280Rem. BOSS Sweet Spot?

[roysclockgun]

For my first range outing, shooting the older 280Rem. model Browning A-Bolt w/BOSS, I fired four loads, five rounds of each. The tightest group was 3/4", center to center. That load used a 139gr, spitzer SP BT and 53 grains of IMR4350 and Win. Std. primers. I loaded the bullets to within .005" of the lands. These groups were achieved shooting off a sled, with fore end and butt cushioned with toweling. I fired five shot groups very slow fire and waited more than 20 minutes between each group. The largest group measured 1 1/4".
I checked Browning's "sweet spot" chart and for 280Rem. using the Fed. 140gr. bullet, they suggest a setting of "4".
I hesitate to move the BOSS off that spot. I also do not intend to mount the second BOSS that has the recoil reduction feature, as the current recoil is not at all oppressive. I will accept the recoil, as opposed the increase in muzzle blast.
I will be foresaking my Browning 78 in 7mmRemMag in the fall and carrying this 280Rem. rifle west for mule deer and pronghorn. The single shot rifle has accounted for a number of game animals, but I want a new challenge.
My questions are: What is the MV for Federal factory ammo loaded with the 140gr. bullet, and fired from a 22" barrel? If when I chrony my 139gr. load and find it to be faster than the Fed. factory 140gr. MV, should I go UP on the BOSS setting, or down?
I have to admit, this being my first BOSS mounted rifle, that I hate the look of that lump on the end of my barrel!
Steven

 

[JD338]

I have never owned a BOSS although I have shot a few.
I think the way it works is start with a recommended setting and then tweek the setting to the load you are shooting.
Since most shooters do not reload, I would think that the velocity of the Federal factory 140 gr load referenced would be irrelevant.
You need to work with your load and you are set to go.

JD338

 

[6mm Remington]

Steven
I can't help you out with the Boss issue as I am like you, they are hideous looking and should be thrown in the trash. I believe for a non-reloader, they provided them the ability to "tune" their barrel to a factory load they wanted to shoot, just as we tune our loads for our barrels by changing seating, powders and amounts, and primers.

I used IMR4350 in my .280 MTN Rifle and it too had a 22" barrel. With 54.0 grs. of IMR4350 and 140 gr. Partitions, they chronographed at 2940 fps in my rifle. You should be right in that ballpark, plus or minus a few fps, but really close. We had a bunch of .308's we used on our team and we all shot the same lot of 168 gr. HSM factory loaded ammo. Even in the same length barrel, some were faster and some were slower. One of the rifles had a heavy barrel 22" length, and it actually chronographed with a higher fps than two of the 24" barreled rifles.

The .280 is a great rifle. Good luck with it as it appears to shoot very well. I see antelope and deer in your future! :grin: \
David

 

[SJB358]

I would adjust your most accurate load 1/10 of a number at a time. I have the BOSS on my 338WM and usually you will see the groups open up or start to close in. So you are at 4, the next setting I would try is 4.1. If it is getting smaller, go to 4.2, and so on. If it is getting larger, just move it the opposite direction. It is very easy to dial in. When loading my 338 with the BOSS, I look for the top speed load and then go to tuning. Once it is tuned to that load, it will put most anything under an inch or better.

David, your right, it isn't pretty at all, but man it works and the brake is a nice feature on the 338. Scotty

 

[YoteSmoker]

You should be able to find the BOSS manual online. Winchester and Browning are one in the same really, both being FN products, at least in years past. I have a Model 70 with Boss in 7mm mag that is my most accurate hunting rifle. For my caliber, they recommend starting at 2.5 for 140 and 6.0 for 160 grainers on the micrometer. Once you shoot a group at the recommended starting point for your gun, if you aren't getting the accuracy you are looking for, then start shooting groups moving 1/4 turn at a time. Then as Scotty told you, move back the other direction past your starting point if groups open up. 1/10 increments would work but cost you a lot more ammo. FWIW, using the two weight bullets and starting points for both in my rifle, I have shot 5 shot groups touching holes respectively, without making any changes with the 140 ballistic tip and 160 Partition (yes, Partition). I did load testing, however, to acheive this. The BOSS was really intended to be useful to guys who shoot factory ammo, but sure works great with reloads too! By adjusting it, you are lengthening or shortening the counter weight that affects the harmonics at the point the bullet leaves the barrel.

That probably wasnt much help telling you to look online for the manual. Let me get off my butt and see what mine calls for in 280 Rem...

165 grain Remington ammo, Set to 6.0/ 150 Federal ammo set to 5.0/ 140 Federal ammo set to 4.0

 

[YoteSmoker]

I just re-read your post, not taking anything away from my previous post here's an additional thought: Since you are tuning the bullet to the harmonics on the muzzle end and since it is designed for factory ammo essentially, forget about going .010 from the lands and set your OAL to the manufacturer's. In your case, Hornady recommends 3.290" for the 139 BTSP on page 369 of the 7th edition reloading manual. I would definitely start there and see what happens!