Light bullets?

[beag_nut]

I have a question, which S&W has not answered (I asked them). Why does my friend's new S&W 340 PD (.357 Magnum) have a warning engraved into the barrel saying: "No less than 120 gr bullet" ?
I can't figure it out, though I know the revolver has a very lightweight scandium frame. S&W hasn't answered me in more than a week; what are they hiding?

 

[Loosedhorse]

I was told it was a concern about flame-cutting on the frame.

 

[Fishslayer]

Light bullets + slow powder = flame cutting. The bullet clears the CB gap while the powder is still generating high pressure & temp.

Some alloy revolvers actually have a replacable sacrificial steel shield under the top strap.

 

[sixgunner455]

Flame cutting may be a concern, but the greater concern that demonstrated itself when these extra-light revolvers came out was crimp jumping.

In other words, each shot, when full-powered magnum loads are used with light bullets, slightly dislodges the other bullets in the cylinders from their cases, since there isn't enough mass in gun or bullet to really absorb all of the recoil.

By somewhere between the third and fourth shot, the cylinder locks up because the remaining bullet or bullets have stuck out the cylinder mouths.

The phenomenon isn't restricted to ultra light .357 magnums. The most interesting case of it I have read of involved a Ruger Alaskan chambered in a high-intensity, large-bored cartridge. The gentleman carrying it was charged by a large brown bear, exactly the reason he had purchased his revolver. He drew, and shot the bear repeatedly as it charged. The fourth shot finally downed the bruin, nearly at his feet. His relief was short-lived, however, when he realized that he could not open the cylinder to reload: the fifth and final round had jumped its crimp, and completely locked the cylinder.

If that fourth round had not disabled the bear, it would have had him - he could not have fired the last round.

S&W hasn't answered me in more than a week; what are they hiding?

S&W isn't hiding anything: they clearly stated the recommended ammunition for your friend's revolver, and engraved it in the side of the weapon so it could not be forgotten.

I recommend that your friend follow S&W's recommendation on bullet weights with his lightweight revolver.

 

[Owen Sparks]

The only time I have had problems with bullets "walking" is with really heavy bullets. As the pistol recoils backwards their mass and inertia causes them to want to stay at rest as the pistol pulls the cases away from them.

 

[beag_nut]

"S&W isn't hiding anything: they clearly stated the recommended ammunition for your friend's revolver, and engraved it in the side of the weapon so it could not be forgotten.

I recommend that your friend follow S&W's recommendation on bullet weights with his lightweight revolver."

Of course he will follow recommendations; but why won't S&W provide the explanation? What do they think they are hiding? Every warning has a reason, and the reason for this one is not readily apparent, regardless of the other posters, who I think may very well be correct.

 

[MCgunner]

I don't like the light stuff, anyway, personally. I carry 140 JHP, easier on guns and 140 Speer is ACCURATE. Too, I've chronographed various loads out of various barrel lengths. In the short barrels with slow powder, the 125 wasn't as hot as a good +P 9x19 out of a pocket 9. The 140 was able to use more of that pressure peak, performed a LOT better. We're talking 380 ft lbs for 18 grains of 2400 and a 125 vs 550 ft lbs for 17 grains of 2400 and a 140 Speer. This was out of a 2.25" Ruger SP101. Hell, my Kel Tec 9 pushes 410 ft lbs and it's one HECK of a lot easier on the hand and eyes and ears.

You can probably tell, I'm not big on .357 pocket revolvers. I have a 3" belt carry, my smallest .357 now, and it's a Taurus 66, medium frame gun. It's an accurate, powerful revolver, but I mostly pocket carry.

 

[rcmodel]

I don't think S&W is hiding anything.

If your friend had bothered to read his owners manual, he might have noticed on page 12:

CAUTION:
Do not use Magnum loadings with bullet weights of less than 120
grains - This will reduce the possibility of premature erosion in
titanium alloy cylinders.

There is also two paragraphs of instructions in the manual on testing any load you use for bullet pulling due to the terrific recoil these light guns produce.


My own observation:
Light bullets are also short bullets.

There is less of them inside the case to provide enough case neck tension / friction to keep them from moving under recoil.

rc

 

[MCgunner]

There is less of them inside the case to provide enough case neck tension / friction to keep them from moving under recoil.

This is why one roll crimps. Heavier bullets will pull quicker due to more mass in my experience. But, in a 12 ounce .357, that don't mean a 110 grain won't pull, either.

I shot one of these things that belonged to a guy at the range, once. I appreciate .38 special a lot more, now.

 

[beag_nut]

rcmodel:
Thanks very much for the quote from the owner's manual. Will send the info along.

 

[BCRider]

rcmodel:
Thanks very much for the quote from the owner's manual. Will send the info along.

Which just goes to show that your buddy is a true man..... He didn't bother reading the manual.....

 

[Drail]

Light bullet loads are for girls.

 

[timothy75]

So which is it? It seems like heavy bullets would be more likely to pull from a light weight gun than lighter bullets. We've seen very good but conflicting explanations given above. So who's right?

 

[rcmodel]

I'd still have to vote light bullets.

Higher velocity = Sharper faster recoil = More G-force.
Less bullet shank inside the case = Less case neck tension to overcome.

There have also been problems noted with heavy lead bullets pulling in these light guns too.
But a grease lubed lead bullet has almost no case neck friction compared to a heavy jacketed bullet.

The problem with heavy lead bullets is that many factory loads use soft swaged bullets. The crimp can't get a grip in the soft lead crimp groove as well as a jacketed cannulure.

rc