300 wby to 30-378 wby

Discussion in 'Gunsmithing' started by sigsupermatch, Mar 18, 2014.

  1. sigsupermatch

    sigsupermatch Well-Known Member

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    I have a Remington Sendero 300 wby. I was curious what would be involved in chambering to 30-378 wby?
     
  2. Gunpoor

    Gunpoor Well-Known Member

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    SSM, the bolt face would have to be opened up, which is the easy part. I am not sure if the action length on your Sendero will work with the 30-378. The case length of the 30-378 is .293" longer than the 300Wby. If your action will accommodate the larger cartridge the chamber will clean up without any barrel set-back. A qualified gunsmith should be able to measure your action and tell you if this re-chamber will work.
     
  3. specweldtom

    specweldtom Well-Known Member

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    Some caveats.....Several years ago, I read that bolt thrust on the .378 based cartridges is pushing the 700's safe limit. However, the MK V Wby 9 lug rifle is factory chambered for the .378 based cartridges and has centerfeed mag boxes, followers, and .378 extractors available as parts. The 700 is factory chambered for the RUM cartridges, but the mag box inside length is 3.7" and the MK V .378 box is 3.8". The extra length is useful. Also don't know if the RUM box and follower will work on the bigger belted case. Both bolt faces can be opened up from Std Mag case head diameter, but not sure if the Sako or M-16 extractor conversion will work on the larger .378 case head.

    Bottom line, for a .30 x .378 I would start out with a 9 lug MK V action, not a Rem 700. However, the .300 RUM might clean up the .300 Wby chamber. Worth checking on, and the .300 Wby bolt face in the Remington works on the RUM case head without modification..........Oh yeah, RUM brass is expensive, but the Big Wby brass is insane.

    Good luck, Tom
     
  4. sigsupermatch

    sigsupermatch Well-Known Member

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    The maximum pressure list for a 300 wby is 65,000 psi, for a 30-378 it is 63,817. That I can find. How would the pressure on the bolt be greater with less chamber pressure?? Thanks for any info.
     
  5. sigsupermatch

    sigsupermatch Well-Known Member

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    Thank you.
     
  6. etisll40

    etisll40 Well-Known Member

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    wtt
     
  7. Edd

    Edd Well-Known Member

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    Because the bolt face is larger. Using your numbers it would go up about 17%.

    You also have the issue of a thin barrel tenon with 1.062" threads.
     
  8. specweldtom

    specweldtom Well-Known Member

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    Edd makes a good point about tenon wall thickness. Both the Remington 700 and the MK V have 1.062" major diameter x 16 tpi tenons.

    In my opinion, thread fit between the barrel tenon and the receiver is critical. A very close thread fit helps the receiver ring support the barrel tenon when torqued up. No scientific proof, just makes sense to me. I don't think factory barrels have the thread fit that custom barrels have (or should have), but they are torqued up hard! Plus, some Remington barrels have some kind of nasty mung in the threads. Don't know what its purpose is (maybe a non-compressible thread filler)?, but it makes them a bitch to get out.

    Tom