles really began, when I went to my 040313 Swiss. This rifle liked the 2016 lot I had much better, but that's all gone. I also have some OE coming to test in this rifle. I have been very impressed with what JKR has done with OE in his .45-70 a few times as he has tested it at recent gong matches.

I am severely handicapped by my lack of a range over 200 meters for my development. I could work out a lot of these things in about two days if I had even 500 yards to work with. Right now I have too many things to try and not enough time to do the testing. Nothing new there!

[Distant Thunder]

As far as the 900 yard thing goes, when you see it match after match and year after year there just has to be something going on there.

The high power shooters have simple solution, go faster and spin the snot out of it. That doesn't work as well with these rifles. I am beginning to believe that each rifle, twist and barrel has a sweet spot in regards to bullet length and that it may not necessarily be tied to twist alone, though that is the overall limiting factor for length. There is still a fair amount of room below the maximum length for a given ROT where one may find the perfect length for that rifle. That could also vary with bullet shape.

I'm probably over thinking this.

Saturday at Rapids it was hot, pretty darn hot! My temperature gage had 107 degrees on the 300 yard line and 97 when in the shade in the back of my open car. Humidity was from 37% to 43%. I know others had some fouling problems, but I seem to have that part under control as long as I pay attention to what I'm doing when I wipe. Fouling problems killed me last year with this .44-77. Saturday my barrel was too hot to even touch as I came off the 300 yard line and the forend was uncomfortable to hold onto. I quickly carried my rifle to the car and laid it down without delay! Yet it shot extremely well for me.

[Don McDowell]

Jim think about this for a moment.
When you guys shoot at Lodi, you shoot the 1000 first. The light is coming directly behind you and lights those targets up. Then you move to 900 and the sun is higher, the temperature is coming up, and the breezes and thermals coming from the temperature increase are playing their cute little games. By the time you get to 800 the light is behind the target, but the target is relatively shaded..

My 17 twist 44 barrel absolutely loves the 434470 bullet, it measures just a tad over 1.35, and comes over the scale at 470ish when cast from 16-1. I'm betting your similar barrel will like that length as well, once you get a powder the rifle thinks it can digest.