Conventional vs polygonal rifling material

[anthony.mendez]

Over the last 2 years, the evidence techs in our office have been trained in basic bullet exams where we are notating weights, est caliber, twist, amount of L&G, and rifling type. Most of them have struggled mainly with identifying the rifling types and do not feel fully comfortable identifying the rifling type since they sometimes feel as though they're guessing. Especially when it comes to the GEN5 Glocks that throw them off since they have railing but on a polygonal bullet. I'm currently trying to put together a quick guide/ PowerPoint for our office to help with this including what to look for and with close up photos.


With that being said doe anyone by chance have any material on these topics themselves they may be able to share related to bullet exams and or rifling types?


Thanks!

[Bob Kennington]

With regard to rifling types, there are at least two manufacturers in 9mmP caliber that exhibit similar rifling.


One, the Sites "Spectre" has a self-described "sinusoidal" rifling. (No sharp edges).

Another 9mmP--whose name has been lost to time--has "ramp" rifling. (One sharp driving edge, and no trailing edge).

Although also lost to time, the term "buttress rifling" may be the correct manufacturer's term for the above "ramp rifling". (Correction).

The manufacturer's name should be available somewhere in a handy book on the subject.

[Aaron Brudenell]

Here's some stuff I've used over the years.  I haven't added new Glock rifling but one thing to note, because it's cool, is that even the .22 Glock rifling has rails on either side of the pseudo-lands (what I call them). 


I recently had a Glock pistol with multiple shots and test fires where only one of each of the rails was reliably marking the bullets, analogous to a driving edge in conventional rifling.

[Bob Kennington]

Just in case our newer examiners feel uncomfortable using rifling terms like "lands and grooves", the identical "technical" terms are used by the manufacturers of drill bits!


I'd expect drill bit manufacture to be older than the rifling process in firearms.