The model 96's were 29" bl. as far as I know. The model 38's incorrectly BATCH-called model 96's due to identical actions, had 23.4" bls. but a bent bolt, rather than the straight bolt of the early models. Again- this is as I understand the differences over the years. This might be BS- but until this is pointed out, so be it.
The earlier, 29" bl.s more often had .264" groove diameters.
Every Model 38 with 23.4" bl. I have measured, was .266".

This does not mean they will not shoot. Quite the contrary - mine consistently put all bullets weights from 100gr. to 160gr. into 1 1/2", 5-shot groups at 100 meters using the battle sights.

If a composite group were drawn up of all bullet weights, 100, 120, 139, 140 and 160 were measured, they would be inside 3" and closer to 2 1/2" for all 25 shots. Mind you, they were shot on different days, but all at the 100 meter range, over the course of a month, or so.