Pressure Signs

[Noveldoc]

I haven't seen this posted recently. Last thread on this I can find was several years ago. All the reloading sites and books say to watch for pressure signs but the newbie may be left wondering what those signs are. So I am going to list how I monitor pressure and ask folks to chime in with their favorite tricks.

The primer is the softest metal in the case so look at it first for over pressure. Think of the primer as the canary in the coal mine. If your primer is rounded, it is not unusual to see a bit of flattering of the center in normal use. But watch for the extreme where the whole primer is flattened or, worse, cratered, and mashed into the sides of the pocket.

Sticky extraction is another early sign. You may get stovepipe jams or cases that do not budge and slip off the extractor in auto pistols and rifles. You should notice a lot of extra work extracting or punching cases out of a revolver or bolt action. You can test this by feeding the extracted case back in the chamber. You should not get more than a little sticking and dragging when you do this, minimal at best.

Much is said about case head swelling but it is hard to detect. Also the case head is not completely supported in pistols like the 1911 so they normally give you some swelling. I do not believe many of us can feel or eyeball the swelling until it is advanced and almost too late. Get a cheap micrometer and measure the cartridge diameter a few millimeters above the base. Do this with every batch and write it down. You will soon find what is normal for your gun and will catch a sudden increase. Note though that some revolvers have oversized chambers and you may see some swelling of the whole case there. A sudden increase there is not good either. I monitor my Ruger Blackhawk by keeping some old cases from full tilt factory loads I fired to compare.

Do you trim your brass? Of course you do. I take at lest a few samples from each lot and trim, watching for increased metal shaved off and thinning of the case mouth. Especially with bottle necked cases, the brass at the tip flows up and thins under excessive pressure.

Finally, inspect for tiny cracks. If you see them pressure is too high or your brass has gotten way too old. I had a guy shooting a classic 30-40 Krag at the range. I picked up a few cases he missed when he left as collectors. Then I saw there were tiny cracks in the body of 2 out of 5 of these old cases. I had our range director call him immediately.

So don't exceed the max load in the manual. Watch for pressure signs and have fun reloading.

Tom

 

[R.W.Dale]

The problem with these traditional indicators is that they're wildly unreliable and may not show up if at all till you're already GROSSLY overpressure. Some guns may never show pressure signs and others may show them at start loads, but not due to pressure but rather due to charistics specific to that chamber.

All you can really do is stay within published data and pay attention to what your chrony is telling ya! But please don't fool yourself by thinking you know what your pressures are from the largely disproven tea leaf readings manuals still tell you to perform

 

[Ret.CWO]

Worn out brass

I don't remember where I read this but I tried it and seems to work. Take a large paperclip and bend it straight. Then put a small approx. 1/36 " L shape bend at one of the ends. Place it inside the case all the way to the bottom. Slowly pull the wire clip out of the case while holding it against the inside wall of the case. If you feel a slight "dip" on the case wall go ahead and throw it in you recycle bin. This is an indicator that the case may be getting ready to come apart in the chamber.

 

[ants]

Reading primers:

270 Win runs at 65,000 psi.
.30-30 runs at 40,000 psi.

Both use the same primers.

So how is the primer supposed to know that it must flatten at 40,000 in the 30-30, but it shouldn't flatten in the 270 Win until 70,000?


Case Head Expansion
According to Hornady, under normal conditions every case head expands about .0001 to .0003 inches each time it is fired. It can expand as much as .0005 inches when overloaded. Most micrometers resolve to 1/100 of an inch. It is extremely difficult to determine case head expansion reliably.




Best way to avoid overpressure: Stick with manufacturer's published load data. Avoid untested data someone on the Internet gave you.

 

[243winxb]

Good reading here. http://www.thehighroad.org/showthread.php?t=375160 More photos here http://www.photobucket.com/joe1944usa

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[Robert Wilson]

Krochus is exactly right. Obvious and gross signs like a completely flattened primer, a bolt or extractor rod that has to be pounded on are definite messages to quit what you're doing. Using pressure signs to "work up a load" the way we did 40+ years ago is a poor practice with today's close tolerance rifles. It's easy to greatly exceed recommended working pressure in a modern rifle with no pressure signs.

