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Thread: 300WSM case pressure

  1. #1

    Question 300WSM case pressure

    Have a 300WSM and have noticed that after a shot, it is effort to try and unbolt and eject. I know this usually means high case pressure. I'm using 180 gr factory winchester ammo. This is a new gun for me and I assume this is a result of shortening the 300 win mag case. Anyone else noticed that?

  2. #2
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    The 300 WSM is not a shortened 300 Win Mag. It is an altered 404 Jeffery case.

  3. #3

    Default High pressure 300wsm

    How difficult is it to open the bolt? Can you do it with a normal hand movement? Are there any obvious case signs of pressure like a heavily flattened primer or the lettering on the bottom of the case looking "smeared?"
    Did this occur from the very first shot? Did you thoroughly clean the chamber and bore before shooting? If you couldn't open the bolt normally and there were pressure signs, you might consider calling Winchester and talking to them, or the rifle manufacturer, whose name you didn't mention. You might also find a gunsmith in your area who is an authorized repair center for your brand of rifle, take the ammo and have him check it out.

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    I can't say that I've experienced that, and I've owned two 300 WSM rifles (still have one, sheep rifle). I don't shoot factory ammo though, but my reloads are at max charge.

  5. #5

    Default case press.

    I've only fired a few shots so far as I'm breaking in the barrel. Chamber is clean, bolt is lubed. Its a Kimber 8400 Montana. I'd say I have to come off my shooting position to better grasp the forearm, almost bracing the stock in my side to un bolt. This is my first 300wsm and don't know if its just a characteristic of the caliber. Cases show no sign of overpressure. The chamber does show machine marks, i've heard of polishing before but don't know if that will help.

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    Member 8x57 Mauser's Avatar
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    Default Trouble ejecting

    My brother has a new 300 Win. Mag. that doesn't like to eject cases - even factory ammo. Took it to a gunsmith who said it had 'burrs' in the chamber. He's polishing them down. Is this a common problem with new rifles? Dad and I had never heard of it, but then we're the kind of family who only own a few rifles.

  7. #7

    Default chamber markings

    Well, it certainly would be a good thing to have a smooth polished chamber, that's a definite. I regret to say that several brand new Kimbers I have examined have some rough places in the action, burrs and rough patches. Unfortunate for a gun that has a bit of a price tag and a beefed up reputation.

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    Quote Originally Posted by AlleninAlaska
    The 300 WSM is not a shortened 300 Win Mag. It is an altered 404 Jeffery case.
    That is what they started with, but I believe finally settled on a rimless modified 348 Win case.

  9. #9
    Member alaska bush man's Avatar
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    Thumbs up 300 Wsm

    The Win Factory load 180 PP is loaded a little hot, many 300 WSM users have expericened this.

    One of my favorite to reload with IMR 4831 and Sierra 165 BTHP.

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    Default Hot WSM or Bad Kimber?

    Having reloaded for 4 Kimber Montanas over the past 2 years I can say that it is NOT a trait of the 300WSM. It is a problem if the load is a bit too hot - I've heard that before on that Win. round you have. Outside of a completely dry bolt, I would try a different box of factory ammo. See if you get the same results. If you do, I would call Kimber customer service and discuss it with them. They can't diagnose too much over the phone so they may have you send it in. Unfortunately in the era of mass production, even CNC machining can't work all the time.
    Keep us posted on what develops.

  11. #11
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    outdsman,
    You might check www.shortmags.org as I don't think it is too uncommon for factory ammo to exhibit pressure signs like yours.

  12. #12

    Default Montana stiff bolt

    I have a montana that also exhibits the stiff bolt after a shot.
    I to am in the break-in stage and have put too many through it yet.
    I am currently using the 220g from Winchester (cheapest) and thought it may be due to the heavy bullet, higher chamber pressure, and the tightness of the chamber. I have looked at my brass and though the primers are a little flat there is still a little breathing room. The prmers are not completely welded into the pockets. I may have to get someone with a little more experience to take a look at it.

  13. #13
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    Default WSM Bolt lift

    O/DMan,

    I have only had three montana's in my hands and all, I would say were a little rough in the cocking cam, which is most of the drag when opening the bolt normally. Is the bolt tight on an empty chamber after dry firing? If it is tighter than that after firing it likely is the case expansion. Try another brand of ammo. I have fired maybe three boxes of factory ammo and did not experience any excess pressure or tight bolt lift. In all my handloads (and factory loads), I was unable to achieve advertised velocity without excess pressure in all of the montana's and other brands of rifles in all (3) WSM calibers I have tried. I think the ballistics are a little optimistic and an attempt to achieve them may be in excess, with the factory ammo. My Sako 75 in 300 WSM is a very good rifle but can't equal the advertised claims even with it's 24 3/8" barrel.

    Also on a side note. The WSM case and the Ultra case are, I guess loosely based on the 404 Jeffery case, in that they have a a body diameter of .545" which is the diameter of the Jeffery. (It is not the 348 case in any way.)The rim however is rebated to .532" to fit the bolt head of the belted mags. The cases are very strong by design but the rounds operate at 65,000 psi which is a lot of pressure. If any lot of brass is slightly soft it would expand and lock up an action after a full power load was fired. I have seen this problem many times before in various calibers. So that is also suspect as the culprit, rather than the load being too heavy. Just some info. Good shootin'.

    Murphy

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    Thanks for the clarification Murph.

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