Hey Smart Guys, Chime in! re: pressure signs and SAAMI

[ILikeLead]

In reviewing a thread (from August) about 357 magnum SAAMI standards which were downgraded from 40,000psi to 35,000psi several years ago due to lighter revolvers and damage to one particular model revolver, I have to ask a few theoretical questions.

Most reloaders can quote the SAAMI max pressure for certain cartridges, but does it really matter since I doubt any significant number of us have the measurement tool for Pressures? Even though the recommended max pressure changed, we will all be looking for "pressure signs" and a I assume that if I see no ominous pressure signs, I'll be under the maximum pressure.

Does SAAMI really tell us anything(except allow us to compare different calibers)??

Please comment for the advancement of the theories and strategies of handloading!

 

[steve4102]

we will all be looking for "pressure signs" and a I assume that if I see no ominous pressure signs, I'll be under the maximum pressure.

No, not really, by the time you see the tell tail signs of "High Pressure" you are well above Max pressure. You can most certainly be above "Max" pressure and not see any visible signs.

 

[Jesse Heywood]

Many reloaders use the bullet velocity as their gauge. There is a relationship between velocity and pressure, but there are so many variables that it gives more than an educated guess.

 

[NCsmitty]

Does SAAMI really tell us anything

Well basically it's the factory designated maximum projected pressure for a specific caliber, that some dummy without a clue, will always try to exceed to test his or her firearm.
And then have to pound out the cases stuck in the chamber.



NCsmitty

 

[R.W.Dale]

SAAMI really doesnt do anything for us as habdloaders other than serve as a basis for comparison between cartridges and the actions they're chambered in.

Quoting myself.

I cite the example of 7x57 vs 270 win.

A lot of folks make the mistake of believing that some form of pressure indication will show the instant SAAMI max pressure spec is reached. The problem in this is neither your rifle nor your cases know a thing about this arbitrary number.

If a person has two similar rifles one in 270 and the other in 7x57 and you don't see overpressure signs with the 270 shooting max loads why in the wourld would you expect the 7x57 to show you anything shooting pretty much the same piece of brass. In other words if the 270 doesn't show you anything at 65,000psi why would you expect the Mauser with it's 51K rating to tell you anything till it's overloaded by at LEAST 14Kpsi

This example is given to illustrate how just through comparison to high pressure rifle cartridges that pressure signs will not show till you've already drastically gone over the line.

 

[Steve C]

In reviewing a thread (from August) about 357 magnum SAAMI standards which were downgraded from 40,000psi to 35,000psi several years ago due to lighter revolvers and damage to one particular model revolver, I have to ask a few theoretical questions.

I'm not so sure this is accurate. One of the advantages of being old is you've gathered lots of information over the years. Looking through all my old manuals ranging form the early 70's to now, SAAMI .357 magstandards where never listed as greater than 35,000 PSI. Early data shows the standard maximum was 48,000 CUP's and most data that listed pressure where 40 to 42,000 CUP for actual loads. I seriously doubt that the ammo manufacturers changed the pressure standards they had used for years but simply converted what was their old standard of CUP to the new pressure units of PSI.

None of the major manufacturers or reloading data sources load to MAX pressure anyway. They provide a safety margin and the goal for the ammunition manufacturers is to provide ammo for the guns chambered for it while the reloading supply companies goal is to gvie their customers the best accurate and safe data for their product. There is some validity to the notion that more modern measuring methods have reduced loads in the various ammunition due to better detection of maximum pressure peaks but I can look at over 40 years of load data using powders like 2400 and Unique and the load data is essentially the same for the same weight bullets though max loads have varied +/- a few 10th grains at different times.

The one aberration is a early Speer book that showed loads universally higher than previous and later books they published. The story is that the company had received improperly calibrated copper slugs that where used in the test barrels to determine CUP pressures which resulted in the higher loads being listed.

As mentioned, once you see pressure signs you are likely well over maximum pressure standards and need to back off.

As also mentioned, velocity over the chrono may give you a clue that you are at the top of the safe load pressure but doesn't tell you if you are over or under. Velocity can actually decline with more pressure until it reaches zero at which point the breach blows out leaving the bullet in the chamber.

Does SAAMI really tell us anything(except allow us to compare different calibers)??

