Pressure Signs

[hardworker]

So I loaded up some jacketed 158gr 357, I used 14.1 gr of 2400 at 1.590''. I noticed one primer appeared flat, but I also noticed that this seemed significantly hotter than factory 357. I know that sticky extraction is an indicator of high pressure, but like an idiot, I fired some 38 first through my gun so that may have accounted for any toughness getting the 357 shells out.

Is there anything else I should look for?

[L_Killkenny]

IMO primers a poor indicator of excessive pressure. I see far too many primers flattened with even moderate loads to think much of it. I look to extraction first, case head second, primers last. Now you seem to indicate some extraction problems and are writing it off. Don't! Clean the gun a maybe try a couple more. Sticky cases = bad. Even my heavy loads almost fall outta my Ruger.

[Unclenick]

I keep a general list of pressure signs here. Revolvers sometimes don't show primer signs before sticky extraction.

[Magnum Wheel Man]

Thanks for the ist NICK... I added it to my favorites, just to everything in one place

[hardworker]

Shot this same load out of an M28 today and extraction was awful. Is this load considered overly hot? I did not think it was but I think I may bump it back to 13.5 gr. the brass also showed what appeared to be stretch marks.

[TimSr]

I've never had .38s cause sticky extraction, and I shoot them a lot. Sometimes the crap they leave in there make it a little gummy when putting the first .357s in, but after you shoot them they should extract easily, even if you shoot dirty .38s.

[Unclenick]

The reason sticky extraction is a revolver pressure sign is that steel is more elastic than brass. That means steel can return to shape from a larger amount of stretch than brass can. During firing, the steel chamber and brass case expand together, but if the pressure is high enough they will expand past the point the brass can fully return to shape. That makes the brass too wide to fit in the unpressurized chamber, so when the steel snaps back to size, it squeezes the brass. That squeeze is what makes extraction sticky when pressure is too high.

The general rule of thumb is to work up a load toward a published maximum in small steps (2% per step; see last paragraph), but back the charge weight down 5% if you experience sticky extraction at any point along the way and limit your charge weight to that.


Hardworker,

Your posted load is lower than the load Alliant posts for the 158 grain Speer Gold Dot seated to 1.575". However, you need to be aware that changing component brands can change pressure. If you use a different brand of bullet or primer or case, the pressure can change. This is due to differences in the lengths of the bullets occupying different amounts of powder space when seated, or due to bullets being harder or softer than the listed load was developed with, as well as due to different brand case capacity and primer vivacity.

Lead bullets, despite being softer than typical jacketed bullets, have been known to exhibit higher pressure with a revolver load than their same-weight counterparts. This was reported by Keith and Skelton, among others. It's possibly because these bullets are soft enough to be upset out into the forcing cone of a revolver, effectively making the back end of the bullet wider. But that's speculation on my part, and not the result of a careful analysis.

There are other causes of high pressure and sticky extraction. One you don't have results from light loads which expand the brass poorly and allow powder grains to blow back in around the cases, jamming inbetween the brass and steel. This is mainly observed with small charges of slower fine grain spherical propellants.

One other cause you might have, since you fired .38 Special loads in the gun prior to firing the magnum loads and if those were lead bullets, is lead build-up in a ring in front of the chamber throat that acts as a collar around the longer .357 cases, causing them to be unable to expand to release the bullet normally. But you usually feel at least slight resistance over about the last 1/8" of inserting the .357 case when this is the problem. If it's severe enough, you can't get the .357's all the way in at all. If the .357's fell into the chambers easily, though, it is not likely to be the problem. It certainly won't hurt to clean the cylinder well, either way. Search this forum and the gunsmithing forum for past threads on removing lead. There are several good methods.

Bottom line here is that you work loads up incrementally and watch for pressure signs and back off the load 5% if one appears. Alliant lists 14.8 grains of 2400 with the 158 grain Gold Dot bullet, but you can't count on that to apply if you used a different case, different primer, or different bullet.

