rifling methods and wear?

I was in a shop the other day and the fellow behind the counter made a comment I thought interesting if not accurate.

He said brand X rifle was button rifled and as such would wear out faster than a more expensive rifle.

It has been my understanding that broach and button rifling both cut lands and grooves into the bore. One does the job with successive cutters and one does the job all at once.
For the life of me, I can not fathom the logic behind this fellow’s comment.

Is there a difference in throat quality between the two rifling methods that would lead to faster throat erosion?

My feeling was the young man was merely full of beans and not information.
I was dumb struck at the time and did not attempt rebuttal; however, I think the issue needs resolving in my own mind.

Help!

Broaching is a form of cut rifling and steel is removed in the process.

In button rifling, a carbide button is either fixed to the end of a rod and pulled or floated and pushed through a drilled, reamed, and lubed blank. No metal at all is removed in the process. In fact, when the button moves through the blank, you can watch and feel a ripple moving over the button as it goes from end to end and measurements of the outside diameter of the blank after buttoning are slightly but measurably greater. When pulled, the machine is set to the required twist and the whole assembly rotates as needed. When pushed, a longer button is used and different rates of twist are achieved with different buttons.

Either way, what wears out a barrel is throat erosion, and the amount of erosion is a function of how hot the loads are and how hot the barrel is allowed to get in a shooting session. Some barrel steels are known to be more susceptible to erosive wear than others. Either of those factors is much more likely to have a greater effect on barrel life than the type of rifling. For instance with a hot round like a .220Swift that has a proven reputation for quickly eroding throats, you can double or more your barrel life by shooting moderate loads as opposed to pushing the velocity/pressure envelope with max loads. Varmint rifles, match rifles, magnum rifles, and military rifles all are nototious for eating barrels due to heavy use and/or heavy charges, but for most rifles it is never an issue.

Personally, I have never seen, heard or read anything that would indicate the style of rifling would influence barrel life. It may be that someone has done such a study and news of it has simply not reached me, but based on what I do know I suspect the person in question is full of fertilizer. If he can actually provide some documentation beyond promo literature from some marketing department I would be interested in reading it. I'm never too old to learn something new, but I have a hard time swallowing that one without something more to back it up than the word of a salesman.

I had never read anything to substantiate his claim myself.
Thanks for the reassurance!

versifier, please correct me if I am wrong:

There is a paradox about what is expensive/cheap.
Button rifling, hammer forging and I think broaching are very expensive in machinery; so only big makers can afford them and thereafter offer "cheap" products (Remington, Winchester, etc)
Small, "expensive", shops still cut one groove at a time, with affordable tooling they can actually make and fix...

About durability there's always the possibility that the maker used sub-standard steel to save on tooling and gave a bad name to his process....
One of the Italian makers of 45-70 replicas is getting a bad name in Europe as shooters have been claiming that their rifling would go in a few hundred rounds.
Closer to us, ROTO barrels are said to be hammer forged, usually a top military choice, but users have claimed that these 1911 barrels were made of soft and not durable metal.

some reading here:
http://www.ojp.usdoj.gov/nij/trainin...ir_m04_t06.htm

Buttoning is one of the cheapest and quickest methods of rifling. Much of the barrel drilling, reaming, and rifling machinery today at least in smaller shops was bought after WWII from government contractors for next to nothing. I had no problem buttoning two barrels per minute when I ran a pull-through machine one barrel at a time. The cut tooling we used on m/l barrels held two barrels at a time, but the run cycle was about an hour. (There are lots of different kinds of tools for cutting rifling and many shops make and maintain their own designs, but I think our shop was fairly typical.) I have no direct experience with either broaching or hammer forging, only what I have read, so I have no idea what the rate of production is, but I am certain that both methods are much much slower than buttoning.

