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Thread: COL question

  1. #1

    COL question

    We've made up a max COL measuring tool. As a staring point we used the Frankford Arsenal tool, but improved it ( at least that is my idea). I shoot 243 with 75 grain HDY and 67 grain Hornady bullets. This only on the range for practice. My first load was about 0,8 mm ( 0,032 " ) of the grooves and lands. Accuracy was reasonable, but not perfect. I could shoot a few 14mm, 3 shot groups at 100m , but also groups wich are 40mm / 50 mm .
    After measuring the max COL we ( my reloading friend and myself) made up the same load but with 0,5 mm of jump. ( about 0,02") and the groups get worse. Checked the loads in the rifle , no marks on the bullets when chambered, no overpressure signs,...... As a starting reloader I have no idea what can be the reason?
    load : 243 win , 75 gr HDY , 44.4 grain Ramshot Hunter - Rifle : Rem 700
    The first load ( 0,8 mm off ) was made up along a reloading book, never measured anything.
    The new loads I tried with the 87 grain bullet and also 0,5 mm jump also have bad accuracy.

  2. #2
    I have to admit that I do not subscribe to the chasing the lands bull, just load to book COL.
    Personally I consider barrel timing to be far more useful in eeking out the precision of hand-loads - that can be tuned with the seating depth.
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  3. #3
    Thats what we did before, just using the values in the reloading manual. That's what my friend does for more than 25 years. We hoped making a step forward, but we didn't.

  4. #4
    I measured the distance on my .308 and with hornady 165gr interbonds the distance to the lands was 2.955". As my floor plate mag can only fit rounds upto 2.82" so i could never chase the lands unless rendering the rifle single shot . Even being so far off the lands I can still average 0.6" groups just by playing with the powder charge.

    If your barrel harmonics are off due to your powder charge, the distance from the lands will not help too much. Try to get the powder right first using standard col from the manual and when your groups tighten then, using that charge, play with the seating depth.

    Best of luck,


  5. #5
    It's an old discussion, but I will resurrect it enough to say that I have all but given up in chasing the lands. It is really only critical in custom chambered and throated rifles. For factory rifles i have been seating to recommended OAL. I have a couple supportive arguments: Neck tension on the bullet as defined by pull weight (the effort needed to release the bullet from the neck) determines the burning rate for the individual charge in that case. The more the bullet is gripped by the neck, the more uniform the neck tension and hence burn rate. This is why factory ammunition is usually supplied with a crimp (and why I crimp all my handloads) My second argument, and this is an anecdotal one, is that the best and most accurate factory ammo you ever shot in your rifle was not seated "X" thou off of your rifling. It was loaded to SAMMI/CIP standards. All handloading data (pressure, velocity, etc) was developed around the resulting seating depth that a bullet loaded to specified OAL provided. Chasing the lands is like trying to reinvent the wheel.

    Seat to OAL recommended and work on getting supreme uniformity in brass with regards to neck tension, case length, primer depth, etc. and you will have more uniform, if not better, results. Lets face it, if you are getting 14mm groups and 40mm groups you are definitely not getting any uniformity in your load. The 14mm group is not necessarily a promise of things to come, it's more than likely a statistical happenstance. JMHO~Muir

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