LF someone with 300 blk headspace gauge set

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  • rushthezeppelin

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    Dec 28, 2012
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    Cedar Park
    Going to be getting my CMMG 300 blk barrel in tomorrow and was wondering if anyone in the area possibly has a headspacing gauge set for this caliber. Want to be extra sure considering I'm using my almost 2k rounds used 5.56 bolt in this build and don't want to find out the hard way my headspacing is off (and of course you never know when fresh from factory barrel might have been reamed a tad too far). Anyone have a set I could come by and use, perhaps trade some beer or just cash for quick use? Or anyone know a smith who has a set for this caliber that can check this for a nominal fee (I would goto the one in Taylor but he has a $40 minimum and this is literally going to take all of 2 minutes to check). Preferably looking for someone on the North side of town.
     

    1slow01Z71

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    Jun 24, 2012
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    Kyle
    Those gauges wont tell you if it was reamed too far just if it was too short. Get a hornady comparator set, you need them anyway to set up your dies properly to minimize working your brass. Take the extractor out of your bolt, size a piece of brass with the die cranked all the way down on your shellholder, if it chambers completely youre good. If youve got too much headspace youll be able to tell with a fired piece of brass and the comparator set. Youre mainly worried about too little headspace, too much and it just works your brass more which isnt great but isnt dangerous.
     

    rushthezeppelin

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    Don't have die set yet. So far all I've got even ordered for this project is the barrel. Just want to know its good before I get stuff put together, mostly want to know if it will close on a no-go so I have at least somewhat of an idea of if it's going to give me chambering problems on reloads. If it doesn't close on that gauge I'm guessing I would need to get a 223 small base sizing die for initial sizing before cutting the shoulder/neck off to form 300.
     

    1slow01Z71

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    Jun 24, 2012
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    Kyle
    Don't have die set yet. So far all I've got even ordered for this project is the barrel. Just want to know its good before I get stuff put together, mostly want to know if it will close on a no-go so I have at least somewhat of an idea of if it's going to give me chambering problems on reloads. If it doesn't close on that gauge I'm guessing I would need to get a 223 small base sizing die for initial sizing before cutting the shoulder/neck off to form 300.

    If youre forming from LC brass its a good idea to run them through a sb die in case it was fired through a machine gun. If you cant find anyone I can size a piece of brass to minimum saami specs for you to try in your chamber. Dies are set up to be smaller than the saami specs to make sure the rounds chamber in all chambers for that cartridge. My dies bump the shoulder back .014ish (going off memory but its a lot) when I only need .003ish for a reliable feeding load. Thats why I say get a comparator set so you can set your dies to give minimum shoulder bump and not overwork your brass.
     

    rushthezeppelin

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    Dec 28, 2012
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    Well after calling literally every gun shop on N side and alot in downtown S side area, it seems Bar None is the only one that even has the damn gauges for 300 blk and like I said they have a 2-4 week backlog before they could even spend 3 minutes to drop them in my barrel. I did however manage to find a local shop that the guy had a personal stash of Remington 220gr that he let me use to at least check for minimum headspace, bolt locked with ease on these. Also tried something another smith suggested while I was there which was to take some cellophane (used some off a cig pack) and rip off a layer into the bolt face, bolt lockup was a wee bit more resistance but still not hard to do without even having something going through the cam hole to give me some leverage.

    Even picked up some of the 110gr hornady custom Whispers. Tried some thicker plastic (calipers show it at 2 thou thick) with them even up to 5 layers I was able to close the bolt without the help of something through the cam pin. Granted the plastic method seems a bit sketchy but I definitely know that I don't have too little headspace and seems like a good chance I have enough for reloads without having to go crazy on sizing. Starting to though wonder if I shouldn't at the very least buy a bolt dedicated to this built if not go ahead and go full on BCG and charging handle.

    Thinking about using this headspace gauge rental service Elk Ridge Reamer Rentals (800) 996-0426. Would cost $19 including shipping, although I'm not sure that includes a return shipping label.
     
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