I was at the sea shore again today pondering רב שך. The issue is this.  שבועות כ''ב ע''א. The גמרא gives one explanation of a ברייתא. This ברייתא is brought as a question on רב פפא who said a vow does not need a size. The ברייתא itself says this שני קונמות מצטרפים שתי שבועות אינן מצטרפות. Two נדרים are joined. Two שבועות are not. [That means to say that if one forbids to himself a half size (of a כזית) of a fig and a half size of an apple, these two sizes are joined, even if he אסר each by a separate נדר. The גמרא asks how are two נדרים joined?  Go here and there is not enough. Go there and there is not enough. [To transgress the prohibition, one needs to transgress the whole amount of a כזית). Answer: he forbade both by one נדר. After this the גמרא brings a statement of רבינא to answer the question on רב פפא. The answer is רב פפא is talking about מכות, the ברייתא is talking about מעילה. At this point the גמרא is holding that the חכמים hold there is מעילה with נדרים. But before this point the גמרא thought the חכמים hold there is no מעילה with נדרים. So now we come to רב משה בן מיימון and the ראב''ד. The רמב''ם writes if one forbids to himself a half size of a fig and half size of another fruit  even with two separate vows, they are joined to make a whole size. The ראב''ד asks this is in contradiction to the above mentioned גמרא that says only when one makes one נדר to forbid two half sizes are they then joined. Not with two נדרים. Then רב שך says that the רמב''ם hold that after the statement of רבינא, the גמרא no longer needs that first answer. For before the statement of רבינא, the גמרא thought there is only מלקות for נדרים, not מעילה. So the ברייתא was only talking about getting מכות. And in getting מכות, only the fact of transgressing the words of the נדרים matter. So two separate נדרים would not be joined. But after רבינא there is no need for this answer. To transgress the איסור מעילה, two separate sizes would be joined just like two separate pieces of any forbidden food. My question at this point is this only applies to a נדר where one says, "This food is forbidden to me like a קרבן." That is the only case where מעילה applies according to the רב משה בו מיימון. And after all it is the רמב''ם here that רב שך is giving an answer for. But if one says, "This food is forbidden to me" that does not have מעילה. So then why does the רמב''ם write two half sizes that are forbidden by two vows  are joined? That should only be the case if each vow ended with "like a קרבן."

(I am cold and tired, so I ask you to take my word for it that Meila applies to nedarim only when he says "like a sacrifice." --I mean this is the Rambam's opinion. Not other rishonim.. But after all, it is the Rambam that Rav Shach is trying to give an answer for.