Throat?

tomf52 · February 24, 2006, 08:10 PM

Can somebody please define for me exactly what portion of a semi-auto barrel is considered to be the "throat". I would like to know exactly where to run the slug in the bore for the proper measurement of the throat area. Thank you for any help you can give.

mtnboomer · February 25, 2006, 12:54 AM

All rifles and handguns have a "throat" or "freebore", just some look different than others. It is the unrifled area just ahead of the chamber where the bullet meets the leade of the rifling. If you look into the chamber with a strong light, and magnifying glass if possible, as you look past the chamber shoulder you will see a slight step where the case mouth shuld end. The area between this step and the beginning of the rifling is the "throat".

joneb · February 25, 2006, 02:06 AM

So in a revolver is the forcing cone the throat ?

caz223 · February 25, 2006, 09:14 AM

No, the forcing cone is the forcing cone.
The area of the bore immediately afterwards, and before the rifling starts is the freebore or leade. (Called a throat in a semi.)

918v · February 25, 2006, 01:22 PM

Not quite.

The forcing cone is the forcing cone. The throats in a revolver are in the cylinder, just ahead of the chambers. In other words, the part of the cylinder where the buller nose/head/etc. sits is the throat. Throats must be of the same or slightly larger diameter than the bore, else accuracy suffers.

caz223 · February 25, 2006, 03:44 PM

In a revo the part he's referring to is called a chamber throat.
But in most good revolvers after the forcing cone the rifling doesn't just start abruptly, it's cut at an angle.
Some aftermarket modifications can be done, like a taylor throat or a maxi throat. That's done AFTER the forcing cone BEFORE the rifling, and the barrel must be removed to do it.
This area is the throat. It is enlarged from 1/3 to 1/2 caliber width to a full caliber width or more on taylor throating to 2 or more caliber widths in maxi-throating. This is done to make sure the bullet is fully in the barrel and aligned enough to hit the rifling as square as possible. Taylor throats are for normal guns. Maxi throats are for guns that are destined to shoot larger than normal for caliber bullets, bullets so long that that any alignment problems are amplified by the longer than normal lead bullets.
That's not the same as having your forcing cone recut, or your chamber throats opened up.
Although most good smiths offer a package, recut chamber throats, 11 degree forcing cone, taylor throat, recut barrel/cylinder gap, polish cylinders for easier extraction, belt mountain base pin, and so on.
This helps .45 colts greatly, esp cowboy guns that shoot nothing but lead. It's almost like a new gun.
It costs like a new gun.
But on a conversation piece or heirloom, it's worth it.
I'm, of course using a cowboy type gun as an example. The terminology is the same.

uscra112 · March 1, 2006, 09:38 PM

Yeah, but he's asking about a semi-auto. Throat is the area just forward of the end of the case when the round is chambered. The bullet protrudes into the throat, which is usually a very short cylindrical section followed by a taper leading into the rifling. The taper itself is sometimes called the leade. There's an old, old article from the American Rifleman called "Proper Throating is the Key to Accuracy", which is as good an explanation of throats as I've ever read. Which issue I cannot remember, but it was 1970s sometime.

caz223 · March 2, 2006, 08:14 AM

Agreed.

February 24, 2006, 08:10 PM	#1
tomf52 Member Join Date: August 5, 2005 Posts: 46	Throat? Can somebody please define for me exactly what portion of a semi-auto barrel is considered to be the "throat". I would like to know exactly where to run the slug in the bore for the proper measurement of the throat area. Thank you for any help you can give.

February 25, 2006, 12:54 AM	#2
mtnboomer Senior Member Join Date: July 9, 2004 Location: Oklahoma by birth. America by the grace of God. Posts: 635	All rifles and handguns have a "throat" or "freebore", just some look different than others. It is the unrifled area just ahead of the chamber where the bullet meets the leade of the rifling. If you look into the chamber with a strong light, and magnifying glass if possible, as you look past the chamber shoulder you will see a slight step where the case mouth shuld end. The area between this step and the beginning of the rifling is the "throat". __________________ Quando Omni Flunkus Moritati (If all else fails - play dead!) Support the Second Amendment. Join the NRA > http://www.nra.org < Oklahoma State & Big 12 - #1 GO POKES!!!!!

February 25, 2006, 09:14 AM	#4
caz223 Senior Member Join Date: May 15, 2002 Location: Michigan Posts: 1,429	No, the forcing cone is the forcing cone. The area of the bore immediately afterwards, and before the rifling starts is the freebore or leade. (Called a throat in a semi.) __________________ I'm not just a gun. I'm YOUR gun. (Hold me.)

February 25, 2006, 03:44 PM	#6
caz223 Senior Member Join Date: May 15, 2002 Location: Michigan Posts: 1,429	In a revo the part he's referring to is called a chamber throat. But in most good revolvers after the forcing cone the rifling doesn't just start abruptly, it's cut at an angle. Some aftermarket modifications can be done, like a taylor throat or a maxi throat. That's done AFTER the forcing cone BEFORE the rifling, and the barrel must be removed to do it. This area is the throat. It is enlarged from 1/3 to 1/2 caliber width to a full caliber width or more on taylor throating to 2 or more caliber widths in maxi-throating. This is done to make sure the bullet is fully in the barrel and aligned enough to hit the rifling as square as possible. Taylor throats are for normal guns. Maxi throats are for guns that are destined to shoot larger than normal for caliber bullets, bullets so long that that any alignment problems are amplified by the longer than normal lead bullets. That's not the same as having your forcing cone recut, or your chamber throats opened up. Although most good smiths offer a package, recut chamber throats, 11 degree forcing cone, taylor throat, recut barrel/cylinder gap, polish cylinders for easier extraction, belt mountain base pin, and so on. This helps .45 colts greatly, esp cowboy guns that shoot nothing but lead. It's almost like a new gun. It costs like a new gun. But on a conversation piece or heirloom, it's worth it. I'm, of course using a cowboy type gun as an example. The terminology is the same. __________________ I'm not just a gun. I'm YOUR gun. (Hold me.)

March 2, 2006, 08:14 AM	#8
caz223 Senior Member Join Date: May 15, 2002 Location: Michigan Posts: 1,429	Agreed. __________________ I'm not just a gun. I'm YOUR gun. (Hold me.)

February 25, 2006, 02:06 AM	#3
joneb Senior Member Join Date: December 10, 2005 Location: Central , OR Posts: 1,888	So in a revolver is the forcing cone the throat ?

February 25, 2006, 01:22 PM	#5
918v Junior member Join Date: September 25, 2005 Posts: 1,372	Not quite. The forcing cone is the forcing cone. The throats in a revolver are in the cylinder, just ahead of the chambers. In other words, the part of the cylinder where the buller nose/head/etc. sits is the throat. Throats must be of the same or slightly larger diameter than the bore, else accuracy suffers.

March 1, 2006, 09:38 PM	#7
uscra112 Junior Member Join Date: February 11, 2006 Posts: 13	Yeah, but he's asking about a semi-auto. Throat is the area just forward of the end of the case when the round is chambered. The bullet protrudes into the throat, which is usually a very short cylindrical section followed by a taper leading into the rifling. The taper itself is sometimes called the leade. There's an old, old article from the American Rifleman called "Proper Throating is the Key to Accuracy", which is as good an explanation of throats as I've ever read. Which issue I cannot remember, but it was 1970s sometime.