24hourcampfire.com
24hourcampfire.com
Previous Thread
Next Thread
Print Thread
Hop To
Joined: Jan 2008
Posts: 5,455
Campfire Tracker
OP Offline
Campfire Tracker
Joined: Jan 2008
Posts: 5,455
First of all I hope this isn't too dumb of a question - I'm really trying to better understand how things actually work when it comes to chambering a rifle.
I know they all go "Bang" when you pull the trigger but I'm trying to learn what makes things more accurate.

Anyway, here is my question and it concerns having a custom barrel installed on a rifle, in this case it would be on a model 700 short action.

So I think I get the chamber part and its need for being concentric to the rifle bore and so on, but where I'm confused is on the throat area of a rifle chamber. Is it correct that this should be keep to as tight a dimentions as possible to make it more accurate?? Or is that a bad idea??

I guess what I'm asking is this, can a new custom barrel be chambered/throated to best perform with factory ammo? I know that with handloading you can always "work up" a specific load to be more accurate, but is it possible to chamber a barrel to be really accurate for most factory ammo - or is that impossible to do the differences in factory ammo??

Again, I apologize if this is a really dumb question to ask.


"Rather hunt Mule deer than anything else"
"Team 7MM-08"
BP-B2

Joined: Oct 2008
Posts: 1,628
Campfire Regular
Offline
Campfire Regular
Joined: Oct 2008
Posts: 1,628
Think of throat as being the "birth canal" of the barrel. What happens there, will have a huge influence on the path the bullet takes over it's short life. If a bullet hops, skips and jumps from the case to the bore, then there is a good chance that it will enter the bore, off center, with regards to it's natural axis. The bullet forms to the bore in this position as spins towards the muzzle. Once the bullet exits, it becomes conflicted between two different axes, the natural and the false. The two struggle all the way to the target. This certainly affects overall accuracy.

Some folks, in an effort to improve accuracy, will purposely seat their bullets out into the lands. A lot of them do so without really understanding the mechanics of the problem. Some folks fireform and neck size their stuff in an effort to improve accuracy without really understanding what it does. The mechanics behind that is to reduce the amount the case shifts when chambered, which can have a direct bearing on the alignment of the bullet with the bore.

For the most part, I machine the throats separately. The throat reamers I use are .0005 over bullet with a one and a half degree lead. This, along with a good set up, assures as straight a path as possible, for the bullet to travel from the case to the bore. It's amazing how much consistency is affected by the 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."
Joined: Jan 2008
Posts: 5,455
Campfire Tracker
OP Offline
Campfire Tracker
Joined: Jan 2008
Posts: 5,455
Ok, thank you for that explanation. I think I'm understanding that - the throat relative to the chamber and bore of the barrel.

So when you machine the throat in your example you give, will the dimentions you end up with shoot "most" bullets accurately?

I may be asking for an impossible solution to what is probably a more complex process. 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??


"Rather hunt Mule deer than anything else"
"Team 7MM-08"
Joined: Mar 2005
Posts: 17,527
D
Campfire Ranger
Offline
Campfire Ranger
D
Joined: Mar 2005
Posts: 17,527
Originally Posted by Oregonmuley
can a new custom barrel be chambered/throated to best perform with factory ammo?


Custom barrel + factory ammo = why bother?



Joined: Jan 2008
Posts: 5,455
Campfire Tracker
OP Offline
Campfire Tracker
Joined: Jan 2008
Posts: 5,455
Originally Posted by dogcatcher223
Originally Posted by Oregonmuley
can a new custom barrel be chambered/throated to best perform with factory ammo?


Custom barrel + factory ammo = why bother?



I know I know - gunsmiths probably all shake their head at this question, but trust me I shouldn't be trusted around loose gunpowder-grin


"Rather hunt Mule deer than anything else"
"Team 7MM-08"
IC B2

Joined: Oct 2006
Posts: 7,445
Campfire Tracker
Offline
Campfire Tracker
Joined: Oct 2006
Posts: 7,445
Yes, a custom rifle can be throated/chambered to shoot factory ammo & then pretty much shoot 1 hole......ask me how I know??

