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signs of overpressure
joshmb1982
Member Posts: 8,228 ✭✭
what are the barious signs of overpressure? the only one i know of for sure is flattened or blown out primers. are there any others?
Comments
If your gunsmith has to unscrew the barrel before he can open the bolt, you were way over pressure.
If your primer pockets get noticably looser after 5 reloads, your pushing the limit of your brass.
If your casehead is "soot" covered, your over pressure (see photo 1)
Considering that the only way to judge pressure via primer flatening requires the use of convex primers, and that they haven't made those in some 50 years...........
Primers make lousy indicators, as they are a symptom of many things other than pressure.
Mid level, book max and over pressure (from the above case)
Note that while the one has slight cratering, it's not pierced
Pierced primers are more commonly a gun problem, and cratering can also be a gun problem
Lacking actual measurement, book loads are the most reliable guidelines. However, if you do see any of the traditional signs as you work up, take it as at least a possible sign of pressure. Stopping too soon is far safer than not stopping.
While I do not recommend jumping leaps and bounds over book loads, I do exceed them carefully, on a regular basis. But not always. I load for the 25 WSSM and a .300 WSM that won't make max. My 6.5 Grendel was close that way when I had it. You always work up in your rifle. Some rifles have long throats and you can get away with loading them hot. Others don't, and you can't.
So, my signs for high pressure are:
#1 The primer:
a) Is it flattened around the edges? If it wasn't like that when you pressed the primer in it means it had excessive pressure when firing.
b) The firing pin indent. If it's just a dent or odd shape compared to the firing pin hole then it's good. If you see a rim around it, it's getting hot. If you see the rim sticking up a ways it's too hot. If it gets 'swiped' when extracting it's way too hot. The would be the top of the crater rim shiny and maybe pushed off to one side. The next thing after this is a sooty or blown primer.
#2 The case:
a) The bottom of the body got sharper in angle compared to new cases.
b) The heat discoloration shows all the way down to the bottom of the body. Light for hotter and dark for not as/unaffected. Normally that line runs at about the top of the web.
#3 The neck:
a) Cracks in the surface of the neck after one or two firings (this might be brass quality as well)
b) Burnholes or what looks like a crack or split.
c) premature thinness. (this may be due also to chamber and die dimensions)
That smoked primer came from using a calculated (not tested) set of load data for a mildly improved cartridge. Later, when I had some "book" data available to me I found that the calculated "start load" was some 7gr over book max for the parent case (Max for that 'cat is actually only 1-2gr higher than the parent case). That's the first (and hopefully last) primer that I've smoked in 35 years of reloading.
I usually load in 1 gr increments. At the first sign on pressure(stiff bolt, flattened primers, case head expansion) I then back off .5 gr and try again. If I still have not gotten satisfactory accuracy, I go to another powder.
Duck Head brings up a good point. Even though the round could take more, the gun, specifically the way it works, may not. He gave a good example of a low pressure gun/round but here's some high pressure guns: Savage 99, Swiss K-31, AR-15/10. The best example I can give in the Savage 99 is a .243 or .308 which can be loaded to 60k psi. Even though it's a lever-gun there isn't much in the way of leverage. A tight case to extract in one of them is difficult. I've run into a little bit of that with my 1899 in .250-3000 as well. Just best to stay down where the round works the best. The K-31 works on the same principle as the AR-15, except it's manually operated instead of gas operated. A bolt in a bolt carrier with a cam. That doesn't give much in the way of leverage when you have a tight case. Besides, the K-31 doesn't shoot hot loads nearly as accurate as standard power loads. The AR mostly shows a problem when you try to re-chamber rounds. But I have had a few hot rounds stick in the chamber after firing. That was an upper chambered for 6.5 Grendel. Not bad mind you, but enough to remind me it's not like a bolt action where you slap the handle hard and it comes open. With an AR you have to pull down on the charging handle and give the butt a firm thump on something. Speaking of which it also reminds you how 'not tough' those rifles are.