Accurate recommends a starting load for a workup should be 10% below listed maximum for rifles and 15% below listed maximum for handgun cartridges. I think, given the wide range of guns in various condition, that's not a bad rule to follow (except where a powder maker lists a not-to-be reduced minimum, as is the case with 296/H110). 85% of 14.8 grains is 12.6 grains, so that would be the starting load I would recommend.

Richard Lee's rule of thumb is to work up in 2% steps while watching for pressure signs. (Many use smaller steps when searching for rifle accuracy loads, where 1% is about as big as you want the steps to be.) I would add that unless you've had the chambers reamed to uniform maximum (a standard revolver accurizing practice) the pressure may not be exactly the same in each chamber, so I would run six rounds at each load level, just to be sure. Clean the gun and don't shoot anything else in it until the load workup is done.

[buck460XVR]

IMO primers a poor indicator of excessive pressure. I see far too many primers flattened with even moderate loads to think much of it. I look to extraction first, case head second, primers last. Now you seem to indicate some extraction problems and are writing it off. Don't! Clean the gun a maybe try a couple more. Sticky cases = bad. Even my heavy loads almost fall outta my Ruger.

^^^ same here. Depending on the primer, when shooting legitimate magnum loads, flattened primers are not a reliable sign of overpressure. Sticky extraction with clean cylinders is tho.....IMHO. Even if the same loads fall outta the chambers of another revolver. Again, why we always start low and work our way up in all the firearms the loads will be used in.


I see your loads are middle of the road in my recipes and your statement of more recoil than factory loads and hard extraction makes me wonder if your powder charge may be heavier than thought. Did your weigh charges or throw them? Anytime I get high pressure signs in low to middle of the road charges when factory loads shoot fine outta the same firearm, I suspect an error in powder charge. Not hard to do....maybe why I'm so anal about double and triple checking and why I use a digital scale to double check my beam.

[243winxb]

Other posts I have read say a magnum primer will produce higher pressure than a standard primer of the same brand. I do not know if its true or not? My max is 13.0 -2400 for 158gr+ cast lswc. This load works with any case or primer I have tried over many years.

[buck460XVR]

Other posts I have read say a magnum primer will produce higher pressure than a standard primer of the same brand. I do not know if its true or not?

When it comes to 2400, many sources advise against using magnum primers with 2400 because of pressure spikes. Handloader Magazine had a good article on this a while back.

[SL1]

Hardworker,

If you really want help with this load, then you need to give us a lot more information about it. We need to know what bullet: jacketed, plated, swagedlead or cast lead, including the manufacturer or mold number. We need to know what primer brand and number. It would also help to know whether the bottle of 2400 powder says "Alliant" or "Hercules" on it.

It would also help some to know what gun you fired them in when you got the results you are suspecting to be pressure signs.

SL1

[Unclenick]

He said in post #5 was a model 28 revolver. But as you say about all the other info—and I'll toss in a measurement of the length of his bullets with his caliper—would indeed be helpful.

[Slamfire]

The reason sticky extraction is a revolver pressure sign is that steel is more elastic than brass. That means steel can return to shape from a larger amount of stretch than brass can. During firing, the steel chamber and brass case expand together, but if the pressure is high enough they will expand past the point the brass can fully return to shape.

Don't you really mean that the yield or elastic modulus of steel is higher than brass?

Overall, your analysis is correct.

[Unclenick]

Yes to the yield, no to the modulus. I said "more elastic" meaning steel can stretch further without failing to return to shape (i.e., its yield point is higher) and not that it is easier to stretch (i.e., its higher modulus and greater thickness make it harder to stretch). I was just avoiding the engineering terminology for those unfamiliar with it.

[hardworker]

The bottle says alliant. I am using CCI small pistol primers and applying a light crimp at 1.600". Bullets are 158gr speer jhp.

