Throat Wear as a Function of Boolit Hardness

[ejcrist]

I have a S&W 686 with a 8 3/8" barrel that shoots best with 14.0 grains of 2400 and clocks in around 1,490 fps average. The boolit is a RCBS 38-150-SWC cast from straight wheel weights which I'm guessing is around a BHN of about 10. I read somewhere that boolits with velocities in excess of 1,400 fps should be cast a little harder than straight wheel weights or the throats will wear out quickly. Is that statement accurate? I don't shoot this revolver much since I'm more of a single action fan but I might want to start shooting it more down the road, and if so I'm wondering if I should harden the boolit up a bit. I hate to change anything though since I have this revolver shooting about 1" consistently with open sights at 25 yards off a rest - with my deteriorating vision that's pretty good. Any info would be appreciated.

Thanks, Gene

[RickinTN]

Gene,
I'm not a revolver man but more experienced with rifles. I will be curious what others with experience that come along will say but I think I'm steering you in the right direction when I tell you that the burning powder gasses are responsible for most erosion of the throats, not the bullets' passage. I'll go a step further and may be spreading wives' tales but I have understood that ball powders are worse than flake powders in that they "bead blast" the throat while passing through.
Lets see what others with more experience have to say,
Rick

[Scharfschuetze]

Surprisingly, barrel steel and fairly soft; thus pressure and heat are your throat's enemies and shooting lots of magnum level rounds will do the deed in wearing out your barrel. Gas cutting will do way more damage to the forcing cone (throat) than the friction of jacketed or cast boolits passing though the barrel. Gas cutting is often seen even on the top strap above the cylinder/barrel gap in addition to the forcing cone/throat. Ammo loaded to 38 Special or 44 Special pressures will not significantly wear your throat out and firearms shooting cartridges at this level of performance will last a long time in more ways than just the wear on the throat.

In rifles, 30/30s shooting jacketed or cast bullets will last indefinitely if cared for. A 308 match or M24 SWC rifle will loose its gilt edge accuracy due to throat erosion in often just 3,000 rounds firing M852 or M118LR ammo. Our Mk 13 sniper rifles in 300 Winchester magnum would need rebarreling in half that number due to eroded throats and our comrades at the Navy SWC replaced their 300 Magnum barrels even more frequently. All those rifles were shooting jacketed bullets, but at vastly different pressure levels and those pressure levels dictate the rate of wear as well as heat generated. Heat is an important consideration here as the steel is much more susceptible to wear when hot. Add high pressures to high temps and you have the formula for the wear you are worried about.

Less is definitely better when it comes to longevity so perhaps a mid range load for your 357 would give you some peace of mind. My goal in my 357s for day to day plinking is about 950 fps to 1,000 fps with cast boolits.

[ejcrist]

Thanks much for the info gentlemen. I used to load exclusively for accuracy only, and that's when I developed the load for this particular revolver. While I was developing the load I noticed the groups kept shrinking with slight increases of 2400. When I got to 14.0 grains I had the smallest groups, and when I went a hair over the groups started opening up so I settled on 14.0. The most accurate loads I developed were usually between 800-1200 fps for a lot of my revolvers and served me well on paper, steel silhouettes, and most everything I hunted, but then I started hunting feral pigs and all bets were off, bless their hearts. Now I try to keep hunting loads between about 1,000-1,400 fps because I found you need it for expansion even when loading softer cast boollits. I don't know about jacketed since I never shoot them anymore. I've been able to make cast shoot much better in my experiences. So anyway, it's a tradeoff for me between accuracy and speed but of course accuracy carries the most weight.

Gene

[44man]

Throats wear if the cylinder does not align or get pulled into alignment by the boolit. If the boolit does not center in the cone, it puts sideways pressure in the throats. That also wears the cone and rifling off center.
Nothing to do with cast because jacketed will also do it FAST.
The revolver is NOT the same as a rifle with throat wear and you can shoot hot loads forever. The rifle is eroded at the rifling, extending distance to rifling. That is caused by powder burn over the melting point of steel and letting the gun get hot.
Maybe Lil'gun will eat up a revolver but 2400 never will.
The worst revolver I seen was a Freedom .454 that was out of line. Wore throats oblong and the cone egg shaped with half the rifling worn on one side with less then 300 rounds of factory loads, gun fit too tight.
The reason for a harder boolit is to make the boolit pull the cylinder without getting mashed.
just water drop the WW boolits.
Play in a cylinder is needed and the boolit is the rudder.