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Thread: Method of finding COL for a new bullet (or a new barrel)

  1. #1
    Boolit Mold
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    Method of finding COL for a new bullet (or a new barrel)

    Let me know if this is already patented, and I'll take it off to avoid the lawsuit

    For rimless case, 9mm/40SW/45ACP for example, I have a method here to measure the maximum COL for a bullet in a barrel. No need to do 10+ times of switching between seating die and the disassembled barrel to find it.

    Drop your bullet into the chamber, so the bullet contacts the barrel lands. Use the caliper (the stick end) to measure the depth of the bullet base. Then pull the bullet out and measure the chamber depth/length itself and the bullet length. The approximate C.O.L is calculated as

    max. C.O.L = [bullet length] + [bullet base depth] + [case length] [chamber length] - [tolerance]

    where the [case length] e.g. for 9mm is 0.754, and the tolerance is the gap you leave for the variance of bullet length due to casting or PC, I set it to be 0.010 (you may find it differently). This will ensure a reliable feeding. After you seat a dummy to this COL do a plunk test, but make sure to crimp the case mouth properly. Because an un-crimped dummy round may fail the test due to the out-of-spec case mouth instead of a long COL. However, this might fool you that you had a long COL so that you would seek a shorter COL than actually needed.

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  2. #2
    Boolit Buddy
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    gotta fit in the magazine and feed into the chamber from the magazine- just another thing to think about.
    Loren

  3. #3
    Boolit Master

    Rcmaveric's Avatar
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    Or just slid a dowel rod down the barrel with bolt closed. Mark the dowel at the muzzle. Then hold bullet in the throat with a pencil and mark the dowel in the barrel at the muzzle again. The distance between the two marks is the Max COL that will be jammed into the lands. Take about .002 to .003 of that as that starting COL. Then adjust from there for feeding and chambering. Keep it simple.

    Frankford arsenal makes these nifty little platic clips that clamp onto the dowels. Then you drop the round between the clips and if it fits it chambers.

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  4. #4
    Boolit Master
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    Quote Originally Posted by Rcmaveric View Post
    Or just slid a dowel rod down the barrel with bolt closed. Mark the dowel at the muzzle. Then hold bullet in the throat with a pencil and mark the dowel in the barrel at the muzzle again. The distance between the two marks is the Max COL that will be jammed into the lands. Take about .002 to .003 of that as that starting COL. Then adjust from there for feeding and chambering. Keep it simple.

    Frankford arsenal makes these nifty little platic clips that clamp onto the dowels. Then you drop the round between the clips and if it fits it chambers.
    /\ Sounds like a winner to me.

  5. #5
    Boolit Grand Master Texas by God's Avatar
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    Seat to magazine length first. I just loaded some 10mm/180XTP to Hornady's recommended COAL and they were a hair too long for the m40 Glock mag. Always have the firearm on hand that you are loading for IME. Will they fit the mag and will they chamber? I'm an odd duck but I don't pay much mind to COAL figures- I set them myself on site.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

  6. #6
    Boolit Master
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    OK, The magazine is the first criteria. After that, the cartridge needs to feed from that magazine and finally: the method from post#3 seems pretty straight forward.

  7. #7
    Boolit Master
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    Just to expand on what Rcmavric posted.

    Cleaning rod/dowel method of finding cartridge OAL

    This is what I use for my guns to determine the max OAL and this eliminates any question of the crimp, incorrect case prep, or other operator induced error.

    This method works well on rifles and single shot pistols as well as Semi-autos. You can use a flat tipped cleaning rod, or flat tipped dowel rod. You will also need a sharp pointed pencil, a short dowel and a bullet sized but clean, of the type you are going to load.

    For Rifles
    Make sure the chamber is empty. Close the bolt, and be sure the firing pin is retracted into the bolt. Insert the dowel or cleaning rod and hold it against the face of the bolt. Mark the rod at the face of the muzzle. Remove rod, open bolt and remove it from the action. Insert the bullet into the breech and hold it snug into the rifling. While in that position insert the dowel or rod again, and with it firm against the nose of the bullet, mark the rod at the face of the muzzle.

    The distance between the center of those two marks is the max cartridge OAL for that rifle, with that bullet sized to that diameter.

