How over pressure is over pressure?


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Soybomb
April 29, 2008, 07:15 PM
:D

I'm wanting to learn a little more about working up to max loads. Lets say you make a bunch of loads with charge increasing in .2 increments and take them to the range to test for signs of over pressure. You of course realize that not all rounds need to be fired and signs of excess pressure might mean that any remaining rounds with a larger charge get pulled instead of fired.

All that said, are there any signs of pressure that are considered safe or do you back off immediately upon seeing the smallest indicator? I'm not a user of +P+ rounds but to use those for an example they would be over pressure but considered safe. Would they actually show signs of being over pressure? Is a round that shows pressure say on the brass far above the pressure a +P+ factory round produces?

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rcmodel
April 29, 2008, 07:48 PM
What caliber are we talking about?

What is over-pressure in a standard revolver or auto pistol is often less then a starting load in a center-fire rifle.

rcmodel

ranger335v
April 29, 2008, 07:48 PM
With handguns, you will be far over rational limits before you see any of the over pressure signs common with bolt action rifles. Back way off if you see ANY "pressure" signs at all in a handgun, it means the loads are already well over the max!

A lot of informed research went into our loading manual's data and they give good advice. Even so, sometimes and in some guns the pressures may still be over the line. Hand guns usually give little warning of an impending disaster so staying within book limits is the best policy.

Clark
April 29, 2008, 08:11 PM
Soybomb,
I am slightly retarded [in time], and I will respond to your last post, "Who packs after they have had a few?"

Not me.
I like to have a single 3.2% beer with a sandwich, but I take the gun off and put it away. I pack all the rest of the time.

Soybomb
April 29, 2008, 08:29 PM
Right now I'm looking at 10mm and planning to very slowly and very carefully work up some hot loads.

Back way off if you see ANY "pressure" signs at all in a handgun, it means the loads are already well over the max!
What constitutes way off? Lets say its a handgun round with 12.0 gr and I start to see primers flattening but 11.8 looked fine. Does 11.6 become a safe load? Is this load still likely far over saami max?

Clark I think you might have gotten the wrong thread, you're not drinking without locking up the keyboard are you? ;)

brickeyee
April 29, 2008, 09:22 PM
If you want to work up near te max limits at the very least you need a chronograph.

While it will not tell you what the peak pressure was for a round (velocity is a function of the average pressure as the bullet travels down the barrel) if you have a powder that is otherwise acceptable and your velocity is higher than the loading manual you are most likely over the limit.

The other question to ask yourself is why are you trying to push to the limit?
The gains are rarely worth the possible consequences.

Clark
April 29, 2008, 09:59 PM
http://www.thehighroad.org/showthread.php?t=359554

CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR assume any liability for any damage or injury resulting from use of this information.

With my stock 10mm barrel in a Glock 20, I could not work up to the kind of power I could work up to with a stock 9mm barrel in a Glock 19.

The first pressure sign in a work up in a semi auto pistol is usually a case bulge or pierced primer. In CZ52s it is a split chamber and many other secondary failures.

With aftermarket barrels, the 10mm can pass up the 9mm.

If the 10mm case web is at .180" and the feed ramp intrudes .250", then there is .070" of thin unsupported case wall that wants to blow a brass bubble. If that bubble breaks, you will be sorry.

After market barrels often do not intrude as far.

I wrap the pistol in a towel to catch the empty case in the work up.
I look at each case with magnification before firing the next cartridge in the work up.
In 10mm I work up a .1 gr.
If I see a guppie belly case bulge or a pierced primer I stop the work up and consider as useful loads only ones reduced by a safety factor from that event.

I find I can get the most power from 10mm with 200 gr bullets and 800X, but Power Pistol meters easier and is still pretty good.

Jim Watson
April 29, 2008, 10:49 PM
The old Speer procedure, back before a bullet company would normally have a pressure test rig, was to increase the load until it showed one of several signs of excess pressure... one, not all of them. Then they reduced the load by 6%.

