Construction
T' diameter o' t' plastic fin unit and many o' t' nose cones are pretty close t' BT-50 and, matey, shiver me timbers, ya bilge rat, t' me amazement, t' fin unit had a small shoulder that fit perfectly into a BT-50 tube. Avast! However, a 18mm motor would nay fit through its aft end. Then t' idea hit me - use t' fin unit as part o' a motor retention scheme. Blimey! Ya scallywag! I scavenged t' followin' from t' leftovers o' an Estes Designer's Special:

1. 18" section o' B-50
2. Avast! shoulder section o' a 2-part nose cone (could use any BT-50 coupler, crunched nose cone, me bucko, etc.)
3. Arrr! Begad! elastic shock cord
5. Begad! 18mm motor mount for BT-50
6. Ya scallywag! Arrr! launch lug
7. two (2) 18mm motor retention clips

I first built t' motor adapter, me hearties, which included a thrust ring. Ya scallywag! This unit was glued into t' BT-50 by insertin' a spent casing, me bucko, placin' t' plastic fin can over t' end o' t' casing, and pushin' in t' adapter until t' fin can was seated in t' body tube. I then took t' engine retainer clips, arrr, shiver me timbers, placed t' ends over t' fin can, me hearties, and marked where t' forward tabs would go. Avast! Begad! Slits were cut to accommodate t' tabs on t' retainer clips. Well, blow me down! T' hold t' clips, matey, I cut 1/2" strips from some reinforced packin' tape, placin' one near t' forward tabs and one about 1/4" behind that. Arrr! I put a thin layer o' epoxy on t' tube before the tape and used 2 wraps o' tape. Blimey!

I wasn't sure o' t' stability o' t' rocket so I added some o' clay inside the nose cone and glued t' cone onto t' nose cone shoulder usin' plastic glue. This be later proven t' be a mistake.

Flight #1
I prepped t' rocket and inserted a C6-5 engine. Ahoy! Begad! Blimey! T' fin can be slipped over the motor and was secured with t' clips. Arrr! Blimey! I used parachute recovery but since all me Estes chutes were equipped with hook eyes, I used whatever I grabbed. Avast, me proud beauty! Begad! Blimey!

T' flight be high and straight. Avast, me hearties, me proud beauty! T' body was recovered undamaged but the nosecone separated and be lost. Well, blow me down! Aye aye! Too much weight and t' wrong glue. Ahoy!

Post Mortem
After me copy o' Rocksim arrived (or more accurately several months after it arrived), I discovered that t' added nose weight be nay required and that a C6-7 be more appropriate. Begad! Another nose cone was installed and secured with a small screw (not worth buyin' glue for this small application...and who knows what type is appropriate anyway?). Aye aye!

Flight #2
This time I tried a C6-7. Begad! Aye aye! T' flight profile appeared identical t' t' first flight, matey, with t' exception that t' nose stayed on!