Exceptional finish. According to the very brown original instructions the motor when inserted in the model should provide that:

"A motor when placed in mount, should extend out about 1/4" from tail end of the missile."

The original mount was a joiner tube with a ring cap on the forward end. In the reproduction for NARAM 50 the mount is a tube with a rolled end to serve as a thrust ring. The rear end of the mount should have been 1.5" from the end of the BT. The mount is 1" long so properly installed the forward end of the mount would have been 2.5" from the aft end of the BT. This would give you the .25" overhang at the aft end.

If your motor will only go in .5", then in all probability the mount was installed short. You could attempt to open out the roll and then add a thrust ring forward to provide both a more aesthetic look and a correctly balanced model. Also, bear in mind that the motor mount provides centering of the motor in the BT. You may still want to add some tape to the aft end of the motor to ensure that there is no wobble under thrust.

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Gravity is a harsh mistress
SAM 002
NAR 91005
"The complexity of living is eminently favored to the simplicity of not."