Yes but Lee still had a lot of 6lb guns, McCellan had more larger, and more rifled guns if we look at the poundage difference and the rifled difference there is a big advantage here. Federal guns could hit and still be out of range of enemy fire. I would assume Jackson did not haul captured guns from harpers Ferry as this would mean a complete reorganization of the artillery.
If you read
Tidball he gives an interesting account of what happened. He says the rebels kept their guns concealed on the reverse slopes waiting for the Federal infantry. The big Federal 20 pdrs spent all day bombarding them, but hit very little because they were concealed. The rebel artillery would only unmask themselves against Federal infantry, and gave the counterbattery on the heights little to engage.
Tidball comments that the rebel artillery was better organised, being fought as battalions. Contrarywise, many Federal brigadiers still considered "their battery" to be part of their brigade.
I have the Federal arty orbat to hand, thus:
1st Corps
L/1st NY - 6x OR - heavily engaged on the right etc.
D/1st RI - 6x 12 pdr light - ditto
B/ 4th US - 6x 12 pdr light - ditto
1st NH - 5x 12 pdr light (1 previously lost) - ditto
-
F/ 1st Pa - 4x OR - ditto
Independent bty/ Pa - 4x OR - ditto
-
A/1st Pa - 4x 12 pdr light - ditto
B/1st Pa - 4x OR - ditto
C/5th US - 4x 12 pdr light - ditto
(NB G/1st Pa is often listed, but was retained at Washington)
Corps total = 43 guns, all heavily engaged
2nd Corps
B/1st NY - 6x 10 pdr PR - heavily engaged at the Sunken Lane etc.
A and C/4th US - 6x 12 pdr light - ditto
-
A/1st RI - 6x 10 pdr PR- heavily engaged on the right
I/1st US - 6x 12 pdr light - ditto
-
G/1st NY - 6x 12 pdr light - heavily engaged at the Sunken Lane etc.
B/1st RI - 6x 12 pdr light - ditto
G/1st RI - 6x 10 pdr - dropped off as fire support onto the Dunker Church, heavily engaged
Corps total = 42 guns, all heavily engaged
5th Corps
D/5th US - 2x 12 pdr light and 4x ordnance rifles; counterbattery fire from the bluffs
C/ Mass. light- 6x 12 pdr light; with Morell, not engaged
C/1st RI - 6x 12 pdr light' with Morell, not engaged
-
E and G/ 1st US - 4x 12 pdr light; heavily engaged across the Porter Bridge
I/ 5th US - 4x ordnance rifles ; ditto
K/ 5th US - 4x 12 pdr light; ditto
Corps total - 30 guns, 12 unengaged
6th Corps
D/2nd US - 6x 12 pdr light; heavily engaged at the Dunker Church
A/Md - 8x OR - ditto
A/Mass - 6x 12 pdr light - reported not engaged
A/NJ - 6x 10 pdr PR - heavily engaged at the Sunken Road giving flanking fire on the CS centre
-
F/5th US - 2x 12 pdr light and 4x OR - heavily engaged at the Dunker Church
B/Md - 6x OR - heavily engaged at the Dunker Church
1st NY - 4x OR - engaged in CB at the Dunker Church, maybe not heavily
Corps total - 42 guns, of which 6 are unengaged
9th Corps
E/2nd US - 4x 20 pdr PR - heavily engaged in fire support
8th Mass - 4x 10 pdr James R and 2x 12 pdr How - ditto
-
E/4th US - 4x 10 pdr PR - fire support then advanced with the infantry, heavily engaged
D/Pa - 6x 10 pdr PR - ditto
-
A.5th US - 6x 12 pdr light - advanced over the bridge and heavily engaged
Coy K, 9th NY Inf - 5x Naval Howitzers - Rodman dropped them off to protect the ford he used, engaged in flanking fire on AP Hill etc.
-
1st Ohio - 6x 14 pdr James R - heavily engaged in fire support from the bluffs
Kentucky Bty - 2x 20 pdr PR, 3x 10 pdr PR and 1x 10 pdr How - ditto
Corps total = 41 guns, all engaged (although 5 only lightly)
12th Corps
M/1st NY - 4x 10 pdr PR and 2x OR - heavily engaged on the right
F/4th US - 6x 12 pdr light - ditto
4th Me - 6x OR - ditto
6th Me - 1x OR and 3x 12 pdr light - ditto
10th NY - 6x 12 pdr light - ditto
E/Pa - 6x OR - ditto
F/Pa - 4x OR - ditto
Corps total = 38 guns, all engaged
Cavalry Division
B and L/2nd US - 4x OR - heavily engaged across the Porter Bridge
A/2nd US - 4x OR - ditto
M/2nd US - 4x OR - ditto
C and G/3rd US - 4x OR - ditto
(a section of M/2nd and C and G/3rd US are detached)
Cavalry Division total = 16 guns, all engaged
Reserve Artillery
Btys A, B and C - 4 x 20 pdr Parrotts each, used to give long range fire support on 17th, out of ammunition on 18th
Bty D - 6x 32 pdr howitzers, same story as Btys A-C
5th NY Light Bty - 4 x 20 pdr Parrots, same story as A-C, 1st NY
K/1st US - 6 x 12 pdr light gun-howitzers; sent to support Richardson at the sunken road. Heavily engaged.
G/4th US - 6 x 12 pdr light gun-howitzers; sent to support Burnside who put them into battery on the Rohrbach house to defend the bridge if the rebs broke his infantry. Not engaged.
Reserve Arty = 34 guns, of which 6 were not engaged
Total = 286 guns present with the army, of which 24 are unengaged (all close range 12 pdrs)