Understanding Pressure Signs.
- Thread starter 350 Mag
- Start date
Thanks for posting.
The article was a good effort, but "Pressure Signs" are notoriously unreliable, and the ones I think you can generally trust as signs of high pressure are:
1. a damaged firearm - pressure was higher than is appropriate for the firearm, be it a Winchester 1873 or a Ruger #1;
2. damaged brass, notably a blown primer pocket; and
3. not mentioned (and a big oversight in the article) - higher than expected muzzle velocity. Pressure translates to MV, and this might be the most reliable sign available to handloaders aside from actual pressure testing equipment.
"Reading" primers is probably the most deceptive pressure sign. Flattened primers are often the sign of excessively low pressure. Pierced primers can indicate a firing pin and/or firing pin hole issue. Case head separations can be due to repeated over sizing. Loose primers can be a sign of worn out brass that was shot at or near the highest safe pressure too many times. Etc.
The discussion of bolt thrust was missing some relevant info in relation to brass not gripping the chamber walls. Lube in the chamber will contribute to increased bolt thrust, but only to a maximum of the shear strength of the cartidge, which for brass is not very high.
The article was a good effort, but "Pressure Signs" are notoriously unreliable, and the ones I think you can generally trust as signs of high pressure are:
1. a damaged firearm - pressure was higher than is appropriate for the firearm, be it a Winchester 1873 or a Ruger #1;
2. damaged brass, notably a blown primer pocket; and
3. not mentioned (and a big oversight in the article) - higher than expected muzzle velocity. Pressure translates to MV, and this might be the most reliable sign available to handloaders aside from actual pressure testing equipment.
"Reading" primers is probably the most deceptive pressure sign. Flattened primers are often the sign of excessively low pressure. Pierced primers can indicate a firing pin and/or firing pin hole issue. Case head separations can be due to repeated over sizing. Loose primers can be a sign of worn out brass that was shot at or near the highest safe pressure too many times. Etc.
The discussion of bolt thrust was missing some relevant info in relation to brass not gripping the chamber walls. Lube in the chamber will contribute to increased bolt thrust, but only to a maximum of the shear strength of the cartidge, which for brass is not very high.
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- Location
- Western Manitoba
Might want to read various articles by John Barsness. He used multiple of his own rifles in various cartridges, and then verified his "guesses" at the lab at Western Powders in Myles City, Montana. Pretty much as Andy posted in Post #2 - "reading primers", measuring expansion ring or belts, bolt "stiffness", etc. sometimes worked on some of his rifles - and sometimes did not reflect unsafe pressure. About the only consistent "sign" for a home hand loader to use, that he found, was muzzle velocity - step-in-step with pressure, absolute numbers have to allow for barrel length differences - can not have more velocity without more pressure. Can also read "pressure" reading in book by Pierre Van Der Walt - he again uses muzzle velocity - finding out what small increments in powder increase / decrease do to velocity - in his rifle - when that rate changes, have now "crossed a line" - he has much better explanation.
Generally no issues following safe reloading practices & data guidelines for use in good condition firearms ymmv. Experimental load development a different game you're on your own. Firearm system only as strong as its weakest link.
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IMHO, the three signs you mention, are all correct.
The first one is a no brainer
The second can be attributed to other issues than high pressure unless it occurs simultaneously with #3.
Over the years, I've had batches of brass under several different brand names, one IVI, another Remington etc. The brass used for making the case was dead soft and expanded around the web area at moderate pressures, around 45K psi, enough to expand the primer pockets as well.
Blown primers can also be an indication of severe head space issues.
IMHO, #3 is by far the best indicator of high pressure.
Can't increase velocities, without increasing pressure or lengthening the pressure curve.
Where this all gets interesting is in the examples like 7mm Remington magnum where a lot of the published data in the lawyer era is way below what the cartridge can do. Proceed with caution and a chronograph is your friend while working up but the older data is much hotter without issues or signs. I won’t publish any of mine here but 5 grains over the published in some cases has not been unusual.
By perusing a number of reloading manuals, one can glean a lot of pertinent information.
By so doing, you may see the "plateau" of velocity that one may expect to see in most
cases.
A good example is the venerable 30-06. With a 180 grain bullet and with a 24" barrelled rifle.
realistic maximum velocities are around 2850 fps at safe pressures. 26" barrels will flirt with
2900, usually.
The problem with trying to judge pressures by brass measurement is the wide variance in brass
quality and hardness in the head area. This variance is even seen in lot-to-lot offerings.
Primer appearance is a poor way to judge pressures, even if using only one brand of primer.
I've been reloading since the early 1960's, and am still learning. Be careful!
Dave.
By so doing, you may see the "plateau" of velocity that one may expect to see in most
cases.
