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gschwertley
saddle soap
Posts: 912
(7/6/05 5:28 pm)
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My favorite gun magazine - article on pressure
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I have had subscriptions to the various gun magazines, but have let nearly all of them lapse except for one. That one favorite is "Handloader," which I read from cover to cover when it comes every other month. I even read articles about calibers I don't have and probably never will because there is always something of interest there.
This latest issue, August 2005, has among other things an article in it about determining pressure levels via velocity readings. Of course, it is full of good stuff, but one area in particular caught my attention. That was the part about the difference in pressure generation based on the use of different primers.
The information in the article referred to gives me more cause for reflection than ever before on which primers to use in relation to powder charges and about primer substitution.
The information presented in the article was based on an experiment run with otherwise identical components loaded into 7mm Rem Mag., the difference being only the primers. Without going into specific load information, the results of the tests as to velocity and pressure showed that from milder to hotter primers, velocity increases were only 1.1% whereas pressure increases were 19%. The pressure increases with the hottest primers exceeded the SAAMI standard for the cartridge used.
Based on the data resulting from the tests, the primers can be categorized as mild to hot in the following order:
Winchester WLRM (magnum)(hottest)
Win. WLR (standard)
Fed 215 (mag)
CCI 250 (mag)
Rem 9 1/2 (mag)
CCI 200 (standard) (mildest)
While not in the test, I guess we can figure that a Fed 210 is milder that a 215 and that a Rem 9 is milder than a 9 1/2.
There are a number of things to think about with this data. Number one, be careful subsituting primers because they are not all the same.
Number two, NEVER substitute a hotter primer for a milder one when using maximum load data. You are inviting a incursion into the realm of over-pressure. Maybe this should be item number one?
Beyond these two safety issues, I start thinking more along the lines of performance. Given that the Winchester (hottest) primers push the load into over-pressure with the same charge of powder that is at or below SAAMI limits with milder primers; and that velocity with these hot primers is within 1.1% of the loads with milder primers; then perhaps you can never achieve quite as much velocity with a WW primer within a safe pressure.
Over the years, I have heard people talk about the merits of various makes of primers as to how they fit in the case, easy or hard, "tight" or not, or whatever. I would think considering the relative "heat" of the primer would be a primary consideration, followed by the fit.
Certainly things to make you go Hmmmmm.
Well, as a chronic reduced-loader, I am the last one to worry about squeezing the last fraction of a fps. out of a load. I did think this was worth mentioning to those of the speed demons among us.
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