Thew trigger guard is not like any Springfiled I have seen. Is it smoothb ore or rifled and what is the bore size. What little I can tell is it looks like maybe an English Enfield or a French musket but then the pictures are not great ((I am a poor one to discuss pictures being mine turn out like a 6 month old took them). I would clean it up throughly but in tat do not take ANY of teh finish off and then lookk for any and all markings. Clear pictures of all markings, over all length, LOP, bore size, rifled or smooth, and ANYTHING that you see that could be of use should be posted. Once that is done I am sure it can be nailed down as to what it is.
Now I am by no means an expert but have been shootging BP guns (mainly flinters) since the mid 1970s. I shoot a lot of flintlocks from the Rev War era but have shot and own several percussion guns. I also do Rev War reenactments as a part time hobby (too many hobbies to call it a full hobby). I am a BP section mod on another onlime gun forum and if I can help you I will but if not, might know just who can.