mark 5 action mods

Discussion in 'Gunsmithing' started by sodwyer, Oct 29, 2010.

  1. sodwyer

    sodwyer Active Member

    Messages:
    26
    Joined:
    Sep 23, 2010
    I have a mark 5 chambered in 300 win mag and I am restricted when it comes to COAL. the action is the same length as the wtby chambering but there is a spacer built into the magazine. I would like to remove this spacer and cut the bolt stop grove longer on the bottem of the bolt. Has anyone out there done this mod to a mark 5? If so what else do I need to take into concideration? Thanks
     
  2. specweldtom

    specweldtom Well-Known Member

    Messages:
    1,066
    Joined:
    Jun 7, 2004
    Piece of cake. If you stay with the Std Mag .535" bolt face, it's all you have to do. For instance, after the mag bulkhead is removed and the bolt stop slot is lengthened, a .300 Wby becomes a simple re-chamber job. A .340 Wby or any of the other long case (.535" head) calibers is a re-barrel job. The action will also take any of the Rem Ultra Mags, but you will need a single stack mag box and follower, (available from Wby). If you go to a .378-based cartridge, you will have to open the bolt face and change the extractor, in addition to using the single stack mag box and follower. The floor metal will work as is.

    These mods are easy to do on a MK V. If you re-barrel, depending on the new barrel contour, you can use the same stock too.

    Oh yeah, if you want to go to a .257 Wby, .270 Wby, 7mm Wby Mag, or any other std length Magnum, all you have to do is just rebarrel. No mag, bolt stop slot, or bolt face mods needed.

    Just my opinion, but the MK V is too good an action to waste on any of the short magnums. It's long and strong. Use it for that.

    Have fun, Tom
     

  3. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,307
    Joined:
    Jul 29, 2004
    +1

    Couldn't have said it better myself.

    J E CUSTOM
     
  4. sodwyer

    sodwyer Active Member

    Messages:
    26
    Joined:
    Sep 23, 2010
    WHEN IT COMES TO LENGTHING the bolt stop grove should I compare the grove length to another bolt or just measure the bulkhead I am looking for the correct length to make the slot.
     
  5. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,307
    Joined:
    Jul 29, 2004
    Just mill to withen 1/16'' of the end and it will work. This leaves enough to be strong but
    handel the longer cases.

    J E CUSTOM
     
  6. specweldtom

    specweldtom Well-Known Member

    Messages:
    1,066
    Joined:
    Jun 7, 2004
    Index the 3/16" end mill at the end of the existing slot and then lengthen the slot .330". As JE said, the new end of the slot will be very close to where the bolt steps down to the locking lug area. A 4-flute end mill cuts smoother. It doesn't have to be center cutting either. My mill is a little 2 hp bench mill, so I make 2 passes with slow feed, and plenty of cutting fluid. (The MK V bolts are HARD). I use 2 V-blocks clamped in a heavy milling vise and then clamp the bolt into the V-blocks. Since you're only making a .330" long cut, the V-block horseshoe clamps can be set up to clear the tool holder. It's important to have the bolt rotated correctly and perfectly horizontal, so that you pick up and extend the slot cleanly. I have measured .055" on the slot depth.

    I would still recommend that if you have access to a MK V in .300 Wby or larger, look at the bolt stop slot on it and take measurements anyway. Can't hurt.

    I spelled out what I do because it will get you there if you don't have a long slot bolt to compare with.

    Tom