How I adjust my BOSS

Discussion in 'Browning A-Bolt Rifle' started by Darkhorse, Oct 18, 2015.

  1. Darkhorse

    Darkhorse Copper BB

    It's been awhile since I've posted. My bad.
    I continue to see where shooters have problems tuning the BOSS on their rifles. I've been through this successfully on a few loads so allow me to share with you my method. It will be a fairly long thread.
    Browning Abolt II Lefthand Stainless Stalker in .300 Winchester Magnum.
    First of all it took 100 rounds down the pipe for my Abolt to settle down and start shooting good consistant groups.
    I can shoot 3 shots to same POI. After that the barrel heats up and starts to string the shots to the left so you must allow cooling time.
    My rifle scatters the shots until I shoot 5 fouling shots, then it settles down and shoots.
    Learning these things about your rifle is vital to understanding what is happening as you continue to tune.
    I am a serious, accuracy minded handloader who fully understands tuning the load to the rifle. But I'm also flexible enough to understand with a BOSS I'm tuning the rifle to the load.
    All my brass is prepared by neck sizing if possible and FL sizing to where the sized case just fits the chamber.
    Primer pockets are uniformed with the proper tool. Then chamfered inside to where all the rough brass is removed and a visible chamfer can be seen through the case neck with a good light. Then lightly chamfered inside primer pocket.
    I turn all my case necks to clean up 85% of the neck. No more.
    I remove the case neck sizing spindle from my sizing dies and remove the spent primer in a separate operation.
    Using a case fired in my rifle my sizing dies are set up to size my cases trued to the chamber of my rifle.
    After sizing I use a sizing die with the spindle installed but the lock nut is left loose and the die is left loose also to be able to "Float" to find the exact center of the barrel axis. Then each case is run into this die to size the inside of the case neck.
    I use Hornady inline seating dies to seat my bullets.
    I then pick the bullet I want to use, the powder, and the charge. Next I will load up 3 and fire them to check for pressure.
    If pressure is OK I go ahead and load 20 or so. You can start at any setting you desire such as the factory sweet spot.
    I use paper with 3 separate bulls. Shoot the first one 3 shots, measure the group and record all data. Next dial back 1 entire turn to the next number. Shoot 3 and record results. Next dial forward 2 numbers. This gets you 1 number past your starting point. Shoot 3 and record.
    If there is no change in accuracy then repeat the process. You should be able to see one of these settings shoot a noticably tighter group. Now go 1/2 turn in each direction and shoot a 3 shot group at each setting. By comparing the targets one of these groups will be tighter than the other. Work with that setting by making small turns in your settings until the rifle satisfies you. Record that setting and all other data for future reference.
    Any changes in powder or bullets will require tweaking the setting.
    My deer load shoots under 1/4" consistantly.
    My elk load shoots .5 to .520" with full length sized cases.

    You, the shooter must be able to shoot a 1/2'" group if you expect your rifle to do so. Sorry, but that's the way it is.
    Your bench techniques and setup must be rock solid also. Remove all these variables and let your rifle do the rest.
  2. SHOOTER13

    SHOOTER13 Guest

    Welcome back Darkhorse...

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