That is an amusing view point. By 1890 English gun production was on the skids. There were other motivations for the English proof house test of various barrel materials.... American gun makers understood their market and how to sell to it.
The tariff became a political point of contention between the parties for years. It was never "aimed" at firearms, but rather at wool and tin plates. The Belgians had no problems with the tariff. In fact it helped fuel their firearms, lace and glass industries. They read the law and proceeded to sell barrels and parts in addition to complete guns. They successfully lobbied congress in this regard.
There were regular hearings in Congress about the tariff. American gun makers routinely denounced it claiming the Belgians were using women and children in their factories all the while lying to congress about these exact same practices which they employed.
Eventually the Belgians reformed themselves regarding child labor. Well ahead of American efforts.
Protectionist laws effectually fail to protect.