Barrel throating pros & cons

[jrw1976]

I would like to know what the process for barrel throating is? I would like to know if throating a barrel for a specific bullet warrents the time effort and expensive of doing it? Also, if I was to throat for a specific bullet how will it effect the accuracy of a different bullet configuration if I decide to try something different down the road? Oh by the way I am thinking about building a custom gun soon in 7mm rem mag and I am just trying to get my ducks in a row before start the build with all my decissions made first.
Thanks for the info in advance, JRW

[NesikaChad]

In my shop I try to stick to what I call the "girlfriend or wife" doctrine.

What that means is only one particular hard cylindrical object ever enters the hole. . . I don't care to stack reamer upon reamer as in my head it just invites the potential for more TIR (total indicated runout) If a cst wants a "X" cartridge with a "Y" bullet and I don't have a reamer made for the COAL I order one up.

That being said I know of many who chase chambers with a throating reamer and the guns shoot just fine. They shoot quite well in fact.

It's a quirky thing for me.


Essentially the primary purpose for doing this is typically so that a chamber can accept heavier (longer) bullets without having a portion of the case swallowing up the bullet in order for the thing to chamber. If your gun was chambered/throated for 40 grain bullets and you suddenly decide you want to shoot an 80 grain Sierra your probably going to discover that a good portion of the bullet is going to be squished down inside the neck. Throating the chamber will allow you to seat the bullet out further to take advantage of case capacity.


It can also be used to breath a little more life in a barrel that's destined for the old folks home. My best friend David Karcher's National Championship win in 2002 at Perry was done on a barrel with over 7500 rounds through it. Every time it opens up at the 600, we just chase it with a reamer and it comes back. (for awhile) He's since decided to have a new tube installed. When the throat starts to look like a dry lake bed you just chase it out a little and then seat your bullets out a little further. In some cases you'll find that you don't even have to do that. More freebore doesn't always make the gun fussy about seating depth.

Hope this helped.

C

[jrw1976]

thank you very much that helps greatly.

[B23]

Chad, or anyone for that matter, would you please explain for the ignorant like myself what actually happens or is taking place when the freebore portion is being created. The names of the tools/reamers or whatever you use would help me understand it better too.

I, sometimes, think I understand it but then I'll read something else and it sends my brain and thought process in another direction.

I often joke that I am mostly ignorant not stupid. Help educate make me and I will no longer be ignorant. If I still don't get it after being educated, well, then I'm just stupid.

[BobbyL]

Most reamers have the freebore already in front of the neck. Some gunsmiths order the reamers without freebore then use a throating reamer to put the throat in it. Most freebores are 1 deg 30 min. So you are cutting taper on the lands in the rifle to allow the bullets to be seated out to length. When i set one up i use a case and seat the bullet so the pressure ring is just starting to enter the neck. This gives us the best accuracy and allows for the most FPS by using more powder. The more room in the case the less the pressure will build with a specific charge. This has to be done carefully or you wont have enough bullet left in the neck to shoot it.

[B23]

When the freebore is cut into the bore part of the tube is that first part of the bore's rifling cut completely out to were it is now a smooth bore or is the rifling only cut away enough as to not come in contact with the bullet until the bullet is up in the bore far enough to touch the rifling just past the freebore part of the tube???

Freebore and exactly how it is created/cut is something I have always wondered about so I appreciate any and all explanations. I have zero interest in building my own guns but I would, at the least, like to be able to know what the heck they're talking about.

[jrw1976]

Ok if I am understanding this correctly, throating a barrel lengthens out the area between the edge of the case neck and the leading edge of the rifling. If this is true is this space tapered into the rifling and if so can you get different angled reamers or is this space square to the rifling. I am also curious what the correct seating depth of a bullet in the cartridge. I am assuming that idealy you would want the base edge of the bullet no deeper or no shallower than the neck shoulder junction (correct?). JRW