The gemarah gives a machloket Rabbi Meir and Chachamim regarding asham talui when. shchutei chutz. The issue is whether you need an issur kavua or not. Both sides agree it does not have an issur kavua because if he did not do the averah it is not kodesh. This is difficult to me because it does not matter if he did the averah in fact. What matters is only that there is a safek and it is preciely the safek that creates a chalos din asham on the animal. The kedushah of the animal depends on only one thing: there being a safek. That is precisely what the shem asham is. an asham is a karban that is kodesh just because there is a safek/ So there should be no question. Shchutei chutz of an asham talui should be assur.
Yehuda Gellman , Yerushalayim
1) The Mishnah below (23b) states that according to Rebbi Meir, if someone brought an Asham Taluy and then it became known that he had not committed an Aveirah, the animal is now totally Chulin and possesses no Kedushah. We learn from this that once the Safek goes away, it is no longer an Asham Taluy.
2) Tosfos here (DH v'Chachamim) writes that according to the Chachamim (23b in the Mishnah), it is totally Hekdesh whatever happens. This sounds like your logic, Yehudah. However, Tosfos writes that the Chachamim here (18a) and the Chachamim below (23b) are not the same opinion. The Chachamim here are even more extreme than Rebbi Meir and say that even before it is known that he has done an Aveirah, someone who slaughters the Asham Taluy outside is exempt.
3) The Lechem Mishneh (Hilchos Ma'aseh ha'Korbanos 18:10) writes that it may be that the Rambam disagrees with Tosfos and maintains that even according to the Chachamim (on 23b), he is exempt if he slaughters the Asham Taluy outside. It is not totally Hekdesh since -- if he would have known that he had not committed an Aveirah -- he would not have been Makdish the animal.
4) After further research, I think I have found that Rebbi Akiva Eiger asks your question in Chidushei Rebbi Akiva Eiger on our Gemara.
a) The Gemara states that if one slaughters an Asham Taluy outside, according to Rebbi Meir he is liable to bring a Korban. Rebbi Akiva Eiger writes that according to Rebbi Meir one is liable for a Chatas. He writes that his source for this is the Kesef Mishneh on the Rambam, Hilchos Ma'aseh ha'Korbanos 18:10. Rebbi Akiva Eiger writes that the reason why he is liable for a Chatas is that as long as one does not know for certain that an Aveirah has not been done, the Asham Taluy that one offered outside was totally Hekdesh. Therefore, one does not bring another Asham Taluy for slaughtering the first Asham Taluy outside, but rather one brings a Chatas because the Asham Taluy one slaughtered outside was totally Hekdesh, not just "maybe" Hekdesh. Rebbi Akiva Eiger writes that therefore the whole issue of Isur Kavu'a is not relevant here, as there is no Safek involved since the first Asham Taluy was totally Hekdesh.
Rebbi Akiva Eigernends with "Tzarich Iyun"; he does not offer an answer.
b) The source for the aforementioned Kesef Mishneh is the Tosefta in Zevachim (Korbanos) 12:4 which states, "If one is Makriv outside an Asham Taluy that is brought because of a Safek, one thereby becomes liable for a Chatas." The Chazon Yechezkel on the Tosefta writes: "An Asham Taluy is a 'Vadai' sacrifice, since the Torah required for a Safek sin a Vadai sacrifice."
The Chazon Yechezkel proves that it is a Vadai Korban from the fact that if the blood of the Asham Taluy was sprinkled on the Mizbe'ach and only afterwards it was found that no sin had been committed, one may still eat the flesh of the Asham Taluy, as stated in the Mishnah below 23b, that "Kiprah Sefekah v'Halchah Lah" -- the Asham Taluy was brought because of the Safek and it atoned at the time for the Safek.
c) Chidushei Rabeinu Chaim ha'Levi, on the Rambam (Hilchos Ma'aseh ha'Korbanos 18:10, DH vehaK'M), asks the same question: "Since the Torah commanded that this Korban should be brought because of a Safek, it therefore becomes a Vadai sacrifice, so what relevance does Isur Kavu'a have in this case?"
d) We will have to work hard to answer the questions of Rebbi Akiva Eiger and Rav Chaim Soloveitchik!
5) After learning what Rav Chaim Soloveitchik writes on this topic, I am aware of the fact that it may be rather naive on my part to think that I can express the depth of what Rav Chaim wrote in the format of a short e-mail, but I will try at least, bs'd, to convey a little of the flavor.
a) Rav Chaim asserts that (a) an Asham Taluy is a Vadai Korban; it definitely has the Dinim of a sacrifice, but (b) one is not liable to bring a Chatas for the transgression of slaughtering an Asham Taluy outside the Beis ha'Mikdash.
Rav Chaim now explains how (a) and (b) can be reconciled.
b) He starts by writing that to be liable for any Korban Chatas one requires two conditions: (a) A prohibition was transgressed inadvertently, b'Shogeg (for example, forbidden food was eaten indeliberately); (b) The person who committed the transgression became aware at the end that he had done this (see Rambam, Hilchos Shegagos 2:6).
c) Rav Chaim now asserts that these two conditions are also necessary in order for a person to become obligated for an Asham Taluy. An Asham Taluy is a special kind of Korban because it may be that he sinned and it may be that he did not sin, but this is the Gezeiras ha'Kasuv; the Torah tells us that for a Safek he is also liable for a Korban. If he did sin, then it is obvious that conditions (a) and (b) apply. However, if in reality he did not sin, we have to say that conditions (a) and (b) are fulfilled by a Safek. This Safek is what enables him to bring the Asham Taluy and stands in place of the Vadai (a) and Vadai (b) of other Korbanos.
d) Rav Chaim now returns to his assertion that even though Asham Taluy is certainly a genuine Korban, nevertheless if one slaughters it outside the Beis ha'Mikdash it is only doubtful if one has transgressed the prohibition of Shechutei Chutz. Again, one must examine whether the person who brings the Asham Taluy really sinned or not. If he had sinned, then clearly he is liable for slaughtering the Asham Taluy outside, but if he had not sinned, this means that the Korban does not atone and can therefore not be considered as a Korban. It follows that if one slaughtered an Asham Taluy outside, one is exempt according to the Rabanan who disagree with Rebbi Meir.
I certainly have not yet done justice to this topic, and should have explained it a lot better, but I will send this in the present form for the time being.