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.308 Win Chamber info

Discussion in 'Big Stuff -- 6.5mm, 7mm, 30 Cal' started by gsg5pk, Apr 16, 2012.

  1. gsg5pk

    gsg5pk

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    Could anyone suggest how to determine the chamber info of my rifle?

    Rifle : Les Baer Tactical Recon (Special Order)
    Info : RH Stiller Tac-30 , ADL T/G, .308, Heavy Barrel 1.240”x 3” Straight Taper to .930 Muzzle @24” Barrel B/C, Recoil Lug 0.30” thick


    When ordering, they do not available any option for choosing Chamber Size. They just mention " chambered using reamers from Pacific Tool & Gauge. Dave Kiff, PT&G’s owner, is widely recognized as an expert in chamber and reamer design and he specially designed the reamers to meet two design objectives. First, the chambers had to be conducive to maximum accuracy. But just as importantly, each chamber had to accept all military and commercial ammunition—a capability particularly important in the .308 Win./7.62x51 mm NATO. "

    The guarantee group was 10 shots within 1/2" MOA by factory match ammunition (FGM 168).

    So, how can I know the chamber spec (Chamber type & Freebore)?
     
  2. Rtheurer

    Rtheurer Site $$ Contributor

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    A call to les bear and ask if they will give you the reamer print # or name.

    You can then call or email PTG and request that print via a PDF file to your email.

    RussT
     
  3. gsg5pk

    gsg5pk

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    I had sent an e-mail to request info from both of them but nothing reply.

    I do not live in USA. So, not comfortable to call them.


    I had measure my fired brass with Dial caliper , RCBS Precision MIC .308 win and got these info ;
    Neck Diameter : .342"
    Based to Datumm : +0.001" from minimum SAAMI
     
  4. LESLEY

    LESLEY

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    Feb 20, 2006
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    The big question is can you shoot good enough to tell the difference. I have had several shooters tell me their custom gun wont shoot. It was not the gun it was them. When you can shoot good enough to tell the difference in chambers you wont have to ask this question
     
  5. rminut

    rminut

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    If you take a measurement of a Sierra 2156 to the lands we might be able to give a guess but it would just be a guess. I'm sure it's one of the more common reamers like Palma'95 or M852, the popular reamers are popular for a reason.
     
  6. 300 RUM

    300 RUM Gene Nowaczyk Site $$ Contributor

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    I agree, and one more chamber it could be is the "Bisley Palma 150"

    Lesley also makes a good point, would you be able to notice the difference, do you measure each bullet type to the lands for you reference/datum point?

    I will brag for a moment here and say I build very nice and highly accurate 1/4 moa rifles for myself, that is when I shoot them, the bullet may not have the same 1/4 moa with you shooting. this does not mean your a bad shot. This means i build to suite, I pick the chamber and re throat if need be, also making any other changes or adjustments as I see fit.

    Also like Lesley stated, if you can shot 1/4 moa why does it matter what chamber it is. Is there a particular reason? In most cases it doesn't matter what the chamber is if your loading to it to began with.

    Measure a Sierra 155gr Palma to the lands, 2.256 is the magic number, then email me I'll let you know what I believe it to be.
     
  7. Keith Glasscock

    Keith Glasscock Team Benchmark Site $$ Contributor

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    If you don't have the palma bullet, a 175 SMK is something I have data for, and I can help you.

    I have two chambers cut with the same reamer. They are slightly different. One is a touch larger in headspace and larger at the base, but both shoot about the same with the same loads. I don't give much credence to chamber dimensions in accuracy. If you can get the bullet into the lands, and have a reasonable amount still in the neck, the rest is rather moot if it shoots. There are just too many other variables to be able to pick out any real differences between chamber specs.

    You could also cast the chamber with cerrosafe. There is an article in the bulletin about how to do it. That would tell you more than the reamer print would.
     
  8. gsg5pk

    gsg5pk

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    I'm just a beginner for Long Range Shooting in .308 win and new for reloading due to limited of factory ammunition available at here. There are only FMMG 168 gr. and old surplus of M118LR (10 years up). Then, these ammunition are not proper for shooting 600 and 800 yards.


    The reason that I ask for chamber size & freebore because I want to get info for reference of choosing heavier Bullet and when re-barrel my 700 XCR with Krieger Barrel.
     
  9. gsg5pk

    gsg5pk

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    My current loading .308 winchester info for 800 yards ;


    Brass : Lapua Brass (Trim to 2.005")
    Neck thickess : .015"
    Neck Sizing : .336
    Neck Tension : .002"
    Bullet : Berger 175 LRBT
    Primer : CCI BR2
    Powder : 43.5 gr. of Varget
    Seat Depth : COAL 2.810"


    AVG MV ; 2,648 fps.
    SD ; 6.9
     
  10. 300 RUM

    300 RUM Gene Nowaczyk Site $$ Contributor

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    The larger statement is are you hitting the paper at 800 where you want to?
     
  11. coreydelong

    coreydelong

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    The only significant reason I see to keeping the chamber size to a "reasonable" size is to minimize how much you have to work the necks when re-sizing.

    I've had a few stock factory barrels that required necking down in two steps just to get enough neck tension back to hold the bullet. With a no turn neck of 0.336" I've had .308's with chambers up to 0.345" and they size right down in one step no problems. You start turning necks and get 0.015" of chamber clearance and you'll be sorry. Your necks will expand against that chamber wall and you'll be neck sizing in two steps to get neck tension back.

    The best thing to do IMHO is call PTG and ask what reamer they supplied Les Baer with. Order the same spec reamer from them and you'll have it forever so anyone can chamber your barrels in the future.
     
  12. ar15topgun

    ar15topgun

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    How much freebore do you have and what is your OAL to ogive with how much off the lands?
     
  13. XTR

    XTR Site $$ Contributor

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    Why does it really matter which chamber you have? Load for the way it's chambered and shoot it.

    Get an ogive comparator, or make one yourself and figure out how far it is to the lands for the bullet that you are loading.

    Mic some of your fire brass and see what the neck is, I'll bet you have a .342 neck, unless someone specifies something tighter that's how they are typically cut.

    Those are really the only data points you need with regard to the chamber, and the only one you are going to use on a regular basis is the ogive measurement, and that will change as you erode the throat.

    If you are one of those guys who just has to know get some cerrosafe and make a casting and mic it to your hearts desire.
     
  14. coreydelong

    coreydelong

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    I've measured a fired case and added 0.001".

    A telescoping micrometer (some call them expanding ball mic's) work really well to measure the chamber neck. A 0.200"- 0.300" and a 0.300"- 0.400" are all you'll likely need.
     

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