Quickload Request

[Unclenick]

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.

GRT produces 2949.7 fps and 2868.5 fps for the short and full freebore, respectively. Perhaps you can get a clue out of that, but keep in mind this assumes a Velocity and Pressure barrel configuration with a bore that is nominally dimensioned and cold. If you shoot for velocity as a pressure check, let the barrel cool for a few minutes between shots. Keep in mind the computer simulators don't take all sources of heat loss into account, so you can only trust its numbers up to a point.

 

[stagpanther]

It's too bad Jim Ristow had to shut down his Pressure Trace business (health reasons, not lack of product interest), as that was the best way for a handloader to check the pressure in an individual gun.

I didn't know that--I still have mine. Is there anyone who is picking up the slack for support?

A longer bullet ogive can do it, too, by allowing more starting gas to bypass the bullet and head down the barrel before the bullet obturates the bore.

I thought about that--but it seems to me dangerous game solids would do almost the opposite (?).

 

[TX Nimrod]

… I note from photos of Hornady's test setup that they have what looks like pressure-measuring instrumentation on the barrels. However, I believe they still load to velocity intervals and then use the last interval load before one when over SAAMI pressure...

That’s not how they used to develop their data. Older manuals showed a graphical solution: they plotted curves which fit the velocities of different powder charges against those charge weights. Where the curve intersected the graph’s 100 fps intervals was the charge weight published for each 100 fps interval. Any load which showed excess pressure was backed down to the next lower velocity interval.

To try to load for exact specific velocities would make no sense. I’m sure that today they use best-fit software to do the same thing - it isn’t 1967 anymore.


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[Unclenick]

They may still develop it that way initially. I know they test their maximum loads in SAAMI V&P barrels. I think everyone does that now to avoid liability issues, but it's just to make sure they don't go over. Rigging strain gauges to their standard test setup is a good way to preview what they can expect from that final test. I'm mainly just pointing out that by dropping to the next lower interval below SAAMI max like that, you will get some instances of that drop being a fraction of an interval and some for which it is almost a full interval. In the latter case, peak pressure can be noticeably below SAAMI max. Also note that they cluster same-weight bullets together so that the same liability concern would likely tend to make them validate the bullet that makes the highest pressure in the bunch, and the others are going to be off a little.

I didn't know that--I still have mine. Is there anyone who is picking up the slack for support?

Jim was looking for an alternative source for the strain gauges, but I don't think he found one. He'd said he'd be shuttering the business at the end of the year, but it was gone already in mid-December, so I hope his health issues didn't force early closure. You can buy strain gauges on Amazon that would likely work fine, despite the shape difference, but you have to deal with the connector. When I was in Tokyo last month, I picked up fifty sets of 2 mm connectors in a small shop near the Akihabara station, where all the small electronic component shops were clustered when I was there in the 1970s. Not much of that is left now, though. The era of disposable pre-assembled electronics has hit those small shop owners hard. Anyway, these connectors looked about right and, even if they don't match exactly, can be wired in to substitute. So, I figure to be improvising this way in the future.

I thought about that--but it seems to me dangerous game solids would do almost the opposite (?).

It really depends on the design details. I don't think there is a universal answer to this, but for the specific Speer BT SP bullet the OP specified, it seemed to work out.