the xx is the standard notation for carbon content 4150 has approximately 0.5% carbon, 4160 has approximately 0.6% carbon.
The letters CM after the name are a redundancy - they are completely unneccessary, as being in the 41XX family of steels, they are, by definition a CM formula.
Depending on how exatly the steel mill made a particular batch, their quality control, etc, 4150 and 4160 are close enough that they could end up being functionally identical. Certainly, the extra .1% carbon does make a pretty big difference, but standard tolerance levels in carbon content mean that 4150 can have as much as 0.55% carbon and still meet grade, and 4160 can have as little as 0.56% and still meet grade.
In a perfect world, there would be a reliable and stark difference between the two, and steel from hign quality, reputable mills does show a notieable distinction, but that isn't ALWAYS the case.
I've looked at the 5C rifling design. It's an interesting idea, canting the rifling like that. It looks like a sharp cornered version of polygonal rifling, being about halfway from traditional to poly. It seems to offer many of the same benefits of polygonal rifling, and has been showing off pretty well in competition.
It's been a hundert years since I seen those metallurgy terms. I was hoping to see "closed packed hexagonal" in there somewhere. That was my favorite.
That was a heck of a good read.
Here's my experience.
I gave up Remington 40X and Hart Actioned/Hart Barrels and the whole bench rest thing when HK brought out the PSG-1 with the polygonal rifling which would out shoot anything that I had. And that out of a semi-auto.
I shoot a fairly high intensity cartridge with a 3 groove Lilja with, I think, a 1-7 twist. It started dusting lighter jacked, long bearing surfaced bullets at about 400 rounds. I'm told that about 50% of the barrels of this design do the same thing. Its definitely hard on the bullets.
The 5R barrel when rifled exactly right seems to be less hard on bullets.
I'm thinking my next barrel will be the Schneider polygonal in a larger slower twist caliber.
I did some experimenting with Frontal Ignition, igniting the powder at the bullet base, but it appeared that the temperatures increased mostly just ahead of the chamber thing migrated down the barrel. Concentration the heat at the throat seemed to be the opposite of what I was seeking. However, Extreme Velocity Spread and Standard Deviation and accuracy were improved. Plus recoil was noticeably less.
The paradigm may have changed with the newer steels. I'd pay extra for the pluses, if they 'really' made a difference.
Keep up the research.
You post 'em I'll read 'em.
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!
Last edited by royinidaho; 03-03-2008 at 10:12 PM.
Sorry, no body centered hexagonal structures here... We're all hoping for the nice, relaxed face centered cubics round these parts! Hexagonal grain martensite is full of nasty stresses that will make your barrel do the twist and other neat things while you shoot!
Another thought has occurred to me... In handguns, polygonal rifling is used as opposed to land and groove style and reports are vastly extended barrel life. This is, of course, problematic for rifles for two reasons: 1: at the corners of the polygons there will be some blowby of expanding gasses. 2: the polygonal rifling will warp the shape of the bullet, paerhapse adversely affecting accuracy.
Would I be correct if I assume you believe the corners of a polygon barrel have sharp corners?
Personally, I believe anyone considering sharp inside corners would be ignoring one simple fact of engineering. Sharp inside corners are where stress cracks are most likely to start.
I would assume a maker of polygon barrels, would have at least a small radius in these corners. Any cutting tool button with sharp corners would quickly wear out those sharp corners. It would complicate calculating a total area that wouldn't cause so much swaging of the bullet as to cause increased pressures. However most mechanical engineers I've met are very good at making the more complex equations such as these. I would think someone with better spreadsheet skills than mine could easily do this. If they in fact do make these barrels, it should (at least in my mind) make those comers much easier to clean.
I sent an Email to PacNor asking a number of questions I wanted answered, but never received a reply. After a month of waiting, I Emailed the other polygon barrel manufacturer (Schneider?) with the same questions. That was over a year ago. Still no response,
I was very interested in a polygon barrel then, but finally decided a potential customer wasn't too important to them. So my conclusion was similar to theirs.