A reliable way to determine COAL

Discussion in 'Reloading' started by sgt_zim, Jun 28, 2020 at 5:26 PM.

  1. sgt_zim

    sgt_zim AH Elite

    Joined:
    Mar 26, 2017
    Messages:
    1,294
    Video/Photo:
    14
    Likes Received:
    1,633
    Location:
    Sugar Land, Texas
    Member of:
    NRA, Houston Safari Club Foundation, NWTF
    Hunted:
    Texas, Louisiana
    after rereading my Woodleigh manual for I don't know how many times, I finally stumbled across a reliable method of determining C.O.A.L.

    I'd been looking because I kept struggling with accuracy and velocity on a TC Encore 308, and while I've been getting stellar accuracy out of my 6.5x55SE, velocities weren't very close to what was published.

    Turns out that the throats on these 2 rifles are much deeper than I realized them to be.

    I'd been working loads for the 308 with ELD-X 178 gr, VLDH 175 gr, and Gold Dot 168 gr. The books on all 3 loads show a COAL of 2.800".

    Using what I call "the Woodleigh method" that some of you probably already know about, I determined that the Hornady and Berger bullets show a COAL of 2.900" when seated to the lands. A 0.1" jump is quite a jump, and both accuracy and velocity were not anywhere near what they are in my other 308, and the TC has a 26" barrel, to boot. Velocities were routinely 100+ fps slower from the TC than they were out of my Savage 10's 24" bbl.

    To get to COAL, it's a couple steps. Also, bear in mind this doesn't give an EXACT COAL, but close enough to work with. I've tried Hornady's COAL tool with inconsistent results, and a few other methods demonstrated by YTers, all to inconsistent results.

    1. you need a wooden dowel that is at least half the bore diameter. A 3/16" dowel will have this covered up to about a 9.3mm bullet. I don't know what a 0.25" dowel will fit in that's smaller than 308 bore, but it certainly own't fit in a .264 bore.
    2. close the bolt all the way, then stick the dowel all the way down from the muzzle until it touches the bolt face. hold a fine pen/pencil to the dowel at the crown, then rotate the dowel until you've completed the circle
    3. open the breech, drop in the bullet, then gently put a brass behind the bullet, then gently push the bolt to the brass. you don't want to force the bullet down any further, but you want enough resistance to feel when you...
    4. stick the dowel back up the barrel (helps if the barrel is angled down a bit). Same procedure as 2, make another circle.
    5. measure the distance between the 2 concentric circles, this is max COAL with the bullet on the lands.
    6. back off 0.02 ot 0.04 from max COAL as is customary, and work from there.

    For my 6.5x55 loads, the book on the ELD-X 143 I am getting good accuracy out of is 3.025", and not-quite-as-good with NP 125 grain is the same COAL. When I measured the dowel, COAL for the Hornady was 3.2", so looks like I should be seating the bullets out to about 3.16 - 3.18. That is WAY, WAY past what Hornady says, and while the published Nosler COAL wasn't as far off, it was still WAY off, with an on-the-lands COAL of 3.16" so looks like I should be seating them out to about 3.12 to 3.14

    Curiously, Woodleigh 160 gr and Hornady 143 grain both measure to an identical COAL of ~3.20

    still need play around a little to see if those COALs will work, at least for my 6.5. Don't have to worry about magazine fit for the TC.

    Anyway, if you've been struggling with this the way I have, hope this helps.
     

  2. sgt_zim

    sgt_zim AH Elite

    Joined:
    Mar 26, 2017
    Messages:
    1,294
    Video/Photo:
    14
    Likes Received:
    1,633
    Location:
    Sugar Land, Texas
    Member of:
    NRA, Houston Safari Club Foundation, NWTF
    Hunted:
    Texas, Louisiana
    I realize that in theory, it is better to measure the distance from the bolt face to the ogive, which is what the Hornady tool does, but I've never figured out how to get consistent results - I got lengths which varied quite wildly, as much as about 0.13" or so. That just isn't useful.
     
    Bob Nelson 35Whelen likes this.

  3. Aaron Nietfeld

    Aaron Nietfeld AH Fanatic

    Joined:
    Nov 18, 2014
    Messages:
    603
    Video/Photo:
    7
    Likes Received:
    554
    Location:
    Alberta, Canada
    Hunted:
    Canada, South Africa
    This seems like a good method!

