There is PBR low-poly gameready model of soviet anti-tank gun. The model was made according to my own design.

Model information:
18878 tris and 10271 verts;
. fbx, .obj, .blend formats;
.png format of 4096x4096px textures (but you can decrease the resolution, which will cause to a decrease in quality);
7 PBR textures of general pipeline
also textures for Unity and UE4
Unity and UE4 engines allow to use packed textures to optimize memory usage (for example, in UE4 textures, metallic map is packed in B channel of OcclusionRoughnessMetallic texture).

For any questions related to the model or problems using the UE4 and Unity textures, you can ask me.