Maxing out on .357 mag velocities...is this normal?

[Hoppy]

I decided to try my hand at loading up some heavy magnum loads with W296 and 158gr hard cast coated bullets. The reloading data for H100/W296 is all over the place. I decided to use 15.0gr as my starting load, and work my way up to 16.7 (Hodgsons listed max). I even loaded up a few 17.0 and 17.2 gr loads to shoot if I didn't see any pressure signs with the 16.7.

I bought some 296 recently and loaded up about 25 test rounds. I have yet to get them to the range. I loaded 158 grain LSWC. I powder coat with the dry tumble method. When I was looking up data it all pointed me to max at about 14.5 with lead. 16.7 is max for the XTP bullet if you go to Winchester's load data website. I cross referenced with handloads.com website and winchester listed lead max at 14.5. I think I worked up in increments to 14.3. Can't remember what the data was from my Lyman book off hand.

I'm curious how mine will do now. I have a Vaquero and SP101, as well as an 1894cs. I want a good load for all of them. I'm hoping for good results with the powder coated version. If not, I'll get a mold for a gas check bullet in the 170-180 grain range.

Thanks for posting results on your 357/296 loads

 

[SHR970]

The OP does not mention any of the usual signs of high pressure (difficult extraction, flattened primers, case head expansion, etc.) so what empirical evidence are you using to determine he's in dangerous territory?

Velocity flattening out IS a pressure sign. Fortunately the OP is using a forgiving powder, not something a bit more spikey like Blue Dot. Reading "pressure signs" is slightly more scientific than reading tea leaves. Where Federal SPM primers are flattening, CCI's SP are not. In many handgun cartridges, if you rely on those "classic signs" you are so far above max that you are well past proof territory.

 

[ShootistPRS]

When you hit a velocity plateau, what is happening is the powder is burning faster, generating a shorter but higher pressure pulse. Luckily H110 and WW 296 have a slow pressure rise and it is not instantly destructive. It is still a signal to back the load down because higher temps or letting a round sit in a hot gun can cause the pressure to jump faster.

To re-purpose and old adage:
There are bold loaders and there are old loaders but there are darn few old bold loaders.

 

[44 AMP]

In many handgun cartridges, if you rely on those "classic signs" you are so far above max that you are well past proof territory.

PERHAPS

And, perhaps not.

There are two things to look at here, one is the paper limits (published standards), and the other is what happens in the real world with all the different factors thrown in. The biggest of which is the specific individual gun & load.

Reading "pressure signs" is slightly more scientific than reading tea leaves.

Agree. But that "slightly" part can be a usable tool.

Not in the sense that "this sign = that pressure" in psi, cup, or whatever units you use, but usable in the sense that they show you what is going on, and not going on in your gun, with your components.

Published load data works as a guideline because the results you get with your gun and load components is generally very similar to what they tested.

But very similar is not identical, and individual guns sometimes can and do show results at both ends of the curve.

I do fully agree that when velocity flattens out, you are done with that powder and bullet combination, and the prudent thing to do is to drop back slightly below the point where velocity flattened out.

 

[Unclenick]

The current SAAMI maximum average pressures for the 357 magnum are only 33000 psi they may be slightly over pressure but if you consider that the SAAMI pressures have been dropped first 5000 psi and then another 2000 psi, after S&W petitioned SAAMI because the loads were shaking the side covers off their smaller revolvers, you know that in a gun that can take the pressures (look at the Ruger and Contender loads) you have a considerable margin for higher loads.

Are you telling me the .357 Magnum used to be rated at 52,000 CUP, same as the .308 Winchester and .223 Remington, and a bunch of other cartridges? I don't think so. Not for the skinny edge of a revolver cylinder.

Yep. True. IMO, it's just as well. These days, I'm just fine keeping my loads to current published data; and thus presumably, 33K max. That's plenty of juice for me.

This is just persistent rumor, AFAIK. The 45,000 CUP MAP is still in the SAAMI standard, unchanged from after Elmer Keith loaded to sticky extraction, reduced 5%, and the resulting loads were put through copper crusher testing.

