Pressure Ring Measurement / Case Head Expansion

[No_1]

Looking for info and experience on this process. Is pressure ring measurement and measuring case head expansion one and the same?

Thanks in advance,

Robert

[NVcurmudgeon]

no_1, the short answer to your question is "no." Pressure ring expansion has the two advantages of being easy to measure, and of showing expansion greater than factory loads at lower pressure than does case head expansion. Ken Waters has a comprehensive article on pressure ring exansion in Handloader No. 99. Pressure ring expansion is Mr. Waters' method of working up loads, and the one that makes the most sense to me. For example, in developing jacketed bullet loads for a Chilean 1895 Mauser in 7 X 57, I wanted to be able to load to factory equivalent pressures. The 1895, considered by most experts to be weaker than newer actions, is not the best vehicle for emulating Roy Weatherby. Using the conservative approach of equalling factory pressure ring expansion, I was able to load to velocities quite a bit higher than factory loads. Of course a 29" barrel with .287" groove diameter didn't hurt! These loads allowed very long case life, perfect function, and no scary pressure signs. Mr. Waters goes on to detail cases where it is safe to exceed factory pressure ring expansion in case of very old cartridges used in modern actions. I have no experience with the case head expansion method. My understanding is that one needs to polish two diametrically opposed places on the rim of the case and measure there. Naturally the rim being part of the solid head, is much harder to expand than the pressure ring. IIRC, Bob Hagel used the head expansion method. Using the pressure ring method I have managed to enjoy high velocity while keeping all fingers and eyes as issued. For best results, you need a .0001" mike. If you need Ken Waters' article, PM me for a copy.

[No_1]

Just arrived. Thanks Bill.

Robert


no_1, If you need Ken Waters' article, PM me for a copy.

[Catshooter]

Mine just arrived also, thank you very much.


Cat

[Pepe Ray]

In case head expansion (CHE), the rim is not the point of measurement. The rim should be trimed at 4 points, 90Deg. apart. to allow access to the case head at the extractor groove, where the measurements are made. A mike that reads to 4 places is essential, accurate to 1 ten thousandth in. is best.
Otherwise the procedures are obviously similar.
There are mikes with blade anvils that enable you to make the measurements w/o damaging the brass but I can't afford them.
I've pondered it for some time but can't think of a good reason why one system is better than the other, unless it's the extra work involved. Other opinions???
Pepe Ray

[No_1]

Very interesting and informative reading. It is somewhat simular to what I have been doing but seems I was calling it the wrong thing. Anyway, it gave me tremendous "food for thought" that I will ponder and incorperate in my testing from now on. Again, thanks for taking the time to send it my way.

Robert