So, a 660 gr round at a posted velocity of 2910 fps, and out of a 17 lb gun. OK, stand by. Gotta do some converting and calcimating.
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OK, here's what I have:
The bullet is taking 0.00126 seconds to accelerate (avg) down the barrel and the rifle is traveling back at a 16.139 feet per second. This equates to about about 226 G's of acceleration into your shoulder. Oh ya, it's attempting to compress your shoulder about 1.8 feet without any friction. Taking into consideration friction (prone or bench on bags), you are probably still looking at approx 1.4 feet of compression. If we estimate a 20% decrease in recoil with the break, you have approx 1 foot of compression.
These are approximates, and if someone sees errors in the math, please let me know. I can re-run the numbers. The G's and compression numbers are pretty close though. Ya, with that light a gun for that caliber, you are going to want a very efficient break. I'm not surprised it left a bruise and marks.
Get something like this, and have BP re-thread your barrel for ya. [Beer]
http://www.gunbroker.com/Auction/Vie...=294707306#PIC
http://pics.gunbroker.com/GB/2947070...x789070077.jpg
My AMAC with Leopold MK 4 scope in 16X weighs just a bit over 35 pounds. That weight and this factory muzzle brake does cut the recoil way down. Flag pole is not really leaning, I was just holding the camera at a goofy angle. Second picture was taken at the NRA Whittington Center, Raton, NM.
http://img.photobucket.com/albums/v3...eldg001jpg.jpg
.http://img.photobucket.com/albums/v3...une1108006.jpg