quote:

Originally posted by Alberta Canuck:

quote:

Originally posted by tnekkcc:
Real men don't wear women's underwear.

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Maybe not, but some of us, even in our old age, keep trying to get into their pants

quote:

Originally posted by tnekkcc:
Real men don't wear women's underwear.

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Maybe not, but some of us, even in our old age, keep trying to get into their pants [/QUOTE] [/QUOTE]

Well at least the subject material has degraded down to something EVERYONE can understand once again...

I've been reloading for over 40 years. I've been using chronographs since '75. I've also been using CHE and pressure ring expansion measurement for about as long as they've been written about. I've found that CHE is not usefull when developing loads for low pressure cartridges. PRE is usefull only some times with those cartridges. The use of a chronograph is essential when loading for those cartridges but a correlation between componants selected and chronographed velocities must be understood and taken into account.

Problem is with any of the above you are never sure of what the pressure really is. For example; in a given cartride there can be a wide varience of CHE and PRE between different makes of cases (or even different lots of the same make) given the same componants loaded to the same velocity. I find CHE and PRE to be valid only when using those exact componants in that rifle but then that should come as no surprise. Switching cases or shooting the same load in another rifle can give different CHE or PRE measurements.

All that aside the point of this thread is supposed to be the value of a chronograph to determine or indicate pressure. Cut and dried the answer is NO. That is not to say the chronograph is not a useful tool when loading or that knowing the velocity and consistancy of your loads is not important.

I too have reached that stage in my reloading career when I'm ready to go the next step. I've a M43 of my own on the way. I've some experience with the M43 as a friend has one. First point I'd like to make is there is no SAAMI "calibration" ammunition. There is reference ammunition and Dr. Oehler explains that very well. My limited previous experience along with my friends extesive experience with the M43 is that it does give "PSI" if correctly used.

We must also realise that SAAMI specs must be interpolated. There is a difference between "maximum pressure" and "mean pressure". Even with the special SAAMI spec test barrels there is alway a +/- psi reading for any mean pressure. If you check they are usually quite large. U.S. arsenal acceptance is pretty much +/-7,000 psi. That means there could be as much as 14,000 psi between one cartridge and another in the same box of ammo. Sounds like a lot right? Well not really as the measurement of pressure with any of the three common methods is not exact, just like CHE and PRE is not exact.

Using CHE and PRE only tells us when we are at the top end of pressure limits or over them. CHE and PRE tell us little below that. Given the use of appropriate componants a chronograph can give a better indication of at least pressure consistancy. The M43 gives a much better picture of pressures than CHE, PRE or the use of a chronograph alone.

I too will have some M43 vs CHE/PRE test infromation available by March or April. I will be interested in particular to see how my results compare with Saeed's.

Larry Gibson

quote:

Originally posted by PaulS:
Neither methods (strain gauge and CHE) measure pressure. The best that you can do is make comparisons.......

Somehow I missed your post earlier, PaulS. I like your logic! I have long thought that allowable pressures for a cartridge are governed by what the case can take - provided the action is strong enough! The action 'strength' is what we cannot measure. But action rigidity and brass strength we can - by your method.

Hi there, Hot Core. I have looked into the 'bullet expanding into the bore' theory and it seems that is exactly what happens and what many reloaders are looking for when developing loads - that point at which the lead core is pressing the jacket against the bore hard enough to increase bullet drag. Well, O.K. that is something I had never thought of before!

Larry Gibson, thanks for a very interesting post! I look forward to yours and Saeed's results.

Good shooting.

quote:

Originally posted by 303Guy [New Zealand]:
I have long thought that allowable pressures for a cartridge are governed by what the case can take - provided the action is strong enough! The action 'strength' is what we cannot measure.

Uh oh!.. there is common sense on the other side of the earth.

We will send missionaries with load books.

They must learn to fear and worship pressure.