I'd hate to tell you "go ahead and give it a try", then you come back and say that something got worse, because of. It seems that this is a product mentioned that should not hard either synethic stock/parts and you'd think other materials on firearms. But if in doubt, ask a gunsmith or someone at a gunshop you knows what their telling you is from experience. If it's from blood, you could actually have it penetrating the finish and bonding to the underlying metal. See what they tell you. If they say fine, start in an area of the firearm not easier visible. If it seems to cause no harm, I'd try to remove the stain carefully using no more of the the cleaner than is necessary.