The standard .30-30 chamber has no "throat" or "ball seat", but simply a 15 degrees, Basic transition from the case mouth diameter into the rifling.
Most production molds for the .30-30 are of two-diameters, a larger diameter of about .309-.311" for the driving bands contained inside the case neck when seated, and only a minimal band in front of the crimp groove, followed by a parallel-sided, ogival nose. In most production molds this parallel-sided forepart is only .3005-.3015" diameter, because they are worried about hard chambering, etc.
Tom Ellis at Acccurate Molds has two designs with tapered noses which are engraved upon chambering in standard .30-30 chambers, but in which the slight effort to chambering is not an impediment to rapid firing, nor does the bullet telescope more deeply into the case or debullet upon extracting a loaded round. FYI this '94 Winchester was made in 1930. My 1942 vintage gun shoots the same loads with the plainbase on the 4th step of the open sight elevator and the full charge load on the first step.
These bullets are the 31-155D plainbase, and the 31-171D in gaschecked version:
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This is what a loaded round looks like after being chambered and extracted:
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I load a "half-charge", i.e. 15 grs. of 4895, 4064, RL15 or Varget with the plainbased bullet, which shoots "on" at 50 yards with the sight ladder raised to 200 yards, and a "full charge" of the same powders, 30 grains, which shoots to the sights at 100 yards with the ladder folded down, using the 171-grain GC. version.
K.I.S.S. principle.