Is your gun a side lever or a top lever break open or..? Does it have a damascus bbl or is it fluid steel? Is it a muzzle loader?!! A picture would help.
Aside from the French Ideals which were not singleshots as Jack noted, the only two 'Ideal's' that I can find ref to are:
1] CK mfd by F. Dusek Opotschno
2] SP mfg by Francisco Arizmendi
I am not positive either of them made singleshot shotguns, but in either case I would expect proof marks to be present from the respective country of origin and a serial number.
Since you say there are no proof marks or serial number [I'm assuming you have removed the forearm & bbl and looked closely]then I would guess that perhaps your gun is an inexpensive American made piece & could have been made by any of a variety of New England or Northeastern manufacturers as what I might ref as a 'catalog' or 'farm gun'. I could not find a ref to an American gun so labeled, but that is not really surprising. I could find refs to others with the same dilima you are having and found one instance where an association w/Marlin was proven incorrect tho they did buy the Ideal Mfg. Co. in the 1800's there is no relation to any shotguns bearing that name from that acquisition. That eliminates one possible source of mfg.
'Ideal' was a widely used term in the gun trade here as well as abroad, L.C. Smith had an 'Ideal' grade, Stevens made 'Ideal' rifles & they were well thought of popular singleshots. It would be logical for someone to market an 'Ideal' singleshot shotgun and obviously they did just that. One that I found a ref to said the buttplate was also marked 'Ideal', but no specific mfg was credited with making it. Its likely no big secret, more a matter of finding the documentary tie to one of several possible makers here. Old mail order catalogs might be a good place to start.
Good hunting, tw
