Low Pressure Loads


Dear Technoid,

In looking over Hodgdon’s Shotshell Data Manual, I noticed a significant difference in the pressure attained between using International Clays & Universal Clays , with all other components being the same & the velocity both being 1200 fps. At least I believe the difference of 1,600 psi to be significant.

That,in essence, is my question. How significant is that difference, especially in terms of wear & tear on a given firearm or any other aspect for that matter. Your wisdom is appreciated.

Garry

Dear Garry,

My wisdom is appreciated? Well, thank you, but I sure would appreciate some more of it regarding your question. Unfortunately, it’s totally lacking in this case.

I don’t really have a hard answer for you. Higher pressure is not always bad. Low pressure is not always good. Some people claim that the recoil is more of a push than a shove when using a low pressure, slow burning powder. Others don’t find it that way. I did a blind test with some friends with shells using a slow burning, low pressure powder vs one with fast, max pressure powder. The verdict was evenly split as to which kicked less.

As to what’s good for the gun, obviously excessive pressure can cause problems, but pressure within the gun’s design limits shouldn’t. In fact, cartridge makers don’t like to go below a certain minimum pressure. Excessively low pressure loads may fail to obturate the plastic skirt of the wad on a cold day. This will cause a blooper. The problem is exacerbated in overbore barrels.

Pressure within normal ranges assures more reliable ignition of the powder and more consistent velocity. As to whether being at the top of a normal range vs being at the bottom really matters, as I said above, I dunno. It would seem that it would have to, but I can’t prove it one way or the other. Perhaps it is one of those things which is true, but doesn’t make enough difference to matter. I always looked at porting that way.

Don’t confuse pressure with recoil. As I mention above, my test subjects couldn’t tell the difference. The formula for mathematical “free recoil” doesn’t take pressure into account. All it cares about is the weight of the gun, the weight of the ejecta and the speed of the ejecta (plus a constant for the escape velocity of gas and some other little stuff). Pressure doesn’t come into it.

One other consideration for the reloader: slow, lower pressure powders like the Universal require larger charge weights to achieve comparative velocities when compared to faster powder. This means that your reloading will cost a little bit more.

Personally, I tend to reload with faster powders (always following a published recipe) when possible. I use a lot of Hodgdon Clays and Red Dot. I feel that this gives me the combination of economy and reliability under all weather conditions. I particularly like the faster powders when I am shooting 7/8 loads because they keep my pressures high enough to insure consistent performance.

There is an argument that slow burning, low pressure powders print tighter patterns due to less shot deformation. I hear this constantly, but I have never been able to prove it to my satisfaction on the pattern plate. Perhaps I just ought to go out and do more work on that. Yeah, right.

Of course, all this hasn’t answered your question about lower pressures being better the gun. I just don’t have any hard figures either way. Perhaps one of SR’s readers will come up with some sort of definitive answer to your question. If someone does, I’ll happily post it.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error, never in doubt.)

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