    For Semi-auto pistols
    Remove the barrel from the slide and make sure it is clean and free of leading or other debris in the barrel and chamber. The dowel or cleaning rod needs to be longer than the barrel. Hold the barrel, muzzle up, and place the barrel hood on a flat surface like a table top. Insert the dowel or rod from the muzzle and mark the rod exactly flush with the muzzle. Remove the rod and insert the bullet you intend to use into the chamber and lightly press and hold it in place with the short dowel. Place the assy muzzle up on the flat surface. Insert the rod/dowel into the muzzle so it rests on the nose of the bullet and again mark the rod exactly flush with the muzzle. Remove and set the barrel aside. The distance on the center of the two lines is the cartridge OAL. Seat a dummy round to this length, or slightly shorter and begin to apply the taper crimp until the dummy passes the plunk test. This is the optimim cartridge OAL length for this bullet in this gun.

    You may need to adjust the seater to shorten the OAL if this does not feed from the magazine, but generally this will be a great fit. Remember, if you seat and crimp in one step, you might force a slight ridge ahead of the case mouth and that will screw up your seating.
    Dusty

  8. #8
    Boolit Master
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    [QUOTE=Texas by God;4517691]Seat to magazine length first. I just loaded some 10mm/180XTP to Hornady's recommended COAL and they were a hair too long for the m40 Glock mag. Always have the firearm on hand that you are loading for IME. Will they fit the mag and will they chamber? I'm an odd duck but I don't pay much mind to COAL figures- I set them myself on site."

    That probably is the reason Hornady loads their FL's to a shorter OAL than specified in their loading book. Or the ones I have measured are.

    Again I mean no hurt, harm, anguish or turmoil by my post I have posted on this posted subject. I am not baiting, trolling or calling out anyone. I am making a post based on my experience, knowledge and/or belief or opinion. That is all.
    We Know Mass Cannot Be Weighed But It Has Newtonian Weight And That Is Derived From Kilograms And Kilograms Can Be Converted to Pounds. But, Still Mass Cannot Be Weighed. But How is the kilograms obtained? Can Kilograms Be Weighed? Evidentally Yes It Can. But, Still Mass Cannot Be Weighed So Kilograms Must Not Exist. Funny Isn't It.
    One good thing out of this the next time I'm at the doctors and they want to weigh me I'll tell them mass cannot be weighed.

  9. #9
    Boolit Grand Master
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    Good idea, but not really new. Sorta BTDT...
    My Anchor is holding fast!

  10. #10
    Boolit Mold
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    Quote Originally Posted by Rcmaveric View Post
    Or just slid a dowel rod down the barrel with bolt closed. Mark the dowel at the muzzle. Then hold bullet in the throat with a pencil and mark the dowel in the barrel at the muzzle again. The distance between the two marks is the Max COL that will be jammed into the lands. Take about .002 to .003 of that as that starting COL. Then adjust from there for feeding and chambering. Keep it simple.

    Frankford arsenal makes these nifty little platic clips that clamp onto the dowels. Then you drop the round between the clips and if it fits it chambers.

    Sent from my SM-G950U using Tapatalk
    ^ is what I like about tossing a stone out there, and somebody's gonna show you a real dimond. Thanks for a better and easier method.

  11. #11
    Boolit Master Hick's Avatar
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    another easy way is to take a case and cut a slot in the neck so that it does not hold the bullet too tightly. Put the bullet in the neck finger tight-- and very long, then chamber the round-- the lands will push the bullet deeper in the case-- remove the cartridge and measure.
    Hick: Iron sights!

  12. #12
    Boolit Buddy
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    Quote Originally Posted by Hick View Post
    another easy way is to take a case and cut a slot in the neck so that it does not hold the bullet too tightly. Put the bullet in the neck finger tight-- and very long, then chamber the round-- the lands will push the bullet deeper in the case-- remove the cartridge and measure.
    A fired cartridge will do a similar thing.
    Last edited by 44Blam; 12-04-2018 at 03:04 AM.

  13. #13
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    Quote Originally Posted by 44Blam View Post
    A fired cartridge will do a similar thing.
    Done it this way for nearly 40 years.
    If it will then fit the mag we are good to go . if not reseat to fit mag. Test feeding . should be good to go
    Then its on to load development
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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check