Reduced velocity for decreasing wind drift

[flatsguide]

Yaa think ? Lol
Richard

[dtknowles]

I’m not sure Michael is correct. A bullet at a standard day at SL is just below the speed of sound at 1100fps. by definition it is air speed and if there is a no wind condition it is ground speed too and is not related to the Mach shock waves on the bullet, which are supersonic. To Michaels second point, unless I am mistaken, it is more a function of the thickness to length ratio or fineness ratio if you will. Say a .45 caliber bullet with a length of 1.750 inches and a PP diameter of .444”, .444/1.750 =.253 or thickness ratio of 25%. For a .22 LR bullet with a bullet length of .480 and a diameter of .222, .222/.480 =.46 or 46% . This shows that a .22LR bullet has almost twice the thickness ratio of a 45 cal BPCR bullet. What I take away from this is the air has to accelerate quicker over the .22LR bullet, but not necessarily further, to create the Mach shock wave on the bullet. It is the thickness ratio that determines the airspeed/FPS that the onset of the shock wave start on the bullet. I believe that is called the Critical Mach number. One only needs to look at airfoils thick curved ones to operate well in the subsonic ( we don’t want any shock waves on these airfoils) and supersonic airfoils that have very fine thickness ratios and non or almost no curvature. Interestingly, I don’t know of any aircraft that are designed to operate in the transonic zone. They are either operating about 15% below the speed of sound or well above it.
Bullets that are decelerating and are just above the speed of sound experience a rapid rise then rapid drop in pressure I think this may rapidly change the center of pressure location on the bullet and that is the cause of the transonic stability problems.
I’m not a ballistics expert, just an old not too bold pilot with just enough knowledge of aerodynamics to get in trouble. Would it not be fun to shrink down, strap a saddle on a bullet and ride it out a thousand yards or so...

I know of a number of aircraft that are designed to operate in the transonic region. Cessna Citation X+ Mach .935 (536 kn; 993 km/h) Cruise speed 528 kn (978 km/h) Minimum control speed 114 kn (211 km/h) Range 3,460 nmi (6,410 km) Ceiling 51,000 ft (15,545 m) Time to altitude 24 min to Flight level 470
First flight: 21 December 1993
Manufacturer: Cessna
Number built: 339: 310 X + 29 X+
Produced: 1996–2018
Height: 19.2 ft (5.85 m)
Cessna Citation X - Wikipedia

Korean war era jet fighters often operated in the transonic region.

The F-15 had so much thrust it could climb to sixty-five thousand feet in just 122 seconds. In horizontal flight, the F-15 could reach speeds of Mach 2.5, and cruise at speeds of Mach 0.9.

Tim

[Claudius]

Almost all the civilian aircrafts operate in the subsonic region, some others can operate in the supersonic region. A supersonic aircraft cannot avoid the transonic region when accelerates to supersonic speeds, but the subsonic jet aircrafts stay below the transonic because the shock waves start to begin. The transonic region is not so comfortable for both the pilots and the aircrafts, because the shock waves are intermittent and not uniform, so the aircraft structure is overstressed.

The jet fighters of Korean war like a F-86 were subsonic aircrafts, but easily could go through the transonic region when diving, for this reason some of them had spoilers to slow down and stay in the subsonic region: it was a safety measure, also.

You can read the memories of the WWII and the Cold War pilots, they had terrible experiences with the transonic regime. Yes, the WWII pilots knew the problem of the transonic regime and it was extremely dangerous when diving. The subsonic jet fighters could go through the transonic regime but just for a very short time because the stress on the pilot first, and the aircraft structure second.

Regarding a subsonic black powder bullet my opinion is that we have to see other more important aspects: a bullet is not an aircraft. Usually a 530gn bullet shot at 1250 fps starts in a transonic regime and stay there for 100 or 200yds, so why a bullet doesn't seem to suffer of the tragic transonic intermittent shock waves? They do, but in a different way compared to an aircraft because their difference of weight and section. At sea level the air density is the same for a bullet and an aircraft, but the first one is small, compact and heavy and its body is rotating, a subsonic aircraft is a complex and fragile structure. And an aircraft flies straight, it is not rotating. A bullet has no wings and no stabilizers or a rudder, just a rotating "fuselage", for this reason we have to focus on good barrels, good black powders, good alloys, good bullet geometries.

