Checking .357 magnum for over pressure

[Guy B. Meredith]

I'll be searching for images of primers showing over pressure, but my question here is about cases being slow or difficult to eject from a revolver.

I put together 25 each 10.8 gr, 11 gr, 11.2 gr and 11.4 gr AA#7 under plated X-treme Bullets 158 gr flat nose bullets. The brass ejected easily from my 686+ and 627 PC at first later they became more difficult.

In my M66 the brass was difficult from the first. I was concerned as I know that I get higher velocities from the M66 and thought the pressure might be in the gray area. I did a wire brush of the chambers and all became good for a while.

I usually shoot .38 spl in the same revolvers and there is little to no degradation in ejecting even over hundreds of rounds.

Am I seeing overpressure indications or just normal increase in ejection resistance due to heating or dirt?

 

[10-96]

How clean are the cylinder holes? Therein builds up a carbon ring from shooting .38's. That's not altogether bad- just requires more work to clean. And from what I recall, after shooting the .38's and then the .357's the pressure will compact that carbon ring even more and can make it look like part of the cylinder.

Now, my 49th Lyman says you're getting 1/10th of a grain away from max. That's pushin it if you don't know what the over-pressure signs are. Not to be a smart alleck, but study up on the front section of several loading books that talk about reloading steps, components, cautions, etc- and get to know the signs of flattened, blown, cratered primers.

Back off and load 6-12 of each batch at a time. You'll be able to tell if that is a good load within that many ctg's. Don't worry about getting to max- speed does not always equal accuracy. BUT sometimes that is where you end up (at max). And, sometimes, you just don't have a happy combo of pistol, brass, primer, powder, bullet, crimp, etc and you have to change one of the variables.

I hope that helps a bit, with what you've written- it's just not that easy to pinpoint your problem with 100% certainty.

 

[Coffeeshop123]

Yep, .38 SPL and .357 Mag, using standard loads for each, are apples and oranges. I've never had a .38 SPL which was difficult to eject, of course never loaded them very hot either. 357 Mag, on the other hand, I've had a few instances, especially max loads or close to max loads, where I've had to beat on the ejector with the heel of my hand. That, or when I've noticed flattened/cratered primers, is where I've backed off. Sometimes it happens where I don't expect it, and like you suggest, other variables such as heat and dirt play a part, especially with hot loads. 10-96 has a great point in that you'll be able to tell very quickly if pressure is too high...Anytime I work up a new load, I do 6 at a time, find a safe pressure range, then within that range I fine-tune the load for accuracy. It takes more time, but I get to shoot more.

 

[Guy B. Meredith]

The primers are flatter than a .38 spl I used for comparison, but I understand a certain amount of flat is expected at normal .357 mag pressures?

Per my 10 year old Spears manual max for jacketed is 11.7 gr at 1140 fps and the 10 year old Lymans's 2nd Edition 12.2 gr at 1125 fps. Knowing that I've chrono'd the 11.2 gr load at 1300 + fps I expect this is too hot. It is the AA#9 that is listed by Lyman at 1330 fps and H110 at 1460.

My intent was to find a load equivalent to either original or current high end commercial .357 magnum specs. It is all about curiosity about whether the plated bullets do well at that pressure and velocity.

 

[Clark]

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

I don't know how many 38 specials I own [mostly Colt and S&W], but I run them all on 357 mag loads.
The ironic thing is that I only own one 357 mag, and I run it on 38 special loads.
That is because it is a Taurus with rough chambers.

When going past the published 357 mag loads in 38 specials, some of the limits I have found are:
1) chamber splits and top strap breaks
2) cases are stuck and have to be pounded out
3) Small Aluminum frame 38 specials can bend the frame
4) primer looks awful.

John Bercovitz wrote this in 1993:

http://groups.google.com/group/rec.guns/browse_frm/thread/68ca10110c80e7aa/f002ce69fa01e631

[I found that 10 years later and recruited him for the "Change the load books about CZ52 vs Tokarev strength" project. He is great guy to work with.]

He in essence says that 357 mag pressures used to be higher, but then they made some 357 mags with thinner chamber walls. That meant stretchier chamber walls. The brass took a set if it stretched too far, and made a sticky case extraction.
So the official max average pressure for 357 mag was reduced.


What does it all mean?
a) As with so many official pressures for strong guns, the max 357 mag pressure is based on the limit of the brass.
b) For advanced handloaders, the trick would be to load until the brass got sticky and then back off a safety margin to prevent sticky cases in an emergency.
c) I can change the length of a 38 special chamber to 357 mag length in a few seconds, but I cannot change the chamber wall thickness to control stretchiness or strength.

 

[.284]

Guy

Plus 1 for the cylinder walls. 10-96 points out a problem that is very common to some one who shoots specials and mags back and forth. There is also a list on this forum of all typical over pressure signs. http://www.shootersforum.com/showthread.htm?t=58763

The list was created by Unclenick and could be very helpfull. Good luck, Jeff.

 

[Clark]

I always have problems with posters who:
1) Think they can divine pressure from primers.
2) Think they can divine pressure from chronographs.
3) Think they can measure pressure with strain gauges [An above link leads to Denton Bramwell].
4) Think that if they knew what the pressure was, that it would be more useful [for individual handloading in a strong gun] than finding the threshold of long brass life.

The trouble with arguing against layers of errors is like saying, "Al Gore's global warming is a scam, and even if you believed in global warming, then his big house and private jet are causing global warming."

And so I say, "You cannot accurately measure pressure with a strain gauge bonded to your tapered and open ended tube, and even if you could, you would be better off finding the threshold of long brass life."

It just doesn't fit in a sound byte with power

 

[WESHOOT2]

try Rainier plated if you insist

I think your loads are over-driving those plated bullets, and your pressure is high.