CAUTION: The following post (or a page linked to) includes or discusses loading data not covered by currently published sources of tested data for this cartridge (QuickLOAD or Gordon's Reloading Tool data is not professionally tested). USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.
A couple of things: One, Barnes Match Burners are not solid copper bullets. They are cup and core match bullets same as the other brands. This is on their website.
Two, in general, thanks to legal concerns, many places that develop loads by watching for pressure signs in production gun barrels (Speer for example) contract Alliant to do pressure testing or will borrow test barrels from others and hire a ballistic technician to do the tests to SAAMI standard methodology with their warmest loads to confirm they don't exceed SAAMI specs. Photos of Hornady's facility reveals they are now using strain gauges to pressure test in-house and are likely confirming with SAAMI standard equipment for their manual data later. It may take some years, though, before all that new information finds its way into the print manuals. It takes several years to refire everything for updating manuals and they don't do it all the time.
If you want to know how a load was tested for pressure, read the SAAMI standard. It includes the barrel length and the ambient temperature range. A sample of SAAMI standard reference loads will have been equilibrated to temperature with the ammunition to be tested. The condition is:
"Ammunition conditioning should be between 60° - 80°F (15.6° - 26.7°C)."
Any error that temperature being on the high or low side produces will be compensated for by first firing a sample of reference ammunition for comparison that has been conditioned the same way. In turn, reference ammunition is tested to a much tighter specification to determine its pressure value:
" {Test} Ammunition shall be conditioned for a minimum of 24 hours at 70° ± 2°F (21.1° ± 1.1°C) with a relative humidity of 60% ± 5% before firing."
I do not know if Barnes, specifically, is getting pressure testing done, but here's another factor: Have you ever noticed that when pressures are listed with load data (Hodgdon, Lyman, Western Powders data, for example) the maximum load given is never at the actual SAAMI MAP (Maximum Average {peak} Pressure)? That's because the manual authors, as Hodgdon explained in one of their manuals, are trying to allow a relatively wide range of powders to be used that aren't always the best choice for the cartridge and bullet combination, and their customers are relying on printed recipes when actual powder lots can vary some in burn rate. So, to have a safety margin for those things, they look at how much the peak pressure swings in their test, then lower the load so the highest peak they got won't exceed the SAAMI MAP number.
That's not what an ammunition manufacturer does. He loads for specific velocity performance and confirms that his ten-shot
average peak pressure result does not exceed the SAAMI MAP and that his pressure variation does not exceed the SAAMI MEV (Maximum Extreme Variation) number for the cartridge. So the manufacturer's average may produce individual rounds that go above the MAP, as long as his MEV is good. This lets him load warmer than the handloading recipes and still keeps his product below the proof load range.
I bring up that last point, because I frankly don't know if Barnes is working like the other load data people with its peak pressures as limits or not. You'd have to call and ask, but this could explain some of the difference.
I note that even QuickLOAD and GRT think the pressure from the Barnes load will be high. They may also have had an oddball lot of powder. But nothing I see suggests their load is within SAAMI limits. I would avoid it and probably use my
Pressure Trace instrument to see where it actually falls, pressure-wise.
