Depends on what bullet you're loading in the .38
The heavier the bullet, the longer the bullet, so if you load the 158 gr bullets the jump will be considerably shorter than say a 110 or even 125 gr. However, the fact is that 38spl chambers will most always shoot 38 spl cartridges more accurately than a longer 357 magnum chamber will. There's a compromise, but the fact that the .357 can load either caliber makes up for any slight loss in accuracy.