How do you determine what the wad seating depth will be or is this a trial by error until you get the final crimp right?

With modern wads, all you want to do is get the wad seated firmly against the powder - I don't know about your Lee, but my MECs have an indicator for wad pressure. All you want is a little "bump" in that indicator at the bottom of the wad seating stroke. You certainly don't need more than 20-25 lbs of pressure.
The "depth" is determined by the type of wad - - wads for 1 1/8 oz. loads, for example, are a little "shorter" than 1 oz wads, to allow for the additional shot. Everything should fit nicely in the hull & give a good crimp if you follow a published recepie. The wad, powder volume, & shot volume should match the particular hull called for in the data. Different wads are required in "straight walled" (Federal) hulls than are used in "tapered" (Rem. & Win.) hulls. Some published sets of components seem to do better at fitting nicely in the hull than others. There are some published loads that will cause crimps to bulge (initially or after a few days) - - a sign that there's too much "stuff" in the hull - - others may "dish" a bit - not quite enough volume. Usually a change of wad will fix the issue, but again, stay with a published load. Most of the "clone" wads(Downrange, Duster, Claybuster) will either tell you which OEM wads they will substitute for, or publish their own loading data - Duster's web site is particularly useful. Final crimp will be a shade under 1/16" deep (about the thickness of a dime) if you get the right components and the reloader is set up right. I think it should be around .055 - .060 if you have a micrometer. Check out the reloading forum on "Shotgunworld" - browsing through their posts or using the search function for specific questions can teach you a lot. There are some very experienced reloaders who post on that site.

Eli

everything that I have as far as components are according to the data listed based on shot size, powder type and wad type. I was not sure or could not find any information that gave a general wad seating depth based on what you were loading. I will check the site you listed. Thanks

As eliscomin said, wad seating depth is largely dictated by the volume of the powder under it. It'll be a different depth for different volumes of the same powder and a different depth for each different powder. It really isn't comparable to seating depth of the bullet in metallic cartridges.

A short answer is that the wad seating depth is determined by the structure of the wad itself and the powder charge, as ACRecurve stated. Unless you REALLY crush the wad into the hull with the wad seating ram, or during final crimping (not recommended), it willl retain its normal dimensions and seat at it's "normal" depth atop the powder charge - - all you need to do is assure that it's seated snug against the powder (slight movement of the pressure indicator at the bottom of the wad seating stroke).

OK thanks.

All of your respondents here have given you good and accurate information.

When you buy wads, get the wad that fits your hull and is designed for the shot charge you intend to load. (I.e. a 7/8 ounce wad, a 1 ounce wad, a 1 1/8 ounce wad in 12 gauge, and so on.) If you use the hull manufacturer's wad (i.e. Remington wads for Remington hulls, Winchester wads for Winchester hulls, etc.) and use it for its designed shot charge, you can be certain to get a good column. If you try to use a wad for a different shot charge than what it was designed to handle, you'll likely run into trouble because your powder+wad+shot column will be either too tall or too short to give you a good crimp.

I use the Claybuster clones of the Winchester wads in 12 gauge. They work perfectly with the older Winchester AA hulls and with the present-day Remington ones (Gun Club, STS, or Nitro 27).

I found that in 20 and 28 gauges, best results come if you use the manufacturer's wad for the given hull (i.e. Winchester for Winchester, Remington for Remington); in these gauges wads and hulls are not interchangeable.

2 1/2 inch loads for the .410 (I've never loaded 3 inch .410 shells) seem to be interchangeable between Remington, Winchester, and other brands of hulls. But .410 is also the most difficult of shotgun shells to load well, at least in my experience.

Federal 12 gauge hulls are a law unto themselves -- you can't get good results with them unless you use a Federal wad or its clone. They are NOT interchangeable with Remington or Winchester ones.