S380 jams at the bottom

Thanks for posting. Reviewing at your picture and dimensions, it appears that the original balances had a slightly more shallow bottom shoe. The Series 380 comes with the 15-005, which is 1" deep, and the smallest shoe in this style currently made. Would you be able to shave off a little from the shoe to make it more like your original? Usually, the older shoe will be smaller than the newer shoe because they wear down from friction over time, but there is an old, discontinued type of balance that specifically used a shoe that was smaller than 1". We find that shaving the shoe down worked quite well.

Keep in mind, however, that you will not be able to return the new balances if you make this alteration. Now, I can't think of another reason why you may be having this issue, but there is always a chance there's another reason you're having this issue that I can't determine based on this information. Let me know how you wish to proceed.