KBA M1450W for AMW 7600 - Need smoke grain measurement

[patelldp]

Anyone out there have a reload that they can measure the length of the smoke grain from? Looking to replace the stock grain with a better insulated one to prevent bubbling a case. I'd also like to know if the liner thickness in the reload is similar to standard EX liners.

Thanks!

 

[pnobile]

2 1/8in long....smoke grain is same casting tube used for the grains. And yes standard EX type phenolic liners.

Preston

Anyone out there have a reload that they can measure the length of the smoke grain from? Looking to replace the stock grain with a better insulated one to prevent bubbling a case. I'd also like to know if the liner thickness in the reload is similar to standard EX liners.

Thanks!

 

[patelldp]

Thanks Preston! I'm going to center a 38mm casting tube with smoke inside a length of 76mm casting tube. Hope this preserves the borrowed case...

 

[blackjack2564]

OR just reverse the supplied smoke grain, putting the RTV side towards grain and heavy greasing the side towards closure. I even epoxy the top of top grain. By the way... I glue all grains in liner with 1450's... glue nozzle & forward...whole shebang....heat crystalizes liner to granite and liner peels right off after flight. I've seen too many toasted case flight with this motor..... 5 of them over the years. [some at bottom-some top]

I toasted my case by a "hot" smoke grain 5 seconds after motor burn out. Put hole in case right at bottom of smoke/fuel grain joint. I don't use them any more....just flip em',


Your solution seems very sound.

 

[blackbrandt]

OR just reverse the supplied smoke grain, putting the RTV side towards grain and heavy greasing the side towards closure. I even epoxy the top of top grain. By the way... I glue all grains in liner with 1450's... glue nozzle & forward...whole shebang....heat crystalizes liner to granite and liner peels right off after flight. I've seen too many toasted case flight with this motor..... 5 of them over the years. [some at bottom-some top]

I toasted my case by a "hot" smoke grain 5 seconds after motor burn out. Put hole in case right at bottom of smoke/fuel grain joint. I don't use them any more....just flip em',


Your solution seems very sound.

Jimmy told me to do the same thing on my L3 attempt with regards to flipping the smoke grain. I never figured out the reason until now. So the smoke grain can melt the case?

 

[patelldp]

It's a lot of heat for an extended period in a focused area that can cause case bubbling.

 

[jsdemar]

The AMW smoke grain for the 75-7600 has a very thick cardboard tube (1/4" thick IIRC). The last 1/2" or so of the smoke grain (facing the propellant) is the same as the propellant (not the smoke). The top end of the smoke grain is HTPB/curative/TiO2, about 1/8" thick.

I have a cooler smoke formula that uses plastic "glitter" and low zinc. I've run 30-sec to 1-min full-size smoke grains without burning through.

It's an EX launch, so you could make a replacement smoke grain. I'll see if I can get the thick AMW smoke grain tube.

Best to glue all the grains in. Put the glue on the outside of the grain and push it in the liner. Remove excess. If there's a grain spacer oring, don't forget that. Repeat, sliding everything up as you go. Watch your time, depending on the glue. Try the closures before it all sets up. You may want to put in the smoke grain from the top first (glued in and greased on the top).

The KBA liners are not as good as standard EX liners. They are thinner and more brittle. Grease up the outside of the liner to get a good fit. Put extra grease on the ends where they overlap the closures.

 

[jimzcatz]

Like Jim and Matt said, I reverse those smoke grains so they don't light. I tried to use one for the third time, and it came apart, causing kool fireworks in the sky. Everything survived intact.

 

[jsdemar]

2 1/8in long....smoke grain is same casting tube used for the grains. And yes standard EX type phenolic liners.

Preston

In comparison, the AMW smoke grains are 2.4" long.

Also, the KBA phenolic liners are much thinner than standard tubes people use in EX.

 

[Dave A]

So is the consensus, the AMW style with the thick cardboard tube would be much safer for the case than KBAs?

 

[jsdemar]

Yes. I have some of the thicker smoke grain tubing. And a couple filled with inert inhibiter. PM me if you need one.

 

[Brent]

Any issues with the 54mm full diameter KBA smoke grains in the 2550 case?