Hi Jerry, good question, but a complex one to say the least. One could go on and on about this subjest. But here is a quick short answer.
Action: Most (but not all) Spanish SL/SLE are based on the H&H action. There are some exceptions, but the Spanish have copied the British Game gun and have based their models on Brit guns and the H&H action is their action of choice. The actions are forged from steel. These forgings are obtained from a couple different foundries, but are forged according to each makers requirments. The actions are then finished by the makers.
Barrels: The bbls are again forged by one firm and then turned into blanks by another. Again, the maker finishes the bbls to their requirments.
Spanish steel is some of the best in the world, with different grades and alloys used. A lot depends on what the maker and customer wants. The old "Soft" Spanish steel is a curse that the Spanish are just now starting to overcome. The soft steel refers to the internal parts not being hardened and thus being soft and prone to breaking and mushrooming firing pins. Most of these guns were the cheap price point guns imported here after the war.
Spanish proofing is tough. The Spanish Proof House is equal to either the Birmingham or London Proof Houses. In some cases it may be even tougher.
If you want more in depth details, Terry Weiland's book "Spanish Best" is the one book you must have.
Hope this helps.
All the best!
Greg
