Bedding a Browning A-bolt with BOSS

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Striker77s, Jan 25, 2011.

  1. Striker77s

    Striker77s Member

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    I have a 300 win mag Browning A-bolt with a BOSS attachment. Browning beds the action of their BOSS rifles with a small dab of slightly rubbery material. I shoot a hand loaded cartridges of 165 gn SST bullets with 73 gn of 4831SC shooting at a velocity of 2947 fps (SD 23 fps). I didn't get very impressive results. I shot 5 groups of 3 rounds from a Caldwell lead sled rest. The vertical group size ranged from 0.5" to 2.2" at 100 yards. Due to the inconsistent grouping I decided to remove the Browning bedding material and properly bed the entire action. The rubbery material is supposed to dampen the harmonics and work in conjunction with the BOSS system. Hopefully the rifle improves instead of getting worse. I'll let you know how it goes in a week or so.
     
  2. Striker77s

    Striker77s Member

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    This was my first bedding job and I set the action and barrel a little too low in the stock. So I skim bedding it again and it turned out very well considering it was my first time. I took it to the range and shot from a lead sled to reduce any human error. I shot three groups of 3 rounds. My vertical spread at 100 yards was from 0.25" to 0.5" which is as good as can be expected for a factory rifle. Unfortunately my horizontal spread was from 1.2" to 2.2". I can't figure out exactly why I'm getting such a large horizontal spread. The wind was very mild. I checked my scope and it was secure and my action was solid into the bedding. The barrel is free floating with a large clearance. The only thing I can think of is a bad scope? Any ideas what could cause such a large variation in just the horizontal spread?
     

  3. shortgrass

    shortgrass Well-Known Member

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    Might try shooting it from your shoulder, on bags, instead.
     
  4. NW Hunter

    NW Hunter Well-Known Member

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    Is 2947fps your max load? My 300 liked to spit out 165's at 3020fps with H1000. This velocity worked well for my barrel. It could be that your velocity is setting up bad harmonics in your barrel. Try increasing your powder charge in small increments to see if groups tighten up.

    On your scope, I too have had a scope's internal adjustments go haywire. Try mounting a different scope and try again to verify what the problem is.

    On your bedding job, is the action stress free? Did you just snug action screws or torque them while bedding material was drying? Torquing action screws can make the action touch high spots in the stock and bend the action to fit the stock.

    IMHO...
    Randy
     
  5. Mikecr

    Mikecr Well-Known Member

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    I don't know that you can improve on a properly tuned BOSS -by changing it's bedding.
    Most people set the tuner to Browning's recommended(in the BOSS manual) number and work up loads as usual. Then, they can tweak the tuner from there.
    Was that the best load you could put together?
     
  6. rscott5028

    rscott5028 Well-Known Member

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    A friend has an A-Bolt. It may be the stalker model. I noticed that the fore stock is very flimsy and may well be making contact with the barrel under some conditions. The trigger is also very heavy. He's not real serious about long range or accuracy. I would have to fix those two things on his rifle before wasting any more ammo. I'm not sure how that relates to A-Bolt rifles in general.
     
  7. Striker77s

    Striker77s Member

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    I also have the stainless stalker with a synthetic stock and noticed the same issues. My trigger is adjustable and one of the first things I did was replaced the spring in the trigger. It now has a nice crisp 1-1.5 lb pull. I also routed the stock out around the barrel when I bedded it to make sure it does not come into contact with the barrel, even when using a tripod. There is plenty of clearance around the barrel.
     
  8. Striker77s

    Striker77s Member

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    Shot some more on Monday with a tripod to make sure the lead sled I was using wasn't impacting my shooting. Same results as before, excellent vertical spread at around 0.5" and horrible horizontal spread at 1-2". I'm going to buy a Sightron SIII 6-24 scope but I'm waiting for their new reticle to become available. Which isn't for another month. So I'll have to wait until then to replace my scope to see if their is a problem with it.
     
  9. rscott5028

    rscott5028 Well-Known Member

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    Have you already done a complete load workup from scratch on this rifle? e.g. ladder test from min to max load at .5 grain or less increments?

    When I re-read your post, it sounded like you've only fired a few groups with one powder charge. Even if it was your best load before bedding, you may well have changed the harmonics of your rifle.

