WOW you can MUSE like none other. just to add a few of my own thoughts and experiences. about your #1 topic 3groove barrel's eroding more slowly. IMHO this is total crap and propaganda, from what I have seen through a bore scope if you have a high intensity cartridge (like every gun I own except 222Rem and 6mmBR) your throat firecracks before it starts to erode forward. a 3groove is much rougher on a bullet in a firecracked state than a 4,5,6 groove barrel ,so it in reality has a shorter barrel life.
It is a mystery to me why a reputable company like Lilja and to a lesser extent pac-nor continue to make these dinosaurs. before I finish my rant on bad ideas,you mentioned moly-fusion. I tried to give it a chance and a FAIR test, but I know too many people who have tried it and it is another miracle cure with no merit.
The best way to get the most barrel life is to break in properly, clean on a regular basis and dont get it over heated in a dog town.
It takes 43 muscle's to frown and 17 to smile, but only 3 for proper trigger pull.
I have read quite a lot about moly fusion, and you're the first I've ever seen give it a negative review. I really appreciate your candor, and the timely information! I will be testing it myself, along with some other products in the relatively near future. In my forge, with abrasives, with acids, salt water, and buried in some reloading poeder and lit! I figure if I can quantify and control the factors that cause barrel problems, and test treatments and coatings against those factors, I should have a decent idea on weather or not to put it into my gun!
Yes, 3 grooves are rougher when firecracked, but does it take longer for a similar amount of scale (cracking) to build?
Have you perhapse been able to substantiate the cut vs button rifled argument?
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.
I would think that both problems could be overcome in the following manner: more sides to the polygon, with better dimensional control. Example, typical handgun poygonal riling is octagonal. Why not 12 sides. Sure there are more corners, but they will be substantially smaller. Squeeze the bullet just a little tighter, and you can force the bulletr right into those corners, eliminating the blowby effect. Further, 12 sides is a lot closer to the original round state of the bullet, which, spinning at high RPM's will carry with it an air cusion anyhow. Sort of like why golfballs have dimples, they are actually more aerodynamic because of them! Again, like many of my ideas, dodecagonal rifling in a tube as long as a rifle barrel is a nightmare to engineer! Even if it could be pulled off, it may not be worthwhile anyhow, as without testing (an expensive proposition at best) we have no real way of knowing weather or not it would ruin accuracy all to hell, or even if it would help barrel life much.
I think that cost is the biggest factor in the barrel makers choice of barel steel , 17-4 is a good bit more expensive , granted it will likley last longer but how much? maybe 20% and if the barrel cost 50% more whats the point? I have a barrel made from 17-4 its made by Lothar Walther for BlackStar company then electo polished by them. The 17-4 is a bit harder than 416 but not realy any worse than CM. If you look at the hardness of the SS barrel compaired to CM you will se that the CM is harder but more prone to "fire cracking" and as a side note CM barrels don't have any carbide in them but carbon thats what makes them harder.
As for the land and groove debate , I think that the idea is that the 3 groove barrels have more surface area on the lands to wear so in theory they will not erode away as fast but as mentiond the increased surface area makes for more roungh surface to eat at the bullet.
Their are some very accurate poly barrels out their , like mantioned the barrels that Tubb uses also the H&K PSG-1 noted as being the most accurate semi auto rifle made uses this style rifling
One of these days after I hit the lotto , I'm going to buy a pile of barrels cut riffled poly and buttoned and shoot them all out in the same caliber to get an accurate "truth" about what last longer
"as a side note CM barrels don't have any carbide in them but carbon thats what makes them harder"
I hate to slit hairs, but I feel I must for the sake of accuracy...
CM stands for Chromium and Molybdenum. The chromium content is not nearly as great as in stainless, but it's there. Among other things, it helps push the pearlite nose on the isothermal transformation curve farther off in time, making it more thoroughly hardening, so a uniform hardness can be had throughout the workpeice.
The carbon content IS much greater in CM than in the stainlesses we are used to seeing, but ALL steels have carbon. Steel, by its very definition is the alloy of carbon and iron.
Chromium LOVES carbon, and chromium carbide is the result. Yes stainless barrels have carbides in them. Yes CM barrels have carbides in them. What makes CM barrels harder is nit the carbon content. That makes it ABlE to be harder. What makes it harder is the heat treat.
Bear in mind that different steel alloys display different levels of tougness (which is the opposite of brittleness, and has nothing to do with strength or hardness) at given hardness levels. A CM barrel wears more quickly not because it is harder, but because it lacks chromium in sufficient quantities to resist the chemical action in the erosion process, which happens at a much accellerated rate under heat and pressure.
With equal toughness and equal corrosioin resistance, a harder steel will wear out slower. Or, alternatively, with equal hardness and equal corrosion resistance, a tougher steel will wear more slowly. Finally, (yep, you guessed it) with equal hardness and equal toughness, a more corrosion resistant steel will wear more slowly.
This is why I like the idea of crucible's high purity modified 17-4. With appropriate heat treat It can be tougher, harder, AND more corrosion resistant than 416R
Remember that fully annealed, all of these steels are way too soft to use. Hardness is your friend, so long as it does not compromise other mechanical properties that are critical. Toughness is also your friend, in the same way, as is corrosion resistance.