When I noticed this claimed drop in pressures was being repeated with authority in forum posts a decade ago, I decided to go to an actual authority to inquire. I called then SAAMI technical director, Ken Greene, and asked about it. He said the illusion is created by the fact the copper crusher rating is 45,000 CUP, while the newer conformal transducer standard is 35,000 psi. The smaller magnitude of the second number makes it appear there's been a change. But he said that is a measurement artifact. That the same reference load that produces a MAP of 45,000 CUP produces a MAP of 35,000 psi in a conformal transducer barrel. We are used to the conformal transducer giving the higher reading at rifle cartridge pressures, further convincing us the pressure was changed, but that in fact the differences are inconsistent, changing both with cartridge diameter and absolute pressure. You just cannot reliably compare the two.

For example, the .223 Rem and .308 Win are both rated at 52,000 CUP. Yet when the conformal pressure transducer is used with reference loads producing a MAP of 52,000 CUP, the .223 reads just 55,000 psi, while the .308 reads 62,000 psi. The CIP channel style transducer reads a max pressure reference load as 62,366 psi for the .223, and reads the .308 as 60,191 psi. Just the opposite of the conformal transducer, the channel transducer puts the smaller cartridge pressure higher. But it's all the same pressure based on the same reference loads shared across borders. The differences are all due to limitations of the measuring systems used and, to a lesser extent, rounding error.

This is why SAAMI has a reference load system. They know that no two copper crushers or transducers will read exactly alike, even within a type. The reference load provides a calibration factor, allowing the operator to adjust for the differences on his system and wind up making cartridges to the same pressure standard anyway, even if the absolute reading on his gear doesn't match.

 

[Road_Clam]

W296 is kinda funny stuff. It doesn't like to be downloaded, and it doesn't yield higher performance when it's overloaded. It just has a sweet spot; and that's where you should run it. A bit oversimplified, but basically, that's how it behaves.

My above-mentioned 158 jacketed W296 load is in that 16.5 neighborhood you just mentioned. Probably a good spot for it.

Load safe.

Agreed. I've generated a lot of velocity testing and i've documented similar findings with ball powders such as H110 and W748. There seems to be a threshold where if you attempt to exceeded you see no gains in velocities and I found that with W748 in 308 I actually saw my velocity #'s decrease.

 

[imq707s]

Thanks for all the info guys. I've decided to go with 16.5 gr of 296 since that's still under published max load data....and I was still getting good velocities.

As far as any pressure signs when I was working up to 17.2 gr, I did have flattened primers.....but I also had flattened primers at my starting load of 15.0 grains. By looking at them, you cannot tell the difference between the primers on the 15.0 loads and 17.2...they both are flattened the same.

None of the loads had sticky brass after firing them....even the 17.2gr loads. I've always heard that flat primers wasn't a very effective way to read pressure in a case.....but if the fired brass started sticking in the cylinder, then you were definitely up into high pressure territory and needed to back off a bit.

 

[Chainsaw.]

Flattened primers is one thing, just part of an equation. Some primers flatten easier than others. Flowing primers is a sure sign of over pressure though. That is an absolute stop sign.

Sounds like you are on a good plan.

 

[Road_Clam]

I also like to keep an eye on cratered primer strikes. My 80 gr service rifle load is with 24.5 gr of Varget and the higher pressure is tough on my primers. I switched to using the CCI #41 5.56 primers.

 

[44 AMP]

I've always heard that flat primers wasn't a very effective way to read pressure in a case.....but if the fired brass started sticking in the cylinder, then you were definitely up into high pressure territory and needed to back off a bit.

This is true. But keep in mind that the "not very effective" way to read pressure from flattened primers is only "not very effective" because of people's (unrealistic) expectations.

Flattened primers tell only one thing with certainty, that there was enough pressure to flatten the primer. They don't tell you what that pressure was, or whether it was above or below accepted operating standards. (and flattened primers CAN happen in either case, or neither, there are other factors involved.)

In some ways, seeing flattened primers is like seeing the road is icy. Doesn't mean you can't safely drive, just means you are outside the "bare and dry pavement" comfort zone.

To continue the comparison, when you get sticky cases, you aren't just driving on an icy road, you are sliding into the other lane, and through stop signs, so, brother, its time to SLOW DOWN...

 

[Ricklin]

Excellent

What a great thread. Esp. the contributions by staff.

THANKS! I learned a lot.