Polygonal rifling & cast

[Sky C.]

Gentlemen-

I am considering the purchase of a Kahr in 40 Smith but note that they (& Glock, H&K, IMI) use the Polygonal type rifling.

Can anyone advise about results for cast using this type rifling & any "rules of thumb" for making the combination work?


Thanks-

Sky C.

[Bass Ackward]

Gentlemen-

I am considering the purchase of a Kahr in 40 Smith but note that they (& Glock, H&K, IMI) use the Polygonal type rifling.

Can anyone advise about results for cast using this type rifling & any "rules of thumb" for making the combination work?


Thanks-

Sky C.

Sky,

My personal opinion is that if you want to shoot cast like cast, then bore condition and dimensions are more important than rifling height or type.

[fecmech]

Skyc--I had a Kahr K9 last year that I put about 3k cast rounds thru with no problems or pressure signs. Accuracy was in the 2.5-3.5" range @ 25 yds. IMO they make a nice little gun, barrel was nice and smooth and leading was minimal. I had my best luck accuracy and leading wize with Blue Dot powder for max loads. I've not loaded for the .40 so I can't help you there. The Kahr manual does not say anything pro or con about cast, just the standard recommendation not to use reloaded ammo. Nick

[Beau Cassidy]

I have had nothing but leading from hell in a HK USP and Glock 30. Same load does fine in other guns- 3.6 G. Clays/ 200 Gr./ ACWW. As expected, i don't shoot those as much as others.

Beau

[Buckshot]

..............Polygonal bore forms have been used for a couple hundred years. By no means first, but more well known beacuse if the fast (for the day) twist was the 6 sided Whitworth form, with it's 20" twist for 45 cal bullets. Extensively tested by the British Small Arms committee against the P53 Enfield .577" service rifled musket. This was in the later 1850's. Naturally it was all with lead booits.

..............Buckshot

[Ron]

Sky C, I have a GLOCK 34 9mm and shoot mainly cast 125 grn TC through it. The boolits are hard cast. If you stick to regular loads without trying to use stoked up loads you should have no problems with the polygonal barrel. Just observe good gun practice by cleaning after shooting, this will prevent any lead build up which may be a problem.


Ron


FESTINA LENTE

[Sky C.]

Gentlemen-

Thanks for the feedback.


fecmech, Beau, & Ron-

Can you advise as to what size bullets you were shooting and estimated velocity.


Buckshot- Yes I'm aware of the Whitworth but IIRC, that arm also used a quite unique cast projectile, one that was cast with a polygonal profile to fit the polygonal rifling. It performed exceptionally well out to 1000yds beating the then current rifle design in accuracy quite handilly.


Thanks again-

Sky C.

[Beau Cassidy]

Sky,
.452 diameter. Felix lube. 800 FPS +/-.

Beau

[Buckshot]

Gentlemen-
Buckshot- Yes I'm aware of the Whitworth but IIRC, that arm also used a quite unique cast projectile, one that was cast with a polygonal profile to fit the polygonal rifling. It performed exceptionally well out to 1000yds beating the then current rifle design in accuracy quite handilly.


Thanks again-

Sky C.

The vast majority of slugs shot by shooters of the Whitworth (including me) shoot round conicals. The boolit upsets to fill the bore upon ignition.

..............Buckshot

[Ron]

Sky C, my 9mm is lube/sized to .357, barrel checked at .356. I use only felix lube. Have no idea of velocity as have never checked it but at 25 yards the groups are very tight.

Ron

FESTINA LENTE.

[9.3X62AL]

The responses to the "lead boolit/polygonal bore form" questions are all over the map. I'm beginning to think of them in the same way I consider Microgroove pattern rifling and its interface with lead--that being, they can work with a little attention to detail.

I freely admit to avoiding polygonal bores and Microgrooves pretty scrupulously--I have only one MG example in my safe, a Model 62 Marlin levercritter in 30 U.S. Carbine. Sized at .311", Lee Soup Cans outshoot j-words in this rifle to 1900 FPS. So, MG can work--and has for me in this instance.

We should also remember that the 9 x 19 and 40 S&W create pretty harsh cast boolit environments anyway. Marie has dropped not-too-subtle hints that a Glock of some kind would be a really cool gift at some point in time. I dislike them ugly damn bottom-feeding dishwasher safe stutterguns aesthetically, but they damn sure WORK. So--at some point I'll be dealing with the issue.

[Oldfeller]

Al,

Glocks have a cleaning issue when shooting lead that has nothing to do with the inside of the barrel.

Powder and lube residue WILL build up on the flat broached slide surface (the one the firing pin comes out of) and can create a sticky, draggy surface condition which absorbs some of the required Glock freewheeling slamming shut lock up motion.

If you don't keep this sticky residue cleaned off every couple of dozen shots, you WILL eventually get an out of full battery slide condition that WILL take place, causing you to ding the top of your slide lock up and mar your Glock super-hard slide coating exposing the steel underneath. Yeah, there is a little bit of nebulous lock-up zone where the pistol will still fire when it isn't in perfect battery (Glock Perfection isn't totally perfect).

I have never had leading or accuracy issues shooting fully hardened cast slugs out of 4 glocks -- but on the small frame guns (the 9mm and the 40) I have seen this engagement issue take place -- both of my guns have damage at the top of the slide lockup to barrel lockup surface on the wonder coating.

I have an OPINION that this may be part of the 40 kbm issues that are occasionally heard about, but will never be able to prove it either way.

Remember to keep the sticky stuff off your broached slide firing pin surface ....

Oldfeller

[Dale53]

I am tempted to reply to all of the problems with plastic guns and .40 calibers, "Shoot a real gun - .45 ACP 1911 Colt, Kimber or Springfield and you will eliminate those problems". However, trying to be the gentleman that I aspire to be, I would NEVER say that....

(The debbil made me do it, really!)

FWIW
Dale53

[fecmech]

Sky--Iwas running .357 sized bullets in a .355(as near as I could measure) groove. I had decent accuracy at 1150fps with the Blue Dot out of a 3.5" bbl. My Kahr had what looked to me like an area of ("freebore") ahead of the chamber. OAL length was limited only by the magazine. Nick

[Poohgyrr]

Not a Kahr, but a 2nd gen G23 I bought new in '91. I don't know how many 500 round boxes of Western Nevada 180 gr SWC's (on top of AA7) I've put through it. Leading is not a problem, but reliable feeding needs a Lee FCD.. The same goes for my two other G40's.

My .40 Hi Power is more accurate and more reliable.