A good example is the venerable 30-06. With a 180 grain bullet and with a 24" barrelled rifle.
realistic maximum velocities are around 2850 fps at safe pressures. 26" barrels will flirt with
2900, usually.
The problem with trying to judge pressures by brass measurement is the wide variance in brass
quality and hardness in the head area. This variance is even seen in lot-to-lot offerings.
Primer appearance is a poor way to judge pressures, even if using only one brand of primer.
I've been reloading since the early 1960's, and am still learning. Be careful!
Dave.Granted, most people use a bolt action gun or an autoloader that will show certain signs that are telling you you have pressure issues. Other guns don't necessarily show them the same way, such as falling blocks and break actions. Velocity alone is not even a good indicator, you can hit pressure before reaching a "book" velocity in some guns, and some guns will allow extra velocity that is above book velocities, and no issues showing. If nothing else, the Primal Rights article has probably some of the best pics around to illustrate what he is presenting. Speer used to use base expansion measurements, then they finally got new pressure equipt and discovered they were as much as 10K psi out of SAAMI map pressure zones on some stuff, Ed Matunas admitted that in an article, so that method sorta got tossed out the window. Probably still the most reliable indicator is primer pocket expansion and velocity, but, primer pockets are subject to material and annealing variables too.
I find...
Velocity that exceeds book value....BUT most chronographs are not perfect.
But ejector marks, sticky extraction, harder force required to eject....is dead giveaway.
Flattened primers on their own(unless severely flattened) are unreliable.
Loose primer pockets, BUT this could also come from sloppy chamber or soft brass.
Velocity that exceeds book value....BUT most chronographs are not perfect.
But ejector marks, sticky extraction, harder force required to eject....is dead giveaway.
Flattened primers on their own(unless severely flattened) are unreliable.
Loose primer pockets, BUT this could also come from sloppy chamber or soft brass.
In order to get brass flow into the ejector you are looking at in excess of 5,000 psi overpressure.
As mentioned velocity will give a more complete picture of pressures than other options available to the average shooter.
The factory Winchester Short Mags are the worst I have seen for this. Winchester rides the ragged edge at times in order to meet their advertised velocities and it is very common to see once-fired WSM brass showing brass flow into the ejector hole.
The factory knows that this ammo will only be fired in new-production rifles so they load it for performance rather than reusability of the fired case.
I dont think its 5000 psi with a faint circle that you have to look hard to see ..
BUT a easy to see cirlce combined with a wipe/shiny spot
I would agree.
The point to understand here is that depending on the brass to tell you if pressure is too high can result in a damaged firearm, for example if your gun's safe upper limit is 30K psi (i.e. most handguns and many older rifles) and you're looking for signs in the brass that are typically exhibited at pressures higher than 60K psi...............
I can't count the number of times I've heard people who are loading for a "weak" action share unsafe loads that they deemed safe because the brass told them so: "they weren't any pressure signs".
- Location
- Western Manitoba
I followed an article by John Barsness about 9.3x62 - he could come up with no reason not to go up to pressure levels of 30-06 - he owned multiple rifles chambered in both cartridges - could not understand why pressure limit would have to be different. He verified his "guesses" at the Western Powders lab, in so far as what breech pressure his loads were running in his 9.3x62. I did similar, but at home - "work up" - to his published loads - got same muzzle velocities as he did - I have no way to get the pressure actually measured, but my rifle was also chambered in 30-06, so "red-neck" me thought similar might apply, in this case. But to reiterate - same rifle (brand and model, year of production) for both cartridges. His rifle was a CZ of some sort; mine is a Husqvarna, built on an FN M98 action. And yes, I am aware that the practice of "long throating" can reduce breech pressure, but I have been presuming that the muzzle velocity would change accordingly? Pretty much of the belief that muzzle velocity reflects pressure?
Correct, as usual Andy. I used Waters' method for a long time until I got my first chronograph. I was lucky and never had any pressure induced failures, but once I could verify bullet speeds, I quickly realized that I was in dangerous territory. The Chroney when it first came out was a godsend for amateur reloaders. - dan
The pressure generated during the ignition is not uniform during the entire cycle. Long throating - something Roy Weatherby used - can reduce peak breach pressure and smooth out the entire pressure curve. This can in most cases result in a small increase in over-all velocity. This is the reason most reloading manuals caution about loading maximum charges for the various Weatherby cartridges when they are chambered in a non-Weatherby barrel.
Also, the much quoted "lawyer reduced" recipes in new manuals are generally the result of actual pressure testing rather then the older "observational" methods most companies used to use. If you compare the older recipes to current pressure tested data it becomes clear that most of the reduced loads are for ball powder which tend to have a steeper "peak" in breach pressure than what was assumed.