    One thing I've always used, it to cut one side of the neck with a hacksaw, then seat the bullet long, chambering the round. The cut allows the bullet to seat to the proper depth, so when you remove it, the cartridge should be COAL, as long as it didn't stick a in the chamber and pull out a bit on extraction.

    Do this a couple times, and you will find the consistent length.
     
    Bob Nelson 35Whelen and sgt_zim like this.

  4. sgt_zim

    sgt_zim AH Elite

    Joined:
    Mar 26, 2017
    Messages:
    1,294
    Video/Photo:
    14
    Likes Received:
    1,633
    Location:
    Sugar Land, Texas
    Member of:
    NRA, Houston Safari Club Foundation, NWTF
    Hunted:
    Texas, Louisiana
    I had originally tried something similar with my 6.5x55, but I hadn't cut into the brass, just used a slightly resized case. I had come to a COAL of 3.10 using that method, but I realize now that there was still too much neck tension on the case, and looks like I forced the bullet down past the ogive's first contact point by a bit.

    Oh well. Better too short with lower pressure than too long and too much pressure.
     
    Bob Nelson 35Whelen likes this.

  5. James Adamson

    James Adamson AH Senior Member

    Joined:
    Dec 28, 2019
    Messages:
    71
    Video/Photo:
    18
    Likes Received:
    137
    Location:
    Shetland
    Hunted:
    Namibia
    I have always used a neck sizing die to gently resize the neck until it grips the bullet enough that I can push a bullet into the brass by hand then do the same as the hacksaw method and close the bolt to find COAL.
     
    Bob Nelson 35Whelen likes this.

  6. Arthur Morta

    Arthur Morta AH Member

    Joined:
    Apr 16, 2015
    Messages:
    20
    Likes Received:
    38
    Location:
    Zimbabwe
    Hunted:
    South Africa, Zimbabwe
    Being a benchrest shooter as well, I have used the process described above as well. However have tried the method in this YouTube video on my 6PPC and 6.5x47 Lapua too, with closer results. Only issue is stripping the bolt to the extent described is a bit tedious...

     

  7. flatwater bill

    flatwater bill AH Elite

    Joined:
    Jun 16, 2013
    Messages:
    1,525
    Video/Photo:
    21
    Likes Received:
    1,906
    Member of:
    NRA endowment member/Life member
    Hunted:
    NAMIBIA, RSA, KYRYG, KAZAKSTAN, MOZAMBIQUE,MEXICO, BOLIVIA, PERU, BRAZIL, ARGENTINA, CANADA, NEW ZEALAND, AUSTRALIA, SPAIN,
    Thanks Sgt.................good data..................FWB
     
    Bob Nelson 35Whelen likes this.

  8. Nkawu

    Nkawu AH Veteran

    Joined:
    Mar 8, 2018
    Messages:
    214
    Video/Photo:
    12
    Likes Received:
    178
    Location:
    Currently in the UK, from South Africa
    Member of:
    KZN Hunting Shooting & Conservation
    Hunted:
    South Africa, Zimbabwe, Sweden
    I use this same method, but I use my cleaning rod. And I use another cleaning rod to keep the bullet up against the lands for the second measurement. Stellar accuracy out of my 308.
     

  9. sgt_zim

    sgt_zim AH Elite

    Joined:
    Mar 26, 2017
    Messages:
    1,294
    Video/Photo:
    14
    Likes Received:
    1,633
    Location:
    Sugar Land, Texas
    Member of:
    NRA, Houston Safari Club Foundation, NWTF
    Hunted:
    Texas, Louisiana
    None of my rifles have bolts which turn that freely. I tried doing this one, too.
     
    Bob Nelson 35Whelen likes this.

  10. Hogpatrol

    Hogpatrol AH ENABLER SILVER SUPPORTER AH Ambassador

    Joined:
    Apr 13, 2013
    Messages:
    5,253
    Video/Photo:
    68
    Likes Received:
    10,546
    Location:
    Delaware, USA
    Member of:
    Atglen Sportsmen's Club, NRA ,SCCFSA, Bridgeville Rifle & Pistol Club
    Hunted:
    RSA, DE, NJ, PA, KS, TX, ME
    @Sgt Zim, Try this. It may give you more consistent results with the Hornady tool. Position the barrel vertically, drop in the bullet, then insert the loosened tool through the action. Remove bullet and check as usual. I use the method described in the video and then double check with the Hornady tool. Am usually within .002 on both readings.
     
