Originally Posted by Dirtfarmer
Originally Posted by flintlocke
4320 is a wonderful powder, much neglected. But, IMHO it is, in 4 out of 5 burn rate charts, misplaced. Not deliberately, not carelessly, just a function of it's unique chemistry. 4320 gets a rapidly faster burn as bullet weight goes up, as internal volume decreases, and as throat length diminishes. And when it gets near peak operating pressure the pressures rise steeply in relation to charge weight increases. I suggest anyone doing unpublished load development to use the Norma Burn Rate chart, which correctly places 4320 down between 3031 and 4895 rather than up with H380. Norma also has the added advantage of using a 2 number ratio of velocity vs pressure...the best burn chart in the industry IMO.

On your suggestion, I printed a copy of the Norma Burn Rate Chart. It does show some differences.

JB has long written than burn rates can vary from application to application.

Thnaks for that info. Not sure how fully I understand their Relative Velocity and Relative Pressure, but understand they're working against a standard, 43.2 gr. IMR 4350 in a .308 with 143 gr. FMJ bullet. I'm thinking about it.

DF
Read the preface to the Norma chart...the baseline is IMR 4350, we are all familiar with it, let's say a load like 57 gr 4350 with a 165 gr bullet is our standard, we will reassign that velocity number from that load as 100. We will reassign the actual pressure number also with 100 (it might be 49,500 C.U.P., it's immaterial). So we can conclude, faster powder will generate increased vel., example, lets say 120 (think of it as 120% higher vel than our standard of 4350) but also we know our pressure increases, let's say the chart says 135 in the pressure column for powder X, so we have learned, the easy way that powder X gave us 20% higher vel. but at the cost of a rather high 35% more pressure. Maybe we want to try a powder that is not so "peaky" pressure wise. Remember, it's just a relative number, like playing poker with lima beans. But invaluable when you are developing loads with no data.

Well this is a fine pickle we're in, should'a listened to Joe McCarthy and George Orwell I guess.