Engineering101
Well-Known Member
I was working up loads for my 1 in 9 twist 7mm WSM using the 168 grain Barnes LRX when I noticed that the carbon smears from bullets passing through the paper tended to be elongated and that one bullet hole looked like two. When I got the velocity up to 3,080 fps, I finally got my first round bullet hole. So I pulled up Berger's twist rate tool and punched in the data for the bullet and sure enough it calculated and SG of 1.23. Less than 1.4 shows "marginal stability" and at less than 1.0 the bullet will be tumbling.
Worse yet, the calculator assumes that the bullet has a lead core which it doesn't. Since it isn't tumbling I know the SG is somewhere between 1.00 and 1.23.
I ended up with a velocity of 3,157 fps which added 0.01 to the SG for a grand total of something less than 1.24. Here is the interesting part. Even though some of the bullet holes are elongated, it still put 5 shots inside 1.6 inches at 200 yards – this all at 750 feet elevation and 39 degrees F. I'll be hunting at 4,000 feet or higher where the SG jumps up by 0.15 to something less than 1.39. Anyway, I'm thinking I can use these LRXs in my 1 in 9 twist but just barely.
Question: Is this a dumb idea to be thinking I can take these hunting?
Worse yet, the calculator assumes that the bullet has a lead core which it doesn't. Since it isn't tumbling I know the SG is somewhere between 1.00 and 1.23.
I ended up with a velocity of 3,157 fps which added 0.01 to the SG for a grand total of something less than 1.24. Here is the interesting part. Even though some of the bullet holes are elongated, it still put 5 shots inside 1.6 inches at 200 yards – this all at 750 feet elevation and 39 degrees F. I'll be hunting at 4,000 feet or higher where the SG jumps up by 0.15 to something less than 1.39. Anyway, I'm thinking I can use these LRXs in my 1 in 9 twist but just barely.
Question: Is this a dumb idea to be thinking I can take these hunting?
