Just finished basing the artillery element for a DBA - RRR or DBA - Hx Venetian army. The Culverin and accessories are by TAG, the crew are customized Ral Partha, and the Gabions were provided by Barry Scarlett of Murray Terrain.
This element is an odd assortment of scales, but they all seem to work with each other. The Ral Partha figures are true 25mm figures. The barrel of the canon is 50mm long which scales to about 11-12 feet in length, making it a large culverin, but by no means the largest that were used in the Renaissance period. The gun is designed for use with 28mm figures, but as artillery in this period was so variable it works quite well. The gabions are really meant for 15 - 20mm figures, but in comparison to the Ral Partha figures they end up scaling out to about 3 feet high, which though not as large as some, seems a reasonable height for gabions on top of a sloping earthwork.