In order to participate in the GunBroker Member forums, you must be logged in with your GunBroker.com account. Click the sign-in button at the top right of the forums page to get connected.
Options

Rechamber 300 Wby?

Ray BRay B Member Posts: 11,822
edited June 2014 in Ask the Experts
I have a 300 Wby Mag barrel that I am considering having fitted to an Oberndorf '98 action. the action is large ring/ large thread so the barrel would screw right in, but the action would need to have the magazine lengthened and the lower lug ramp moved forward, which I'm reluctant to do. so an option would be to take a thread or two off of the barrel and rechamber for a shorter cartridge. If Weatherby made a 300 similar to the 257/270/7mm case, that would be the obvious choice- but since they don't I'd have to get custom made dies, which I'd prefer to avoid. So of the cartridges that fit the bill as standard action/30 caliber/magnum, I'm leaning toward the 30/338. I prefer it to the standard 300 Win Mag. Other than opening the boltface, there should be minimal action changes- I think. am I correct??

Comments

  • Options
    charliemeyer007charliemeyer007 Member Posts: 6,579 ✭✭✭
    edited November -1
  • Options
    MIKE WISKEYMIKE WISKEY Member, Moderator Posts: 9,987 ******
    edited November -1
    you would still need to lenghten the magazine (to .30/06 lenght). actualy this isn't that hard to do.
  • Options
    AmbroseAmbrose Member Posts: 3,173 ✭✭✭✭
    edited November -1
    Standard length 98 Mauser magazines will accept cartridges 3.30" long. Much of the reloading data for the .30/.338 recommends a C.O.L. shorter than that. You might have to modify the action rails to feed belted cases but maybe not.

    My .30/.338 is built on a 1903/A3 action and feeds fine. Of course that magazine will accept a C.O.L. of 3.34".
  • Options
    Ray BRay B Member Posts: 11,822
    edited November -1
    I measured the magazine box and it is slightly over 3.3" length. The opening in the action for the box is about 3.4" so if needed some metal could be removed from the box without touching the receiver. these measurements are nearly identical to those on an older M70 338 so it seems to me that either the 30/338 or the 308 Norma out to work with the only modifications being to the boltface and possible the rails.
  • Options
    tsr1965tsr1965 Member Posts: 8,682 ✭✭
    edited November -1
    Ray B,

    By the time you shorten the chamber end of the barrel enough to rechamber it for a shorter belted magnum, to be able to clean up the old 300 WBY chamber, you might not have enough meat in the chamber area. Something to look into.

    However, you might have enough to chamber something like the 300 WSM, or 300 RSAUM. You will have to adjust the feed ramp, action rails, and magazine follower, for anything you rechamber to, but would not have to adjust the magazine length.

    Best

    EDIT 1



    quote:unless one of the 404 based cases was used.?


    Those full length 404 cases would not fix your magazine length problem...your sole reason for wanting to rechamber to a shorter magnum to start with.

    The WBY is 0.492 at the shoulder, as a distance of 2.298 from the head face. A regular 300 Win(Belted) is 0.489 at the shoulder, at a distance of 2.196...all on inches. All meaning you will have to go deeper yet to totally clean up the WBY chamber. With anything you do, you will have to clean up the minor case neck to shoulder radius too. Since you are going that deep, if you go with the WSM or RSAUM, you can clean up the whole WBY chamber, and still have enough meat left, and magazine room...the latter being the reason you are rechambering in the first place.

    Best
  • Options
    Ray BRay B Member Posts: 11,822
    edited November -1
    quote:Originally posted by tsr1965
    Ray B,

    By the time you shorten the chamber end of the barrel enough to rechamber it for a shorter belted magnum, to be able to clean up the old 300 WBY chamber, you might not have enough meat in the chamber area. Something to look into.

    However, you might have enough to chamber something like the 300 WSM, or 300 RSAUM. You will have to adjust the feed ramp, action rails, and magazine follower, for anything you rechamber to, but would not have to adjust the magazine length.

    Best


    I'm a little confused on this- it seems to me that the shoulder of the 30/338 would only need to be far enough forward to absorb the double radius Wby shoulder. I'm guessing that the reason to go farther forward would be if the body diameter of the Wby was larger than the 338 then virtually the entire chamber would need to be removed, unless one of the 404 based cases was used.?
  • Options
    nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    Rather than trying to guess at dimensions and how much to remove from the existing barrel, here are two fairly simple line drawing of the cartridges in question.

    .300 Weatherby Magnum

    300_weatherbymag.JPG

    .338 Winchester Magnum

    338_winchestermag.JPG

    All you need to do is some simple subtraction to figure whether or not this is possible. Given that the M98 Mauser thread tenon is only about 0.625" or so long and you need to shorten the chamber by 0.325" just to make the shorter cartridge you ask about, you have lost 1/2 of the thread tenon right from the get go. It's not just a 'thread or two'.

    So now you have to create a new tenon length and thread it if you find that the original chamber features will clean up using the new, shorter chamber reamer. This includes the WBY neck and shoulder of course, so check the dimensions carefully. If they don't clean up then you need to remove more of the tenon, all of it most likely.

    Then you need to determine if there is enough straight line shank on the barrel left in order to create the new tenon.

    By the way, we've been modifying M98 Mauser actions to accept the H&H line of cartridges safely and reliably for quite a few decades now. So you might consider leaving the chamber alone, fit and adjust the headspace and buy some new or modified bottom metal. Otherwise a different barrel might be more appropriate.

    Best.
  • Options
    Riomouse911Riomouse911 Member Posts: 3,492 ✭✭✭
    edited November -1
    Nononsense has the idea that will keep this from becoming a money pit. If modifying the action for the H&H length round is too much, I'll say sell the barrel and get one in a caliber that'll fit the action without breaking the bank.
  • Options
    Ray BRay B Member Posts: 11,822
    edited November -1
    I talked with the gunsmith on Saturday, with '98 action and FN barrel in hand. When the barrel was cut for 300 Weatherby it had a full diameter taper for about 2 inches forward of the receiver, so the shortest way to the answer was leave the internal dimensions of the action alone, shorten the barrel sufficient that the 30/338 reamer would trim to the front of the neck. the original chambering was cut to minimal dimensions, so the 30/338 reamer will trim out to all new metal. So the rails may need a little modification for the larger diameter shells and the boltface increased to magnum dimensions; drill and tap for the era side mount, affix the Kollmorgen 26mm tube scope, possible slight adjustments to the safety lever and bolt handle and violin, I've got a very good Oberndorf 30.338 mag elk rifle,
  • Options
    nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    Ray B,

    That's what I wrote above in the first two paragraphs. Good news is that you have extra tenon length and diameter sufficient to complete the new chamber correctly.

    Good Luck! We'd be interested in a field test when you get it back from the gunsmith.

    Best.
Sign In or Register to comment.