I'll bet they could kill a horse at 400 yards. That's 32 years before 1776 allot of experimenting can go on in that time.
So would a round ball and it did.
Elongated cloth patched bullets have problems with accuracy. In fact until the advent of the guide starter and the false muzzle ABOUT 1830, accuracy would have been unusable.
If this is doubted I suggest you have some moulds or swages made and try it.
Using a cloth patch it is necessary to have a short bearing surface that will allow the patch to wrap without lumps and folds. This is born out by bullets and moulds used in the 19th century.
I have a 40 caliber 48" twist barrel that I have made a swage for that makes a flat base/flat nose "picket" well under the maximum for the twist rate.
I had initially tried a radius base with a pointed nose. The bullet needs to have a FLAT BASE to shoot well at least in my experience and from looking at surviving bullets of the 1830-1880 period.
I first made a simple starter that matched the bullet nose and made a loading rod with a bore sized end that matched the bullet nose and a brass ring about 10" back up the rod that was also bore size so everything was aligned with the bore. Lousy accuracy. 6-8" at 25 yards.
I finally turned the muzzle round and made one of these:
By using this and on recommendations from picket bullet shooters increasing the powder charge to 80 gr of ff (remember its 40 caliber) I started to get accuracy.
Then comes the problem associated with high pressure, nipple errosion, blowing the hammer to half cock.
In a flint gun made with an marginal to low quality iron barrel that is not particularly heavy you run the risk of bulging or bursting. Then there is the problem of extreme vent erosion in soft barrels. Not only is the pressure higher but its higher LONGER due to the heavier bullet.
So until someone comes up with some evidence that the elongated bullet was in something like common use prior to the percussion era I will remain unconvinced. Something like a rifle with a provision for a piston starter that can be dated to 1750 or 1776 would be interesting. But I will not hold my breath.
Its not as simple as just making a longer bullet. Making the bullet is easy. Making it work is the hard part.
The final evolution of the bullet in ML TARGET arms used paper patches. Usually consisting of 2 or 3 strips placed in grooves in the false muzzle, a steel ring placed over these to hold them then the bullet, using a piston starter that fit the false muzzle, was pressed through the muzzle the paper strips then folded around the bullet to make a patch with little or no overlap of the strips. These shot long bullet 3 calibers or more in length and were extremely accurate at long range.
The Piston starter is heavy, its hard to make so its expensive and its EASY TO DAMAGE as is a false muzzle and its related equipment. So use in the field hunting, much less in war, is not a good idea.
Some picket and slug rifles were used by snipers during the Civil War. But this is hardly daily infantry use.
Finally the large bore wall guns made for the American Army during the Rev-War were large bore (about 1") ROUND BALL rifles. Had they shot elongated bullets they would not have needed to be over 45-50 caliber.
This alone debunks the bullet rifles in the REV - War. Telescopic sights, if they were developed would likely exist in England, which has a large collection of American rifles in museums etc. Had they made any and some English rifleman like Hanger found one he surely would have taken it home with him.
The Ferguson rifle would have been a wonderful place to use a conical bullet. No patch no loading problems. It used a round ball...
The British service rifle of 1800 was a 20 bore rifle with a slow twist using a round ball. This is 60 years or so after the "oval bullet".
The American service rifles were all RB rifles until the advent to the Minie ball.
None of them had telescopic sights.
Just because someone had an idea is no indication that it was workable.
Unless there is some definitive evidence trying to place slug or picket rifles with telescopic sights in 1776 is revisionist history of the highest order.
Dan