PaulS wrote: |
Handloader, PaulS: You got that round to just over 5000 fps with 67000 PSI on a strain gauge? Was the gauge calibrated with some ammo or ? H: No. The contacts were glued in place between specific points on the receiver and barrel. Incidentally, said glue is somewhat a challenge to get off these items. Part of the presumption is that the gauge is accurate per se and, at the very least, gives relative increases in pressure corresponding the increases in velocity. This is why CHE is a backup check, along with the other "normal" signs of pressure. FWIW, double based powers, such as N540, tend to spike rapidly in the pressure curve; as such incremental increases warrant very careful monitoring. PaulS 1: you did the research to find a powder that could deliver your velocity with under MOA accuracy. 2: You documented every step of the way as a true experimentor But what makes me really proud to know you is that you are going back to that old standard load that has served you so well over the years. H: This was simply an excursion into that grey area of handloading. Requisite are some guidelines and tools/equipment to monitor results. Anyone using a good chronograph will be able to watch the results of added pressure by the concomintant velocity increase and when that ratio is disrupted (ie marginal velocity gains per increased powder charge) one knows that the effective pressure limits of the powder are being approached. This is not the comfort zone of operation and my standard load allows respectible velocity below SAAMI max pessures by a considerable margin. I looked up the SAAMI specs and the 220 Swift max is 54000 CUP and looking at other cartridges that have both pressures listed it looks like close to 65000 PSI is close to the same (There is no direct correlation between PSI and CUP readings - and the difference is more variable with the large volume and small caliber cases) I would tend to think that your loads , if the gauge had been calibrated with SAAMI /ANSI pressure test rounds, would be closer to 70,000 PSI than 65000 PSI. (This is only my guess) Would you tend to agree or disagree with my guess Handloader? Just wondering... you don't need to answer. Paul |
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