Pressure Signs?????

[harry.hacking@kiewit.com]

I have heard alot about the signs of pressure but I am not quite sure that I understand them. Today I was working up some loads in my 270 wsm and my 6.5x284. My first two rounds had what i thought was a stiff bolt lift, but the next two incremented up by .5 grs had no stiff lift at all. So i continued through my loads I had come a full 3 grains in progression before I got another stiff bolt lift. I then shot 3 rounds of facotry winchesters and the bolt lift was a about the same stiffness as what I thought was a stiff lift on my reloads. I have heard of some of the other tell tale signs of pressure but I am not sure exactly what I am looking for. Also, I have heard the term cratered primers alot but would like to know exactly what it means?

thanks in advance,

Hack

 

[lynn]

Hack
As I wasn't there I have no way of telling how hard your bolt lift was.
It is extremely common for guys to clean there guns and leave cleaning solvent in the chamber.On the next shot after cleaning they think they are high on the pressure scale only to discover a couple shots later that all is well.
When you look at your brass after shooting it in a wet chamber it looks like it has a very dense pattern on it not on your other brass.
Lynn

 

[Bob3700]

Hack,

A lot of target shooters will, upon completion of cleaning, take a patch wet with solvent and swab the chamber to remove carbon and soot. Then, wipe the solvent out with a dry patch. Now wet a patch with lighter fluid or alcohol and "Dry" the chamber.

This will ensure that excess liquid from cleaning is not in the chamber.

Bob

 

[lynn]

Hack
Tere are several things you will notice when your getting up into some serious pressure.

The web area of the case will expand 0.001 on a normal load and much more on a hot load.

The primers that have nice rounded edges before firing will have flat sharp edges that completely fill in all the area around the primer pocket.When you deprime your brass the spent primers will resemble a mushroom in shape as the top is now wider than normal.

On the cratering your primers will flow back into your firing pin hole and your brass will no longer sit flat it will lean.That is because the primer has flowed backwards.It will look just like a volcanos crater in shape hense the name.

Most modern actions have a margin of error built into them.Brass will begin to flow like toothpaste at around 73,000 pounds of pressure and your primers will fall right out of a case with this much pressure.
Lynn

Lynn

 

[Shynloco]

Hack,
In response to your question about what is "cratering" and how can you tell it exists in a load, after firing a round, run your finger or fingernail across the surface of the primer. If there is any rise in the primer or the crater is higher along it's edges OR it's outer edges feel an abrasive edge that is no longer smooth as it was before firing the round, you have signs of pressure. One of the things that can also be done, is ot remove a fired primer and "mic" the edges (top and bottom of the rounded polished portion) of primer and if they are uneven or different in measurement (and I've seen them off by as much as .002 when pressure exists) you have pressure thats just a step away from having the primer blown out of the casing.

Alex

 

[MrMajestic]

Depending on the action you might see a smiley face were the brass flowed/was forced into the ejector. If this happens when you cam the bolt it may also leave a shiny ring around the case head were the bolt face shaved it. Also cases may stretch more under high pressure and require trimming more. During load development the case length growth between loads tells me much.

 

[bigedp51]

Hack

One more thing you can do is fire a few factory rounds and use the primer and case as a reference starting point to 'read" your reloaded cases. The majority of factory loaded ammunition is loaded well below the rated chamber pressure for that particular cartridge (3,000 to 5,000 cup lower than rated chamber pressure)

Also remember this, there is a reason why American competitive shooters are using Lupua brass.

NOTE: In 2001 Winchester lost the bid at the Lake City Army Ammunition plant to produce ammunition for the military, and in 2007 Winchester sold off its brass manufacturing division. Remington lost the bid to prior to this to Winchester at Lake City, and now Alliant Techsystems (ATK) and is the single largest producer of small arms ammunition for the United States military. (ATK= CCI, Speer, Federal)

Bottom line in the U.S. the quality of a product is controlled by the bean counters and stock holders and the world is a changing place.

The pressure signs you read on your cases are no better than who made your brass, metallurgy, heat treating, and manufacturing tolerances.