I don't know if real subsonic bullets are better for accuracy, I have my doubts on this because they were designed just to make less noise, and not for the transonic problems.

Longer the distance, longer the barrels, longer the bullets, heavier the black powder loads: I think that subsonic speeds can be obtained just shooting with black powder revolvers and pistols.
The round bullets can go well over the transonic regime, but their symmetrical design is not efficient aerodynamically, and not for transonic reasons.

[flatsguide]

Wow! General Aviation has sure upped their game with high performance aircraft. A bullet in an ideal world would spin about its axis and any shock wave pressure would be evenly distributed, but when a bullet is processing the shock waves would be in different places and I think that’s what causes the instability.

[MichaelR]

Richard you are correct. With the same ogive different caliber bullets would have the same trans sonic properties. But trying to get to 1000 yards or even 500 with the least wind drift has been a goal of most BPCR shooters. But in practice faster seems to beat out slower in practical application.

[Mr_Sheesh]

In WW2 the P38 aircraft, at first, had BAD problems in dives etc. with compressability stalls, been a while since I was up to date on that but I remember they had PROBLEMS. Boolits have it easy, they're much more solid and stronger by comparison, than an aircraft. Always more to learn tho

[Claudius]

In the attached photo you can see a modern rifle bullet slowing down to transonic speeds, you can see how the shock waves behave, moving the centre of pressure to the rear of the bullet. This has a really negative effect in accuracy because the centre of pressure is applied on the tail! In an aircraft the problem is caused by the shock waves forming differently on different surfaces (wings, tail, rudder, etc.).

In our BPCR the bullets start at transonic regime but after 100 or 200 meters they will transit to the auspicated and beloved subsonic speeds. I think that for this reason we can get very good results at the long distances. Also our bullets are heavy and after a flight of 1000 yds they have still a lot of energy.

[Chill Wills]

As you can see in this G1 based chart below, the typical BPCR Creedmoor ammo is does not drop out of the transonic range until most of its flight is complete to 1000 yards. Again, because there are so many contrasting qualities to useful BP match ammo or accurate ammo if you like the term better, you end up balancing one improvement against creating a liability. In other words, tradeoffs.


Drag Function: G1 Ballistic Coefficient: 0.45, Bullet Weight: 540 gr Initial Velocity: 1300 fps

Zero Range: 1000 yd Chart Range: 1000 yd Maximum Range: 4671 yd
Step Size: 50 yd
International Standard Atmosphere Altitude: Sea Level (0 ft)
Barometric Pressure: 29.92 Hg Temperature: 59° F Relative Humidity: 50%
Speed of Sound: 1116 fps

Range Vel[x+y]
(yd) (ft/s)
0 1300
50 1246
100 1197
150 1153
200 1114
250 1080
300 1049
350 1022
400 998
450 976
500 956
550 937
600 919
650 903
700 887
750 872
800 858
850 844
900 831
950 818
1000 806

[Chill Wills]

The dynamic nature of a bullet's Bc is shown looking at the 250 of 300yd mark on the chart. See how the Bc really climbs. This points out one aspect of the better subsonic 22rf match ammo competing to 200 meters.

[Claudius]

@Chill Wills, regarding the transonic region, we know that the critical speed for bullets and aircrafts is CLOSE to the speed of sound. So following your measurements we see that the most critical value is at 1300 fps, at 200 yds the speed is still critical, after the flight is without any stress. So, why the books say that the transonic region is starting from M 0.8 to M 1.2? because the altitude: the air density decreases with altitude, and the speed of sound follows the same physics.

Your data were taken at sea level at standard values, so we can easily understand that the real subsonic flight starts just after 200/230yds.

Anyway, your value of 1300 fps is one of the most critical for a 540gn black powder bullet because normally I see 1100/1250 fps. Higher muzzle speed is not necessarily bad, I had 405gn bullets from a Lee mold that flew just a bit over 1400 fps with very good results at 200 meters, but it was a failure when I wanted to repeat the experiment.

[Kenny Wasserburger]

Reducing the vertical is the key. Going slower in my experience isn’t the answer, anyone that has experience at 800-900-1000 yards, knows it’s not.

