Many narratives of the famous siege of Orléans (1429) mention the actions of this gunner. Jean d'Aulon testified [some time after the event, at the rehabilitation trial of Jeanne d'Arc] that on the first day of attacking Les Augustins, he instructed the French gunner, Jehan de Lorraine, to take out "a large Englishman" who was causing great harm to the French attackers at the gate to the compound. The gunner succeeded in striking the particular English warrior just before the French rushed and seized Les Augustins. One author summarizes the activities on the gunner, Jehan, who was a "phenomenal shot with the culverin," as follows:

"The English were already well acquainted with the gunner. From his post under the pier of a bridge he had inflicted almost as much damage upon them in his few days at Orleans as all of Gaucourt's garrison [defenders of the city] in the seven months of the siege. In spite of their attempts to retaliate, the fellow seemed to lead a charmed life. He obviously thought so too, for with a grim humor that was not without its risks he would pretend to be lying dead within full view of the enemy. Then when he thought they had rejoiced enough, he would cast gloom upon them by getting up and strutting insolently away, to repeat his deadly performance on his culverin." [Frances Winwar, The Saint and the Devil, (NY, 1948) p.104. The summary is based upon several contemporary sources.]

Another account of the siege of Orléans (1429) is le Journal du siège d'Orléans [believed to have been maintained during the event and written by an observer inside of the city] mentions that on 3 March (1429), "Jean [Jehan] de Montesiler, originally from Lorraine, a very skilled couleuvriner ... killed in two shots 5 English, of whom [was] Richard, lord of Grey, nephew to Salisbury." Some authorities note that this "signaled the advent of this new arm." [André Corvisier, ed. Histoire militaire de la France p.188.]
The killing of more than one individual with a single shot, suggests a sizable projectile -- possibly a stone ball, no larger than a human fist, but not a small lead shot. This, in turn, suggests a gun barrel of some caliber [diameter] -- slightly smaller than a modern infantry-carried mortar. Such a 'handgun' was probably too large [heavy] for a man to hold and aim without some assisted support for the gun. But certainly not so large that it could not be propped on a wall or large shield [pavise, used by crossbowmen]. Such a supported gun is an individual gun -- properly a 'hand-gun' or 'hand-cannon'.
The next question is how well could the gun be used in a marksman's role -- which is the role ascribed to Jehan de Montesiler. Could Jehan have performed his feat without a matchlock? Was it possible to aim an individual's firearm that could not be raised to the gunner's eye level? Depending on how large the shot, the required accuracy of aiming may have differed -- smaller shot requiring more precision.

The specific configuration of Maitre Jehan's gun remains an issue. Was it hand-held or hand-welded. It is questionable that the hand-held guns at the time were shoulder supported. Certainly, since the early fifteenth century there were handguns of very small barrel diameter and supported by the long wood shaft [stock] braced under the gunner's arm -- not an ideal position for marksman aiming. A slight advancement came about sometime in the early fifteenth century when the wood stock was shortened and braced aside the gunner's upper arm -- possibly even atop his shoulder. This certainly would improve the aligning of the eye to the gun barrel, and permit better aiming at a single target. What evidence is there that such a configuration existed in 1429 Western Europe?

It should be noted that the marksman role was not the incentive for the early adoption of small firearms. The mass employment of the early handguns did not require marksman aiming to be effective. A large number of under-arm supported guns would contribute in disrupting an enemy's attack in the open, harassing crews operating siege artillery or workmen reparing damaged fortifications -- the traditional rolls for crossbow weapons.
If the S- or Z- shaped lever for aligning the lit match to the powder hole were part of the guns, then there is a possibility of the gunner being able to point (aim) his peace with more precision. It should also be noted that a number of individually operated small guns would be more effective than the same number of tubes on a single multi-barreled gun in sustained encounters, as the former could be reloaded more quickly and directed more effectively toward targets. Of course, it required more gunners. With missile weapons, rate-of-fire is often more important than mass.

What would cast considerable light on gunner Jehan's ability to have aimed his piece like a marksman is to know if his gun were configured with a matchlock. Burt Hall, and a few others who have examined the evidence of early medieval handguns, agree that one of the defining features of the first arquebus [to distinguish it from a short-barreled 16th-century musket that was also called an 'arquebus'] was the use of a mechanical device to align the match to the powder-hole. The first such mechanism was a Z-shaped lever that pivoted at a point along the side of the gunstock. As the rear end of the lever was squeezed to the stock, the front end lowered a hot coal or lit match to a touchhole and priming powder near the breech end of the gun barrel. The earliest evidence of such a device is an image in a 1411 manuscript now in the Österrichische Nationalbibliothek, Vienna.
The barrel of such guns rested on a wall, wagon side, a large shield, a pole support. Many of these hand-directed guns had projections ['hooks'] extending from beneath the stock of gun barrel. These 'hooked' on to the side of a wall, or wagon sideboard, and absorbed some of the recoil when the gun was fired.
There are indications that primitative Z- and S- shaped mechanical locks were significantly introduced by 1430, and were used in the Hussite Wars (1419-1434) as well as by the gunner at Orléans in 1429. However, Burt Hall delays dating the effectiveness of these early 'arqubuses' until better [corned] gunpowder became available to propel the small shot at high velocities, which he suggests is about 1450. This tracts with the timeframe of recognized French artillery prowess. [B.S. Hall's Weapons and Warfare in Renaissance Europe (Baltimore, 1997) pp. 96, 119-121, 147-151.]