Swiss 1.5F or 2F?

[Skirmisher]

This is good stuff.  I just came back from another frustrating session with a .38 rifle that once shot great, and hasn't since.  It just occurred to me that I had switched to OE3, which has proved to be superb in my pistols.  So now back to the range with a selection of other powders.  That may be all it is.  My OE3 groups looked a lot like Herb's.

[yulzari]

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What effect does the difference in burn rate have on breech pressure?
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For the same weight of charge a faster burn rate will give a quicker rise in pressure which will increase the maximum pressure. The rate of burn is a function of the grain size for the same powder. Thus a change in charge from 1F to 3F will need a 10-15% drop in charge weight to keep the pressure down to the same level.

It is not a bad rule of thumb to use as coarse a powder as will do the job. This will keep the breech pressure down. I note that Ned Roberts advised the same in 'muzzle loading cap lock rifles' for accuracy also and he had the ear of the old boys of the 19th century.

Another useful rule of thumb is to chase accuracy rather than velocity. In hunting placement of shot trumps power of shot.

[Daryl]

Lyman's data in their first black powder handbook, showed considerably lower pressures for 2F when loaded to the same velocities as produced by a given load of 3F.  In other words, it took more 2F but produced less pressure at the same velocity as 3F.

Back in the 70's we found in rifles from .50 up, 2f produced better accuracy and LESS fouling than did 3F.  This was likely due to the 3F's higher pressure being harder on the patches we were using.

I understand this 'phenomena' today, so I used even better patching that will work with both powders equally. So, in .36, .40. 45 and .50 and .69 rifles & the .62 smoothie, I developed accuracy loads for both 2F and 3F, producing similar velocities and the identical accuracy. Thus, no matter what powder I have in possession, I already have proven loads for any of my guns with THAT powder.