BULLET SUPPORT IN MULTI CALIBER CHAMBERINGS

[kody]

    I see a lot of mentioning of seating of hand loaded bullets to just clear the rifling. Is there any support of the bullet short of the rifling?  If so, to what length? It seems that actually imprinting on the lands would create pressure problems. How far away from the rifling could a bullet be fired? What kind of problems could occur if that distance became too much? Specifically ,I'm concerned about firing a .38 Special in a .357 Max. Why do people seat their bullets as close as possible on the one hand and  then shoot .38s in .357 mag or .357 Max rifle chamberings?     kody   

[YRUpunting?]

My basic approach hand loading for the handi is to seat the bullet out just into the rifling then set in a little so it will chamber and close easily.  That's the starting point, from there I'll try some with the the bullet a little deeper.  I've been lucky enough to send some time around the competition bench rest shooters at my club.  They change seating depth as often as they adjust the charge.  Every rifle is different, there's not an absolute answer. 

What concerns do you have about shooting 38's out of a 357 Maxi?  It's safer than shooting a 38 out of the 357 mag revolver and I've never given a second thought to that.  Now I expect the Maxi to be accurate since that's my deer round but 38's and 357's are more for plinking.  Although I've had 357 mags shoot very well.  I've not found a 38 load yet.

[RangeRat]

Seating a bullet against or into the rifling can indeed cause excessive pressure. On the other hand seating the bullet too far from the rifling leaves the bullet with little or no support as it travels through the leade ( throat ) often, but not always resulting in less than optimal accuracy. Firing shorter cartridges in some chambers so designed is usually more economical.

[gcrank1]

You are right in what you state except that 'into the lands would create pressure problems'; rather, it could, but not with lead bullets if loaded to book data as they easily swage to the bore, then down and out. Compare the load data with the same powders for lead bullets and jacketed bullets. You will likely find the lead is at a reduced velocity, thus a reduced pressure already; also, lead will usually achieve a higher velo with the same load than jacketed, as jackets have more friction to overcome.
Now I know you did not specify just lead bullets, so lets consider your questions as pertains to jacketed. Here we are talking pistol caliber, specifically the nominal .38 cal. (which really should have been called the .36, but I digress). Pistol calibers are usually at a much lower pressure than rifle calibers and shoot much less powder. Unless you are shooting a 'hot' handload for a pistol caliber rifle in a weakly designed pistol, there wont likely be any issues. Use handgun data to load handguns and handgun or rifle data to shoot in rifles.
Where trouble can begin with hot (ie, full charge book data) in rifles tends to be hard jamming a bullet into the rifling. The load is more intense in pressure and velo., and no free run can spike the start pressure to launch. This is why Roy Weatherby had his cartridge chambers 'freebored' some, to drop pressures, and why some guys dont load into the rifling with their hot 'hunting' loads with any caliber.
As to pistol caliber rifle chambers, and some vintage cartridge chambers, they often, sadly, have no 'real' throat (or, as in rifle nomenclature 'ball seat') of bullet dia., rather just a continuation of the same case mouth dia. right on up to the poorly angled 'leade' into the rifling proper. Some gentle angle to get the bullet into the rifling is good for jacketed and essential for lead, and the factory chamber is oten just plain too abrupt. This should not be, but it is.
The ability to shoot different length cartridges in a given long chamber is attractive, and may give you satisfactory groups for your purposes, but may not me. Or, to put it a different way, I might be happy with the pinking/funnin' shooting of 38Spl. in mine but wont use those if really shooting for groups to the potential of the rifle. There I want to use brass that fills the chamber to get the lead to the rifling (a 'little' engraving on the nose, thank you) and the crimp, if any in the crimp groove when this occurs. This may mean that I have to fine tune the brass length for the bullet I choose to use. This is why I reload, the quality control is all up to me, not what a factory necessarily offers.