What SAAMI does is to provide the pressure limits that subscribing industries will stay within when producing their ammunition.

It gives the manufacturers of firearms a minimum level of pressure they need to design their guns to operate safely under, Some countries have mandated industry proof standards for firearms sold in their jurisdiction.

What it does do for the reloader is to assure them that if they load their ammo using data that does not exceed their maximum pressure standard, their firearm can shoot that ammunition with relative safety.

 

[Grumulkin]

In reviewing a thread (from August) about 357 magnum SAAMI standards which were downgraded from 40,000psi to 35,000psi several years ago due to lighter revolvers and damage to one particular model revolver, I have to ask a few theoretical questions.

Most reloaders can quote the SAAMI max pressure for certain cartridges, but does it really matter since I doubt any significant number of us have the measurement tool for Pressures? Even though the recommended max pressure changed, we will all be looking for "pressure signs" and a I assume that if I see no ominous pressure signs, I'll be under the maximum pressure.

Does SAAMI really tell us anything(except allow us to compare different calibers)??

Please comment for the advancement of the theories and strategies of handloading!

With some guns, the first pressure sign will be when the gun blows up. Also, pressure signs differ depending on what gun you're shooting. Unless I had pressure testing equipment, for the usual revolver, I would be slavishly following a manual since at the pressures they operate at, you will find no high pressure signs on inspecting cases and primers.

It's guns with stronger actions where pressure signs are useful. The S&W XVR revolver and the FA Model 83 revolver are designed to take pressures up to 65,000 psi so you can use pressure signs with those to guide you; your first indication will be difficult case ejection.

 

[ILikeLead]

Wow! Thank you all for the insightful info!

That info leads me to another question. I assume that there are usually a range of "pressure signs" with flattened primers being one of the earliest signs as the pressure rises. I will always back off loads if I see flattened primers. Only once have I seen primer flow around the firing pin.

The Question. If a primer is slightly flattened, is that probably over-pressure?

Thank you!

 

[Jesse Heywood]

The Question. If a primer is slightly flattened, is that probably over-pressure?

Possibly instead of probably. A primer can be moved by improper seating. Usually not deep enough or being loose in the pocket. If the primer moves to the rear and against the pin hole it can be flattened. This is different than the primer case being stretched due to over-pressure.

 

[ranger335v]

Steve, #6: "... simply converted what was their old standard of CUP to the new pressure units of PSI."

And THAT is/was the change.

 

[Grumulkin]

Wow! Thank you all for the insightful info!

That info leads me to another question. I assume that there are usually a range of "pressure signs" with flattened primers being one of the earliest signs as the pressure rises. I will always back off loads if I see flattened primers. Only once have I seen primer flow around the firing pin.

The Question. If a primer is slightly flattened, is that probably over-pressure?

Thank you!

A primer will always be flattened centrally. With the proviso that you DON'T use this criteria with lower pressure revolver cartridges, the flattening doesn't indicate high pressure until one or several of the following occur:

1. The primer is flattened clear out to the edge with no slight curve where the primer and primer pocket meet. This means that high pressure is being approached.

2. Rather than being shiny in the middle, you start seeing slight irregularity on the surface of the primer from being pushed hard against the bolt face.

3. A little raised cup around the firing pin indentation. In the early stages, this means high pressure is being approached. It can also be caused by too large a firing pin hole.

4. A blown primer or primer leak always means pressure is excessive.

5. Primer pockets that become loose after 2 or 3 firings probably mean excessive pressure unless you're using Federal brass which can be a bit soft.

 

[ILikeLead]

Thanks for all the replies so far. As suspected there are a lots of variables to consider. Now I realize the mechanism of primer flattening, I can appreciate the several causes!

Now I'll just go back to lurking and see what else I can learn.

 

[CraigC]

I must defer to John Linebaugh on pressure signs. Basically, it is far too unreliable in straight-walled pistol cartridges. It is highly likely that by the time any pressure signs present you are WAAAY over maximum. You have to trust and adhere to your data.

 

[rfwobbly]

Does SAAMI really tell us anything(except allow us to compare different calibers)??

I'd say so. For instance, it tells us not to shoot modern +P ammo in a older gun from the 60's that might otherwise be in great shape.

 

[Robert Wilson]

I am convinced that there are no reliable pressure signs. To wit...

