Excessive pressure?

[Pal Val]

Yesterday I tried a batch of .357 mags with a 6"bbl GP-100. It was a load of 158 gr lead swc's over 13 gr of 2400, Win WSP primers. It was a bit of a stout load, but didn't give me any bad signs, other than not making a group smaller than 5" from 25 yds. Didn't like the accuracy. My usual load of 12.5 grains 2400 makes groups half that size.

Back home, I looked at the shells and found the primers all flattened out. Was 13 grains of 2400 too heavy a load? The manuals all list it under the max.

What else would cause flattened primers? I'm a bit confused.

 

[Rick Courtright]

Didn't like the accuracy. My usual load of 12.5 grains 2400 makes groups half that size.

Hi, Val

Some random thoughts:

A buddy loads quite a bit of 2400, in both .357 and .44 Mags. I don't load it at all, so can only relay what I've seen w/ his loads.

2400 seems to be one of those powders where one's gonna find a "sweet spot" and sometimes the window is pretty narrow. I dunno what he settled on for the .357, but w/ the .44, he's got about a half grain window, w/ the midpoint roughly halfway between a starting load and Alliant's max recommendation.

He's found the same thing w/ accuracy you did: within that "sweet spot" range, his accuracy is good enough for 200m silhouette use, but much variance from it makes it hard for him to keep everything on paper at 50 yds.

Others have reported similar results, so maybe your lighter load is "right there" for your gun/ammo combo?

On the flattened primers, I'm not always sure what to think there. I've had a couple of loads that were obviously high on the pressure curve, judging by extraction difficulties, yet they showed no primer flattening that would be of concern.

OTOH, I've got some .38 Spl loads, max for the "non-+P" charts, that regularly show rather flat primers. I use mostly Winchester primers, which I think are mid-range in the hardness of the cups. IME, Federals are usually at the softer end, CCIs at the harder end, though there are always exceptions.

One explanation I've heard about my .38 Spl experience is that a lower pressure load can sometimes allow the primer to push back into the breech face before the rest of the case moves back to the same place. The effect is it's being "deprimed" by the initial firing, which flattens the primer, then the case "reseats" it.

Dunno if there's an ounce of truth to THAT story. But it's interesting... if only cuz someone had a creative imagination?

Someone here knows more about the subject, I'm sure!

Rick C

 

[Mike Mulligan]

Is it also possible that your load was too hot for the lead bullets you are using- pushing them too fast down the barrel, while only slightly hot for pressure?

 

[Boge]

Flattened primers are no more an indicator that a load is "hot" than high heels indicate a woman is a good lover.

 

[WESHOOT2]

I suggest both upping your charge to 13.5g and lowering it to 12.0g and testing.
If neither shoot accurately try a different bullet.

Don't look at the primers....

 

[mikld]

I've come to believe flatened primers aren't a reliable indicator of high pressure. When a round is fired in a revolver the primer is blown out a bit, then the case slams back into the recoil shield and reseats/flattens the primer. There's a bunch of other things that an cause flattened primers within safe pressure limits.

 

[Pal Val]

The accuracy was subpar, but I got no leading from 50 rounds of that load. I'm trying a .5 gr up, as I already know what 12.5 gr does.

I like this powder. I've used it for my .44 mag quite a bit and it works fine. I was talked into it after making a mess of my gun with Blue Dot. My other choice for heavy loads is H-110, but I got some heavy leading from shooting lead bullets with H-110. I now use it only for jacketed bullets.

 

[Peter M. Eick]

I would have said not enough powder.

13.5 grns of 2400 with a 158 is my lowest charge I would load. I normally do 14.5 grns of 2400 up to 15.3 grns of 2400 with a 158 lasercast.
15.3 grns of 2400 is the lasercast book max load on a 158 SWC.

 

[M'BOGO]

Flattened primers are no more an indicator that a load is "hot" than high heels indicate a woman is a good lover.

Well said

 

[Pal Val]

I loaded small batches with 13.5 gr and 14.0 gr of 2400 and was surprised with the find. There were no flattened primers, and accuracy was best with 14.0 grains. Seems like this GP100 (6"bbl) likes the heavier load. No extraction problems, no leading, and better accuracy than with the lighter loads. I only shot four groups of 5 rounds, so I'll load more and try again. Perhaps it's a personal quirk, but to me it's satisfying to shoot a really stout load and get small groups on the paper.

 

[Jimbo357mag]

The accuracy was subpar, but I got no leading from 50 rounds of that load. I'm trying a .5 gr up, as I already know what 12.5 gr does.

I like this powder. I've used it for my .44 mag quite a bit and it works fine. I was talked into it after making a mess of my gun with Blue Dot. My other choice for heavy loads is H-110, but I got some heavy leading from shooting lead bullets with H-110. I now use it only for jacketed bullets.

Sorry to hear you didn't like Blue Dot. It is one of my favorite powders in the 357mag for both revolver and rifle. But then I shoot copper plated bullets usually about 10% below Max charge and I don't have very much experience with lead. :? :?

...Jimbo

 

[gramps]

158 gr swc over 13.5 grs 2400 is my plinking round for my 3 inch sp101
gramps

 

[Pal Val]

Blue Dot shot OK, actually pretty good for jacketed 158 grainers, but it also left a sticky carbon mess that was a chore to clean. I tried it with lead bullets, but got leading with all but the lightest loads.

Then came the warning not to use it with light bullets in .357 mag. I tried it with jacketed .44 mags and can't complaint. At least, it burns better in the .44 mag and doesn't leave the sticky carbon mess.