How to slug a Polygonal rifled barrel?

[billmc2]

I brought home today a new H&K HK45. It has polygonal rifling. Do I need to do anything different when slugging this?

How about bullet sizing? With the polygonal rifling, I assume I measure the widest part, then size 0.001" over that?

I'm planning on powder coating the bullets. I read on the HKPro site that the leading issue with Glocks has to do with a right angle at the start of the rifling, that HKs are tapered and do not have the same issues.

If I'm wrong about any of this please correct me.

[Johnch]

OK Here is MY take on slugging pistol barrels
I Don't do it

I have a Glock 17 and a Glock 22
I shoot cast in both with no problems

I tend to go on the idea of letting the barrel size the cast bullet if needed

What I am saying is
My Glock 17 I use powder coated cast sized to .357
The Glock 22 gets feed .4015 powder coated bullets
Both have chambers more than large enough to fit those size bullets
When the bullets go down the barrel , the barrel reduces the dia of the bullet as needed
With IMO not hardly any increase in chamber pressure
I also have shot groups at 25 yards with both pistols
They both shoot better groups with the slightly oversized bullets

Just my 2 cents

John

[JonB_in_Glencoe]

It's easy to slug a polygonal barrel, but it's difficult to get an accurate measurement of the slug.
I wrap a strip of popcan metal around the slug, measure with a 1" Mic, then subtract 2x the popcan metal thickness.

Now, the best I could measure my 40 cal IMI Baby Eagle, it measured .401
But I found I needed to size to .403 as well as drop the charge a bit, to eliminate lead fouling.

[Bigslug]

There are A LOT of 1880's rifles and replicas that have virtually zero leade cut into the throat, and they get the job done without lead-plated bores. With the Glocks it's likely an issue of bullet fit, as it is elsewhere. Many of us loading 9mm have experience with our brass swaging our carefully-prepared bullets down below ideal diameter and have had to use different expander concepts (i.e., a .38 S&W sizing die) to prevent this.

I don't know what profile an HK .45 will have exactly, but one of the useful tools in the caster's arsenal is a V-anvil micrometer that allows you to measure the diameter of slugs from 5-groove offset rifling by using three points of contact. What I CAN'T remember is which of the two available V-angles is best for our purposes - hopefully someone reads this and can expand.

[FergusonTO35]

My gen. 5 Glock 19 is the most cast friendly Glock I have ever seen. Rounds plunk perfectly and there is even less fouling than my aftermarket barrels that Doug Guy has worked over. The gen. 5 has the "Marksman" rifling which resembles Marlin Micro Groove, another controversial subject here. These days I size all my .38's and 9's to .358 and they work great.

[ioon44]

I brought home today a new H&K HK45. It has polygonal rifling. Do I need to do anything different when slugging this?

How about bullet sizing? With the polygonal rifling, I assume I measure the widest part, then size 0.001" over that?

I'm planning on powder coating the bullets. I read on the HKPro site that the leading issue with Glocks has to do with a right angle at the start of the rifling, that HKs are tapered and do not have the same issues.

If I'm wrong about any of this please correct me.

I use Hi-Tek coated cast bullets in my Walther PPQ .45ACP which has a true polygonal rifling, I size .002" over and don't have any leading or accuracy issues.

I don't know what the H&K HK45 rifling looks like, you can do a Google search on polygonal rifling and see what true polygonal rifling is.

Glocks are not true polygonal rifling.

[FergusonTO35]

Agreed, it would be better described as conventional rifling with rounded lands and grooves devoid of sharp corners.

[billmc2]

OK, I took the advice and did do some reading on polygonal rifling and did learn a few things. I have a pair of Walther PPS which I haven't shot in years, I completely forgot they have polygonal rifling. Looking down the barrel of the HK, its looks like the pictures of polygonal rifling but I'm no expert at this.

Pretty much everything talked about uncoated lead bullets being the problem. Because I intend to powder coat the bullets, I'm thinking this shouldn't be an issue. A couple of articles refer to the Hi Tek coating and jacketed as being OK.

I don't have a V angle micrometer (or any micrometer) and it seems as if several of you are sizing the bullets slightly larger than what would be considered normal, I may do as Johnch suggested and let the barrel size the bullets and see what happens. My 45 cal bullets are coming out of the mold at 0.454". I'm using the Lee push through sizers and the largest one I have at the moment is 0.453" I'll have to make up a couple of dummies and see how they fit, then go from there.

The forecast here is for rain the next couple of days so I won't be doing any shooting until that is through.

Thanks for the help guys.

[Cast10]

I’ve slugged all my Glocks; 9mm and 10mm. I size 9’s to .357 and 10 to .401. I also PC the boolits. All good with zero leading. My melt is 11.3 BHN. I’ve run my 10mm to 1600fps in a 16” carbine.

Fishing weights…..