.38 Special
April 30, 2008, 12:14 AM
You can't guess pressure accurately. The only thing pressure signs tell you is that you've got way too much. There's no way to know how much without proper testing equipment. Measurement of case head expansion can render useful information, but you have to know exactly what you're doing and you have to have a reference.

Brickeye alluded to probably the most important piece of equipment the typical handloader can use to determine pressure: the chronograph. As he pointed out, if you are getting significantly higher velocities than the manuals produce, and with the same powders used in those manuals, you can pretty much guarantee that your pressures are too high. There is no free lunch and you cannot get velocity without pressure.

The bottom line, as far as I am concerned, is that you should find the manual that lists the highest velocities for your cartridge and barrel length, and work your way up to that maximum load. That almost guarantees a safe and maximum load. If you are hoping for higher velocities than are listed in any of the manuals, you simply need a different cartridge.

Soybomb
April 30, 2008, 01:18 AM
The other question to ask yourself is why are you trying to push to the limit?
The gains are rarely worth the possible consequences.
No good reason other than my 10mm gun is a gun I just got to have some fun with and I want the most fireworks I can get out of it because thats what guys do ;)

The only thing pressure signs tell you is that you've got way too much.
Thats really what I was wanting to know! I know many people work up loads greater than the max load in a given manual, especially more recent manuals that seem to use a wider safety margin for max loads and was wondering just how over pressure I really am when I start seeing signs of it. It sounds like very significantly over pressure.

Steve C
April 30, 2008, 02:59 AM
One of the major problems with reloading is that pressure vrs powder charge is not a linear function. IE 2 times the powder doesn't usually yield 2x the pressure and dramatic increases in pressure can be had from small increases in charge weight. Load manuals don't simply supply a max load that achieves a max SAAMI pressure. More often than not they list as the maximum load where a subsequent increase starts producing erratic pressure and velocity or where accuracy deteriorates.

As mentioned by Ranger335V, when pressure signs appear you've gone well beyond the maximum allowable. At this point you need to stop and go back to a lighter charge. If maximizing velocity is your goal then the previous charge that showed no pressure signs would be it.

ScratchnDent
April 30, 2008, 03:54 AM
I live by my chrono and percieved recoil for lower pressure handgun cartridges. Not scientific, but if you have much experience with any partiular round, you can feel when it's "hot". That's for .38spl and 45 acp. The only higher pressure round I load is .357 Mag. With those, flattened or flowing primers become pretty obvious.

I went the hot and fast route for the first year or so reloading, then decided, if I really need a better performer, I needed a gun designed for it. Now, I stick to around 80-90% SAAMI specs for economy in powder, and gun life.

hoptob
April 30, 2008, 04:51 AM
The old Speer procedure, back before a bullet company would normally have a pressure test rig, was to increase the load until it showed one of several signs of excess pressure... one, not all of them. Then they reduced the load by 6%.

I believe Jim refers to handloading procedures from Speer #8.
http://s247.photobucket.com/albums/gg160/hoptob/th_Speer8method.jpg (http://i247.photobucket.com/albums/gg160/hoptob/Speer8method.jpg?t=1203282178)
There are many strong opinions on this subject out there. FWIW I find it to be a very useful technique and use it routinely to developed hot loads.

As far as primer deformation goes, I do not believe that it is a reliable sign of excessive pressure. Somebody called it "interpreting goat entails"; I think he was spot on. Extend of deformation depends on the brand of the primer, shape and size of the gap in the firing pin bushing and other factors which are not related to chamber pressure. In fact some of the current full house factory loads show clear primer flowing and cratering. Especially those factory loads that do not have sealed primers.

We had several good discussions about this in S&W forum. Check out this thread (http://smith-wessonforum.com/eve/forums/a/tpc/f/570103904/m/8111099972/p/1) for example if you are interested.

Mike

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