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Thread: So I slugged the bore and determined ?????

  1. #1
    Boolit Master Bad Ass Wallace's Avatar
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    So I slugged the bore and determined ?????

    I am always taken me to task, when casters say "slug" the bore to determine the correct size cast bullet to use.

    I say, all that determines is the size of the tightest spot in the barrel, better to start a bullet into the muzzle and make sure the rifling at that point (the last point of contact before exiting) contacts both the top and bottom of the lands. Then size your projectile to that dimension.

    Take the humble 303 British;

    According to the Small Arms Identification Series by Ian Skennerton "Magazine Lee-Enfield Rifle" Page 29

    1) Lee Metford and Lee-Enfield Mk1:
    Barrel Specification:
    Barrel Length - 30.5"
    Rifling Metford - 7 groove L.H. 1 turn on 10"
    Rifling Enfield - 5 groove L.H. 1 turn in 10"
    Bore Dia - 0.303"
    Metford Rifling Depth - 0.004"
    Enfield Rifling Depth - 0.0055
    Metford Land Width - 0.023"
    Enfield Land Width - 0.0936

    From book "The British Service Lee" by Ian Skennerton Page 86
    2) Short Magazine Lee Enfield Mk 3:
    Barrel Specification:
    Barrel Length 25.2"
    Rifling Enfield - 5 groove L.H. 1 turn in 10"
    Bore Dia - 0.303"
    Enfield Rifling Depth at muzzle - 0.0065
    Enfield Rifling Depth at breech and to within 14" of the muzzle - .005
    Enfield Land Width - 0.0936

    From book "The British Service Lee" by Ian Skennerton Page 158
    3) Short Magazine Lee Enfield Mk 4 & 5:
    Barrel Specification:
    Barrel Length 25.2"
    Rifling Enfield - 5 groove L.H. 1 turn in 10"
    Bore Dia - 0.303"
    Enfield Rifling Depth at breech - .005
    Enfield Land Width - 0.0936

    It would seem from this data that an Enfield 303 could be .303" over lands and a bore of up to 0.314" at the breech and up to 0.316 at the muzzle.

    My Martini Enfield 303's shoot best with a .314 dia projectile which would seem to fit with the above specifications and bore diameter of .313"
    Hold Still Varmint; while I plugs Yer!

  2. #2
    Boolit Master

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    Well, just for the sake of conversation, if your bore has a tight spot, and the bullet passes through that tight spot, it's not likely to get bigger again after passing it. So I would say that is valuable information to have. If there's a gross difference between the tight spot and the average of the rest of the barrel, then for better accuracy I would consider re-barreling.

  3. #3
    Boolit Master Char-Gar's Avatar
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    One more time....Sugging the bore of a rifle to determine the proper size of cast bullets is an unmitigated waste of time. Whatever number you get will be irrelevant.

    The size of the throat/leade/free bore ahead of the chamber is the only number of significance. Size the bullets as close to that as you can get without going over.

    This has been said, over, over and over again, but some folks still have not gotten the memo. The old "slug the bore" myth persists despite all attempts to drive a stake through it's heart.
    Disclaimer: The above is not holy writ. It is just my opinion based on my experience and knowledge. Your mileage may vary.

  4. #4
    Boolit Master gpidaho's Avatar
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    Do a chamber cast or next best what folks call a pound cast and determine the size of the throat. The barrel of a rifle is just a long sizing die. And as Char-Gar said slugging the bore doesn't tell you anything. Well it may tell you if there's a real tight spot I guess but not much else. Gp

  5. #5
    Boolit Master


    williamwaco's Avatar
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    Quote Originally Posted by char-gar View Post
    one more time....sugging the bore of a rifle to determine the proper size of cast bullets is an unmitigated waste of time. Whatever number you get will be irrelevant.

    The size of the throat/leade/free bore ahead of the chamber is the only number of significance. Size the bullets as close to that as you can get without going over.

    This has been said, over, over and over again, but some folks still have not gotten the memo. The old "slug the bore" myth persists despite all attempts to drive a stake through it's heart.
    yeah! ^ ^ ^ ^ ^ ^ ^ ^ ^ ^

    what he said.
    First reload: .22 Hornet. 1956.
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  6. #6
    Boolit Master

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    I have a set of brass rods that I use to slug with, a short one and a long one. I put a round ball into the bore and expand one at the muzzle and one at the breech for the most accurate slugging. If I push a ball through and hit any tight spots in the middle that bore needs to be lapped.

  7. #7
    Boolit Master


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    Quote Originally Posted by Char-Gar View Post
    One more time....Sugging the bore of a rifle to determine the proper size of cast bullets is an unmitigated waste of time. Whatever number you get will be irrelevant.

    The size of the throat/leade/free bore ahead of the chamber is the only number of significance. Size the bullets as close to that as you can get without going over.

    This has been said, over, over and over again, but some folks still have not gotten the memo. The old "slug the bore" myth persists despite all attempts to drive a stake through it's heart.
    Exactly.....
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  8. #8
    Boolit Master
    swheeler's Avatar
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    sugging? Take a case fired in the gun and measure the inside neck diameter of it, size to that.
    Last edited by swheeler; 07-21-2017 at 07:42 PM.
    Hell, I was there!

