Pushing the envelope with Herco in .38spl+P

[TD1886]

Perhaps there is a reason most newer manuals don't show data with Herco in the 38 SPL? Could be with the advent and now common usage of piezo-transducer and strain gauge psi measurements which give a complete "picture" of the pressure curve they've found some powders aren't really suitable in some cartridges. Yesterday ran a pressure/velocity test of Alliant Herco in the 38 SPL. Pressure was measured in a Conteder with 7.94" barrel via the Oehler m43 PBL. Fps are muzzle velocities. I used the Lee TL358-158-SWC because when seated with the case crimped in the 1st lube groove it gives about the greatest seating depth of any cast 150 - 160 gr bullet. The Cartridge OAL was 1.465". The bullets were cast of COWW + 2% tin, lubed with LLA and sized at .358 and weight 162 gr fully dressed. Cases were Winchester W-W with WSP primers.

I loaded 10 shot test strings of 5.4, 5.7, 6.0 and 6.3 gr of Alliant Herco (purchased last year).

We mostly expect the measured pressure traces (time/pressure curves) to be nice smooth lines going up to max pressure and then tapering off to muzzle exit. Many times they do do that. However, many times they don't. Particularly with straight walled cases we many times see a secondary "bump" in pressure. Sometimes these are sharp bumps and are many times referred to as "spikes". I have seen a lot of secondary pressure bumps and some spikes over the many pressure tests I've conducted. As of this date I've never seen any spikes like the ones I got testing the Herco powder in the 38 SPL.

Now, before anyone gets all excited and wants to insinuate the Contender test barrel and/or the M43 has some " noise" in it before and after testing the Herco loads I ran a test string of Remington 125 gr jacketed HP factory loads. The traces were as smooth as one would expect w/o any bumps or spikes. Previous test with that Lee bullet have also produced smooth traces with other powders. Thus the test equipment was good leaving suspect the Herco Powder.

The test results;

The 5.4 gr Herco load ran 1003 fps, SD 11, ES 27 fps, psi 19,100

The 5.7 gr Herco load ran 1070 fps, SD 15, ES 40 fps, psi 23,000

The 6.0 gr Herco load ran 1092 fps, SD 14, ES 42 fps, psi 23,200 ...... all the traces showed very high secondary spikes occurring during each shot. This is the first time I have ever seen a secondary spike in the trace exceed the psi of the primary chamber psi...... perhaps this is why we no longer see Herco data for the 38 SPL?

Attachment 269024

The 6.3 gr Herco load ran 1135 fps, SD 12, ES 30 fps, psi 25,200

A subsequent test of the same Herco in the 44 SPL under the RCBS 44-250-KT did not show the sharp spikes but just little secondary bumps in psi which, as previously stated, quite common. Thus, while the internals measured quite uniformly the very sharp and high pressure spikes with Herco in the 38 SPL are of a concern. Caution should be exercised if using Herco in the 38 SPL due to the high end +P+ range of psi in the 38 SPL along with the occurrence of the very sharp and high pressure spikes..

Perhaps your test would reflect different if those loads were fired from a revolver which has a cylinder gap. I'm not talking about a difference in velocity or pressure, but the spikes. Maybe they might not be there or maybe they could be worse. I'd like to know.

[Larry Gibson]

Perhaps your test would reflect different if those loads were fired from a revolver which has a cylinder gap. I'm not talking about a difference in velocity or pressure, but the spikes. Maybe they might not be there or maybe they could be worse. I'd like to know.

In researching all the loads tested with that barrel having had 2 different gauges on it I've concluded it is simply an anomaly of this particular barrel. The spikes always appear just before, during or after bullet exit. Might have something to do with the way the barrel flexes during pressure relief(?) in the Contender action but I don't know. Similar "spikes" appear in some other test traces I've seen published, including those when an oscilloscope is used. Such "spikes" are more common than not.

As to pressure testing with a revolver, the revolver would have to have an unfluted cylinder with sufficient clearance between the cylinder and the top strap for the gauge to fit. The revolver would need to be a DA because the gauge and wires couldn't be rotated through and around. Only one chamber could be tested then the cylinder opened and that chamber reloaded. A revolver with the cylinder opening to the left and which rotates clockwise would also be best. The finish on the cylinder would be removed where the gauge would be attached. Anyone have a doner revolver in 38 SPL meeting those requirements?

[TD1886]

In researching all the loads tested with that barrel having had 2 different gauges on it I've concluded it is simply an anomaly of this particular barrel. The spikes always appear just before, during or after bullet exit. Might have something to do with the way the barrel flexes during pressure relief(?) in the Contender action but I don't know. Similar "spikes" appear in some other test traces I've seen published, including those when an oscilloscope is used. Such "spikes" are more common than not.

As to pressure testing with a revolver, the revolver would have to have an unfluted cylinder with sufficient clearance between the cylinder and the top strap for the gauge to fit. The revolver would need to be a DA because the gauge and wires couldn't be rotated through and around. Only one chamber could be tested then the cylinder opened and that chamber reloaded. A revolver with the cylinder opening to the left and which rotates clockwise would also be best. The finish on the cylinder would be removed where the gauge would be attached. Anyone have a doner revolver in 38 SPL meeting those requirements?

Does the industry have some sort of test barrel with some sort of cylinder (although there won't be a cylinder per se) because I'm sure they don't go through the trouble you just described?

[Larry Gibson]

What "the industry" uses;

"Vented test barrel assembly for revolver ammunition


A test barrel assembly for a universal receiver includes a cylinder, having a cartridge-receiving chamber, and a barrel secured to the cylinder in a manner such that a rifled bore of the barrel is in axial alignment with the chamber. Spacer means between the cylinder and barrel provides a gap of predetermined thickness therebetween and the resulting controlled venting of propellant gases through the gap during firing results in reproducible pressure and velocity readings which can be used to accurately predict actual performance of a cartridge in a revolver. Manufacture of the cylinder and barrel from a single piece of steel ensures proper alignment and uniform spacing of these parts."

[Larry Gibson]

Additionally, any published pressure data will have been obtained in a fixed barrel test with a vented or unvented barrel. None will be from a revolver.