Dear All, I was wondering whether you could help with this:

I'm planning to have a couple of hunting rifles built on M1999 actions (keep on working Rod! ). Nothing exotic, a long action .270 Win and a short action 7x57. I'm prepared to spend the cash necessary to obtain good parts, e.g. first rate barrels. I'm pretty familiar with the process of selecting the parts (twist rates, stock, scope mounts etc), and familiar with the general idea having to choose the "right" smith, to ensure everything is put together straight.

Where I'm at the end of my tether, is when it comes to the dimensions of the chambers - and the tools used to chamber.

To that end the following questions:
1) would it make sense to have reamers made up to match the brass that I plan to use??
2) does it make sense to make chambers in hunting rifles be at (or towards) minimum specs?
3) are there advantages with respect to bullet seating depth/freebore to have reamers made to specification??
4) or, since the calibers I'm looking for, are pretty much run of the mill, can I just get the smith to use whatever reamer he has handy?
5) or, does all of this not matter a hoot in a hunting rifle??
6) or am I barking up the wrong tree in my quest for the mythical .5 MOA hunting rifle?? Are there other considerations, which would help me more than chamber dimensions?

Still dreaming of the perfect rifle

- mike

From an accuracy standpoint, chamber dimension are not critically important (within reason). Throat dimensions can be important however.
There is no reason for the base diameter of the chamber to be any greater than .470" and no reason for neck diameter to be more than .015" over nominal bullet diameter. Apart from this chamber dimensions are not critical.
The throat should be parallel with a 1.5 to 3 degree included taper up to bore diameter at the front. Throat length should be such that around 1 calber of bullet length is contained in the neck. Mostly these calibers work well with a throat between .200 and .250" long.
In general, concentricity and alignment are more important than dimensions. Regards, Bill.

mho,

You need to determine how much effort you are willing to put into your handloads and you need to think about what would happen if you and your specially prepared ammo were separated during an expensive hunt.

Would your rifle be capable of feeding standard off the shelf ammunition, or, would a tight chamber limit your ability to use other ammo?

Were it my rifle, I would cut a standard chamber as precise as humanly possible concentrating on the throat and headspace. I would keep the throat tight and centered to provide a perfect entry into the bore. Because I would want as little case shift as possible, and because I was using a standard chamber in the event I was forced to use factory stuff, I would set the headspace snug and to further reduce slop, I might neck size.

As far as free bore goes, free bore will be present by whatever degree you seat your bullet. I would keep the throat length limited to a specific bullet and make that throat work for any other loads.

Malm

Thanks Guys, good input! Seems like concentricity and neck/throat dimensions are among the main factors you are looking for. I can definitely see the point about possibly having to use factory ammo.

Do keep the advice coming!

- mike

Just a thought . . .
What difference does the chamber/reamer make IF the dies do not come close to matching them/dimensions?

LouisB

If you've got the money, honey.

Doubt that you will kill any more game or kill it any cleaner with what you are building than with stuff you can get off any used rack for a fourth or less than what you are laying out.

You wanna buy a work of art or a rifle you can be really proud of, go to it. But don't kid yourself that you really need it in a hunting rifle. (Exceptions noted, but those exceptions would not be likely to be chambered in 7x57 and .270.)