I think it might have something to do with this revolver. The gun was rusted pretty badly. Previous owner put it in a rust tank and got the rust off, but there is pitting everywhere including the inside of the cylinder. I am gonna take some of the copper chore boy pads and clean the cylinders really well and try it again next time I have a chance.

As to my measuring with powder, I am using the lee beam scale that comes with the press. It's finicky to say the least, but I wouldn't expect more than a 10th in either direction as far as error.

EDIT

Here is a picture of a couple of the shells after firing. It was only a few of the cylinders that really hung up, but like an idiot I didn't mark which one to keep track. I'll do it next time.

[SL1]

Hardworker,

I got the impression from your second post (#5 in this thread), that you fired the subject loads in a SECOND revolver, which is a Model 28.

Can you clear-up whether they have behaved the same way in 2 revolvers, or if they have all been shot in the rusted M28.

From your photo of the two fired cases, all I can say is that the part of the cases that expanded to fill the chambers appears very rough. But, the cases are dirty, and that may make them look unusually rough in a photograph when they really are not. Another picture of the case after they have been wiped clean might help. A picture showing the primers would also be interesting, now that we know the brand. A lot of us have shot 2400 in various brands of .357 Magnum cases with CCI-500 primers over the last few decades.

You wrote that the bullets are Speer JHP. Because Speer has made different versions of their 158 grain JHPs over the years, it would also be helpful to know if they were the old cup-and-core type (with a little lead exposed around the outside of the hollow point) or the more recent thickly plated versions (variously called "Unicore," "Gold Dot," and "Deep Curl").

SL1

[hardworker]

I have shot this load in a 19 and a 28. They stuck in both, worse in the 28. Both times I had fired some 38 before. I am going to clean the 28 before the next time to rule out 38 fouling of th cylinder. Do not have a picture of the primer here at work but some were flattened.

[SL1]

13.5 grains of 2400 is below the start load for Speer 158 grain bullets in all of the manuals that I have.

There are a lot of possibilities, such as wrong powder in the container, wrong scale setting, etc. that are hard for us to check from here on the Internet.

It would be helpful if you could fire some factory .357 Magnum loads with 158 bullets from one of your guns after you clean it and before you fire the handloads again. Then, we could compare cases to see if the handloads are indeed showing different signs. (Of course, with factory ammo availability at about zero right now, I understand that this might not be practical.)

SL1

[Unclenick]

SL1,

I think maybe his cases are mirroring the surface rust pitting inside the chambers.


Hardworker,

Do you have a set of check weights for your scale? If not, do you know anyone else who reloads? If so, have them trim a length of wire for you until it weighs 13.5 grains on their scale, then put it on your scale to make sure they agree.

To verify the primer, it is a CCI 500 and not a CCI 550, correct?

Assuming the CCI 500 primer, QuickLOAD gives me anywhere from below to right at to above SAAMI MAP with 13.5 grains of 2400, depending on which bullet length I use, 0.630", 0.640", or 0.680", for the JSP #4217, JHP #4211, or the HP GD #4215, respectively, all seated to 1.600". It's interesting to note that is long for the crimp cannelure, because Speer uses 1.570" COL for the first two, and 1.575" COL for the last one. And yet their starting load is 13.8 grains. Makes me wonder if they had a can of 2400 on the slow side of average, since both your experience and QuickLOAD think the pressure from the Speer data would be high.

If the cylinder cleaning doesn't work out (if you are using the Chore Boy, put some penetrating oil in the night before to help loosen the lead; Kroil or PB Blaster work). If the 28 is pitted as badly inside the chambers as the brass looks, I'd be surprised if lead didn't try to stick to it. In fact, I'll be surprised if copper doesn't try to stick to it, too. You may need a copper removing cleaner in the end, as well. The gun may be a good candidate for firelapping to mitigate the roughness, but that's a topic for another thread (or you can search for one on the subject that's already here).

