Cone shaped bolt heads?

[tripcrow]

How critical is the fit between a cone shaped bolt face and the cave shaped chamber end of the barrel? How difficult and important is it for a gunsmith to match them up while correctly headspacing a barrel? What’s the purpose of the design? Can a cone shaped bolt be made to headspace with a flat faced chamber?
Thanks,
Bill

 

[AlNyhus]

The purpose of a coned bolt is to allow better and/or faster feeding of the cartridge into the barrel. The cooresponding angle on the back of the barrel allows the tip of the bullet to guide the cartridge into the chamber, elminating any hangups. With short/fat cases this can be a real help.

Obviously, having matching angle between the bolt nose and bolt recess at the back of the barrel is imperative. Most custom actions have angles of 25, 27 or 30 degrees depending on mfg. 'Smiths work with this all the time so it's not an issue at all. Winchester model 70's with the claw extractors have coned barrels, for example.

Normal clearances between the bolt and barrel are in the .005-.010 range depending on the 'smiths preference. There isn't any benefit to running them any closer than this, IMO. Clearances less than .005 invite problems from carbon, a small piece of powder, a brush particle, etc. to get between the bolt and the barrel.

Coned bolts are a good thing........... -Al

 

[expiper]

Ditto on what Al says.....and another thing ....it reeellllyyy helps in the case of .222 class ctgs....in the day when Ralph was building lots of .222 .222 1/2 etc. shooters were just starting to want to shoot "FAST" and the tiny lil shells were layin clear in the bottom of the feed ramp with the bullet tip much further below the bore/chamber centerline there were lots of feed problems,,,just like a 722,,,the tips were hitting on the flat spot or ledges in the "3 rings of steel" stair steps that were on the breech!!!!or the flat breech on the early Pandas...like post 64 M-70)) ooo and another thing....cone breecing also helps when extracting a fired case...when you are draggin a spent round out of the chamber you arent draggin it down that set of stair steps on the rear of a flat or rem. style breech,,kinda like in the cartoons!!!))instead a smooth movement out on the funnel shaped cone breech and then bak thur one of the bolt ways))and folks wonder why the extractor lets go of so many cases on that style action/breech in a true Benchrest gun with a weak ejector spring---they get rattled loose on the way down the steps.!!!...I always tell new shooter to never feed a empty round in to their rifle without flippin it up into the breech/chamber so that the case mouth doesnt get a lil,or big) ding on it,,like when setting sizer die)).....this will cause case mouth splits later and erattic shots, will make your ES go up and down) because of different grip or drag on the shank of the bullet...
so,,besides this,,there is very lil difference....Roger
PS....I hope u can tell ...I like the cone breech ...!!

 

[ArtinNC]

I agree with AL. Here is a tool I made to check the barrel tenon length to the action.. Art

 

[RickB]

Well Al, I am glad to see that somebody agrees with me about cone bolts. Unfortunately, none of the action makers seem to believe that cone bolts are any good as they don't,and won't) make them with repeater actions...so I got some myself and put them in some actions.

I simply do not like the "cut off" bolts that the Nesikas, BATs and so on,which I have) use with their repeaters. My belief is that they do not like the extra work involved with a cone bolt and hence don't do it...though, for the life of me, I can not see any difference in the amount of work involved when using modern CNC machinery. The action manufacturers seem to begrudgingly use cone bolts in single shot actions because their customers demand them.

Cheers