I'm very new to reloading. I bought a Win 70 300 Win Mag with synthetic stock that is "molded" to the barrel the entire length of the stock. I couldn't get it to shoot under 2.5" groups! I was just about ready to sell it when I started reloading. Today I took out my first 300 Win loads and I was oh so surprised.

73 gr RE19 Win LR Mag primers
165 gr Sierra BTHP
1.75" @ 100
Better but not good

74 gr will all else the same
.76"
I couldn't believe it so I shot another 3 shot group. .84"

75 gr opened back up to 1.4"

Can any one tell me how one grain of powder cand make such a diff???

Barrel harmonics my friend. My 300 ultra does the same thing! 88.5 gr of IMR 7828 with the 180 Scirroco does .75 - 1" at 200 yds @ 3260 fps. Increase it to 90 gr of IMR 7828 groups open up to 1.75" at 200 and 3330 fps.

Some rifles are more susceptible than others to harmonics.

------------------
"If guns are outlawed...only outlaws will have guns!

What kind of Winchester do you have?

Also, try out some match-grade bullets, such as the Sierra MatchKing, and the Hornady AMAX. Real eye openers, with the proper load.

------------------
Happiness is a 200 yard bughole.

My rifle is the Black Shawdow. (I believe that's what it's called) blued with syn stock, 26" barrel, push feed

I picked it up at a show for about $300. I got it as a one time elk trip rifle, but now I'm thinking of keeping it to shoot big cutovers for wt deer.
I'm guessing I'm getting around 3,100 fps. Next time I'll know for sure!