    I also recall reading an article once that described a situation/technique whereby you could hone in on an accuracy node by manipulating seating depth/jump to the lands ever so slightly and that moving in or out would change the group formation from horizontal to vertical and at some point in between you would get your tightest group.

    I've never exactly reproduced that (perhaps not thorough enough), but I've seen something similar.

    Good luck.
    Richard
     
  10. Striker77s

    Striker77s Member

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    Supposedly the point of having a Browning with a BOSS is to eliminate the need for ladder testing with different charges. You can adjust the BOSS to match the harmonics instead. I have adjusted the BOSS and it does impact the vertical spread but hasn't improved the horizontal. However maybe I'll change my load up as you suggest and see what happens.

    I plan on purchasing a headspace bump gage and a Hornady overall length gage to set the bullet depth more accurately. There are so many things to adjust when reloading and shooting long range. I'm trying to systematically eliminate each one. It just baffles me why harmonics and reloading techniques, etc would only improve the vertical spread but not horizontal spread. It seems both would be impacted by adjusting these factors. That is why I suspect my scope. It is a used Pentax lightseeker and I don't have a long history with it. I'll keep working at it and let you know if a new scope helps once Sightron starts shipping their new scope.
     
  11. rscott5028

    rscott5028 Well-Known Member

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    Sure... scope, bases, action screws, anything touching the barrel...

    ...and load workup with seating depth being one of several key variables.

    BOSS sounds good on paper. I've just never spent enough time with it to convince myself that it works although I see a lot of testimonials.

    Let us know what you find.

    Richard
     
  12. cstilt

    cstilt Well-Known Member

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    Any luck on the load development?

    Also, would you care to post a picture of your bedding job? I'm wanting to bed my A-Bolt as well and wanted to see an example before I tore into it. Did you remove the trigger to do it?

    I sure hope this thread isn't too old...
     
  13. Hondo64d

    Hondo64d Well-Known Member

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    A good bedding job can't hurt, but if you are not methodically adjusting the BOSS to find the best setting for your load, you might as well have it cut off.

    They do work as advertised, but every time you change the load, you may have to find the optimum setting again.

    I would recommend that you work up a load to the velocity/SD you want with the BOSS set in the factory recommended sweet spot, then start adjusting the BOSS WITH NO CHANGE TO THE LOAD, perhaps in increments of five or 10 at a time on the graduated scale:

    Fire a group and let the barrel cool.
    Adjust the BOSS 5 on the scale.
    Fire a group. If the group is better, adjust five more in the same direction and fire another group. Continue doing this until the group starts to open again and then back up to the adjustment that gave you the smallest group.

    If after your 1st adjustment your groups are worse, make an adjustment in the opposite direction and proceed with the above method.

    Most people that say the BOSS doesn't work for them have not tried graduated methodical adjustment or they keep changing loads, which changes the barrel harmonics and necessitates adjusting the BOSS again.

    The devices do work, but you need to stay with the same load, be methodical exercise some patience until you start seeing a change in groups.

    John
     
  14. Jay Kyle

    Jay Kyle Well-Known Member

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    I've put hundreds of round through a BOSS equiped Stainless Stalker trying to find the optimum method for tuning these beauties.



    The best method I've found so far is to:
    1. Set the BOSS to a recommended setting, or one that is close according to the manual. Approximate if you have to.
    2. Stay with the factory COL, I've tried different lengths but ended up chasing my tail by changing the COL, then ending up messing it up by following that change with a tweak to the BOSS.
    3. Follow any ladder style load development method to determine that point of powder charge insensitivity where if you vary the powder charge by (e.g.) 0.2 grains the center of a group doesn't change.
    4. Adjust the BOSS to tighten up the groups. This takes the place of varying the bullet depth step which would normally follow on a non-BOSS equiped rifle. This is fine work. If you change the setting any more than 2 increments per group you risk jumping over a good group. Also tracking your groups in a log book really helps.
    When you run your test groups ALWAYS allow cooling time between each shot. I've found that by the time the 3rd shot is taken, the barrel has heated up and walks off-target - took me many range trips to figure that one out. But it makes sense as these are hunting rifles first, designed for a limited number of shots in a string before things change. That's a desgin trade-off, rapid fire accuracy vs weight.

    Lastly, the stocks are so soft that they CANNOT be muscled into position on a bi-pod - this will cause horizontal stringing. Allow the rifle to naturally find the target and use a light grip.

    Jay
     
    Last edited: Jul 18, 2011