Bullet seating depth. Any magical formula?

[StraightShooter]

I have been reloading ammo for my precision .243 rifle for some time now and the only thing i am not sure about is seating depth. Is there any info out there to suggest a certain distance from the lands than another. Right now I am seating the bullets .002 from the lands just for the heck of it. I pretty much do everything there is to do to ensure the perfect reload ( neck turning, weight sorting, trimming, etc..) should i even worry about seating depth? Does it make that much difference? I know I get slighter more velocity when it is seated farther out but as far as its effects on accuracy i havent seen any. Any input?

[ocabj]

Depending on the bullet, it will make a difference. Standard BTHP match designs like the Sierra Match King are very tolerant of jump. You can set .020" jump and you're good to go.

But VLD bullets like the Berger VLD can be very finnicky and may require it be seated right at the lands for 0 jump or even into the lands in order to perform well. This means you have to 'chase' the lands as the throat erodes away (as the round count goes up). Some people don't want the hassle and prefer to use traditional match bullets instead of VLD. That is why Berger recently designed a new 6mm non-VLD bullet for their match line, and also why they are testing a new heavy .22cal non-VLD which I had the opportunity to beta test (in an 80gr and 82gr design).

If you don't see accuracy differences with varying seating depths, say .020", .010", 0, and .010"+ jammed, then I would think the load itself is not depth sensitive.

[rksimple]

Like ocabj said, it depends. Play with it a little using a known load thats accurate. See if setting it back a little deeper does anything for accuracy. Conversely, try jamming them a little. See what happens.

[brando]

I'd like to add that the best time to start playing with seating depth, I've found, is once you've gotten a ballpark charge weight. I use it as the second stage of load development.

[StraightShooter]

thanks guys, i appreciate the info. One question, does seating it so it touches the lands tend to erode the throat faster?

[rksimple]

thanks guys, i appreciate the info. One question, does seating it so it touches the lands tend to erode the throat faster?

Don't think so. Haven't read anything that proves otherwise. Touching the lands or jammed can increase pressures though. Since the bullet immediately encounters resistance, chamber pressures rise. When the bullet has a little jump, the initial pressure is less since the bullet encounters less initial resistance. In other words, I wouldn't try it with a max load.

[ocabj]

No. The bullet isn't what erodes the throat. It's the hot gases when powder is ignited. So seating depth doesn't affect throat life.

Your main concern when seating at or into the lands is increased pressure. Watch your fired cases and look for excessive pressure signs.

[6079Winston]

Avoiding rapid fire is probably the best way to minimize throat erosion. One reason the .243 didn't last long as an across the course round is that the rapid fire stages cut accurate barrel life to something like 2000 rounds. An article in Accurate Rifle Feb 2002 describes developing loads and changing the seating depth as the final tuning step once the best charge weight had been determined.

[StraightShooter]

Thanks guys, i think ive got all the bases covered now.

[30Cal]

0.002" off the lands? How accurate is your comparitor?

I would either go at least 0.010" away from the lands or soft seat the bullet into the lands. Where you're at, I'd be concerned that some will end up against the lands (which gives you a pressure kick) and some won't. So, I think you'd be better off in one region or another, but not right at the breakpoint.

Ty

[Prc329]

One thing I noticed with my savage is using SMKs it did not matter if it was mag length or close to the lands.

[ocabj]

SMKs are very jump tolerant, which is why most people stick to 80gr SMK vs the better BC of the Berger VLD. Less worry about seating depth and chasing throat erosion.

As far as a 77SMK set to magazine length vs 77SMK set close to lands in an AR, I think it will make a difference. After all, seating a 77SMK to 2.255 +/- .010 is a lot of jump to get to the lands. A friend of mine actually has separate standing ammo. He shoots 77SMKs seated to lands for standing, 77SMKs seated to magazine for rapids, and 80SMKs seated to lands for prone slow. He has found the 77SMKs seated close to the lands shoot better in testing.

As far as in a Savage or other bolt, what is mag length for .223?

[Prc329]

I think it is the same. I was talking about my savage in 308. Srry for the confusion there

[rksimple]

SMKs are very jump tolerant, which is why most people stick to 80gr SMK vs the better BC of the Berger VLD. Less worry about seating depth and chasing throat erosion.

As far as a 77SMK set to magazine length vs 77SMK set close to lands in an AR, I think it will make a difference. After all, seating a 77SMK to 2.255 +/- .010 is a lot of jump to get to the lands. A friend of mine actually has separate standing ammo. He shoots 77SMKs seated to lands for standing, 77SMKs seated to magazine for rapids, and 80SMKs seated to lands for prone slow. He has found the 77SMKs seated close to the lands shoot better in testing.

As far as in a Savage or other bolt, what is mag length for .223?

I'll have to check when I get home exactly what it is on my 12fv. I just remember having to load the 75gr A-Max so long that it I could only fit one round under the feedlips of the mag. Even then it wouldn't feed well. The Savage 223 doesn't have any feedramp or radiused area around the chamber so feeding issues have been a complaint. The Savage 223 also has a little insert in the magazine to make it shorter. This correlates with a little baffle on the bolt to prevent it from coming all the way to the rear. If it were like a normal short action, you could load the 223's as long as you wanted.