while trumpy release 128mm ATG,it does not provided 1/35th ammo to go with it.
I am ponder using greenfield tube to scratch built spend shell for 128mm ATG.do anyone know the right (1/34th) size and right dimension for the trumpy 12.8cm ATG spend shell?

Check out armorscale.com if you want to save the hassle and just order some. 11€ is not a bad price.
I'll check my German armour encyclopedia in the morning. It may have a picture in the back of the shell. I'll do some measurements of it.

I believe the diameter tubing you would need is 4 mm. for a 12.8 cm (or 5") round. But you also have to cut thin disks slightly larger diameter for the base, with a small divot in the center.

Thank's for the info,but what about her Lenght?

Divide the above numbers by 35 . ( or whatever scale you are building at )

Per the table, length of casing = 840mm = 24mm in 1/35 scale
diameter of the casing at the rim = 192mm = 5.48 mm in 1/35

Plus the casing should have some taper to it from the shell opening to the base. You can decide for yourself if you want to go that far though.

A quick calculation gives the cartridge case a diameter of 3.7 mm at the end where the projectile is, and then tapers slightly as Paul states. But, unless you have a lathe, you have to use the closest tubing you can find.

For all the trouble, I'd rather order what is commercially available.