[Linked Image]


[Linked Image]


[Linked Image]

Last edited by 300MAG; 11/13/12.
Joined: Oct 2006
Posts: 7,445
Campfire Tracker
Offline
Campfire Tracker
Joined: Oct 2006
Posts: 7,445
300 WM - throated/chambered for Federal Premium 180 grain Nosler Accubonds:

[Linked Image]


.308 - throated /chambered for 168 grain Federal Gold Medal Match:

[Linked Image]

Last edited by 300MAG; 11/13/12.
Joined: Mar 2005
Posts: 17,527
D
Campfire Ranger
Offline
Campfire Ranger
D
Joined: Mar 2005
Posts: 17,527
Handloading is a simple process. If you can read basic english and operate simple tools, then you can handload.

Joined: Oct 2006
Posts: 7,445
Campfire Tracker
Offline
Campfire Tracker
Joined: Oct 2006
Posts: 7,445
Originally Posted by dogcatcher223
Handloading is a simple process. If you can read basic english and operate simple tools, then you can handload.


I agree Drew but I have just never got into it - maybe someday.......

Joined: Nov 2007
Posts: 4,320
1
Campfire Tracker
Offline
Campfire Tracker
1
Joined: Nov 2007
Posts: 4,320
Malm:

How do you determine the correct depth (length) of the throat.

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.

I measured the throat depth (length) om a very accurate factory .30-06 rifle and throated to that length. IIRC, it was about 5/16 inches, Or about or a little over, one caliber.


IC B3

Joined: Jan 2003
Posts: 3,363
Campfire Tracker
Online Content
Campfire Tracker
Joined: Jan 2003
Posts: 3,363
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


Forbidden Zoner
Joined: Oct 2008
Posts: 1,628
Campfire Regular
Offline
Campfire Regular
Joined: Oct 2008
Posts: 1,628
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!


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."
Joined: Oct 2008
Posts: 1,628
Campfire Regular
Offline
Campfire Regular
Joined: Oct 2008
Posts: 1,628
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.

[Linked Image]


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."
Joined: Oct 2008
Posts: 1,628
Campfire Regular
Offline
Campfire Regular
Joined: Oct 2008
Posts: 1,628
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."
Joined: Mar 2005
Posts: 17,527
D
Campfire Ranger
Offline
Campfire Ranger
D
Joined: Mar 2005
Posts: 17,527
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.

Joined: Oct 2008
Posts: 1,628
Campfire Regular
Offline
Campfire Regular
Joined: Oct 2008
Posts: 1,628
.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."
Joined: Jun 2004
Posts: 7,124
G
Campfire Tracker
Offline
Campfire Tracker
G
Joined: Jun 2004
Posts: 7,124
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


Moderated by  RickBin 

Link Copied to Clipboard
YB23

Who's Online Now
360 members (160user, 257 mag, 1lessdog, 12344mag, 01Foreman400, 2UP, 40 invisible), 2,033 guests, and 899 robots.
Key: Admin, Global Mod, Mod
Forum Statistics
Forums81
Topics1,187,593
Posts18,397,962
Members73,815
Most Online11,491
Jul 7th, 2023


 







Fish & Game Departments | Solunar Tables | Mission Statement | Privacy Policy | Contact Us | DMCA
Hunting | Fishing | Camping | Backpacking | Reloading | Campfire Forums | Gear Shop
Copyright © 2000-2024 24hourcampfire.com, Inc. All Rights Reserved.
Powered by UBB.threads™ PHP Forum Software 7.7.5
(Release build 20201027)
Responsive Width:

PHP: 7.3.33 Page Time: 0.135s Queries: 14 (0.004s) Memory: 0.8762 MB (Peak: 1.0015 MB) Data Comp: Zlib Server Time: 2024-03-28 11:13:23 UTC
Valid HTML 5 and Valid CSS