243winxb, I'm afraid of any handloading advice that starts with "The maximum loads in the books are printed by lawyers. Do what I say and you'll get the REAL maximum loads."

 

[Noveldoc]

Just to clarify, I don't recommend going above published max charge. At the same time, it is a bad idea IMO to just go straight to pouring max. Imperfect though the signs are, I still think start 10% below max and working up by small increments watching the pressure is good advice. I have fired many pistols and have seen a few that produce disturbing looking cases in carefully loaded rounds below manual max. Yes, watching for the signs helped in these cases.

And watch the factory ammo too. There is some junk out there along with some shot out used weapons. I mentioned the Krag incident. Had a friend who bought a antique Arisaka military rifle. Second trip to the range, the bolt blew out, barely missing his head.

It's easier to go high pressure with modern powders. And besides damage to you, this can create problems with the gun. You can batter your firearm and have much premature wear.

I believe high pressure and velocity can also effect accuracy. It is possible to go so fast you sort of overdrive the rifling and get some wobble in the bullet. I have found going about 75% of max load gives great accuracy when punching paper at the range in my 45s and even in my Garand. A retired military armorer friend told me the name of the game with the military Garand load was not making tiny groups; it was hitting a human trunk sized target with a lot of impact. And my M1 did much better on paper targets when I dropped the charge.

So stay within the manual specs. Not worth risking your gun or your life because your first pressure sign may be catastrophic failure.

Tom

 

[Marlin 45 carbine]

as noveldoc says hot loads are rarely the most accurate loads. sometimes with some cast slugs at the risk of fouling hot loads may be tighter grouping at least in my experience (admittedly limited to only .380acp, 9Makarov, .357mag and .45acp) but hardly worth the effort required in cleaning of the bore.
I have found a good 'hot load' with cast 158gr slugs in .357 but it isn't a load I will gave data for and it's only for hunting back-up for me and nephews.

 

[USSR]

Had a friend who bought a antique Arisaka military rifle. Second trip to the range, the bolt blew out, barely missing his head.

Congratulate your friend, he did something the great gunsmith P.O. Ackley couldn't do. Ackley proved the Jap rifle to be the strongest and safest bolt action military rifle ever made. He actually failed to blow one up. It was the only military rifle he could not blow up. He took a 6.5 Arisaka and bored out the chamber to 30-06 and then touched it off expecting to see a large mushroom cloud in the after math. The barrel was of course ruined and the stock splintered into match sticks but the action held and was in perfect condition.

Don

 

[R.W.Dale]

If it's a 6.5 the odiously the rifle used by PO ackley wasn't a non heat treated "last ditch" type 99, a rifle that SHOULD NEVER be fired with ANY load no matter how mild

I'm reminded of a test that was preformed over on gunboards several years back where some folks tried to blow up a few t99 barreled actions using large quantities of red-dot, The rifles head up to more than you'd ever suspect. But in the end there were some quite spectacular failures

 

[Noveldoc]

All I know is I took John to the ER and had great fun picking the powder specks out of his cheeks and nose. Thank God he did wear eye protection.

I suspect they did make some real crap before the end of the war. We took the rifle back and the dealer gave John full credit on another piece he wanted. He was very sorry and po'd at the distributor. Said he had had another returned when it shot a major gas leak out of the bolt firing just standard ammo.

At this point I want any old piece like that gone over buy a gunsmith.

My Garand I bought from a gun smith who had assembled and tested it. Much safer methinks than buying a true antique.

Tom

 

[R.W.Dale]

This is why old relics such as this get the "tire" or at least the at arms length with safety glasses test on the first shot

 

[Noveldoc]

Ask the folks from the Titanic what happens when you substitute softer high sulfur steel.

From what I have heard quality of both German and Japanese manufacturing went way down as the war went on. Guess all that bombing accomplished something.

Tom