Hard cast in polygonal barrel?

[Japhy]

Curious if there any issues running hard cast 9mm +p through polygonal barrels?

[Chiro1989]

I have done it, a couple boxes worth and then cleaned it, didn’t seem to be to bad IIRC, a steady diet and no cleaning might be a problem, not sure if a box of jacketed bullet afterwards would have removed some fouling

[CPJ 2.0]

For $30 you can have a new
regular barrel.

[Bigslug]

Big can of worms that we've discussed at great length over on Cast Boolits.

We've discussed issues specific to loading cast in 9mm as well, and I think that's a bigger challenge than polygonal.

I've run pin gauges and pounded soft slugs to get both bore and groove diameters in Glock (both poly and Gen 5 Marksman) and other barrels, as well as run a series of pin gauges in the chambers to get a feeling for the chamber's taper. The conclusion I came to is that - other than the rifling profile - there's pretty much zero difference in the spec of a Glock tube versus everybody else. You get roughly a .346"-.347" bore and a .355"-.356" groove, and what you want in most cases is a .357" bullet (some guys run .358"). The Glocks do have the advantage of being very smooth and uniform.

A problem that many have run into with 9mm is that a lot of standard die sets don't expand the brass large enough to properly accept a .357" bullet. What then happens is your brass swages your bullet down to below ideal diameter and you get gas blow-by and leading. My solution was to swap in a Lee .38S&W sizing die and adjust carefully. Different paths have been taken to get there.

And then add in the problem of commercial cast bullets. "Hard cast" is one of those fingernails-on-a-chalkboard phrases to bullet casters, as it doesn't really tell you anything and promotes the idea that harder is automatically better - it isn't. If the bullet is fat enough and not swaged down by the brass, harder is usually OK, but if it is undersized and too hard to obturate up to fill the groove diameter, you'll get blow-by and lead fouling from Hell. In handguns, I've been having the best luck with an alloy that's plastic enough to slug up and seal - usually in the slightly softer than wheelweight hardness spectrum of about 10 BHN (Brinnell Hardness Number - pure lead is 5, wheelweight usually around 12-14, Lyman #2 at 15, printer's linotype about 22). My last batch of 9mm was at 12, but the 10 stuff is working better in .44 Special, .45 and .357/.38, so that's where I'm headed next.

Bullet lube also matters - more as a sealing gasket than an actual lube. It won't entirely make up for poor alloy choice or bad bore fit, but it will work to prevent blow-by when things are close. I've been switching to tumble-lube bullet designs (they're quicker to produce), but I'm still perfecting my technique to get them to shoot as clean as traditional grease groove slugs (see switching to softer alloy comments above).

The short version is that if you have that understanding and control over the variables, I don't think a polygonal tube is any more challenging to shoot cast through than anything else, but the 9mm has it's pitfalls.

[CPJ 2.0]

Big can of worms that we've discussed at great length over on Cast Boolits.

We've discussed issues specific to loading cast in 9mm as well, and I think that's a bigger challenge than polygonal.

I've run pin gauges and pounded soft slugs to get both bore and groove diameters in Glock (both poly and Gen 5 Marksman) and other barrels, as well as run a series of pin gauges in the chambers to get a feeling for the chamber's taper. The conclusion I came to is that - other than the rifling profile - there's pretty much zero difference in the spec of a Glock tube versus everybody else. You get roughly a .346"-.347" bore and a .355"-.356" groove, and what you want in most cases is a .357" bullet (some guys run .358"). The Glocks do have the advantage of being very smooth and uniform.

A problem that many have run into with 9mm is that a lot of standard die sets don't expand the brass large enough to properly accept a .357" bullet. What then happens is your brass swages your bullet down to below ideal diameter and you get gas blow-by and leading. My solution was to swap in a Lee .38S&W sizing die and adjust carefully. Different paths have been taken to get there.

And then add in the problem of commercial cast bullets. "Hard cast" is one of those fingernails-on-a-chalkboard phrases to bullet casters, as it doesn't really tell you anything and promotes the idea that harder is automatically better - it isn't. If the bullet is fat enough and not swaged down by the brass, harder is usually OK, but if it is undersized and too hard to obturate up to fill the groove diameter, you'll get blow-by and lead fouling from Hell. In handguns, I've been having the best luck with an alloy that's plastic enough to slug up and seal - usually in the slightly softer than wheelweight hardness spectrum of about 10 BHN (Brinnell Hardness Number - pure lead is 5, wheelweight usually around 12-14, Lyman #2 at 15, printer's linotype about 22). My last batch of 9mm was at 12, but the 10 stuff is working better in .44 Special, .45 and .357/.38, so that's where I'm headed next.

Bullet lube also matters - more as a sealing gasket than an actual lube. It won't entirely make up for poor alloy choice or bad bore fit, but it will work to prevent blow-by when things are close. I've been switching to tumble-lube bullet designs (they're quicker to produce), but I'm still perfecting my technique to get them to shoot as clean as traditional grease groove slugs (see switching to softer alloy comments above).

The short version is that if you have that understanding and control over the variables, I don't think a polygonal tube is any more challenging to shoot cast through than anything else, but the 9mm has it's pitfalls.

Or, you FAFO. You may Find Out everything works fine without sprinkling the blood of a chicken in your melting pot.

[Bigslug]

True, but the brass-swaging-bullets problem is very much a thing. Lot of really experienced guys lose their minds when going to cast in 9mm. You could say it's kind of a mini-epidemic: since 9mm has become everyman's cartridge, there's a lot more folks taking it on at the reloading press and casting pot.

I've not gotten into bake-on powder coating, but those that are swear by it and it many of the commercial casters have been selling their bullets done that way - I probably saw my first ones about 25 years ago. Much like a real jacket, the plastic "M&M shell" is going to keep the fire away from the lead - regardless of bore fit issues. If you're not pouring your own and just want to load and shoot without all the Weird Science, it's probably the way to go.

[GrapeApe]

the 9mm is a fairly short case & It has an internal taper. Use "standard" weight or light for caliber bullets and you won't have as big an issue with the case swaging your bullets.
There's a reason Hornady adds the extra step of swaging a boattail on their 147gr 9mm bullets, and I am fairly certain it is NOT for better down range ballistics.

I didn't know better when I got my first glock (Gen1 G19) 30+ years ago. I was running the 121gr TC bullets in the S&W 9mm I replaced. I continued to run the cast bullets until I'd used all of the approx 1k I had on hand. Only change I had to make was upping the powder charge, since I had worked the load down to just above the minimum reliable load for the Smith, and the Glock required more "oomph"
I cleaned the Glock every once in a while, and never had any issues.

YMMV