Loading revolver for accuracy; Seating depth

[GSSP]

When loading rifles bullet in rifles for accuracy, DOL (Distance Off the LANDS) is very important for tuning barrel harmonics to tighten groups.  When doing it for revolvers, is it the same?  Take for instance my Ruger NMBH 50th anniversary model in 357 Mag.  I have a bunch of 160 gr LBT FN I cast up years ago.  

SAAMI is 1.590".  Does jumping help/hurt accuracy in revolvers?

When I seat to the bullet's ogive is just touching the cylinder throats, it 1.626"; .036" longer COAL.  



When I seat to 1.590" it looks like this.  .036" jump to the cylinder throats.  




.220" and .495" cylinder mouth clearance.

[contender]

Only actual accuracy testing will show if your gun, and the load combination is more or less accurate than "normal."

I didn't do much "deep seating" of bullets over the many years,, but since David kept mentioning it, and showing how it can be accurate,, I've been playing with that concept too a bit more. But my own observations show that all guns can exhibit good or bad results by changing all sorts of things. So,, I usually try to find what works best in a specific gun vs trying to apply a "blanket" approach.

[bradshaw]

Jun 15, 2024 18:39:54 GMT -5 GSSP said:

When loading rifles bullet in rifles for accuracy, DOL (Distance Off the LANDS) is very important for tuning barrel harmonics to tighten groups.  When doing it for revolvers, is it the same?]

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*****

No.

By dint of chambers bored through a cylinder separate from the barrel, revolvers are the King & Queen of FREEBORE. No way around it, the bullet is compelled to travel a smooth tunnel, jump a gap, leap across a piece of no-man’s-land called the FORCING CONE (which in a rifle is called the LEADE), which forcing cone hopefully aligns the bullet to seat the rifling GROOVES. (A bullet which rides the LANDS without support of the grooves may find its axis eccentric to the BORE AXIS.)

Compared to a streamlined rifle bullet, the regular revolver bullet has the ballistic coefficient of a barn door. The down side to a low BC is increased wind drag. Which has some upsides:
* Bullets at subsonic velocity shed velocity slowly. The faster a bullet flies, the more it compresses the air in front of it and the faster it slows down.
* Providing it posses dynamic balance----and, for long range accuracy, its CENTER of GRAVITY (COG) is not in the same spot as its CENTER of FORM (COF)----the bullet has a good chance for accuracy from supersonic to subsonic.

Seating depth directly affects combustion dynamics, and thereby may influence accuracy. Years ago PPC competitors and gunsmiths experimented with short cylinders, specifically to tune utmost accuracy from the .38 Special @ 50 yards. Far as I know, results were inconclusive. In the steel game, where rules of the International Handgun Metallic Silhouette Association (IHMSA) specified a stock pistol for the Production categories (Production, Revolver, and Standing), there was no room to experiment with cylinder length. Top revolvers and shooters recorded astounding accuracy out to 200 meters, and, on occasion far beyond.

Revolver accuracy is an orchestra of dimensions. Load accuracy starts with a accurate bullet. Powder selection comes third.

In order of importance
1) Revolver accuracy.
2) Bullet accuracy.
3) Load accuracy.

DEEP SEATING
* Improves efficiency with fast and medium powders while upholding accuracy.
* Improves efficiency with lower charges of slow powder under a heavy bullet.
* My preferred method with nearly all cast bullets.
David Bradshaw