[jepp2]

hardworker,

Just a little input. As you develop more experience and get to know your firearms more, you will learn how they tell you overpressure more accurately. I can tell on my revolvers if I am approaching the maximum pressure by many signs, the least of which is primer condition. For rifles I find bolt lift, case headspace length , and case appearance including the condition of the fired primer to be most telling. For my revolvers I mostly rely on extraction and the bulge at the base of the case. For pistols I use ejection patter to tell me the most. Second would be the impressions on the outside of the case wall from the cylinder.

These are all somewhat non-descriptive but very telling to me. So I can quickly tell if something changes that indicates pressure. But for you firearms they may be significantly different. But I do know that primers are the least accurate of all my indications of pressure. Take your time and learn your signs for what you shoot.

[hardworker]

Yeah I know not to trust primers. I've seen a bunch of flat primers on factory ammo as well as 38 reloads of mine. So far my biggest indication of the pressure has been the satisfying kaboom I hear echoing off in the distance when I touch one of these off. Maybe I'm just used to factory stuff.

As far as starting loads, every source you check is different. For 357, it is significantly different. I figured that 14 gr was a starting load.

[SL1]

Unclenick,

From the pictures, I too am suspecting the cartridge cases are showing imprints of rough chamber walls. But, the pictures are not clear on that with the dirt on the cases. Another possibility is that the pictured roughness is really just powder residue from a LIGHT load. That is why I asked him to wipe off the cases and send us another picture.

The pictures also show a significant angle between the expanded part of the case and the smooth part of the case on the right. But, from the photo provided, it is hard for me to tell if that angle is due to an over-expanded case due to high pressure in a large chamber or the opposite, from a carbide sizer ring reducing the case diameter a lot near the head and a light load not expanding it very much. The shadowing makes it hard to resolve the perspective.

As for QuickLOAD pressure estimates, they are not so good for revolver rounds. Velocity and pressure are often over-predicted with measured case capacities as well as the default capacities in the program (as you already know). That is why I rely more on pressure-tested data in manuals for the revolver cartridges. But, with .357 Magnum, there is a substantial difference between old CUP data and more recent psi data. And, apparently the factory ammo is likewise not as powerful as it was a couple of decades ago (except "Buffalo Bore" and "Grizzly" ammo). So, even seeing how his guns perform with factory ammo will be somewhat ambiguous unless we know exactly what ammo.

SL1

[hardworker]

Here are those two pieces cleaned up.

The factory ammo I was comparing it to was 158gr jsp federal 357

[SL1]

The roughness on the cases seems similar to what I sometimes see when cases are fired in very dirty chambers. When that happens, the small spots in the photo would be dents going into the case. But, it is also possible that what look like dents in the photo may actually be raised spots where the case metal was forced into pits in the cylinder wall. So, it would help if you told us if there are small raised spots or small dents.

What does strike me about those photos is the apparent angle in the case on the left. It appears that the case is square to the head up to the point where the roughness begins, then abruptly angles off to the right in the photo. But, the case does not seem to be over-expanded in the rough section. Comments from others?

SL1

[wncchester]

"The reason sticky extraction is a revolver pressure sign is that steel is more elastic than brass. That means steel can return to shape from a larger amount of stretch than brass can. During firing, the steel chamber and brass case expand together, but if the pressure is high enough they will expand past the point the brass can fully return to shape. That makes the brass too wide to fit in the unpressurized chamber, so when the steel snaps back to size, it squeezes the brass. That squeeze is what makes extraction sticky when pressure is too high."

Nick, I copied that because it's worth restating. In nearly 50 years of reloading, reading hundreds of magazine articles and many books on reloading you have given the FIRST accurate description of what makes for sticky cases I've ever seen. And anyone looking for 'pressure signs' on primers, especially for handguns, had better be paying attention to sticking because that tells more than any other single factor I know of. Sticky says, "Heads up, you're on the ragged edge kiddo!"