Lead and polygonal barrels


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Captaingyro
September 21, 2012, 06:14 PM
I just bought an H&K USP .45 Tactical from a guy for a fairly low price.

When I examined the barrel during the purchase, I thought to myself, "I though all USP's had hexagonal barrels. This one sure looks like it has conventional rifling." I suspected an aftermarket barrel, but, sure enough, it was the H&K original, with a matching serial number.

Once I got it home and broke it down, (the previous owner didn't seem to be a nut about cleaning), I started in on the bore. What came out was lead...a lot of it. There was so much lead in that barrel that it had started filling in the angles of the polygonal rifling, looking for all the world like conventional lands and grooves. Evidently, no damage was done, because I now have a mirror-shiny bore, but I got a first-hand look at how shooting lead out of a polygonal barrel can create a hazardous situation.

I'm now wondering if I got such a good price on this gun because he thought he was unloading an innacurate shooter?

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bds
September 21, 2012, 06:24 PM
Shooting lead loads in HK polygonal barrels was discussed on this thread recently - http://www.thehighroad.org/showthread.php?t=634206

For me, concern with shooting lead loads in polygonal barrels had more to do with increased gas cutting from voids between the bullet and the barrel. Although Glock barrel is not a true "polygonal" barrel, it has longer leade and very smooth start of rifling with rounded rifling that allows more gas cutting and faster fouling build up. These factors essentially will result in a smooth bore reduced diameter barrel that will not spin the bullet fast enough as it exits the muzzle and may increase chamber pressure. Not enough spin will reduce accuracy and too much chamber pressure increase can lead to KaBoom. I don't subscribe to the notion that "Glocks never need cleaning" - I clean my Glock barrels after each range trip and when I am shooting lead loads in factory Glock barrels, inspect every 200-300 rounds and clean as necessary.

If your HK barrel is not polygonal, then I would see it as a plus. Does the bore look like the picture on the right? If you reference the linked thread (http://www.thehighroad.org/showthread.php?t=634206) above, you may have success shooting lead loads in your HK depending on bullet hardness and powder/charge used.

Traditional land/groove rifling and polygonal rifling - http://en.wikipedia.org/wiki/Polygonal_rifling

http://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/Polygonal_vs_normal_rifling.svg/493px-Polygonal_vs_normal_rifling.svg.png

I don't know why people claim Glocks have "polygonal" rifling. I think Glocks have hexagonal rifling but not a true "polygonal" rifling. Look at the picture below of Glock barrel/rifling - Do you see a polygon? I see a cylinder (circle, not a polygon or hexagon) with six rounded rifling ... :confused:

http://www.thehighroad.org/attachment.php?attachmentid=163255&stc=1&d=1335152658

kelbro
September 21, 2012, 10:35 PM
Maybe the lead that he was shooting was too hard. I shoot a ton of lead through my USP45 and HK45 and have absolutely no leading. I shoot an alloy that is half clip-on wheelweights, half stick-on wheelweights, and about 2% tin which is oven heat-treated for a tough shell.

Captaingyro
September 22, 2012, 07:31 AM
Whatever he was shooting, it was turning the polygonal rifling into a smoothbore, by filling in the angles. The perfectly symetrical streaking made it look similar to lands and grooves (although I was using direct sunlight for a bore light, so there was quite a bit of glare).

At any rate, with plated bullets so good these days, and so cheap, I just don't see the point of shooting store-bought lead in polygonal barrels. If you cast your own, of course, and can customize your alloy to avoid leading, that's a different story.

hentown
September 22, 2012, 02:14 PM
Some Glocks have octagonal rifling.

918v
September 23, 2012, 04:30 PM
Shooting lead bullets that fit correctly does not create a hazard.

Trent
September 23, 2012, 04:45 PM
I shot a bit of lead out of my USP tactical. I got tired of scrubbing that crap out so now I only shoot jacketed bullets, and save the lead for my wheel gun. :)

hentown
September 23, 2012, 05:10 PM
Shooting lead bullets that fit correctly does not create a hazard.

Please edify me. What does "fit" have to do with it? How does a lead bullet "fit" or not fit??

918v
September 23, 2012, 05:18 PM
Why don't you edify yourself and read The Paper Jacket or 40 Years with the 45-70. These explain the mechanism of leading very well.

kelbro
September 23, 2012, 11:22 PM
Fit is important. Very important. Drive a soft lead slug through your barrel. If you can size to .001 over your slug size and still chamber the round, you will discover that you can shoot a lot more for around 6 or 7 per shot (if you cast your own).

Hardness is NOT a cure for leading.

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