Dreadnought w/ TL Autocannons

I've had a thing lately for converting vehicle weapons from the new Space Marine codex that don't have any official bitz available locally. Sorry for the pic. I should have taken it mid-conversion with better light.

In any case, the new Dreadnought can replace the Multi-Melta arm with a twin-linked Autocannon, and another option to to replace the Dreadnought close combat weapon arm with a twin-linked Autocannon. Of course I thought, "what if I replace both arms with TL AC's!" The Black Reach Dread is inexpensive enough to chop up without the twinge of "I just chopped a $40 model up" regret that comes with modding the regular Dread.

The conversion is a few Woodland Scenics styrene tubes (3/32" and 5/32") nested to make the barrels. The Multi-Melta arms had an obvious place to attach the autocannon. For the CCW arm, cut off the CCW and glue a bit of the cut off Multi-Melta barrel to the front of the arm at the same location as the other arm. Use some epoxy putty to build up the arm to the same general shape as the other arm. Privateer Press' P3 modeling putty cures harder than green stuff, and can be filed to the crisp lines that look good in applications like this. I can't remember where the ammo boxes on the outside came from... just regular rhino/razorback accessory sprue I think. I filed off the hinges to try and make it look more like a magazine and less like "box glued to the side of an arm." By the way, I use these same tubes to make Ork Big Shootas by drilling holes in the larger tubes as cooling, and putting the smaller diameter tubes inside as the barrel. It looks pretty good, and will give some of my deffcoptas a different weapon option.

So back to the Dread... other than looking a little too much like a Macross Defender Destroid, what good is this thing? It gets four shots, twin linked, with 48" range. With BS4 and twin linked you aren't going to miss much. With a Venerable's BS5 you are pretty much never going to miss (okay, well, you'll miss 1 in 36 shots statistically.) So what are four S7 AP4 shots good for? The only thing that comes to mind is Ork Nobs in heavy armor. Wounding on a 2+ with no armor save... but they'd still get a "feel no pain" roll if they had a Dok in the unit. A Predator might take a glancing hit or two. A Dread will probably take at least a glancing hit. Against heavy infantry I don't think autocannons would be as effective as an assault cannon. Both wound on 2+ against T4 and assault cannons get rending.

So... now that I have the thing converted, what should I use it against?