Ok, I'll check this....
You may type here at once all systems you are interested in. If I type them on Artillery weapons page that means that I have information on them. At least about its features, and in many cases drawings and photos and sometimes about history.....
(Of course,the history of rare types of weapons sometimes unfortunately can't be traced.)

Besides there may exist drawings or even photos. I have no other troubles with scanning them but time
Besides, I know where to find a cool information, maybe even more complete then I have now about artillery systems, but this book is too explensive (~$40) for me now... Not sure that I manage to buy it as I have plans to buy more other books (some of them are upcoming)
They are "T-26's history" (in 2 volumes) and "Battles in Belorussia, 1941"
A few days ago I've bought a new book about Grabin's (soviet artillery designer) guns (ZIS-2, ZIS-3, F-22, et. al) Maybe soon I'll load here some table data from it.....

It was designed in 1936. Was adopted in 1939. On June 22 1941 in RKKA there were 47 Br-5 mortars (45 Serial+2 pre-production model)
On May 01, 1945- 48 units (Including 1 280mm B-33 mortar. B-33 was an experimental mortar)

Br-5 Features:
Caliber-279.4mm
weight-18,400kg(battle) 19,700 kg(transportation)
Barrel length-17 calibers
Shell weight-200kg (high-explosive) 246 kg (armor-piercing)
Range-10,950m
Initial shell speed - 420m/s
Rate of fire- 0.5 shots/min
Maximal elevation angle-60 deg.
Arc of fire - 8 deg.
Transport-Mechanical, self-propelled
Speed-12-15km/h (highway, unpaved road), 8km/h-impassibility
Guncrew-15 men

8 Separate super-heavy battalions (Suprime command-in-chief reserve) were equipped by Br-5 mortars. Each battalion had 6 mortars

The drawing of this mortar I'll load later. It looked like 203mm howitzer B-4 M1931