Barrels: Cut Rifling vs. Button Rifling
Our barrels come in two forms: cut rifled and button rifled. The price difference is simply the cost difference paid to our primary barrel supplier, Rock Creek. We pay $125 more for a cut rifled blank so we charge $125 more for it. They charge more for it because it takes substantially longer to produce due to the way the rifling is imparted to the barrel’s bore. At PVA that is the end of the differences. The CReS material used is identical, the material is drilled and lapped with the same equipment, normalized the same, then lapped and normalized again… the same.
The discussion of “cut rifled vs. button rifled” barrels dates back quite a way in the world of precision rifles. The vast majority of barrels in the world are button rifled for the simple fact that they’re much less time consuming to produce. That doesn’t mean that they’re any less accurate than a cut rifled barrel. In fact, there are some conditions that cut rifled barrels are actually LESS consistent barrel to barrel than a button rifled blank. This is because of how the cut rifling head needs to "float" inside the bore hole and it scrapes away material.
The button rifled approach swages the steel of the barrel into the form of the rifling. Most lower cost barrels formed this way have a critical step not included after the rifling is formed; stress relief. Stress relief is also known as “normalizing”. We normalize the material before drilling and reaming, then we normalize again after buttoning and before finish lapping to get the most consistent finish inside and the most consistent results downrange.
Some concerns are brought up continually from customers looking to understand what the difference in process means to them. Some of the most common concerns or discussion points are listed below.
- Longevity (barrel life)
- Accuracy (most correctly termed ‘repeatability’)
Across the industry this is not the case to have otherwise identical processes for 2 product lines. Typically, the largest commodity barrel makers out there are using much softer material for their button rifled blanks. It is easier on the buttons, easier on normalizing (if they even normalize after buttoning) and more reliable in bulk process not to break buttons off in the blanks. The hardness of the barrels is critical in only 1 metric and that is longevity.
Softer material breaks down in the bore faster and the life of the barrel is diminished due to it. We have seen several competitor barrels in 6.5mm Creedmoor that only lasted 1800-2000rd before they were unable to hold 1moa at 100yd. Upon dissection the material hardness was measured and shown to be 5-6 points lower on the Rockwell C scale. That is the difference between a 6.5 Creedmoor that lasts 3000rd and one that goes only half the distance.
This is a valid argument by the proponents of cut rifled barrels lasting longer however it is generally a bit misleading because most folks use the bulk commodity button barrel as a basis in comparison to a flagship cut rifled product. We know that a $95 barrel blank isn't comparable to the attention and work in a $300+ blank. It doesn't matter how it was created, so we need to compare similar products to have a reasonable chance at a fair comparison.
Therefore we spend more money on the raw material to get a better starting point for our barrels. We aren’t out to just cut the cost, we needed a product that was just as good through the use of actual engineering and process control. So a word of caution when it comes to comparing barrels with ours: the barrel may shoot very well (a nod to the gunsmith’s skill) but the softer barrels don’t shoot as well for anywhere near as long as a harder barrel.
As far as how the two shoot on paper is indistinguishable in our testing. If there is an advantage to the cut rifled barrels in performance or longevity the advantage has yet to be realized with the standard that PVA holds its barrel blanks at. This is true of the cleaning and break-in as well. Since the barrels are double lapped the break-in for either prospect is the same (see our Break-In article) and cleaning regimen is the same. Similarly the Osprey blanks are micro-honed and final check lapped. They behave just like any other high end, 416 based barrel.
So the next question that begs to be asked on the topic of "hole control". Before the barrel is rifled, the control of the bore hole is extremely importatnt.
Cut rifling barrels MUST be lapped before and after rifling in order to remove the scraping marks of the rifler. This chatter that's removed is done with a lead lap through either machine or hand lapping. Both of them involve stroking a lead lap back and forth in the bore until the bore is polished. There are many benefits to this but there are also some detractors. A barrel that is "fully lapped" after rifling is a barrel where the minute geometry of the rifling lands and grooves are worn away as part of the lapping/polishing process. There are distinct benefits to lapping, especially when it comes to making sure there are no tight or loose spots in a barrel. However the modern method that replaces most lapping necessity is micro-honing.
Micro-honing is a process in where a diamond coated stone is stroked down the unrifled bore and the bore hole is controlled to tolerances exceeding 2 microns. This gives the rifling machine as near perfect of a hole as possible to rifle, cut or button. When testing barrels that were micro-honed it was statistically impossible to find the barrels that were cut rifled versus button rifled. The parent material was identical, it was drilled, reamed and honed indentically, and the performance on target was identical. Which is to say, it was fantastic.
As our company motto states we are "Engineering Repeatability". Therefore we look at the problem at hand and attempt to solve it in the most effective, efficient way possible. The reason that Osprey Barrel Works blanks were chosen to be button rifled was to avoid the breakdown of the rifling after the barrel is finished in most of the machine processes. The way this could be accomplished without sacrificing the "hole control" of the barrel was by micro-honing the drilled blanks. This choice has proven out in testing to be an extremely effective method of applying modern manufacturing technology to the age old problem that is the precision rifle barrel.