Anyhow, I agree for the most part with Tailgunner in that accuracy is really the key in reloading. The bullet is going fast enough. If it isn't going fast enough it's a matter of a small elevation change to get it to the target. Adding 100 fps isn't going to make or break the amount of energy needed to kill an animal. It won't change very much how the wind is going to affect the bullet while shooting long range. The BC of the bullet is going to be a bigger factor than 100 fps muzzle velocity.
Also, to clarify what I load above the manuals. Those are mostly Mauser cases like the .257, 7x57 and 8mm. The data on those has traditionally been low. Fortunately, some books give pressure data on their max loads and it's usually way below SAAMI pressure limits. Even though 6mm Rem is a Mauser case I usually find it loaded like a hot-rod in the books. So, I don't go over published max's with it. This too is a case where you consider the gun. If you had a 1903 in the "bad" serial number range or a Spanish 1916 rebuilt into one of these chambers I would hesitate to go hot with it. If you had a brand new 700 or Savage 10, I would take the case to where it shot best even though it's over what the last book showed.
The ONLY absolutely safe and effective way to set load increments is by percentage. From the book max load, subtract 10% to get your Start load. Assuming that is safe, work upwards in 2% load increments. That will give you five loads between Start and Max. (You may round the increment off a bit to get one that's is easier to weigh.)
Once you find the most accurate load of the five, test two other loads 1% either side of the promising one.
Example: Book max is 50 grains. Start load is 90% of that, or 45 grains. The load increment is 2% of 50, or 1 grain. Your test series will be 45, 46, 47, 48 and 49 grains. (Possibly, but rarely, you might get all the way to 50.) If the most promising load came at 48 grains, try two more at 47.5 and 48.5 grains. Done.
Josh, as pointed out, case capacity makes an arbitrary load increment either dangerous or wasteful. A half grain in a Hornet or Fireball can take you from safe to "Boy Howdy", whereas a half grain in a 30-378 won't even be noticed.
The ONLY absolutely safe and effective way to set load increments is by percentage. From the book max load, subtract 10% to get your Start load. Assuming that is safe, work upwards in 2% load increments. That will give you five loads between Start and Max. (You may round the increment off a bit to get one that's is easier to weigh.)
Once you find the most accurate load of the five, test two other loads 1% either side of the promising one.
Example: Book max is 50 grains. Start load is 90% of that, or 45 grains. The load increment is 2% of 50, or 1 grain. Your test series will be 45, 46, 47, 48 and 49 grains. (Possibly, but rarely, you might get all the way to 50.) If the most promising load came at 48 grains, try two more at 47.5 and 48.5 grains. Done.
+1 Rocky,
Thats the way I do it.
unless you are using a strain guage to measure pressure, velocity is the second best determining method. If you are getting velocities that are much higher than book max, you are over pressure, even if NO signs are present. Pressure signs don't start to show until low-to-mid 70K psi, which is already much too high.
which raises another possibly stupid question from me. why is it that in say the 30-06. you use 48gr of x powder and gives you 51,000psi in max load. and then max load for y powder is 47 grains and 49,00psi. whyy doesnt the book bring them up to closer to the same pressure for each max load? does the faster build of pressure from a faster burning powder creat more of a shock in the chamber that may damage it?
The closer to SAAMI MAP (max average pressure) they show, the more consistant that powder burned in that bullet/case/powder/primer combo
Numbers for example only If MAP = 60K and MIP (max indivudal pressure) is 61K
Powder XX at 50ksi with +/- 10k spikes could hit 61K often
Powder YY at 55ksi with +/- 5k spikes would hit 61K once in a while
Powder ZZ at 58ksi with +/- 2k spikes would hit 61K only rarely
Usually the most accuate loads are somewhat below maximum.
"Better to hit your target at slightly less velocity than miss with slightly more velocity".
Also seems to me these guys are missing a great opportunity. If your .308 isn't powerfull enough don't try to make a 30/06 out of it by cramming in more powder. This is your excuse to buy another gun.
Go buy a 30/06 or maybe 300 Winchester!