Load development HELP on Win M70 with a BOSS

meangreen75

meangreen75

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Prescott, AZ
I'm looking for some help on figuring out how to develop a new load using Barnes LRX 190 out of my M70 300 win mag. I previously shot only factory Hornady 180 gr out of this gun but now I've been reloading and trying to get a group going. I've got the SD and ES pretty good and I've started messing with seating depth, but I have not been able to get anything to group tighter than 1" at 100 yards. It's incredibly frustrating. I began thinking that the BOSS maybe my problem since it was set to the 180 factory rounds (which did group around 3/4" at 100). Has anyone had issues getting a load together on a BOSS system?
 
Link below for some good info on the BOSS, you should be able to tune to most any load/bullet combo. In my experience, I have 3 BAR's and a M70 Super Grade, all with the BOSS. I'm able to tune whatever combo I'm feeding them.

BOSS Owner's Manual

www.browning.com www.browning.com

Very important is at 0-0 when fully seated, and small increments make a big difference on paper. If I shoot 2 shots and they're far apart, I don't waste round 3, I let gun cool and move to next setting.
 
That was one of the big sales pitches for the boss unit when they came on the market. Get a load with very little shot to shot speed variance. Then tune the barrel with the Boss unit.
 
amu_shooter said:
Link below for some good info on the BOSS, you should be able to tune to most any load/bullet combo. In my experience, I have 3 BAR's and a M70 Super Grade, all with the BOSS. I'm able to tune whatever combo I'm feeding them.

BOSS Owner's Manual

www.browning.com www.browning.com

Very important is at 0-0 when fully seated, and small increments make a big difference on paper. If I shoot 2 shots and they're far apart, I don't waste round 3, I let gun cool and move to next setting.
Click to expand...
So are you shooting 2 then adjusting the BOSS by .5 or 1 whole number setting?
 
I usually start at recommended setting on chart based off bullet weight, then I work under in .2-.3 increments for 2 groups, if nothing works I go back to recommended setting and work up same way. You're final setting won't be that far away from recommended setting.

Lastly once I find good grouping, I'll try .1 under and .1 above where groups look best.

Be sure and let barrel cool between groups.
 
Only time I shoot 2 is if the first too are far apart, no need to pursue that setting any further, especially with the Magnum Calibers.

Rest of time I shoot 3 if first 2 look promising.
 
amu_shooter said:
Only time I shoot 2 is if the first too are far apart, no need to pursue that setting any further, especially with the Magnum Calibers.

Rest of time I shoot 3 if first 2 look promising.
Click to expand...
Sounds good. There one problem is that Winchester didn't put in the time (or bullets) that Browning did. 180gr is 0.2 and 200gr is 2.8, 220gr is 3.6, they never tested anything beyond those 3 bullets in 300 win mag. That is a lot of rounds going up/down .2 of a turn trying to find the spot. I think I'll start at 2.8 turns out and work my way back in going down .5 of a turn until I see the groups start closing in.

Thank you for the help AMU.
 
amu_shooter said:
Meangreen75, got curious today about setting on my M70 338 Win Mag, chart shows 3.25 for both A-Bolt and BAR, that was my start point.

Ended up at 3.95 shooting a Barnes 185 gr MRX into cloverleafs at 100 yards.

Just an FYI.
Click to expand...
Went out and shot 25 rounds looking for the spot today, but no joy. Pretty frustrating process. I started at the setting for 200 gr and came down looking for the 190gr setting but never got better than a 1" group... I'm seriously considering a APA comp over this whole process.
 
if it was my rifle I'd set the tuner at zero stated above. Seems as if you have played with seating depth. Have you changed powder? Have you changed primer? Also how clean have you cleaned the barrel, and I mean clean clean. Next thing to consider after that is maybe it is the bullet not all rifles will shoot a particular bullet well. Twist rate you should be just fine, but harmonics, powder, primer, bullet all are a very important aspect. Sometimes you just have to say f it and try a different bullet, powder ext.
 
TopPin said:
if it was my rifle I'd set the tuner at zero stated above. Seems as if you have played with seating depth. Have you changed powder? Have you changed primer? Also how clean have you cleaned the barrel, and I mean clean clean. Next thing to consider after that is maybe it is the bullet not all rifles will shoot a particular bullet well. Twist rate you should be just fine, but harmonics, powder, primer, bullet all are a very important aspect. Sometimes you just have to say f it and try a different bullet, powder ext.
Click to expand...
I'm working with 4831sc and 4350 on loads that are solid all around. I've cleaned the barrel extensively. I'm probably going to go down to the 175 gr LRX and see if that does any better. I'm trying to stick with the LRX since I've had really good results with it on multiple animals and distances.

I'll update this if the 175 works out better.
 

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