Pro38 5G In PML KS 38mm?

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Active Member
Apr 3, 2004
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Anyone fit a 5 grain Pro38 in a PML Kwik Switch 2000? I saw a reference on Rocket Reviews that someone could by friction fit. It was 1/4" off with his retention device. Anyone else had better luck and what did you use for retention? I can't use the PML retention because the BT is not large enough.
Thats a tuffy.
Is the KS 54 to 38 or is 38 the biggest.
The reason I ask is, if it is 54/38 you should be able to put a couple blind nuts in the aft CR. If its 38/29 I don't know what you could do.
Obviously you cant use a slimline or similar if your motor is 1/4" too long. UNLESS, you buy a second KS and build it with a slightly longer motor tube.
Scratching my head.
I personally don't like friction fits but that is always an alternative.
Not wanting to answer for Jason, but I think the KS is 54-38-29. Maybe somebody on the forum could machine a extended retainer custom. Midpwrguy may be able to make someting.
Friction fitting with masking tape is not as dangerous/risky as it sounds, although if done improperly, someone's bound to chime in with something along the lines of "you get what you pay for"...

The key thing is to put a couple of wraps ~1 inch from the aft end of the casing. Then as a safety precaution, add a spiralling wrap along the length of the casing (think along the lines of screw threads) so that when you insert the casing with a twisting motion, it would resemble "screwing" it into the MMT tube.

Add/remove tape until you have a snug fit. More specifically...

If you can shake the rocket & the casing begins to work its way loose--add more tape.

If you have to force the casing at any point during insertion--remove some tape.

This technique works surprisingly well for almost any sized motor.
Originally posted by lalligood
This technique works surprisingly well for almost any sized motor. [/B]

Out of the 15 or so rockets I've built, only 4 have motor hooks. The rest either didn't come with them, or I've intentionally left them off in favor of friction fitting. I also don't put thrust rings into any of my rockets, since I never know what size engine casing I may someday want to put into them.

I've never had a rocket kick a motor that wasn't designed to.

I am an ardent supporter of the tape retention method for all single use motors. If you loose the motor (and hope it had enough time to pop the chute) on ejection, you loose nothing. However, when I went to 29mm reloads, I did not feel like loosing my casings, even though I agree tape would work fine. ive progressed from cheap washer/threaded inserts to PML retention system all the way to slimline.

The only reason I really don't use tape retention is the fact that when firing, the tape smushed between the motor and motor tube heats up and the sticky part of the tape seeps out, and when the motor cools, its like gluing your motor into your rocket! No sure if this happens on reloads though.

Ever try to get a G37 out of a tight motor tube after firing?
I just got a 5 grain case and noticed the same problem with the standard lenght PML Kwik Switch mounts. 1/4" too long on the case to fit the standard KS 38mm adapter. I even wrote to PML first to check to see if it would fit. They said no problem.
My solution was fairly easy - I just got the PML 38/54 Heavy Duty adapter and with that, you can still use the PML 29/38 KS motor retainer.
Now that I have the HD adapter, I'm all set to run with not only the Pro38 5 grain, but I can now also fit the Pro38 6 grain motors & 38/1080 AT motors. So this one small investment gives you lots of options down the road.
Good Luck
(I just got my PML Eclipse "A" kit in the mail yesterday - I plan on using that adapter and the 5 grain on it as well !!!!!! )
Maybe KenParker and PGerringer will chime in here. I believe one or both of them modified their KS adapter by grinding out the inside diameter of the plastic screw threads to allow the motor casing just enough room to pass through. I know that they both used a Pro38 6 grain for their level 2 flights.
I ordered an Aeropack retention system and 54 to 38 adapter. Hopefully that will fix things, as the adapter doesn't go all the way to the end.