General Reloading Advice - Pressure and Velocity

[TaperPin]

So if you measure case head expansion with a micrometer what change in dimension are you looking for? Alternatively do you just take a piece of brass and shoot it 8 times and if it survives you're good?

35 Whelen explained it well. I’d just add, it helps to get a meaningful measurement if the micrometer touches the brass in the exact same place. A sharpie mark can be made, or simply lining up on a letter in the head stamp works just as well. When you’re learning the technique it’s fun to load up 6 or so cases with loads from max on down. I number the cases with the load and a sharpie #1 through #6 and write down the case head diameter. Each time the same case is loaded with the same load and expansion is recorded. It will quickly become clear which loads are not causing much expansion and which are - if you continue with enough shots the cases begin to develop separation rings or loose primer pockets, you now know for that brass how much expansion correlates to case life for other loads. It’s fun watching the progression. At one time this technique was included in some reloading manuals, but it must have caused more confusion than it was worth. Careful measuring can’t be stressed enough or the numbers will seem quite random. A .0001” micrometer is also essential - even the $30 Shars brand will take reliable measurements, and used NSK brand can often be found for about the same price and are top quality. Poland micrometers are also affordable used and I’ve seen them for $20 in good condition. All the kids in our family and extended family get one as gifts - most don’t measure case head expansion, but at least they have the tool and know how to go about it.

Yep, pressures judged by the number of times a case can be reloaded works well to avoid over pressures and is as easy as firing the same case a number of times, but that is hard to do if the range is hard to get to. Feeling inside the case with a paper clip for case head thinning isn’t required, but is really interesting to feel the thinning start and gradually progress - you can feel the thinning section a number of reloads before it shows a ring on the outside and that ring shows up one or two reloads before the case will actually split. Most people are surprised it’s so easy to feel a minor ring many shots before the case is toast.

 

[TaperPin]

Interesting discussion. I think much of the difference has to do with different testing equipment, different test barrels, different lots of powder, and different conditions when the testing was done.

I load monos differently than I do traditional cup & core or partition style bullets. With monos I find that I usually end up somewhere between 50% to 75% of max load for the given bullet before I start to see pressure signs I MY rifles. The first monos I loaded were Barnes 7mm 140 gr flat base way back when. Those were for a pawn shop Ruger Mark II. I didn't get to 50% of max before I was pounding the bolt open.
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Those things were awful. These days I tend to start right in the middle of a min - max load and go from there.

For load data on monos I like to/prefer to use the data from the bullet manufacturer if I can. I also like to see if the powder manufacturer has data for the exact bullet. As others have mentioned, it is good/interesting to look at multiple sources and extrapolate from there.

Wow those are vintage! lol
I can remember fighting with them back in the day.

 

[TaperPin]

It might not have been said, but when measuring case heads you will hear online people talking about numbers and techniques that seem quite different. Some measure the point of largest expansion in front of the case head, while I’m talking about measuring just a dime or nickel width in front of the extractor groove that isn’t touched by the resizing die.

 

[35WhelenAI]

For consistent measurement I look at the head stamp and line it up on opposite sides at the same place on each case. Also can put a scratch for reference on the head stamp as well, one scratch will do as the other side will automatically be 180° opposite. For me I take it as close to the extractor groove at the back of the case head as I can. Typically it's a similar width to a dime in front of the extractor groove, but in any case I keep it as close as I can to the extractor groove to get the reading.