Thread: 6.5 v 7mm

Greetings All,
First I must apologise to @Fisherman for hijacking his thread and in penance offer the following. It doesn't matter if you use the 6.5 or 7mm, they are pea's in a pod for any practical purpose so use what you like.
Getting back to the discussion on AI cartridges I did a bit of number crunching with the following results. It is hard to get pressure tested data of the same vintage for standard and AI cartridges but they do exist for the .280. I selected data using a new powder, IMR4451 and the 140 grain Nosler Partition and BT respectively. The relationship between pressure, velocity and powder charge is linear at normal pressures so it is possible to interpolate (calculate) all between start and max loads. Max pressure for the .270 and .280 AI is 65,000 PSI and the .280 only 60,000 PSI. Most handload data is a little under this so I calculated the powder charge needed and velocity for the AI at 280 max pressure. The velocity was near the same for both cartridges but the AI needed an extra grain of powder to get there. The .280 AI max load gained about 70 fps in velocity for another 1.3 grains of powder so most, if not all of this gain would apply to the standard .280 if loaded to AI pressure. This is what has been found in other pressure tested comparisons between standard and AI cartridges that I have read over the years.
Getting back to the .270 as this is already loaded close to 65,000 PSI the AI version loaded to the same pressure does not gain 400 fps, or 100 fps but somewhere between 30 fps and nothing at all. Some will dispute this but the pressure tested data is clear.
Regards Grandpamac.