    Bob Nelson 35Whelen likes this.

  11. Bob Nelson 35Whelen

    Bob Nelson 35Whelen AH Elite

    Joined:
    Dec 4, 2019
    Messages:
    1,706
    Video/Photo:
    125
    Likes Received:
    2,225
    Location:
    Australia
    Member of:
    SSAA
    Hunted:
    Australia, Africa
    @sgt_zim
    I used to use your method Sarge but tired of it.

    Nowadays I'm even lazier.
    Neck size, insert projectile and close bolt to seat the bullet.
    This will leave land scratches on the projectile.
    Measure the scratches and deduct from the length
    E.g. 308 loaded 3 inches when it comes back out the length is 2.9 inches with measure the land scratches say .020

    Your safe length to the lands is then 2.88 inches.
    If you want the bullet say 30 tho off the lands it is now
    2.88- .030 = 2.85
    So your new COAL is 2.85 inches giving 30 tho jump to the lands.

    Not 100% accurate but horribly close. Using this method my son's 308 groups .3 inches at 100 yards, my 25 cal give 0.8 inch 200 yard groups and my Whelen regularly cuts clover leaf groups so I must be doing something right.
    It's quick, simple and reasonably foolproof.
    Bob
     
    ve7poi likes this.

  12. bruce moulds

    bruce moulds AH Elite

    Joined:
    Aug 10, 2018
    Messages:
    1,820
    Likes Received:
    2,065
    something must be wrong if the hornady gauge is not both faster and more accurate and repeatable than any of the methods mentioned above.
    it would be worth seeking out the problem in order to live an easier life.
    bruce.
     

  13. shootist~

    shootist~ BRONZE SUPPORTER AH Veteran

    Joined:
    Jan 9, 2019
    Messages:
    225
    Video/Photo:
    6
    Likes Received:
    165
    Location:
    Albuquerque, NM
    Member of:
    NRA Life Member, USPSA Certified Range Officer (inactive), NRA Certified Instructor (inactive)
    Hunted:
    USA, Mexico
    +1
     
    bruce moulds likes this.

  14. bruce moulds

    bruce moulds AH Elite

    Joined:
    Aug 10, 2018
    Messages:
    1,820
    Likes Received:
    2,065
    thinking about the problem, it raises the question of the throat dimensions.
    the throat seems tight.
    this could be from an undersized reamer, or possibly a carbon ring formed there.
    or maybe oversized bullets.
    there should be about 0.004" clearance there, and a bullet should drop in fully up to touching the leade angle under gravity.
    with a hornady tool, you should be able to slide the bullet in and feel a definite "clunk" when the ogive hits the rifling.
    putting a little case lube on the ogive will reduce confusion as the ogive is less likely to stick in the leade.
    none of the other measuring methods mentioned here are accurate enough for precision bullet seating.
    if you have to chase the rifling with say 0.010" jam or jump in an fclass rifle you need something definite, repeatable, and accurate to do this.
    even with the hornady tool, absolute consistency of use is a must to get +/- 0.001" with the same bullet.
    measuring from the ogive is more accurate, but you need to check that the cartridge will fit the mag with a final measure on the nose.
    bruce.
     
    fourfive8 likes this.

  15. fourfive8

    fourfive8 AH Elite

    Joined:
    Apr 27, 2017
    Messages:
    1,147
    Video/Photo:
    214
    Likes Received:
    1,644
    Hunted:
    USA, South Africa, Mozambique, Zimbabwe, Zambia, Botswana
    True! The Hornady type gauge works. Basic enough in design that I was able to make one that works the same way as the Hornady. Simple, repeatable and accurate. If the leade angle is shallow and the bullet has a long ogive, the accuracy and repeatability of "jam" length measurements become much more difficult. Another bugger issue that sometimes skews such measurements is throat/leade erosion, especially irregular throat/leade erosion.
     

  16. bruce moulds

    bruce moulds AH Elite

    Joined:
    Aug 10, 2018
    Messages:
    1,820
    Likes Received:
    2,065
    458, yes eroded throats etc do make it harder, but this means that a ham fisted approach is to be avoided.
    i have found that a cleaning rod in the barrel can be pushed by the bullet as it is moved forward, and seems to aid feel of the bullet touching the rifling.
    lubing the ogive with case lube also seems to aid fee as you touch.
    bruce.
     
    Bob Nelson 35Whelen likes this.

Share This Page

 
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice