Barrel Forcing Cone Undersized

T

Texas Tony

Inactive
I put this in the tail of my last post but decided it actually warrants a thread of it's own for the sake of making it easier for future users to find. I received my handgun back from repair for other problems and they stated in the repair sheet:

"Barrel Forcing Cone Undersized. Adjusted."

My question is "So what"? Can someone explain the impact of an undersized barrel forcing cone?

Thanks and sorry for asking the question in the other thread where it arguably didn't belong.
 
The cylinder throats and forcing cone of a revolver need to be matched with proper tolerances to allow the bullet to make a smooth transition from cylinder to barrel. The forcing cone allows the bullet to align itself in the bore without shaving off any lead.

And undersized forcing cone will cause lead shaving and particle spitting.

Bob Wright
 
Thanks Bob for the quick reply, but I'm still new to this... I promise I'm not in the least trying to be rude, but why do I care about lead shaving & particle splitting? Is it less accurate? Less consistent? Less damaging? More dangerous to me as the shooter?
 
for one, it would make quite a mess if your just using plain lead, shearing off before entering the barrel and going between the cylinder, and who knows how bad it could be with a jacketed bullet, but i would guess iit would split the jacket and not only effect accuracy but causing more severe problems as well

but thats only if the cone is bigger than the barrel, if the cone was smaller, i guess it would just be an accuracy issue

im just guessing btw, i dont know very much about wheelguns

edit: i just saw it said UNDERSIZED, so i dunno, i would assume just accuracy
 
The purposes of the barrel forcing cone are to compensate for a difference between the diameter of the cylinder throat and the groove diameter of the barrel, compensate for any slight misalignment of the cylinder and barrel, and provide a leade for the bullet into the rifling.

Obviously, the ideal would be for the throat, the barrel groove diameter and the bullet diameter to be exactly the same and for everything to always be in perfect alignment. That is not going to happen in anything like mass production. So the bore at the end of the barrel is made cone shaped, to allow the bullet to enter the barrel in reasonable alignment and even allow the bullet to align itself as it makes the transition from the cylinder to the barrel.

If the cone is too large, and the cartridge is high enough pressure, the bullet will be expanded by the pressure as it leaves the cylinder and swell to the diameter of the forcing cone. It will then be squeezed back down as it enters the barrel. That expansion and contraction is not good for accuracy.

But if the cone is too small, (meaning the rear of the cone, since the front of the cone cannot be smaller than the barrel) and the alignment between barrel and cylinder is less than perfect, the gun can shave lead as the bullet tries to enter the barrel and that can also lead to inaccuracy.

I recall one poster who declared that his revolvers didn't have forcing cones since all of his revolvers were totally perfect and that he would never own any revolver that did not have perfect alignment. I had to conclude that he did not understand the terminology, since I know of no revolver that does not have a forcing cone (even the Russian Nagant has one), it being needed to provide that bullet leade even if alignment is good.

Jim
 
Reading the revolver thread it seems many revolvers have tight chambers and forcing cones and this does NOT make the gun unsafe.

But why doesn't a tight forcing cone 'break' earlier in its life. Doesn't a tight forcing cone get 'battered' more than a loose forcing cone?
 
The biggest problem with shaving lead is loss of accuracy. However, extreme particle spitting is dangerous to anyone who might happen to be standing next to you. And shaving bullet jacket material will puncture your thumb or fingers and leave particles embedded in your thumb or knuckle that is near the barrel/cylinder gap.

Bob Wright
 
Actually forcing cones rarely break or even give any trouble. The one case most mentioned, the S&W Model 19, was a rather unique situation. Because of the use of the K frame, the forcing cone area of a .38 has to cut away at the bottom, a situation that gave no trouble until the Model 19 (Combat Magnum) was produced. Even then, there was no problem until hot .357 ammo with light, jacketed bullets came into existence. That ammunition overstressed the weak forcing cone and in some, still rare, cases caused it to break.

S&W's solution was the L frame, larger enough from top to bottom to allow a forcing cone of more than adequate thickness. Now there is a new K frame .357 on the market; I have not seen one yet and don't know how they solved the forcing cone problem.

Jim
 
Split barrel stubs are not all that rare. I've experienced it in one Ruger Super Blackhawk and in one S&W Model 29. My son-in-law has had it happen twice on a Dan Wesson .357 Magnum.

In my case the barrel was replaced free by S&W. I did not want to return my Super Blackhawk (a Three Screw) to the Ruger factory, so paid my gunsmith to replace the barrel.

Don't remember my son-in-law's solution.

Bob Wright
 
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