A Few Experiments with Supersonic Wadcutters


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Why is it wadcutter loads are sub-sonic? The speed of sound is about 1100 fps. Most wadcutters are loaded to 750-850 fps.

Very few sources list supersonic loads for wadcutters, however I did find that the Lyman manual lists wadcutter loads for the .357 Mag that go up to about 1375 fps, and in fact they list the top load with 4227 as potentially the most accurate load. Why don’t more people shoot supersonic WC loads? Faster bullets mean less time of flight and potentially less wind drift. Wouldn’t this be an advantage in outdoor bullseye competition? Or would it?

Personal tests have shown that common subsonic .38 button-nose wadcutters (~800fps muzzle velocity) stay stable out to about 90 yards. Things get a little shaky at about 100 yards, and the wadcutters are tumbling wildly by 120 yards. But subsonic bullets don’t have a bow wave, they have more or less conformal air flow over the surface of the bullet (it may be turbulent or laminar depending on the form of the bullet, but either way it’s basically conformal flow down the sides of the bullet, there is no bow wave). A supersonic bullet compresses the air in front of it and creates a high pressure bow wave emanating from the front of the bullet. These bow waves are clearly visible in high speed spark photography of bullets in flight.

I suspect the reason that more people don’t shoot supersonic wadcutter loads is that the lowly wadcutter doesn’t make the transition back down through the sound barrier very gracefully, and starts to tumble when the bow wave collapses (this phenomenon is well-known in long-distance rifle competition). It occurred to me that I needed to test this.

Speer reports that their swaged lead wadcutter has a BC of 0.052.

Using an online ballistic calculator and assuming a muzzle velocity of 1200 fps, the calculation shows the wadcutter going subsonic at about 11 yards. When the MV = 1300 fps, the transition to subsonic is about 22 yards. The big high-pressure bow wave from that blunt profile really slows them down quickly!

For the sake of comparison, when the Sierra .30 caliber 168 grain Match King is in free flight, it takes over 25 yards to slow down from 1130 fps to 1110 fps. Our friend the wadcutter makes a similar deceleration in less than 3 yards! This means that when the supersonic high-pressure bow wave collapses for the wadcutter, it does so very, very abruptly. The blunt, angular profile of the wadcutter also means that this collapse will probably be considerably more turbulent than that of the sleek Sierra Match King. Can the wadcutter survive this aerodynamic violence and still fly true?

Not wanting to get in trouble with pressures, I knew from previous experience that I couldn’t put enough 4227 into a .357 Mag case to get in trouble with pressures using a standard weight bullet. I knew that this wouldn’t give me top velocities, but it would get me supersonic. I also knew that with heavier cast bullets in the .357 Magnum 4227 has given me exceptionally good accuracy. It should give a good platform to test the hypothesis – do wadcutters tumble as they transition back down through the sound barrier?

Reinforcing this conclusion, I found as I dug around that the Lyman Cast Bullet Handbook (3rd Ed.) gives loading data for the Lyman 358495 wadcutter in .357 Magnum using 4227. 12.3 grains of IMR 4227 was listed as producing 1084 fps @ 22,200 CUP (from a 4” barreled revolver. The maximum load is listed as 16.3 grains of 4227 for 1365 fps @ 39,600 CUP. I chose to go with 13.0 grains of 4227, which gave almost 100% load density with the Lyman 35891 wadcutter. Based on the Lyman data, I would predict this load to give a little over 1100 fps from a 4” revolver. Since I was going to be shooting these loads out of a 8 3/8” S&W 586 with a proven track record of fine accuracy, I was guessing that they would give me about 1200 fps at moderate pressures.

I cast up a batch of the 148 grain Lyman 35891 using a mix of recovered range scrap and a little linotype (overall BHN about 9), sized them .357” and lubed them with a mix of Lyman “Black Goo” (i.e. the old Lyman lube), and NRA Alox formula (I used this lube mix because that’s what was in the lube sizer that I got in a trade from my buddy and I wanted to use it up). I loaded these bullets into Federal .357 Magnum cases on top of 13.0 grains of IMR 4227, and the CCI 550 Small Pistol Magnum primer.

The first tests were carried out at 25 feet using sandbags, shooting a very accurate 8 3/8” S&W 586. The 5-shot group was very tight, almost 1 ragged hole. All bullet holes were cleanly cut and round – exactly what you would expect from a wadcutter.

S&W 586 and 357 WC loads 25 feet.jpg
S&W 586 and supersonic wadcutter load at 25 feet

The second round of tests was also carried out using sandbags, but this time at 50 feet. The 5-shot group opened up notably, and had a flyer, but all of the bullet holes were still cleanly cut and round. We may be seeing the first indications of instability at 50 feet (~17 yards).

S&W 586 and 357 WC loads 50 feet.jpg
S&W 586 and supersonic wadcutter load at 50 feet

The load was chronographed and was found to be going 1150 fps 15 feet from the muzzle, so the initial assumption of a muzzle velocity of 1200 fps was pretty close. In any event, this load is clearly supersonic.

Plinking at 50 yards was revealing – aiming at softball-sized rocks on a dusty dirt bank, about 1/3 of the time the shots fell close to the selected target, and about 2/3 of the shots missed by 3 feet or more (in random directions). Clearly, the majority of these wadcutters were unstable and probably tumbling. Subsonic wadcutters are still stable at 50 yards, and very accurate. This instability seems to be coming from the supersonic wadcutter transitioning back down through the speed of sound (i.e. the sonic boom of the bow wave collapsing) and starting to tumble.

Thinking over these results, I was reminded of an afternoon about 25 years when I had RO duty out on our local range. Things were fairly slow that day, so I had brought a favorite revolver (S&W 686) and a bunch of plinking ammo to shoot if things got slow enough. This ammo was loaded with the Keith SWC (Lyman 358429) loaded with H110 to about 1200-1250 fps. Sure enough, things got slow, and I had lots of fun burning that ammo up plinking at the 300 yard gong (half of a gas cylinder on top of a t-post -- they ring like a church bell when struck with a bullet!). I was hitting the gong about 1/3 of the time (offhand), and the misses were generally good in terms of elevation, just off a few inches right or left. The thing is, those Keith SWCs were going sub-sonic at about the 100 yard mark, yet they continued to fly true well beyond that point. Clearly the supersonic bow-wave was collapsing in such a way as to not perturb the bullet’s flight. Keith SWCs are renowned for their long-range stable flight, and the nose shape plays an important role in this behavior. Sadly, the homely wadcutter does not benefit from this advantage.

This may have been the single least meaningful shooting project I’ve undertaken, but it gave real satisfaction because it answered a legitimate question, and gave me a deeper scientific understanding of a cast bullet’s flight. Now I know the real reason why people don’t shoot supersonic wadcutter loads – it’s not just because they have the BC of a brick and suffer lots of bullet drop, it’s because if they start out above the speed of sound then all hope of accurate flight is lost as they slow down through the sonic transition. If a wadcutter starts out subsonic, then this issue is moot and the wadcutter flies true. This project has also helped to re-emphasize to me why the Keith SWCs have enjoyed such broad appeal.
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