Drilling is a critical operation and the quality of the hole is determined by the skill of the machinist who sharpens the carbide tipped deep hole drills and by the skill and experience of the operator to hear when there is a problem with the bit. A good driller can operate eight or more spindles on double horizontal drilling tables and his time is spent going from one spindle to the next, removing the drilled blanks and replacing them with a undrilled ones. The drill is forced into the spinning blank (running at up to 5000rpm IIRC depending on bore size) with high pressure cutting fluid forced through the center of the bit to both cool the cutter and push the chips out to prevent them from clogging the hole. When all goes well, the drill produces a certain pitch sound, and if one spindle is having a problem, it produces a louder and higher pitched whine. Experience and good hearing enables the operator to quickly figure out which spindle is in trouble before the drill bends and snaps, spraying cutting fluid in a 20' radius all around. We used to call it "getting a shower" when it happened. It didn't happen very often, and when it did there was usually hell to pay because production was thrown off and the VERY expensive bits had to be replaced. You could always tell if anyone had messed up when we took a break as our light green work uniforms would turn to forrest green after a good dousing with cutting oil. Any blanks with off center holes are tossed (too many culls means the drills were allowed to get too dull). I operated the drills when the regular operators were sick or on vacation, but it was not a fun job. I constantly wished for a second set of hands and a prehensile tail. I had real trouble running more than four spindles and my butt was really dragging after an 8 hour shift.

Next, reaming is done in several stages to remove tool marks from drilling and to get the bore a consistant size. If there is going to be skimping, this is the stage where many companies choose cut corners. On a cheap barrel, they may run it through only one reamer, while on better ones, two, three, or even four passes are made with progressively larger reamers until the bore is smooth and to size. The more consistant the quality of the bore itself from barrel to barrel, the more accurate the barrel will be regardless what method of rifling used. Many shops will even run a smooth button after reaming before cutting rifling, especially on bigger bores, to help with consistant size. If there are deep tool marks left in the bore after reaming, the rifling will not be smooth and even, the barrel will be difficult to clean, and accuracy will suffer. Bore sizes are checked with GO and NOGO gauges and anything that doesn't pass is scrapped. I remember my boss looking into the reject bucket one day and commenting "These are the world's most expensive pea shooters. We don't make pea shooters here. Mic those reamers and change them."

Then the bores are completely cleaned (by hand with rods and patches) of all cutting fluid and lubed with a teflon compound. After the vehicle in it evaporates, they go to the buttoning machine.

As you can see, most of the time in a buttoning operation is the prepping of the blank. Cutting the rifling doubled production time or more per barrel. We did not finish the outsides of the blanks. That was up to our customers in the industry. Neither did we choose the barrel steel, except on own BP barrels, so every run was different and it really kept the drillers on their toes.

In contrast, the US barrel maker whose match barrels were setting and holding all the HP and BR records at the time used one specific stainless steel, vertical multispindle drills, three consecutive reamings, and push-through rifling. They made one barrel at a time slowly and carefull with much hand work and the quality of their finished barrels was absolutely amazing. I had a great time visiting their shop and discussing the advantages and disadvantages of the various methods and techniques. Our own production barrels were noticably more accurate than most other production barrels in the industry of the time. It is all a matter of choosing the correct steel and properly prepping the blanks before rifling them, rather than the actual method of rifling itself, that determines the quality of the barrel.

If you are curious, you can go here: http://www.gmriflebarrel.com/sitemap.aspx and check out the various stages and even see the actual machines I worked on in the '80's.

Dear Versifier,

Thank you for spending the time on your most complete and informative response.

I also received this link which has a very thorough explanation of the processes.

http://www.border-barrels.com/articles/bmart.htm

A hero of mine said to me ”Konrad, when you have a question, make sure you go to somebody smarter than you, not dumber that you”.

The next time I’m in that shop, I’m going to be able to discuss his statement with a modicum of knowledge. I am quite sure this fellow was spitting out some sales pich he had heard and never verified.

Thanks again,
K