RE: Jett powered anyone?
Id say go with an 8oz in the Rifle. You will get 5-7 minutes of flight time.
Also take a look at the various size Tetra tanks .... one of those might fit better.
Consider this.....
You can only effectively use 2/3 of the fuel in a conventional tank. With a 12 oz tank, that gives to 8 oz of usable fuel. You can safely draw about 9 oz from the tank without uncovering (at least partly) the clunk inlet, in at least a minimal flight attitude other than level.
With the bubble jett tank or tetra tank, you can use 100% of the fuel.
Also, you can litterally cram it in place - no foam padding needed (other than physical protection of the plastic tank)
A regular tank, combine with a hopper is an alternative, if it means you can properly foam pack both tanks... in that case, it would be a good alternative.