Polygonal Bores and Cast Bullets

[schmeky]

I know this has been discussed many times. I am looking for a few real world scenarios. I picked up a Baby Eagle in .40 S&W the other day and it has a polygonal barrel. I test fired a few Missouri Bullet 18 BHN rounds through it to see how the barrel's bore would do. To my surprise, there was quite a bit of lead that peeled off the bullets and left long slender "shards" in the barrel.

I found these deposits cleaned out easily. I made a few passes with a brass brush followed by a patched jag. I don't want to try and make a square peg fit a round hole, and if I need to to, I'll break down and buy some jacketed bullets.

But I want to know how well your poly bore gun has done with hard cast ammo, i.e. is it accurate, reliable, difficult to clean after -X- number rounds . . . . .

 

[shoen1200]

Cleaning was a bit ugly but the real issue for me was accuracy.
I have a Kahr PM9 and an HK P2000SK in .40sw. which have that type of rifling.
Both have problems with accuracy using plain lead bullets.
Using plated bullets I can get accurate loads with the HK.
The Kahr was another story.
Plated bullets are not accurate in the Kahr unless pressure/velocity was at edge of spec .
I use only jackets bullets in the Kahr.

 

[1911Tuner]

The problem that cast bullets present to polygonal bores is that there is no defined rifling that will cut into the sides of the bullet and pick up lube from the lube groove the way standard rifling does. Not as big a problem if the bullet obturates and seals off the bore...but most commercial cast bullets are too hard, and don't bump up readily. The lube itself helps to seal off the gasses, and when it isn't picked up by the rifling...it exacerbates the problem. Lead builds up ahead of the chamber throat...and pressures start to spike.

Hard commercial alloys will lead in standard bores, but not as badly as polygonal bores.
Using a softer alloy, along with soft lubes pretty much put lead fouling problems to bed in standard bores. It will help with polygonal bores, but won't completely prevent it.
Cast lead bullets can be used in polygonal bores, but frequent cleaning is imperative. Depending on the gun...it may require cleaning as often as every 10-15 rounds.

 

[Maj Dad]

I have used plated 230s from Jake at Rocky Mountain Reloading with great results in my Glock 21. I watch the bore closely, but haven't had any problems with any lead/copper stripping. They're a bit more than standard lead slugs (especially if you cast your own, as I do), but I shoot the home-mades in my Colts & S&W revolvers and not the Glock. I have an after-market rifled bbl on my Brownell's wish list & will eventually get it so I can play more. I do like the polygonal bore for jacketed bullets for its superb results (at least in mine).

 

[MCgunner]

I won't own a gun that won't shoot cast bullets. Sold a Smith and Wesson 1917 for mostly that reason. The rifling in those guns is cut shallow, made for ball ammo, and at least mine didn't work for toot with cast. No Glocks or Kahrs in my stable.

 

[ultramag44]

MCgunner said: "I won't own a gun that won't shoot cast bullets. Sold a Smith and Wesson 1917 for mostly that reason. The rifling in those guns is cut shallow, made for ball ammo, and at least mine didn't work for toot with cast."

I have a WW1 1917, a Brazilian 1937 and a 1982 production S&W 25 All shoot cast very well. Cast 'em hard, lube well, and most important, make sure they are .452 or .452

 

[1911Tuner]

The rifling in those guns is cut shallow, made for ball ammo, and at least mine didn't work for toot with cast

The rifling was cut to the same depth as 1911 barrels, and they work nicely with cast bullets. Yours probably had damaged rifling at the muzzle from improper use of a cleaning rod. On a gun that old, it's also possible that the bore was just flat worn out.
Back in the day, those revolvers...like GI 1911s...could be had for a song. I remember my father buying two of'em at a gunshow...one Colt and one Smith...for 35 bucks for the pair. Surplus ammo was like 2-for-a-penny if bought in bulk. A seemingly never-ending supply of cheap guns+cheap ammo, they tend to be shot out pretty quickly.

 

[robertbank]

I have a Tanfoglio Model "L" with the .40cal top end. It has polygonial rifling and shoots great. Gun is extremely accurate and I have yet to have any leading of any kind shooting my Lyman cast bullets, cast from WW.

Take Care

Bob