The store that I buy my bullets from is down to nothing in stock. I bought a box of TSX 150 grain bullets for my 270 win. The box says that it is suggested for a 1 in 9.5 or faster twist. I've always had good accuracy with 150 grain bullets in my 270 win. What's different about these TSX's? My rifle is a 1 in 10 twist, I think. It's a vanguard stainless.

Solid copper bullets are less dense than their lead-cored counterparts and are therefore longer for a given weight. The longer a bullet is, the faster twist you need to stabilize the bullet in flight. I'm guessing that the 150 grain .270 TSX might not always stabilize with a 10-inch twist.

One thing to look out for in marginal twist rates is hunting range vs shooting range.

The 75 gr Vmax in a 1 in 14" twist 6mm barrel at ~ 3000 ~ 3100 fps will shoot .1" groups at 50y, but occasionally keyhole at 100y.

The 65 gr never keyholes at 100 yards.

What does it all mean?
If you shot perfect groups with your 270 at 100 yards, you might be keyholing on game at 500 yards.

What is keyholing?

The bullet goes into a wobble and hits the target sideways....leaves not a round hole but one that looks like a "keyhole" like the funny hole on old door locks.

Thanks. I thought that was what it probably was. So if I load these and they don't keyhole at 100 yards they might at 200 yards? And if they don't keyhole at 200 then I shouldn't take a shot at a big game animal over 200 yards cause it might still "wobble" further, or if it has stabilized at 200 yards then it will probably stay stable?

I'd say the odds are if you're shooting good groups and see round holes at 200 yds you're good to go.

I shot a deer through the lungs in November with a 270 at 500 yards, after I ranged it with the Leica and did a few feet of hold over. I got lucky.

The longest range around me in Seattle is 100 yards.

I need to find a longer range and do some more realistic practice.