Fine tuning using seating depth

Discussion in 'Ammunition & Reloading' started by ah141nj, Feb 20, 2010.

  1. ah141nj

    ah141nj New Member

    Ok, so I have been doing some load developement with various powders & bullets.

    I think I have a couple of promising loads.

    Seating depth/OAL is the final step for a pet load (from what I have been told)

    What increments should I start playing around in OAL?

    Do you start a maximum magazine length & just leave it there?

    Do you start at max OAL & work down in ? increments until minimum?

    The 2 loads I will be developing are...
    Varget with Hornady 55 gr FMJ's
    TAC with Nosler 69 gr HPBT

    They are both for an AR 16'' w/ 1/9
  2. Catfish

    Catfish Member

    I never mess with OAL on ammo loaded for the AR. I simply load it as long as I can get it and have it still feed well through the mags. I have never found any load in any AR that would shoot better at a shorter lenth.

  3. hunter Joe

    hunter Joe New Member

    On my T/C Encore, which is a single shot, I'm .008 off the lands. On magazine fed firearms I believe your limited to the length of the magazine, if feeding through the magazine.
  4. hunter Joe

    hunter Joe New Member

    To find the Max. OAL, I put a projectile in fired brass, take an overall length measurement, chamber the cartridge, work the action, and wery, wery carefully extract the round and take another measurement. I too cheap to buy the gauges.
  5. Tuner

    Tuner New Member

    First off it is important to understand that if a bullet is pushed into the rifling on a load that was developed where the bullet did not touch the rifling the pressures can jump significantly. If you have a hot load to start with you could be excessive if you are touching the rifling with that load, back off a grain or two. Bench rest shooters typically develop their loads with the bullets touching the rifling, but they are developed that way. Since you have already developed a load you will want to know at what length your bullet will touch the lands. Your magazine may very well limit the length and prevent you from seating the bullet out far enough to touch the rifling. I would probably start with my bullet 10 thousandths off the rifling and then go to 20 not knowing what kind of pressure you are working with in your present load.

    If you have a measuring caliber and use the following procedures you can determine the maximum overall length for any bullet to touch the rifling and then work form there.

    Purchase a rod that will slide down your barrel, a cleaning rod will work perfectly.
    Close the bolt and insert the rod carefully down the barrel from the muzzle to the point where it touches the bolt face. Take something like a knife or razor knife and put the edge on the rod and the side of the blade against the crown of the muzzle and rotate the rod so that you produce a scratch on the rod. You can blacken that area with a magic marker.

    Pull our the cleaning rod a several inches (4) and now open the bolt and insert into the chamber a bullet you intend to reload (not a loaded cartridge) and with something like a short dowel gently push the bullet up into the chamber until it is stopped by the rifling.

    Push the rod in until it touches the bullet. Here it is helpful if you have a second person to help who will apply slight pressure to the dowel that holds the bullet to the rifling. Mark the rod in the same manner as you did the first time.

    To get your maximum overall length take your caliber and measure the distance between the two scribed marks. ONE THING, IF YOU USE A CLEANING ROD YOU NEED TO HAVE THE WHOLE IN THE END OF THE ROD PLUGGED UP. If using a sub-caliber rod you may want to apply some tape around the rod in several places so it stays centered in the bore.

    I have a lathe and made a special rig with brass bushings and lock screws that allow me to lock the bushings in place after each measurement and then take a direct measurement off the bushings to get my maximum overall length.
  6. hunter Joe

    hunter Joe New Member

    Turner, as you can see I'm .008 of the lands, not touching.
  7. tuck2

    tuck2 New Member

    Hornady Tools

    I use the O.A.L Gauges with a Modified Case and the Bullet Comparator now sold by Hornady. They are tools to regulate bullet seating depth. I also like using the Headspace Gauge to set my reloading die. I started reloading in 1953 and tried various ways to set bullet freebore but now all I use are the Hornady toools.