I believe its generally true . On the subject of wider opened muzzle common in such arms if not peculiar to them theirs are oft as not, Not rod wear since the rifling follows them. Yes it seemingly aids the easy starting & in moderation this is true but it isn't too easy to put the ball if patched as oft as not goes cockeye on you ..Down the barrel it goes then like as not the breach area is open your patched ball sits prone to gas blowing by it while on exit the blow by gases may or may not disturb the flight . Rod wear errosion deliberate plan ??? all three? , but this is typical of such barrels .
Most modern shooters would be aghast at going that route if some gentle lead in coned muzzle is by many acceptable & I factor some lead in. I file grouve's deeper on PB rifles to make them look deeper , But nothing like the Islamic barrel survivor's tend to be .
One thing they are not is stupid, they made some of the finest barrels much admired by Europeans' and mounted by the top gunmakers . Much as latterly the Spanish barrels where esteemed for there qualities .If in Spain's case usually smooth bore barrels & they were also open at the breach & relived at the muzzle by design.
Rudyard
Rudyard makes some good points here. The Ottoman area made barrels may or may not have a slight swell at the muzzle, especially the smooth bores. With the smooth bores, if you plan on shooting the original barrel, you need to measure about 3-inches or so into the muzzle to determine the caliber. I remember when my Albanian barrel was at Bobby Hoyt's to get a new liner. He called me and asked if I wanted to keep the swell at the muzzle. I said no. Just make it regular cylinder bore it's entire length. At least with the smooth bores, based on original loads being extracted from the barrels, it appears the locals did not use a greased patch. The ball (usually under-sized) would sit on top of the powder with a wad of tow on top to keep everything in place.
The rifled barrels, I'm not sure. I supposed some had a swell at the muzzle. But the original - rifled - barrels that I have do not. And I lead slugged the barrels about 3 inches into the barrels just to make sure.
As Rudyard mentions, we generally like to use a greased patch with the ball for loading. But with a swell at the muzzle, it would make it just as easy as not to get the pre-cut patch cock-eyed while starting into the muzzle. (Which in my case, I found the use of a loading block to be very useful LOL )
During the period, we seldom find a Spanish (or Italian for that matter) gun with a rifled barrel. Even ones for hunting/sporting use. For some reason they didn't find a rifled barrel any advantage. Curious. The only two Spanish sporting shoulder guns I've seen, one had a German barrel and the other a Turkish barrel.
Here is the muzzle of my Sindh rifle. It's a .41 caliber and takes a .400 ball with a thick patch. There is no swell at the muzzle. But the way the rifling is cut makes it look like a larger caliber than it is. Possibly more for decoration than anything else. And notice the round bottom rifling.
Based on the remaining specimens today, it seems the Ottoman/Turkish barrels run about 50/50 rifled versus smooth bore.
Rick