Sorry about the bandwidth but I just had to comment! In the G. Charter Harrison account it's obvious to me that the author intends to misinterpret historical documents in order to accomplish a selfish agenda. His comment, 'Obviously there was something unusual about this particular repair, but what?' is not at all indicated or supported by the Lewis journal's words. No particular 'unusual' aspect is even hinted at in even a vague way. A generalized aside, a passing comment, 'We have been much indebted to the ingenuity of this man on many occasions...' hardly qualifies this Mainspring repair as an astounding feat of metallurgical marvel and cleverness. It rather says that he was a very skilled and clever fellow in general, indispensable to the expedition. Otherwise it simply says the smiths fixed the bellows and made the Mainspring, period, no astonishment added.
It's additionally a given that their expedition smith was surely a master craftsman of some considerable repute, or he wouldn't have been chosen for the expedition. Due to particular needs expected, he would be a master gunsmith. Therefore when repairs were effected it's more than safe to assume that like any other master gunsmith or accomplished master craftsman and artist: the 'repair' would be entirely indistinguishable from the piece before it was repaired! No reason at all to think that the Mainspring repair would be immediately or ever recognizable as such a repaired piece. If it was then the clever master gunsmith failed miserably.
"My airgun was out of order and the sights had been removed by some accident. I put her in order and regulated her. She shot as well as she ever did." The author goes on about the installation of a sight on coincidentally his subject gun and remarks about the sight's groove and soldering. Lewis clearly says in plain English that he and nobody else repaired the gun. Does this mean that Lewis somehow learned the blacksmith's - gunsmith's delicate and challenging soldering skills in the course of the expedition? Of course not. It means that soldering wasn't necessary at all, nor were the skills of a gunsmith! Drift the sight back in, regulate the mechanism, good to go, let's get shootin' here! Certainly if the sight was previously soldered it would have taken quite an event to completely remove it in a mishap? So, it was apparenlty drift-adjustable. Also there's no indication at all that the sight problem was caused by dissimilar metal's expansion coefficients as stated by author. On the contrary, Lewis specifically says, "...some accident..." caused the problem which fully eliminates a metallurgical expansion problem as the cause.
I find interest in the comment by Lewis, "...I regulated her...". At first glance this implies some adjustment factor of the air charge/discharge. Not sighting in, as he was a military officer and no stranger to the correct parlance or military lingo. Therefore it's imperative that the genuine L & C airgun will be adjustable in some way, able to regulate air pressure, and most likely in discharge or exhaust cycle because he verbally connects it directly to the gun's shooting performance.
The reference to Lewis '...charged the gun....' means nothing particularly specific. He being a military officer it is most likely a colloquialism common in the day. Referring to all firearms in general, be they powder, pneumatic or otherwise, they were necessarily 'charged' before firing. It only says he "...charged the gun..". The method of charging simply isn't described. Possibly it was a gun that used interchangeable air flasks that could be pre-charged, then installed on the gun to 'charge' it. Just as well, it may have had an integral pump, single acting or double acting, and an air reservoir to charge.
What we clearly see is that he got 7 shots out of 1 charging. That's an irrefutable indicator that it most assuredly was not a spring-piston gun but rather a purely pneumatic arm of the common type of the day. As well, after Lewis fired 7 shots it had enough reserve power to shoot a bystander, potentially mortally had it not been a miss instead of direct hit. The genuine Lewis & Clark expedition airgun has an air reservoir sufficient for 8 shots at deadly velocities. Nothing there implies the method of charging. Nothing dismisses any particular type. He charged the gun and got 8 shots.
The author's ruminations as to source from which it was procured mostly ignores the key fact that Lewis was a ranking officer in the United States Military of the day. The intimate connections, associations and personal experience expanding out from that would be the first suspect in where the gun was purchased. If there were any military airguns in the United States inventory at any time prior to the expedition Lewis would have tended to lean in that direction, simply from familiarity and personal experience with those products. True, he may have ordered a custom built arm with improvements on a standard military design, yet the military supply line is the most likely connection to who built it. Lewis may have had adventures in other countries or intimate knowledge of other country's offerings from his position as a military officer so that isn't discounted either.
The author is a master at starry-eyed conjecture from pure, thin air! The fact that he focused his major attention on the least likely identifiable factor, that being a supposedly noticeable repair being done, yet by a master gunsmith, characterizes his credentials. If he could just find and procure a period airgun made in his preferred Philidelphia that had any glaringly obvious repair he would surely know that it was the exact Merriwether Lewis expedition gun! Even if there's no sign of any repair to a Mainspring, any repair at all will suffice, thanks. It's somewhat astonishing for the author to be so simple of thought as to consider Lewis, a military officer and expert with armaments, to be so incredibly stupid and inarticulate as to describe a repair to the air reservoir ball, a hokey and potentially violently dangerous patch job at best, being referred to as repairing of the 'Mainspring'. Not only that, but two different people make the same extremely elementary mistake in expedition journals! Even a buck private wouldn't screw that one up so badly.
The authors later commentary regarding the patch box inscriptions stretches credulity beyond the breaking point! He discovers an American Eagle and Shield on a gun, very well. Where he found some indistinct outlines, possibly a result of metal corrosion, damage or simple artistic flourish, coincidentally on his gun, that was then neatly transformed into artistic renderings of L & C expedition members faces copied from none other than hand drawn sketches done by Lewis!?! From this highly questionable discovery he then assumes that Lewis must have been a co-designer of the expedition airgun! Huh? These faces are not even clearly legible at all and again, only imagination creates them on the gun's patchbox. I cannot clearly see them at all for the life of me. This is an amazing leap of supposition and insults ones intelligence. Matter of fact, so does the entirety of both of the articles written by Harrison.
The genuine Lewis & Clark expedition gun is possessed of a Mainspring. The Mainspring is of such a design as to be readily field-repairable or exactly copied by an accomplished gunsmith using a blacksmith's forge and common tools. This Mainspring may be over-stressed by design, such that it is liable to breakage. It has a Rear Sight that may be relatively easily moved out of and back into position, as being of drift adjustable variety. There's no reason to believe it would be soldered in place, but on the contrary it is able to be drifted into place in the field. The genuine article has an air reservoir of some sort, integral or detachable, with sufficient capacity for a minimum of 8 shots at mortal injury velocities without recharging. By design one person may readily render it 'charged' and ready for firing. It has a trigger mechanism liable to accidental discharge by those unfamiliar with the particular design. Assumably all men on the expedition would have a more than passing familiarity with firearms and their safe operation in general, so possibly the trigger mechanism differs from common and standard designs of the day in some unique way. The weapon is of such accuracy that it is described as hitting its targets on all of 7 shots and no remark about inaccuracy is included.