A good start and I will add to this.....and this has been beaten to death.....and before I get deep into this I will say all barrel making methods can make a very good barrel and can make garbage. It goes back to the barrel maker paying attention the best they can to all aspects of they're manufacturing process.
Button rifling work hardens the bore so on average a button barrel (barrel life wise) will not last as long as a cut barrel. On average the cut barrel will go 15% to as much as 25% longer in barrel life. This isn't just me saying this or that either....for one it's what I've always seen and also based on actual data from ammunition test barrels that we make for bullet makers, ammo makers etc....They keep exact round counts and load data and test the barrels in controlled conditions. Even when the button barrel and cut barrel where made out of the same lot of steel.
Twist rate uniformity....cut barrel wins the consistency hands down. Some button makers are trying to help guide the rotation of the button. The twist is built into the button. What happens is if the button hits a hard spot or soft spot in the steel usually it will slow the button down. The button can speed back up to what it is suppose to be doing for the twist but when this happens either way you end up with a non uniform twist or a barrel with a negative twist rate. This leads to accuracy issues and to me the barrel is more load temperamental as to what it will shoot etc...I've seen button barrels where the twist rate went slower towards the muzzle to the tune of as much as .75 of a twist.
Bore and groove size diameters and uniformity. You can get a button barrel with a uniform bore and groove size but again the consistency goes to a cut barrel. Why? Button rifling is a cold swagging process. Button rifling doesn't remove the material when making the grooves it displaces the material. This is a common misconception. Where as cut rifling we physically cut the groove away. During button rifling the steel will expand and relax as the button goes down the barrel. This also goes back to work hardening the bore also. The button maker if they use a different button or gets a different batch of steel or uses a steel with a different diameter will have to play with button sizes. The more uniform the bore and groove sizes are it will only help the accuracy of the barrel and velocities and pressures. We just inspected (in the last 6 weeks) a couple of button rifled ammunition test barrels. The ammo maker sent them to us to look at and gauge them because our barrels where running right on the money. They couldn't figure out why they where getting pressures a full 8000psi above max. and couldn't get the velocity. I told them my guess was the bores where under size. Sure enough the bore and groove size where both a full .0005" under size and it wasn't just for one barrel either. It was for a few of them. This is why some button makers offer different grades of barrels. Uniformity.
Also they have to button rifle the barrels as I said before as a blank (no contour). Any variance in the o.d. of the barrel will effect the uniformity of the bore size as well. They button it as a blank and then have to restress relieve the blank and then they contour the barrel. It's the only way you can come close to doing a consistent bore size on them. The other problem you have is residual stress in the blank. No barrel maker can measure for stress in the blank. When the barrel gets contoured and during the turning operation the turning work if it hits a stress point will relieve the stress and this will cause the bore to open up on you. Again goes back to consistency. The last place you want the bore to go sour is at the muzzles crown. If this opens up when the muzzle is threaded and or just cut and crowned it will/can have a negative impact on accuracy. Same goes for fluting. This is why some button barrel makers say if you flute they're barrels it voids any warranty etc... We contour our barrels primarily before reaming and rifling. If we are going to lose the barrel due to any residual stress it will happen here for us. With cut rifling not inducing any stress into the blank we don't have the problem with bore size uniformity and this includes fluting the barrel after it's rifled etc....
Here is a couple of good videos (we didn't make them and had nothing to do with them)....
The first one below shows the muzzle going sour/opening up during/after threading. All of the first barrels are button rifled. The last two are ours. The point of the video isn't to hack on any barrel makers but to make the muzzle thread diameters as large as possible to help fight the bores going sour.
[video]https://youtu.be/###_YXzJJOU[/video] -
My add: this video won't hyperlink because CGN has stupid censorship rules - the three ### is C U m if you want to look at the video for yourself.
The next one is a button barrel. Watch real closely right about the 8 second mark when the button goes into the barrel. Watch the face of the barrel blank deform. You can see it better starting at the 6:20 mark and also look at the face of the barrel at the 6:40 mark. You can see the steel deform.
Also at the 5:10 mark they talk about straightening the steel bars. Bad! You never want to straighten a barrel blank. Especially after it's been finished. Trying to straighten the barrel blanks induces more stress into the steel and some wonder why the POI shift on some barrels! Especially as they heat up. It will work against you.
With all of this being said...when we we're starting up we we're offered jobs at a couple of different button barrel makers. I politely declined the offer. One asked as to why? I said we know the short comings of a button made barrel. I cannot work at a company where I don't believe in the product. I couldn't talk to a customer or look them in the eye knowing and or feeling we are not making the best product out there.
It all goes back to consistency. The more consistent the bore and groove sizes are over the length of the barrel, the more uniform the twist, the straighter the barrel blank and the more stress free it is the more forgiving the barrel is going to be. No way around it. Again a button barrel can be a very good barrel I just don't see the consistency from one to the next like a cut barrel is.
Later, Frank
Bartlein Barrels