Primer condition: softer primer cups will flatten more than harder ones. A hot load may not flatten a hard cup as much as a mild load flattens a soft one. There may be some validity to comparing the primers in a factory load to those in your handload, if you can be sure you and the factory are using the same primers - and that's a big if. The same is true for primer "cratering". A gun with some slop around the firing pin will crater just about everything. A precisely fitted pin won't crater primers until pressure is way over SAAMI specification.

Bolt lift: a bolt gets hard to lift when the lugs set back in their recesses or when brass begins to flow into the ejector. A rifle with poorly machined lugs or recesses, or with a large ejector cutout, will show this pressure sign very early. One with extremely precise machining may not show it under any circumstance.

Hard extraction: depends largely upon the condition of the chamber/s. A highly polished chamber will extract easily even with massive overloads. A rough chamber may not want to let go of even mild loads.

Case head expansion: again, if you compare expansion with a factory load and then ensure that your handloads are using the same brand and lot of brass (good luck determining that) AND you have an accurate blade micrometer and know how to use it in this particular application, then it's a useful gauge. But if you're just slapping a mic onto random cases, hoping to stay below an arbitrary number, you're kidding yourself.

There are only two ways I know of to ensure safe pressures: one is to get yourself a pressure testing set-up, which runs about 100 grand. The other is to get a chronograph, fire a variety of factory loads through the gun to establish average velocity in your gun, and then work your way up to that velocity within the framework of suggested loads in major loading manuals. The hot-rodders will soundly poo-poo such a pedestrian approach, of course, but there you go.

 

[deepseabob]

Does anyone have comments on this problem? I was shooting handloads for 44 magnum, no visible over pressure signs, the spent cartridges ejected without sticking, but of the fifty rounds I discharged three cases separated perpendicular to the wall. The edges appear torn but square to the rim. The point of separation appears to be about midline of the powder compartment and all three separated in the same place relative to the rim. Do you think this is a pressure problem or a problem with the gun. The gun is new Henry's big boy rifle. I was also shooting a Contender super 14 that day, but only the Henry's rifle had the problem. The chamber also appears smooth without a notable area that could contribute to this problem. So what do you guys think?

 

[noylj]

SAAMI is strictly for the manufacturers and does not pertain to us directly. There are very few real signs of over-pressure until you are already deep in the heart of KaBoom land.
One of the first indications in the real world is if you suddenly notice a sharp increase in recoil or if it feels worse than factory loads. Most people find their "happy spot" well before max load and never work up into that range.

 

[noylj]

DeepSeaBob:
Sounds like a headspace issue. Contact the manufacturer or a good gunsmith.

 

[Grumulkin]

Does anyone have comments on this problem? I was shooting handloads for 44 magnum, no visible over pressure signs, the spent cartridges ejected without sticking, but of the fifty rounds I discharged three cases separated perpendicular to the wall. The edges appear torn but square to the rim. The point of separation appears to be about midline of the powder compartment and all three separated in the same place relative to the rim. Do you think this is a pressure problem or a problem with the gun. The gun is new Henry's big boy rifle. I was also shooting a Contender super 14 that day, but only the Henry's rifle had the problem. The chamber also appears smooth without a notable area that could contribute to this problem. So what do you guys think?

First of all, it's not a headspace problem.

Generally, one thinks of head separation which it sounds like you had, more in the domain of bottle necked cartridges and that is the most common scenario. It can also happen, however with straight walled cartridges.

When a cartridge is fired, the case expands to fit the chamber/cylinder. When it's resized, the brass is squeezed in and has to go somewhere. That somewhere isn't going to be toward the case head where the brass is the thickest but toward the mouth of the case. With multiple firings, there is thinning in the brass above the web. If the chamber/cylinder the cartridge is fired in is larger than it should be, the case has to be resized more and this problem will occur sooner.

I've never had this problem with 44 Magnum cases but have with 460 S&W Magnum high pressure loads.

 

[deepseabob]

Grumulkin:
Thanks for your input. I noticed this is happening with the same lot of cartridges I have cycled a few times. Your explanation of case wall thining would be congruent with what I see in the damaged cartridges. All three separated approximately 13.25mm from the rim of the cartridge. I will be running some tests with factory loads for comparison and I have some expert reloaders in my area to help with this problem. In the years I have reloaded I have never had problems of this nature. Thank You again.

