Hi! I "discovered" something neat, and thought I'd share it here- can't find it listed elsewhere!
I built an Estes Magnum as a clone from plans on either JimZ or here, can't remember, but had tons of fun with it. I didn't have a way of cloning the clear payload bay, however, so mine had a 5" longer BT.
Have learned since (thanks to this site and TRF) that the larger-diameter fluorescent light cover sold at home centers is a rough approximation to BT-60. I finally bought one, in a attempt to make my Magnum more authentic. It's just a smidge too large to fit on a coupler, so I was getting ready to fabricate an adapter when I realized that I wouldn't need the shoulder on the NC-60 from my Magnum if I could cut it and stretch it. First, I'm cheating- using a NC-60B on this bird because it's what I had. Second, I've totally ruined the Magnum, so hold your tongue if you're going to lash me out! The image on the left (with no clear payload bay) is how she was before her "nose job". Since I'd be repainting part of her anyway, and I was never happy with the previous layout (too boring), I took this opportunity to add some stripes as well, keeping with the Navy theme.

I cut the nose cone about 1/4" up from the shoulder, and was messing with fitting the 5" piece of clear tube in, when I noticed that the factory-supplied end-caps (for the fluorescent light protector) fit perfectly within the ID of the cut nose! Sure, now I"ve got an extra transition where I wasn't expecting one, but I've also got a really sweet little pay load bay! Glued in a balsa disk to seal the payload from ejection charge gasses, painted the adapters to match, and boom! a pretty sweet little appendage!

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I also am building a Magnum, and I'm also using a tube guard to create my payload section... However, I found another method to solve the problem of the fit.

I cut a ring of BT-60 3/4" wide, then slid this inside the slightly larger diameter piece of clear material, and then simply slide the unmodified nosecone into it. You can see this in the photographs below from my Supernova upscale build, and my Cherokee D (Phantom version) build.



For the nose block (Semroc), I took another ring of material (15/16" for the upscaled Supernova, 3/4" for the Magnum), split it, and removed a strip about 1.5 mm or so from it. Next, I put it partially inside the clear payload, and then pushed the noseblock up inside of it too. Sometimes it comes out at a odd angle , but fully recessed into the clear section, it will not slide down over the cardboard body tube.




Oh, and (for the Magnum) I cut the payload section a little longer (to eliminate that odd shoulder that Estes nose block has), and I mounted my launch lugs on a flat wooden stir stick before gluing that to the body tube, just to make sure that the launch rod doesn't come have issues due to the lip formed by the clear tube and the carboard body tube.

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Dreaming of making the rockets I dreamed of as a kid (and then some).

"The Guide says there is an art to flying", said Ford, "or rather a knack."
"The knack lies in learning how to throw yourself at the ground and miss."

Launching is Optional... Landing? That Depends on Trees.