I’ve decided to build a M109 (with the short m126 gun). I’ve already made an A3 so the earlier version, used I the Danish forces, is only natural.
My A3 version has full interior, and as I already have Black Dogs interior set, it would only be natural to make it with interior too.
However,.........
Black dogs kit is of an A2 or -3 version - so what’s the difference internally between them. I haven’t had any luck on finding pictures to illustrate this.
Help would really be helpful

The biggest difference really will be with the gun, breach, and recoil systems. I believe, and you'd need to see if you can verify this, but the breaches were very similar.

Post pics when you can!

Same breech as on the M185 gun.

A couple of years ago a chap in the US built an M109 and described the project in the AMPS journal Boresight. As I recall he was a former gunner himself and he used a preserved example of a damaged vehicle returned from RVN (and thus not subsequently upgraded) as a reference source. I’ll be using the article for my own project when I get round to it, using an AFV Club kit as s base with bits from Italeri’s 109 and the Black Dog interior. And lots of ammo.

You may be able to obtain a back issue from AMPS.

The main visual differences on the interior of the M109 and an M109A2/A3 is a different rammer and an ammo rack in the left rear corner of the turret. On the M109 there is a rammer and tray attached to the rear turret ring. The rammer/tray folded in the middle and to the rear to fire. On the A2/A3, the rammer is only attached to the breech of the gun. Most of the rest is the same. I have the Black Dog interior and Italeri M109 parts and plan on using them for an M109 that I will convert from the AFV Club M109A2 kit. I also found a 3D printed floation collar for it on Shapeways. In Boresight Magazine (AMPS publication) from Jan/Feb 15, there is a build article that shows exactly how to do it.

M109 interior from youtube video showing the crew conducting a fire mission. https://www.youtube.com/watch?v=iswntrU0z6I