 

[buck460XVR]

Does anyone have comments on this problem? I was shooting handloads for 44 magnum, no visible over pressure signs, the spent cartridges ejected without sticking, but of the fifty rounds I discharged three cases separated perpendicular to the wall. The edges appear torn but square to the rim. The point of separation appears to be about midline of the powder compartment and all three separated in the same place relative to the rim. Do you think this is a pressure problem or a problem with the gun. The gun is new Henry's big boy rifle. I was also shooting a Contender super 14 that day, but only the Henry's rifle had the problem. So what do you guys think?

Lever action rifles lock up at the rear and the action can "spring backwards" when shooting. In pistol calibers when shooting max or near max loads, this allows the case to stretch.......similar to excess headspace. This is why many reloading manuals recommend using only virgin or once fired brass for max or near max loads in pistol caliber lever actions.

 

[Eagle103]

My 14 year old son, who I regularly reload with, had one of his teachers tell him he works up loads by the 1/2 grain until the primer starts to "mushroom" and then backs it off 1/2 grain. No books needed. I **** you not! He also claims to have shot deer with a pistol of some sort but considers a .243 "inhumane". Some good laughs for sure!
As far as reliable pressure signs for those of us without a pressure guage I go by the chronometer telling me it's going faster than it should and better yet, primer pockets loosening after 2 or 3 reloads. IMO anyone who tells you they can visually see pressure signs is either a) lying, or b) misinformed.

 

[ranger335v]

Primer flattening is perhaps the least reliable "pressure" sign available but writters often resort to it, I suspect becasue it's 'conventional' wisdom and the other signs are too difficult to expain. Or they simply don't know much.

Problem with handgun reloads is, as has been stated, we are usually WAY over pressure before most common signs appear.

Solution for handguns is, stick with book data. We paid for it and they probably know what they were doing.

Handgun pressures are much more predictable/repeatable than rifle pressures, partly becasue of the very low expansion ratios of straight wall cases. And, considering the lousy ballistic qualities of handgun bullets, there is precious little benefit in hot-rodding the ammo anyway.

 

[deepseabob]

buck460XVR:
Thanks for your input. I was shooting Speer 240gr JHP with 23.0gr of Win 296 powder. The book range is 22.0gr to 24.0gr for both rifle and pistol loads. I measure every load and monitor scale calibration throughout the process. I fill and seat in one step so innacurate measures are minnimized. I wouldn't have considered this max or near max loads for this cartridge. Your explanation for lever action rifles is interesting and may be contributing to this problem.

 

[Grumulkin]

In regards to chronographs, be it known that they give only an indirect indication of pressure. I have never nor will I probably ever use one as a pressure indicator. The velocities obtained can differ because of multiple variables such as barrel length and, as pressures increase, the velocities can actually decrease.

On another forum, a gunsmith posted velocity results obtained with identical rifles and loads (at least 10 rifles as I recall) and the velocities between the rifles varied up to almost 200 fps.

I would take issue with primer flattening being the "least reliable" pressure sign. I believe the biggest mistake is using it as the most important pressure sign or even the only pressure sign and assuming the primers are going to look the same with a given pressure in any firearm they're shot in. You need to know the pressure signs for YOUR gun and use them all without necessarily making one more important than another.

Just some examples:

1. Thompson/Center Contender - primers don't help me but I know to stop and back down when the action becomes at all difficult to open.

2. Thompson/Center Encore - slightly sticky extraction is OK but primer cupping and flattening is a good indicator of approaching maximum pressure. Most useful sign in this gun is groups opening up after initially tightening with load increase.

3. Freedom Arms Model 83 - difficult ejection indicates maximum pressure. This is a very strong gun built to take 65,000 psi.

4. SKS 7.62X39 - primers of no help. As pressure increases, scuff marks appear on the body of the case and ejected cases rather than being thrown to the right in more or less the same spot, start being ejected more randomly and sometimes are ejected to the left.

5. Weatherby Mark V 378 Weatherby Magnum - primer flattening is a useful sign as is groups opening up. In fact, this is the way it is with most bolt actions I've shot.

6. Ruger Vaquero - DON'T go there. Don't load higher than a manual says because you could very well blow the gun up before any signs of high pressure appear.