Coned bolt

[carlsbad]

The first used barrel I bought that had a .735 counterbore I was stunned. At first I thought it was just sloppy or an error. Then I realized the previous owner had probably had an M-16 style extractor and had to make clearance for it. this is why I don't like M-16 style extractors on magnums. No problem on .473 boltface as the M-16 extractor stays inside the bolt diameter.

 

[TRA]

I can't agree with this. Sure, if enough pressure is applied, anything can and likely will fail.
One reason the bolt nose comes completely off in some cases is if the counterbore is too big, id. Again, .003-.005" is the designed clearance. The bolt nose can only be expected to yield so far before it breaks off.

"Breaks Off" ????

The cone can be cut flatter than on the bolt and there is no problem but if the cone is more acute, the amount of exposed case is greater. No reason not to cut it the same if you are going to cut it at all. I always go for .005" clearance and accomplish this by cutting the cone deliberately shallow. I then insert the bolt into the receiver and screw the action on to the barrel until the bolt contacts. I then use feeler gauges to determine how far I have to go. So. if the barrel shoulder is .031 away from the receiver face, I cut the cone .036 deeper and there you have it. I use a dial indicating on the carriage to set the cut.
I am quite sure Remington (Mike Walker) did deliberately engineer the "three rings of steel" into the 722 action. Had they not, there would have been no reason for the counterbore at all and the lugs could have gone right to the end of the bolt. The Remington does do a good job of sealing the high pressure gas in the event of a case failure. A coned breech does not and does no better than a flat breech in this regard. WH

Look at an action and a appropriate barrel and see what would be compromised if the barrel tenon was shorter. Be it a rem style or a cone style.

I can't agree with this. Sure, if enough pressure is applied, anything can and likely will fail.
One reason the bolt nose comes completely off in some cases is if the counterbore is too big, id. Again, .003-.005" is the designed clearance. The bolt nose can only be expected to yield so far before it breaks off.

What's the clearance have to do with the "bolt nose comes completely off", as you say? The smaller the clearance the higher the possibility that the bolt will erode and spray molten metal every which way, which in turn becomes a cutting torch. There's way too much energy and gas expansion, in a catastrophic failure, to contain it. Releasing it is the safest bet.

 

[Will Henry]

I have seen Remington bolts contain some pretty impressive pressures. One rifle, a 30/06, was fired with 49 grains of 4227 behind a 180 Sierra (and so noted on the cartridge box. The owner must have figured 4227 was pretty close to 4320). The bolt nose expanded to seal the counterbore and the only hint of a problem was when he couldn't open the bolt. I made a split bushing to squeeze the bolt nose back down , replaced the extractor, and the rifle was fine. His buddy was firing a Ruger 77 and fired one of the same cartridges. As it is designed to do, the Ruger vented as the case failed. The stock was split, the floorplate, follower, and spring were blown out. The extractor was never found. The scope (a steel Weaver) was dented and bowed upward. Bolt body and receiver were fine but repairs were costly.
If, in an action with a coned bolt, a flat breech is used on the barrel, the only thing which is lost is about a thread and a half. Clearance between the extreme front of the bolt and the barrel is the same. When I'm fitting a barrel for a customer, I cut a precise cone. If I'm doing it for myself, I'm not quite so fussy because I know it doesn't matter. In either case, clearance is .005". WH