Wednesday, December 13, 2017

.357 Magnum, Heavy Bullets, Dwell Time

The .357 Smith and Wesson Magnum is one of the more interesting cartridges I've ever encountered.  A shooter can go from mild to wild in the caliber, shooting everything from mild wadcutter target loads to full-house magnum loads, and do it in the same cylinder of cartridges if he wants to.

Back in my early law enforcement days, the revolver was king, and the .357 magnum ruled the roost.  And, we noticed something.  That fixed-sight revolvers were generally regulated for a standard 158 grain bullet traveling about 1200 fps.  When we changed to the 125 grain hollowpoint, the revolver tended to shoot low.  On a man-sized silhouette, shots aimed at the chest would tend to hit about the belt buckle, depending on the range.  We finally realized that what we were seeing we defined as "dwell time".  Those little 125 grain bullets were screaming, at over 1400 fps and while the little bullets had less momentum recoil, they were a lot faster, so the barrel of the gun tended to rise less while the bullet was actually in the barrel.  Hence, they shot low.

The converse was also true.  Heavy cast bullet loads tended to shoot higher.  If you had a 180 grain bullet traveling close to 1200 fps, the gun had more recoil due to the heavier bullet and the barrel rose more while the bullet was traveling down the barrel, so the revolver tended to print the bullets higher on the target.  Dwell time.  Pure physics.  While the bullet is in the barrel, the barrel is rising, and the bullet goes higher.

Those of us with adjustable sights simply adjusted the sights.  Those with fixed sights either found a load the printed to the point of aim, or made adjustments based on their knowledge of the gun.  Either way, you had to hit what you aimed at.

Several years ago, I stumbled on a heavy 180 grain load that used L'il Gun powder.  I talk about it here.  It's a recoil hoss.  My son tried it in his Uberti Cattleman, and reported that it shoots a bit high.  I cogitated on it, not realizing what I was seeing, and told him I'd think about it.    Today, it hit me like a ton of bricks.  Dwell time.  I happen to have a box of factory 125 grain fodder, which generally shoots low in a standard .357 magnum.  Lighter bullet, faster travel, less dwell time.

He's coming up this weekend, and I told him to bring the Uberti.  Maybe we'll get a chance to do some shooting.


The Displaced Louisiana Guy said...


Hell, that makes a lot of sense. I'm looking forward to experimenting.

Old NFO said...

I'll be interested to see the results of that comparison!

waepnedmann said...

First observed this with my first .44 mag.
I ran some SuperVels through it and then some .44 Specials.
At 25 yards the .44 Specials grouped about a foot higher than the SuperVels.
I had to scratch my head for awhile before I figured out what was going on.

DiamondD said...

My first carry gun was a 3" Ruger SP101 in .357 Mag. It shoots 158s to the sights but lighter bullet loads don't. I dealt with this by carrying 158s. I just bought a 2 1/4" SP101 in 9mm. Haven't shot it yet but I'm really hoping 124 grain HST's will shoot to the sights. If not I'll have to experiment with 115s or 147s depending on the results.

David aka True Blue Sam said...

It's fun to dink around with bullets and different powder charges. I bought a short barreled Vaquero in .44 Mag last year and have settled on 10 gr of Herco under a 200 gr XTP. More than a Special load, and not quite a Magnum. I have made the front sight fit that load, so I can shoot with confidence.