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#7072978 - 11/13/12 05:13 PM Re: Question about rifle barrel - chamber/throat [Re: 1234567]
Al_Nyhus Offline
Campfire Regular

Registered: 01/01/03
Posts: 900
Loc: Lower Dakota Territory
Originally Posted By: 1234567
Malm:
I have throated a few rifles that were chambered without a throat on the reamer. I could not find any information on how to determine proper throat length. Some sources said to throat for the bullet you are going to use, but did not offer any advice on how to throat for any particular bullet.


Seat the bullet so that the base of the bullet ends where you want it in the neck. Then, throat the barrel until the bullet in your 'dummy' case just contacts the lands.

Good shootin'. -Al
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#7073162 - 11/13/12 06:02 PM Re: Question about rifle barrel - chamber/throat [Re: Al_Nyhus]
Malm Offline
Campfire Ranger

Registered: 10/03/08
Posts: 1628
Loc: SLC, Ut
Originally Posted By: Al_Nyhus
Originally Posted By: 1234567
Malm:
I have throated a few rifles that were chambered without a throat on the reamer. I could not find any information on how to determine proper throat length. Some sources said to throat for the bullet you are going to use, but did not offer any advice on how to throat for any particular bullet.


Seat the bullet so that the base of the bullet ends where you want it in the neck. Then, throat the barrel until the bullet in your 'dummy' case just contacts the lands.

Good shootin'. -Al


Yup, just like that!
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Lock, Stock and Barrel gunworks
SLC, Ut
USMC 69-73

"This is my rifle, there are many like it but this one is mine. My rifle is my best friend, it is my life."

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#7073899 - 11/13/12 11:18 PM Re: Question about rifle barrel - chamber/throat [Re: Malm]
Malm Offline
Campfire Ranger

Registered: 10/03/08
Posts: 1628
Loc: SLC, Ut
A little further explanation on how to accomplish it with minimum tools. Place the barrel vertically in the vise and drop an empty case in the chamber and take a measurement from the base of the case to the torque shoulder of the barrel. Then, insert the "dummy" round and re-measure. Advance your throat reamer the difference between the two measurements.

When customers leave it to me to determine and set the throat length to a particular bullet, without providing a dummy, I simply drop an empty case into the chamber, as in the above example, and take the measurement. Then I drop the actual bullet into the chamber where it comes to rest against the lands, and with my depth mic, measure the distance from the mouth of the chamber to the base of the bullet, and then transpose that to where the bullet would sit in the empty case to determine the exact distance needed to go to set the depth.

It's a lot less of a hassle using a seated dummy round if you can. And if the customer doesn't have any preference for seating depth, I always set the throat so that the base of the bullet is flush with the base of the neck. And if that bullet is a boat tail, unless otherwise specified, that area is the transition point where the parallel portion of the bullet ends, and the boat tail begins. Of course, whatever you do, it has to fit the magazine.

_________________________
Lock, Stock and Barrel gunworks
SLC, Ut
USMC 69-73

"This is my rifle, there are many like it but this one is mine. My rifle is my best friend, it is my life."

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#7073922 - 11/14/12 12:24 AM Re: Question about rifle barrel - chamber/throat [Re: Oregonmuley]
Malm Offline
Campfire Ranger

Registered: 10/03/08
Posts: 1628
Loc: SLC, Ut
Originally Posted By: Oregonmuley

Can you chamber/throat a barrel so that its accurate firing a variety of bullets - as long as they are of the same weight?? Or is that too much of a wildcard with any given barrel??


Provided the bullet weight doesn't exceed the twist rate of the barrel, all bullets within a given caliber benefit from a straight, minimum diameter throat.
_________________________
Lock, Stock and Barrel gunworks
SLC, Ut
USMC 69-73

"This is my rifle, there are many like it but this one is mine. My rifle is my best friend, it is my life."

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#7074624 - 11/14/12 08:05 AM Re: Question about rifle barrel - chamber/throat [Re: Malm]
dogcatcher223 Offline
Campfire 'Bwana

Registered: 03/29/05
Posts: 13648
Loc: Kolorado
Malm, what is your recommened clearance in the mag well? I have heard leave a gap between the bullet tip and the magazine of .050-.100" when making a dummy round.

Thanks.
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#7074925 - 11/14/12 09:59 AM Re: Question about rifle barrel - chamber/throat [Re: dogcatcher223]
Malm Offline
Campfire Ranger

Registered: 10/03/08
Posts: 1628
Loc: SLC, Ut
.050 clearance is a good number to follow. That will still allow you to seat the bullet out a touch more without interference. Always leave yourself some wiggle room just in case.
_________________________
Lock, Stock and Barrel gunworks
SLC, Ut
USMC 69-73

"This is my rifle, there are many like it but this one is mine. My rifle is my best friend, it is my life."

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#7075354 - 11/14/12 12:20 PM Re: Question about rifle barrel - chamber/throat [Re: Malm]
greydog Offline
Campfire Ranger

Registered: 06/11/04
Posts: 2480
I also usually throat rifles with a parallel throat which is .0005" over nominal bullet diameter (ie. a 30 caliber wil get a .3085 throat). This generally works out well but not always. Upon occasion, one may get some bullets which are a bit large and this can be a problem.
The primary requirement for the rifle's throat is that it be concentric. The 1.5 degree angle in is SOP nowdays though some still prefer the 3 degree and one reamer maker thinks a 3/4 degree might be better. Who knows?
I have shot some very accurate rifles which were chambered with the typical long, tapered, European style of throat. Shultz and Larsen target rifle barrels were chambered this way and worked real well.
If the throat is concentric and of .0005" over bullet diameter, the amount of freebore (distance to the lands)does not seem to be real critical in the world of hunting accuracy.
I still favor the throat as described by Malm but the longer I do this, the less certain I am that anything is certain.
The most accurate hunting rifle I have in my rack has a long tapered throat and the bullet is nowhere near the lands. The most accurate target rifle has a parallel throat and shoots best with the bullets well into the lands. GD

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