'It is likely that the Grande Armee were in possession of Russian pieces at Borodino but where did they get the horses to pull them. They were left upon the field because the Russians could not withdraw them.'
The French could also have had captured Russian artillery from Austerlitz and 1807. One of the reasons that the Systeme AN XI was never fully implemented was the huge amount of captured allied ordnance the French had. As an example, the French captured the Vienna arsenal intact in both 1805 and 1809. So much allied artillery was captured in 1805 that Napoleon had some of it melted down and made into a Paris monument.
'As far as I was aware Borodino was a bloody draw with the Russians leaving the field of corpses to the French. There was no pursuit and the Russians gave up Moscow without a fight.'
At Borodino Napoleon drove the Russians from a very strong defensive position and prepared to fight the next day. Kutusov, however, did not want to fight anymore as his losses had been very heavy and the French artillery dominated the field. Kutusov had committed all he had and still lost. The French still had 30,000 troops that had not seen combat that day. Finally, the French held the field and the Russians retreated very quickly, heading for Moscow. Those are not indicators for a draw.
'The only guns that arrived back in Poland and Germany were from the Northern and Southern sectors.'
True. What's your point here? The subject that I brought up was that the French had captured unicorns in the artillery parc in 1812.
'If the Unicorn was so prized then why was the Russian gunnery so poor. Now I hear you go through the training etc...I have not read any independent sourse that says this.'
I would recommend Wilson's account of 1807 as well as the Zhmodikovs' excellent two-volume work on Russian tactics of the period. Russian artillery officers were poorly educated and were not as skilled as their counterparts in France, England, and Austria. If your artillery officers are not up to standard, then the artillery arm is at a great disadvantage.
'It was doing a different tactical job to that of the French. There were issues of the gunners pre-1807 firing at too long a range as they were tied too closely to the infantry.'
What was the tactical mission of the Russian artillery? It was employed solely as a supporting arm and for too long would not risk losing a gun and would actually leave troops they were supporting in the lurch if the guns were threatened. The French on the other hand would defend their guns to the end if need be and would also risk losing them if an advantage would be gained. The French also developed their artillery as an offensive arm that would advance either alone or supported by infantry. The French developed their artillery arm not only into an independent combat arm but a supported arm instead of merely a supporting arm. The French also had an army artillery reserve that could be employed where needed by the army commander. Further, French corps artillery chiefs were overwhlemingly artillery general officers which gave the artillery a voice with the corps commander. The Russians certainly improved after 1807, but their command and control, doctrine, and training were not up to what the French were accomplishing, even after the ruinous French artillery losses in 1812.
'Also I remember the statement that Napoleon learnt from the Russians about concentrating artillery at Eylau.'
From whom or what? Competent commanders had been concentrating their artillery on the battlefield for at least 100 years before the great wars started in 1792. Napoleon massed his artillery as early as 1796 at Lodi. Napoleon was a product of the best artillery education system in Europe, and, among other things, stressed infantry/artillery coordination which the Russians did not do. Two of Napoleon's artillery teachers/commanders were the du Teil brothers, leaders with Gribeauval of the French artillery reform movement after the Seven Years' War. Napoleon may have been impressed with the Russian artillery performance at Eylau (they had three large batteries at Eylau, not just one as some authors have stated), but the French artilleryman that probably took note of what the Russians did was Senarmont, who was the artillery chief of Augereau's VII Corps. It should also be noted that the Russian artillery fire was generally inaccurate and they had to make up in mass/quantity what they lacked in quality of gunnery. That is a usual Russian practice.
'The Unicorn was so prized because it was longer calibre and hence more accurate. It had twice the calibres to the Gribeauval 6.4in which had not seen service since 1800s. Those in Spain were Spanish. The M1795 Long Porte and AnXI 24-pdr were 7 calibres long compared to the Gribeauval 6.4in of 4 calibres. The Unicorn was 10 calibres.'
The unicorn was what would be termed today a gun-howitzer. It had the characteristics of both. It was at a disadvantage compared with how the French howitzers were usually deployed, which was in a depression or behind a rise of ground or a large ditch. The French could hit unicorn units from those positions while the unicorns could not hit the French howitzers as the unicorn could not be elevated enough. This is in the Zhmodikovs' book.
'Although I can see why it was probably used as the Grande Armee expended most of its ammunition and supply was a problem no doubt. The logistic side of this war has been poorly supported with glimses in Digby Smith's books.'
The unicorn was used because the Grande Armee employed captured ordnance and admired the unicorn. If employed properly, it was an excellent weapon. The French established large depots in Russia, so the availability of artillery ammunition was not a problem. I have no doubt that the French could have manufactured ammunition in their depots in Russia if necessary. The French line of communication was well-organized and supplied and supply convoys did get to thte main army during the campaign. An excellent overview of how the French logistic system worked is in Chapter XXVII in Swords Around A Throne by Col Elting. The only time the French came close to running out of ammunition was at Leipzig in 1813. The French trains were cut off in Eilenberg which caused a shortage. The French artillery performed superbly at the Berezina in November 1812 and only a few guns were lost-the artillery was taken across the river and got away. The abandonment of most of the French artillery happened at Vilna because of the weather conditions and how the gun teams were shod. They couldn't make it up an ice-covered hill and had to be left behind. You might also want to refer to Lejeune's memoirs for a view of the retreat from Moscow and some of the logistics involved.