454 Casull Case Comparison Study

By M.L. (Mic) McPherson

Synopsis: Recently several players have entered the 454 Casull ammunition game. While all brands of cases are not necessarily interchangeable, all do share the combination of a small primer pocket and a standard (large-diameter) flash hole. In an effort to compare case quality and to see if a smaller flash hole might improve ballistic uniformity, I obtained a batch of Hornady cases with smaller (0.059-inch, versus 0.081”) diameter flash holes and did a few ballistic comparison studies.

As of late 1999, the 454 Casull had entered far enough into the mainstream so that four case producers or ammunition manufacturers now produce this case. Available brands have the following headstamps: F-A (Freedom Arms), WIN (Winchester), Hornady and Star-Line. While there are no significant external dimensional differences, there are significant differences in case weight. Weight differences can reflect differences in web thickness, body wall thickness or length of untapered case wall. (Differences in case head hardness, which reflects how much pressure the case can withstand can also exist but I did not test for this.)

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We now have at least four choices in 454 Casull cases. While external dimensions are quite similar, there is enough difference in capacity to warrant handloading caution. See table for comparative data.

Approximate accuracy of measurements:

1 - 0.0005-inch;
2 - 0.001-inch;
3 - 0.010-inch (unusually heavy bullets require the longer untapered case neck; e.g., my 475-grain WC load will only work in the F-A case);
4 - 0.0002-inch.

All 454 cases must have two important features: 1) sufficient case head hardness to support peak chamber pressures as high as that used in any magnum rifle load 2) a hard and thick case neck, to resist inertial bullet pull during recoil - no amount of crimping can substitute for adequate neck tension. One convention in this case is unusual, the combination of a small primer pocket with a standard large-primer-size flash hole. This combination harks back to the days of the invention of this powerful revolver round.

Dick Casull believed that in order to get good ignition of the compressed charges of the hard to ignite powders he had to use in order to achieve maximum performance, he needed to use a rifle primer. In that era, that was probably true. Equally, he felt that the heavier cup used on rifle primers might mitigate the potential for piercing (a non-issue when the firing pin and recoil shield are correctly sized). Mr. Casull might also have suspected that the smaller primers would be easier to properly ignite with the relatively mild firing pin impact produced by a typical revolver (which is not necessarily true). However, since large size rifle primers are taller than large pistol primers, he would have needed to deepen the primer pocket to use rifle primers.

The problem with that approach was that the web was already quite thin in the 45 Colt cases used in his experimenting. Deepening the primer pocket the required 0.006-inch weakened the case. Therefore, he devised an alternative solution. He made steel inserts to press into the existing primer pocket (Freedom Arms still stocks these!). These were sized to allow use of small rifle (or pistol) primers in 45 Colt cases - small rifle primers are the same height as large pistol primers. Of course, there was no need or desire to reduce flash hole diameter.

When the 454 Casull case was created, the small primer pocket was adopted. Meanwhile, pistol primers had been “improved” to the point that the ignition issue was moot - e.g., current CCI 350s are hotter than all but three large rifle primers! Today, the recommended primer for all full-power 454 Casull loads is the R-P 7½ (small-rifle benchrest).

One interesting question is this: Is the large diameter flash hole the best choice? It is a fact that with the typical compressed charge of slow-burning powder, as used in typical full-power Casull loads, the primer’s blast will move the bullet before the powder ignites. Moreover, it is likely that the larger the flash hole, the further the primer’s blast will move the bullet before effective powder ignition occurs.

A study with the 38-40 WCF, in which I fired over 3000 rounds, demonstrated this point. In those tests, I saw an inverse correlation between flash hole diameter and muzzle velocity. The only reasonable explanation is that as flash hole diameter increased, the bullet moved further before the powder effectively ignited. Essentially, loads in cases with larger flash holes acted as if the bullet were seated further out, which increased boiler room and thereby decreased resulting pressure and velocity.

I attempted to test whether the primer blast would move the bullet in the 454 (which has many times the neck tension of the venerable 38-40) using the following technique - please, do not try this at home! I began by sealing the flash hole with fingernail polish. This protected the primer from the WD-40, which was first swabbed into the interior base of the empty case and then sprayed onto the powder charge before that was pushed through a funnel and into the case. The purpose of the WD-40 was to try to prevent the primer blast from igniting the powder - this did not work! The powder insisted on igniting - after a significant delay. Cancel that idea.

I then decided that a reasonable volumetric and space filling substitute for smokeless powder was soft PVC, as used in P-Wads (800-451-3550) - P-Wads are used as an effective base seal for cast bullets used in blackpowder and Schuetzen style smokeless loads. I inserted three, 30-caliber P-Wads and then ten, 44-caliber P-Wads into the case. Seated the 250-grain XTP and then primed the case. To lubricate and maintain a similar bore condition for each shot I swabbed the Freedom Arms bore with a bore brush wrapped in a patch that was saturated with Moly-Slide.

For this study, I compared otherwise identical Hornady cases with flash holes of 0.059-inch and 0.081-inch. I prepared five rounds in each type of new, unfired case using precisely identical loading methods - crimp, neck tension and all other variables were held as nearly identical as feasible. Since these are the norm for this round, I used R-P 7½ primers. The bullet was Hornady’s 250-grain XTP.

To measure how far the primer moved the bullet, I used a hardwood dowel to gauge bullet nose location before and after the primer popped. Note that of itself this test does not necessarily prove anything. In the real world of a live load, even if there were a significant difference in how far the bullet would ultimately move in response to the blast from the primer, there is no reason to suspect that it would move any particular distance before effective powder ignition occurred - such ignition might occur before the bullet stopped or after it stopped. For that answer, we have to look at muzzle velocity results from live round tests - the flash hole size that results in the highest muzzle velocity probably results in effective powder ignition when the bullet has moved less. However, higher velocity might simply indicate that the primer ignited a greater percentage of the charge! Other explanations are possible.

As it turned out, reality was evidently some complicated combination of these effects. Evidently, the smaller flash hole resulted in less bullet movement before effective ignition occurred but it also resulted in reduced ignition efficiency. See the live ammo test results.

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For the flash hole comparison study, these Hornady cases were specially drilled with 0.059 and 0.081-inch bits. At question is whether the standard (0.081-inch) flash hole is the best size for producing consistent loads - test results indicate that it probably is.