o/u double rifle in 9,3x80R SN 11571
post war scope, possible later replacement for the lost original

http://bazar.hunting-shop.cz/inzerat/113749-kulova-kozlice-w-collath-frankfurt-ho/

Drilling 8x72R / 16ga (?) SN 14280
notice there is the same stock magazine like we see on the double rifle 11571 so this probably the original magazine Collath made.

http://bazar.hunting-shop.cz/inzerat/38843-trojak-collath/

16 ga double gun - just remember most 16 ga guns offered are actually No. 4 and the 12 ga are No. 1

no serial number given , only Wittener Exelsior
http://bazar.hunting-shop.cz/inzerat/26239-brokovnice-collath-16-16/

a very old double gun SN 1793, Cal. No. 0
till now the only gun in No.0 I have seen and I dont believe this chamber was anymore made after 1900.
on the barrel rib "F.Schoenemann Maker" (Frederick Schoeneman, USA, 1833 - 98.)

sold by Kessler/Switzerland in 2007
http://www.kesslerauktionen.ch/Kataloge/Katalog/Katalog22.pdf

Drilling in 12ga (No. 1?) and 8x72R
SN 21349 http://www.egun.de/market/item.php?id=5263636

Drilling in 7x65R Brennecke and 16/65
interesting late made Drilling after 1917 when the 7x56R came out. same problem like I have with the 9x57 Double rifle 282785 on page 2. SN looks like 6 digits and I believe to see 288...
this will puzzling me for a while

http://bazar.hunting-shop.cz/inzerat/3159-trojak-wilhelm-collath/

Collath reach the 20000 serial number zone between 1912 and 1914 and with the outbreak of the great war we can imagine hunting gun production war was very low. and now with two guns made after 1917 or better after 1918 we see some 280000 serial numbers? iirc, Collath was making signal flare pistols in the great war and this could be an explaining. maybe the own serial numbers were used for such pistols