Loading For my AR (1)

As you can tell by the title I intent to make this a series that, because of my somewhat busy life, will most likely span a period of months.

When I start working up loads for a bolt action rifle I first determine the 'sweet spot' for each bullet I intend to try. It's my experience that each cartridge, gun, bullet combination, regardless of powder or velocity, has a specific bullet seating depth that is the most accurate. With some exceptions it's the point where the bullet starts its flight .005" to .020" from the rifling. Those exceptions are shooting very light bullets in my .303 SMLE and 7mm Mag. Those can't come close to the lands because they're too short.

I know that bench rest shooters sometimes have the bullets touching the rifling, but that requires a whole lot more precision than I'm willing to spend the time doing. Also, doing that has the very real danger of causing excessive pressures.

This week I measured the over-all length to the bullet olgive where the bullet touches the lands. The bullet is the Sierra 55 grain HPBT. What I found is that with the over all cartridge length at maximum to fit in the magazine, the bullet is .056" from touching the rifling. So unless I want to shoot this auto-loader as a single shot, having the bullet close to the rifling just isn't going to happen. So my first loads are going to start at the maximum length and then shorten by .005", .010" and .015". Being that far away, I don't know if length will have much of a difference, but I'll find out.