  9. #9
    Boolit Master Jack Stanley's Avatar
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    What Char-gar said is the shortest way to get it right . I generally use a throat impression to find the size but I have bumped a bullet just into the throat to get close .

    Jack
    Buy it cheap and stack it deep , you may need it !

    Black Rifles Matter

  10. #10
    Boolit Master Texas by God's Avatar
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    I kinda like to see what I see and feel what I feel by slugging the bore. Also if someone asks "What's your groove diameter"?- you can say ".358". That's knowledge even if It's of no consequence.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

  11. #11
    Boolit Master rondog's Avatar
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    So, is there a tutorial or sticky here somewhere telling how to do this throat impression and chamber/pound casting? Not all of us know this stuff. And searching here - I always end up out in Google land......

  12. #12
    Boolit Master GhostHawk's Avatar
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    Very good sticky on chamber casting.

    I will say this, I slugged several barrels, got them stuck, and unstuck.

    And then I tried a chamber cast. Nothing got stuck. I got the most accurate cast shooting rifle I'd ever had. 50 yards 3 bullets in one hole sighting the scope in. Less than an inch at 100 if I can hold up my end. Which is often debatable.

    I repeated the process on my next rifle, and got the same results. Cloverleaf's at 25, and 50. I would have had one at 100 but I pulled the last shot half an inch.

    I know which one I use. The one that works. Chamber cast. YMMV

  13. #13
    Boolit Master


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    Ya can't go wrong with cerrosafe. However you must follow the directions and measure the casting at a certain time after making it. Over time the casting will change measurements and it is not a permanent casting for future reference. It is easy to do and it works. I have a couple of Enfield's which are very different from each other. Each chamber was different and calls for a different dia. boolit to be accurate. I have had to file a notch in the rim to keep the brass separate. Before casting I was guessing and had lousy accuracy in both rifles. Now I can put my rounds out there to 250 yds and slam the steel gong with regularity. With the standard Ed Harris Red Dot loading I have a very comfortable rifle to shoot and they are cheap to load for as I recover the alloy from the backstop and recycle it again and again.
    Pax Nobiscum Dan (Crash) Corrigan

    Currently casting, reloading and shooting: 223 Rem, 6.5x55 Sweede, 30 Carbine, 30-06, 30-30 WCF, 7.62x39, 327 Fed Mag, 303 Brit., 32WS, 7.92x57, 38 Spcl, 357 Mag, ,380 ACP. 9x19, 38-55 Win, 41 Mag, 44 Spcl., 44 Mag, 45 Colt, 45 ACP, 454 Casull, 457 RB for ROA and 50-90 Sharps.

  14. #14
    Boolit Master Texas by God's Avatar
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    Quote Originally Posted by swheeler View Post
    sugging? Take a case fired in the gun and measure the inside neck diameter of it, size to that.
    I want to try this on the SMLE I'm fooling with. It slugs .312" tight the whole way through. I'm going to try some Sierra 180 .311" sp that are already loaded first. I've cleaned it up to sell for a friend but I'll probably buy it.......and a mould........
    Best, Thomas.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

  15. #15
    Boolit Master Char-Gar's Avatar
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    Quote Originally Posted by swheeler View Post
    sugging? Take a case fired in the gun and measure the inside neck diameter of it, size to that.
    This notion has been floating around this site for a while now as a short cut. This will tell you the maximum size of a bullet that can be fired in the chamber and in that case, but will give you zero information about the throat. It also does not account for the variety of case neck thickness in various makes and batches of brass.

    I have several rifles with either large or worn throats. I must neck turn to thin the brass, so it will hold the proper size bullet and still have some room for the neck to expand and release the bullet.

    Measuring the inside of a fired case may or may not work. A cast or throat slug will always work.
    Last edited by Char-Gar; 08-06-2017 at 11:49 AM.
    Disclaimer: The above is not holy writ. It is just my opinion based on my experience and knowledge. Your mileage may vary.

  16. #16
    Boolit Master
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    Oh it'll work
    Hell, I was there!

  17. #17
    Boolit Master Char-Gar's Avatar
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    Quote Originally Posted by swheeler View Post
    Oh it'll work
    Oh, I am sure the bullet will trundle down the barrel and strike the target. However that is not what I am after. I am after the smallest group possible.
    Disclaimer: The above is not holy writ. It is just my opinion based on my experience and knowledge. Your mileage may vary.

  18. #18
    Boolit Man
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    Quote Originally Posted by rondog View Post
    So, is there a tutorial or sticky here somewhere telling how to do this throat impression and chamber/pound casting? Not all of us know this stuff. And searching here - I always end up out in Google land......
    im with rondog, how do we do it?

  19. #19
    Boolit Master Outpost75's Avatar
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    If you barrel has a tight spot, the answer is to lap it out until its dimensions are uniform.


    https://www.google.com/search?rlz=1C...w=1254&bih=894
    The ENEMY is listening.
    HE wants to know what YOU know.
    Keep it to yourself.

  20. #20
    Boolit Master Hannibal's Avatar
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    Quote Originally Posted by zymguy View Post
    im with rondog, how do we do it?
    I don't know how to post links, but in the Cast Boolits sub-forum, there is a 'sticky' for 'how I do a pound cast'.

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BR Bench Rest M Magnum RN Round Nose
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