Thoughts about pressure

[Curmudgeon]

Morning,
There is much talk about pressure when reloading. Other than anecdotal information concerning bolt sticky, primer flat, crater in primer strike and the excessives, blown primers and wooden mallets how can pressure be tested by the home reloader? We sometimes see devices attached to actions the well known shooters take to the range but I want to know if there is something the rest of us can do? The one most important piece of reloading information I have read is " when determining max load work that load up with your bullets jammed". Thanks, any info would be appreciated.

 

[jonbearman]

measure the base of the web before firing,look at the cartridge drawing and you will be able to see where to measure. Then measure after each firing and if you have more than a thousandths of expansion you are way to hot.I follow the book for starting loads and work up.I never load lazer hot because of heat and barrel life. Never go over what the book says unless you absolutely sure that there are no excessive pressure signs.There are good books out there you should buy on this subject of advanced loading.

 

[kemen4]

I wonder about the expansion measure ... there has to be expansion and contraction in the firing cycle to allow for loading / gripping the chamber the extraction. Given that necks seem to alter with repeated firing/ reloading (?) then why should the base not be variable too?
Just to be contrary, I have a batch of cases that are underspec at the base: with my standard, medium load they had to take up more than 5th, and after firing were still 2th under spec. There were no pressure signs and the fps were slightly higher.
Because of the variables I'm not sold on the mechanics of brass behaviour, it may only be accurate at the extremes?

 

[BoydAllen]

If you are going to look at web expansion, I think that standardizing on cases that have been fired one time before being used to test would be a good approach.

Some years back, a friend wanted to have a new barrel chambered in .300 Weatherby, with a tight neck (required turning) and a throat that was short enough that 180 gr. bullets could be loaded to touch, or slightly engage the rifling and still fit in the magazine. Needless to say, this was a considerable departure from the usual freebore of factory chambers. Knowing that we needed to be cautious, we did a pressure test, loading at the range, with weighed charges. We measured the diameter of the belt before and after firing. We marked the case head so that measurements would be taken at the same point each time. The belt diameter moved on the first firing of a new case, but there were no other pressure signs. After that, it did not change (We used a mic. that measured to .0001.) until the sixth increase in powder charge, at which point there was already a smear on the case head at the ejector location. By reloading the same case for each shot, we were also able to track primer fit. When the belt moved the second time, we quit, noted the load, temperature, and humidity, and picked a maximum to use that was below that. It was summer, and hotter than it would be for any hunt. Based on that experience. I would evaluate pressure based on head expansion of a case that was fired a second time from new. If one were doing this on a rimless case, a blade micrometer that measured to .0001 would allow measurements to be taken at the bottom of extractor grooves. Loading at the range, and doing the pressure series with a single case allowed us to monitor primer fit, and slowed the process down. I don't know how many times I have seen, or heard of someone that saw signs of excess pressure, and did not stop firing that ammo. I have also seen fellows that would start at a top manual load, figuring that it was safe, and who were surprised to learn that with their particular combination that it was too hot. I have since come up with a term for those who recklessly pursue velocity. I call them "chronograph idiots". BTW the rifle that I referred was used to take a good sized bull elk at about 600 yd., dumping him on the spot with a high shoulder shot.

 

[lynn]

Curmudgeon
Most shooters don't have there reloading dies fitted properly to there chambers and this often gives them false signs of pressure.
Most sizing dies in my opinion push the shoulder back way too much without sizing enough of the cases base.
If your gunsmith is real good and puts in a very straight chamber you need real tight dimensions on your sizing die.
If your gunsmith puts in a sloppy chamber it bellmouths and makes your sizing process much easier.
As to the jamming of bullets causing pressure it does this on a bell shaped curve.
I don't want to write about it here and stir the pot but can be reached at lynn_dragoman@att.net
Lynn

 

[rayporter]

does anyone have the new 8208XBR on quickload? ray

 

[TonyR]

does anyone have the new 8208XBR on quickload? ray

The Feb 2011 Update has it. What do you need?

 

[mikecr]

I measure at the webs while working up loads. These must be fireformed non-FL sized cases.
As I go up in charges, I'll see where the webs have opened to chamber dimension and sprung back(~1-2thou). This growth levels off.
As I continue charge increases there will be some point where I'll see another .0005" step change.
With a .473 head cartridge this pressure is typically ~56Kpsi per calibrated QL, and regardless of SAAMI MAX, this is MY MAX.
This is the point where the brass has yielded(exceeded springback), and would require FL sizing -everytime.

There may be other 'signs' near that(usually are). But you know how inconsistent they are, and that they are not a direct result of pressure in itself. They are headspace, firing pin, flash hole, ejector, or bolt head/face issues brought to the surface with enough pressure to do so.

 

[RDavies]

I have up until recently used case head expansion as a way to judge pressure, leveling off at .0005" as well. But then with some new Norma brass, it is getting .002"-.003" expansion with loads which gave less than .005" expansion with Win brass. I have had similar findings with some norma 7x57 Brass as well, very soft batches.

Also, some of the loads and velocities I have seen listed seem WAY higher than I get with a few different barrels. I wonder how much pressure some people realy are pushing?

 

[rayporter]

TonyR
mail sent
ray

 

[dreever]

I measure a new unfired case at the web. Then I load and fire that case. if the expansion is more than .001 I consider the load to hot and adjust accordingly. I strive for less than .001 on the first firing and never anymore than an additional .0005 after that regardless of the number of loadings.

Danny