Hi,
Snapper, I agree with you about many later high-quality English and Irish guns. With respect to earlier times (18th century), if you look at books like Neal and Back's Great British Gunmaker series, you often find that the barrel tang screws are aligned with the bore. However, most of those pictured have hooked breeches and on those the tang screw is almost never removed. However, most of the side bolts are not aligned and of course they would be removed frequently to clean the lock after shooting. The photos include examples from the finest gunmakers working in England at the time so screw alignment was not necessarily a high-end versus low-end phenomena. When examining lower quality guns and military firearms on which the barrel tang is attached to the breech plug, some screws are aligned and many are not. I love these discussions but sometimes it seems we lump a lot of time together as simply "back then". A Holland & Holland sporting gun made in 1861 is the product of a very different time than a William Bailes gun made in 1761. Having said that, however, if any of you have a copy "Great British Gunmakers: Messrs Griffin & Tow and W. Bailes" look at the Bailes' gun on page 164. He created a sideplate with silver wire including wire screw heads, which are aligned with the bore. Clearly, the ideal was alignment but in practice, I suspect they did not worry overly about alignment for any screws likely to be removed over time.
dave