Pop Quiz: How was this barrel rifled?

[CJB]

http://i46.photobucket.com/albums/f141/Abraxxas/DSC_5804.jpg

Hey I already know how its made, and will reveal and defend the answer sometime Monday evening.

So, the pop quiz is - how was this barrel rifled? What method, how do you know for sure?

Just seeing if folks are on their toes!

Folks answering correctly will get he combination to the Col's liquor safe!

[Bills1873]

Looks like rotary/reciprocated type milling, not drawn.

[CJB]

How does one leave machine marks like those...in the grooves??!!

[Bills1873]

That's my question. The marks are perpendicular to the rifling. Pretty good trick to machine like that. I give up, how's it done?

[muggsy]

Could it have been broached?

[Buzzard45]

hammer forged? then various machining steps, boring chamber, leade, etc. and broaching grooves?

dont worry colonel, if i win, i dont drink MUCH!;)

[zaitcev]

Could it have been broached?
Muggsy is the winner. These marks are chatter marks. I have a Charter Arms revolver in .45 ACP where these marks are far more severe.

[Bobshouse]

Flow formed.

[CJB]

The key to seeing is a little photo enhancement.

http://img.photobucket.com/albums/v214/bandersnatchreverb/MAIN/5804_zpsrqf1abyt.jpg

Have a look at the marks on the lands, and grooves. This is not chatter.

This is remnants of the tool marks of drilling a blank, slightly greater in diameter than the groove size - not bore, but groove size - and placing a mandrel within it, and beating the living snot out of the metal until it conformed to the shape of the mandrel.

There's another telltale - which can be seen at the lead in (or miscalled "freebore") for the rifling. The rifling takes a dip, midway in each land. Well how in hell did THAT happen, and have the tool marks as they're seen? Answer: That's one tell-tale of the hammering process. And one which is hidden, btw, on polygonal rifling.

The tool marks are exceedingly shallow. Exceedingly. The land to groove height is about .0045 (according to SAAMI spec, not measured in this barrel). That means.. jeeze... those "marks" we see are very very VERY shallow. Muggsy help me here, but I'm thinking they're in the "micron" range, which is roughly a third of one ten-thousandth of an inch. Very small.

So we have two bits of compelling evidence for hammer forging. I'll stick with that one. Chatter marks from button rifling? I dunno. I saw in one place that Charter used to rifle mounted barrels with broaches, from forcing cone to muzzle. That seems rather cost prohibitive in today's manufacturing environs, where you can make up (or buy) a button rifled long barrel, and cut it into whatever barrel length you want for your pistols - all automatically. All they need is some fitting to each frame - the human interaction part. Gotta go look at my .45 Pitbull... see how they did that. I've yet to see a button rifled barrel with anything but glass smooth interior, excepting defects in the drilled blank that got through QC and somehow made it through the process.

Thats my story, and I'm stickin' to it! :p

And, that is a Kahr barrel, from a photo on our website. So... when you hear about that "expensive hammer forged polygonal rifling", keep in mind, the same process is used for conventional rifling, and frankly... it may be easier to hide some defects, non-conformity, with the polygonal rifling. Technical advantages and disadvantages aside, the expense part of all of that is marketing hyperbole.

[Bills1873]

Thanks for that interlude, CJB! Give us some more. Interesting to discover how our guns are manufactured.