Brief:
By setting the motor tube a few inches aft, it allowed a PML urethane tail cone and Slimline retainer to be added.

Modifications:
The motor tube had to be moved aft of its normal position, 11/16" forward of the aft end of the body. The exact distance needed was simply to match the motor tube through to tail cone and seat it in the Slimline retainer. Total distance was about 3". When these were fitted, the FinLok guides were centered under the slots and the tube marked. The motor section was removed and the thrust ring inserted to give 11" of clearance between it and the retainer (for Ellis HPR S/U motors, specifically H50, plus anything shorter with adapters cut from 29mm motor tube coupler stock). This required forcing the steel baffling material into the last 2 inches of the motor tube rather than its expected 6". Blow tests showed there was still plenty of flow. Still, a Nomex® protector was added in case the baffle wasn't as efficient as intended. Once all fitting was complete, the motor section was glued into place and then the fins.

Construction:
Stock AT Mirage plus:

• PML 2.6" to 1.1" urethane tail cone
• 29mm Slimline motor retainer

Much of this mod was guesswork on the fly. I can't see much way around that. Just don't glue a section before you're sure all parts are going to fit properly.

A pro for this mod is using epoxy. It's far more forgiving if something goes south. Luckily, nothing did.

Flight:
This hasn't been flight tested yet due to lack of proper motors, launch equipment, and flying area. Between the mods and the massive paint job (two cans of cobalt metal flake blue and two cans of clear) the bird weighs in a 2 lbs 12 oz before motors. Even on a G80 I'm not certain the 5 foot AT rod is enough run-up space. I've picked up an extender for the rod. Hopefully, the next CATO launch will see it fly.

Summary:
I've always thought that rockets with big empty butts were a waste. Way too much drag for no reason other than lack of appropriate design. The PML tail cone completes this rocket and should do well to decrease drag enough to make up for its weight. The Slimline is a good choice among the many for replacing the AT big fat engine hook. With this mod, it looks like it means business.

Although if were I to do it again, I'd ream out the tail cone so the Slimline sat inside it, rather than riding behind it.