Establishing maximum load?
- Thread starter RichCoyle
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I normally work my way up the powder ladder till I see the normal pressure signs, ie bolt lift, swipe marks, flat primers. Then I reduce the charge till all signs are gone and do 1/2 grain more for safety. Then I will take a virgin case and load that same load in that case till the primer pocket expands or the case fails. If I get north of 6-7 firings then I feel I have a safe max load with those components in that rifle. I have always felt that good case life is an indication of safe pressure. JMW
shinbone
Well-Known Member
All of those are commonly done by many people to find the best accuracy. Although I bet few people repeat doing a primer test 30 times. The same with powder testing, etc.
How does repeating a test to find the maximum pressure 30 times contribute to finding the best accuracy?
Rich Coyle
Well-Known Member
This was to show the absurdity of firing three 10 shot groups with each powder or primer or bullet.
shinbone
Well-Known Member
I guess I missed the sarcasm.
Barrelnut
Well-Known Member
Same as bang bang.
Same powder, same bullet, same primer? Why?
The only reason I can think of to do that is to improve the accuracy of the standard deviation value for whatever is being evaluated. SD is the dataset's relationship to the mean of the dataset (mean is a fancy way of saying average). Small SD, less spread out compared to the average. Large SD, more spread out compared to the average.
If I shoot 3 rounds of the same primer and get a velocity SD of 10 (just throwing numbers out there, I've never done this), numerically speaking, I might be convinced that this lot of primers needs to be tested further. If I shoot 30 rounds and get an SD of 10 (still tossing numbers) I'm going to "know" that the SD is stable. If I do that 100 times, even more stable.
The problem I see with that is you need to own a lot (not like a bunch, like a lot, the same lot number) AND that lot has to contain the same or very close to the same "widget" (whatever you're testing). Plus... as you shoot through the lot, you're running out of parts. It could be that they just like to shoot.
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There are alot of factors to consider...factory barrel vs custom, barrel length, individual barrel, loaded cartridge length..... I say this because we have many reloading sources available to us today that are backed by pressure test equipment. If one is significantly higher than published data ( or something like quickload) for comparable testing, we may be over pressure.
All that stated, I will generally find what I consider max in my rifle using published data as a reference and other visual and tactile ques ( sticky bolt, primer shape, ejector swipe, case head expansion, etc...). I will generally go back and verify this at least once during load development and at the earliest confirmation, I will stop, pulling bullets from rounds above this point.
All that stated, I will generally find what I consider max in my rifle using published data as a reference and other visual and tactile ques ( sticky bolt, primer shape, ejector swipe, case head expansion, etc...). I will generally go back and verify this at least once during load development and at the earliest confirmation, I will stop, pulling bullets from rounds above this point.
There are so many things that can effect pressure in loads. When you start using a different barrel, powder, bullet, brass, and suppressed vs brake, everything you thought about a load can change. I recently ran some load tests using a bullet and powder I was was familiar with and ran into ejector swipes and heavy bolt lift way before I was expecting. The variables were new Peterson brass and suppressed. There is no reloading manual info for this bullet and bullet combo. I had to pull several bullets. Was it the brass or suppressor or both? I hate pulling bullets, but that is price we pay for chasing the top end performance.
One thing those of us that use digital scales might not have considered is the accuracy and repeatability of the scale. I have an RCBS Chargemaster 1500. It's been a good scale. It still is a good scale. When I dump a charge from the Chargemaster on to my TRX-925 sometimes it's spot on, sometimes it's off a few hundredths of a grain, and sometimes it's off by 0.05gr to .1gr. I correct the charges in the last catagory. Truth be told, if I'm ladder testing or loading a final "version" I'll try to hit the number exactly. It's not hard to do. If you still use the balance beam scale then you're probably good (test it though).
I've spent a lifetime in process controls (oil and gas). The one thing we never know for sure is the accuracy of the device that we are using to check the accuracy of the device
I've spent a lifetime in process controls (oil and gas). The one thing we never know for sure is the accuracy of the device that we are using to check the accuracy of the device
nksmfamjp
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I see some value finding true max for me, but it is a zone where little good comes from my loads. So, I only need to see true max, or actually over max once! I use bolt lift and case head extrusion into the ejector as my measures. Those are too hot by 1-2%.
That plus velocity at that point tell me how too hot shoots!
That plus velocity at that point tell me how too hot shoots!
Mikecr
Well-Known Member
Rich was statistic baiting.
It didn't seem to work in this case, but still fun to watch.
It didn't seem to work in this case, but still fun to watch.
Barrelnut
Well-Known Member
Rich could also post such stuff in the Humor forum.
