High Pressure/Over Pressure Signs of Brass

S

SEHunter

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Want to ask all the seasoned hand loaders what you look for concerning pressure signs during load development. There are several but what do you tend to see first? Which signs indicate approaching over pressure and what signs absolutely mean STOP. I don't mean a blown up gun, my wife could determine that's over pressure. What I mean is strictly reading the spent brass cases before real trouble happens.

There are chambers that are small and can't handle some published data. This is one of the reasons for this thread. Others are when you have a large chamber and max published loads still may be 3,4,5 grains shy of that rifles perfect load. At this point, it's completely experimental and up to the hand loader to use experience and common sense to be able to be the load developer for that unique firearm. This thread isn't to encourage irresponsibility but to inform and protect.

As for myself, I've loaded some hot rounds in a few modern bolt guns during the development process and I have only encountered mild flattening of primers and a sticky bolt once. No loose pockets or cratered primers. That said, I tend to try to read the primer since it's the first sign I see and what my own experience has shown. What about you all?
 
I maintain a list of pressure signs on another forum: here. Which sign you see first depends on the gun. You can, for example, get sticky extraction in a revolver long before the primer flattens, whereas in a rifle it is generally the other way around, even with hard primers.

Board member Clark is an engineer from a family of firearm engineers and has intentionally blown up a lot of guns as part of his work. PM him and you will learn it is not as easy to do as you might think.

Most people don't seem to understand the SAAMI pressure standards. Not their fault. It's a boring read, even for engineers like myself. The usual number given as a pressure "limit" is the SAAMI MAP (Maximum Average Pressure). But it is not a limit. It is the average of maximum peak pressures from ten rounds randomly sampled when the ammo is freshly made and the bullet has not had time to cold solder or corrosion bond to the neck. The actual maximum would be the proof loads, but you don't want to fire too many of those as they beat the gun up. The maximum for non-proof loads would be 0.9 parts of the SAAMI MEV (Maximum Extreme Variation) of the individual rounds fired in the MAP. This works out to be the MAP plus about 18.35% in the worst case in most instances. The Europeans (CIP) use a flat 15% above MAP as maximum for individual rounds participating in the average. This is all important because it means that if you can produce rounds with less than SAAMI's standard 4% standard deviation in pressure, you can actually load them higher without any individual round exceeding the SAAMI +18.35% or the CIP +15%, as long as you don't mind your gun wearing out sooner.
 
"Others are when you have a large chamber and max published loads still may be 3,4,5 grains shy of that rifles perfect load."

I've got to say that the "size of the chamber" has less to do with a "max load" than the inside of the barrel.
Case in point: I have a Savage .243 that has a very tight chamber(requires a special sizer die) but has no problem with hot loads.
 
Or, as in one case for me, the published max load is over pressure for your rifle.

Always start at the starting published loading, and by that I mean as in actual printed book.
 
Good stuff, UN. That's a great resource, and I'd love to hear some of Clarks stories.

So which of these do you guys find are the most common in your own personal experience?
 
Which signs indicate approaching over pressure and what signs absolutely mean STOP.
Click to expand...

Any signs indicate you are already over pressure, they don't show up when you are approaching over pressure. In fact many loads are over pressure and show no signs of a problem.

The best way for most reloaders to stay out of trouble is to use a chronograph. If the loading manual says 2800 fps is a max load, then when you reach 2800 fps you are at a max load in that gun regardless of the powder charge.

In some cases you may reach that before you reach the max charge weight. In others you may be able to go 1-3 gr over the max charge weight before you reach 2800 fps. That load may be safe in your rifle. But I don't advise going over the max charge weight in case your loads end up in another gun.

I know some folks load over max. But I stop at the max speed or charge weight whichever comes 1st. If accuracy is where I want it to be then I stop. If accuracy is poor then I start working back down or trying other tweaks.
 
I've experienced issues with the chrono and I don't know what the culprit is. I live in middle Georgia and have been loading for about 15 years. I've never, not once came within 100fps of any published velocities with the corresponding charge in any gun even with the same length barrel. Makes me wonder if elevation makes that much difference and if all the major bullet/powder manufacturers test in a different elevation than the average in the south east.

I still use a chronograph but I am always over max published loads before I reach or begin to approach their claimed velocities. Bugs the crap out of me.
 
Chronographing has its pluses and minuses. First, the exact accuracy of the chronograph is impossible to know. Some can go haring off pretty badly in less-than-ideal lighting conditions. I've seen two chronographs disagree by 200 fps out of 2600 in afternoon light. Most folks who are really serious about getting good readings buy the artificial light kits normally meant for indoor use, but then build a box-shaped tube around the chronograph to shade if from the sun and run the artificial lighting inside it.

One way around the above is to avoid optical chronographs altogether and go with the MagnetoSpeed device. Bryan Litz likes their large unit and it will measure speed accurately. My only objections are you can't measure velocity down near the target with it and the weight on the muzzle prevents doing accuracy load work ups with it.

If you think your chronograph is precise enough, there are several reasons you may not get the results the load data has. Load data for which pressure is tested, such as Hodgdon's, is fired from SAAMI standard test barrels. These have chambers held to SAAMI minimum within half a thousandth of an inch. The idea is to make worst case high pressure, which they usually do, but not always for every single gun in creation with that same chambering. Their barrels have specific lengths, usually ±0.010" in rifles, and specific rifling configurations that produce a specified cross-sectional areas and they are high quality custom grade barrels with smooth, lapped bores. If your gun is different from that in any significant way, you may not get the same result. If you don't use the exact same bullet, case, primer and powder, and don't use the same lot numbers, you will seem some variation from that.

And yet, with all that standardization, when a SAAMI member sends a lot of reference loads to a half dozen different test facilities to be tested in a half a dozen different pressure test guns, they still see velocity variation among the facilities. In the rifle standard they have an example of 7 labs testing one lot of .30 Carbine and getting 3.5% variation in average velocity. 3.5% of a medium power rifle with a velocity of about would be about 100 fps out of 2850 fps.

All sorts of things can cause that. SAAMI calls for positioning the powder over the primer for uncompressed loads. Some folks do that better than others. SAAMI calls for conditioning the gun and cartridges within a temperature range, but some may hurry that a little. Denton Bramwell showed that barrel temperature has a big influence on outcomes, and some may have different rates of fire than others. Some may let the cartridge "cook" in the chamber a little longer than others, etcetera, etcetera.

Exact ballistics are a little like sight picture wobble. You accept a range of error in your hold, always working to improve it, but seldom completely getting rid of it. Same with load performance consistency.

As to pressure signs, most of them tell you what your brass and primer are doing. Few tell you what the gun is doing. Among those that do are sticky extraction and velocity increase with powder charge flattening or actually decreasing. These are signs the steel is stretching somewhere.
 
UN, thanks for the detail on the chrono. I've not heard that explanation before and it helps to resist worrying about falling short of published velocity readings.

Based on the research I've done, I still pay attention to the dos' and donts' of using a chrono. I have Shooting Chrony brand and make sure it's completely unfolded and that the lenses are clean. I always use the diffusers if it's sunny and I shield the chrono from the side (not directly overhead) so that a shadow covers it. If it's partly cloudy, I usually plan around that so that the sun peeking in and out doesnt change how it reads. I'll use it with the sun out or overcast but not on a day that it's both at random. I prefer solid cloud cover but funny how my schedule always allows me time to shoot on bright and windy days. :rolleyes:
 
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