Edwin Perry’s book tells of working up your load, to reduce the vertical then adding 1 or 2 more grains of powder. Modern Observations on Rifle Shooting, the 1880 edition.

My load at 1 mile has a vertical of 18 inches from top to bottom bullet strike. It starts out around 1418 FPS. It is with a 537 gr PP bullet.

The key is to load to reduce the vertical, then the deep dark secret is to learn how to read the conditions and know what your bullet requires to correct for it.

Fouling control and being mindful of that, goes without saying.

Kenny Wasserburger

[martinibelgian]

I agree with Kenny - for long range shooting, going slower will create more issues than it solves. For short-range work, it might have some merits though... Still to be proven.

[flatsguide]

I agree with Kenny too. As the OP, I was tossing this idea out for two hundred yard shooting only. I’m out of ideas on how to load PP with reduced loads and still keep the the seating depth of the bullet into the case of .120”. I’m a bit leary of fillers especially at this reduced of a load. I do have a GG 530gn mini groove that I may be able to get down far enough in the case with a single .063” LDPE wad only; hoping that the bullet lube alone will prevent leading as I’ll be cleaning ( BACO bore pigs with dry patch one shot cleaning that works fine with PP loads.) between shots. Any recommended lube? I do have some SPG on hand. As a reminder I’m shooting a .45-70 and want to get the load shooting around 1050-1100 FPS. No insult intended about GG bullet on this venue...lol.
Thanks guys

[rfd]

In the past I've used a wad stack with 60+ grains of 1-1/2f, and 400 grain slicks for 200yd matches with some winning results using a rolling block. My current load is 80.5 grains of 1-1/2f under a .060 LDPE wad, under a 529 grain Jim444530E slick and that's kinda overkill for my local 200yd matches. I just loaded 65 grains of 1-1/2f under the same wad and deep seated slick in an effort to start looking for a reduced short distance PPB load - still an excess of lead. Haven't had the weather to test it out yet, but do have an Accurate 405 grain slick on order and will revisit a redesign of the wad stack, and maybe try grease cookies, too. The fun never ends.

80.5 vs 65.5 ...


Wad stack ...

[Don McDowell]

Richard, 1 f powder combined with a .030 fiber wad, and a 1/8 in felt wad will likely get you down in the velocity you're looking for.
Seating a patched bullet deeper into the case is not the detriment some on the internet would have you believe.

[Gunlaker]

Kenny has it right. The name of the game is controlling vertical and then understanding how to read wind and mirage. There is a reason that in nasty conditions the bigger cartridges usually come out on top in long range.

With respect to the transonic zone, because of pressure differences around the bullet, different parts of the bullet will see the shock wave at different velocities, so the nose of a bullet may have no shock wave, but each grease groove might for instance. I think this is at least part of the reason why ballisticians say the entire velocity range is trouble.

Chris.

[Don McDowell]

The velocity thing is something I don't think will ever be settled. I know I feel better shooting bullets just short of what the twist will allow at 1300 fps or better. But having said that I've seen national records and championship's won in midrange with 535 gr bullets trotting along at 1200 or a bit less.
Recent case in point would be Steve Ferringers run at Byers Money match,Phoenix and 3rd place finish at Lodi. His 45-70 load is reported to run at 1175...
The just to muck things up a bit more, Chip Mate's win in the 1000 yard match at Phoenix and his placing in the top 3 overall, with a 450 grain bullet.
So there are examples out there that defy the " accepted" knowledge.

[Good Cheer]

You guys are making me want a spire point mold for the .52 cal with 38" barrel.

[Keith Andersen]

My .45-70 might reach 1200 fps but mostly it runs 1180 and it will do just as good at the 1000 yard as the .45-100, 110, or the super horsepower .45-3-1/4. It's not the speed it's the shooter that gets the job done.
As far as the vertical, Yes, head, tail, full factor, halve factor will cause verticals but mostly it's a bad load development that puts it in the grass or over the top.

Shoot straight

Keith

No Good Cheers, you don't want to go there.

[Good Cheer]

Keith, it maybe might be some fun to experiment with but ponying up for a custom mold... nuh-unh.
But why in your experience do you think no?