5/16 hose on a 3/16 Beer Ball Lock

I see some problems with your idea. Is your gas 5/16" line food grade? Most CO2 lines are really not for transferring beer. If not I wouldn't attempt. Not exactly sure how you're making connections, but attaching 5/16" to liquid-side MFLs isn't typically done. You expect the liquid fittings to be 1/4" (barb or swivel nut) so this puts you behind the eight ball. I suppose you could clamp it enough it wouldn't leak at these low pressures but it's a round-about way of doing it.

My experience is nothing works better than connecting 3/16" beer line (I use BevLex) to a 1/4" barb. A little heat . . . a little force . . . and you have a leakproof connection that will have to be cut off when replacing. I use this for all my beer lines: fermenter to keg, keg to keg, keg to faucet.

Just saw your second post: I don't see agitation as a problem, plus, if the lines are properly purged the beer doesn't care if it's stirred up. Aside: I find it works okay to sanitize the keg with starsan (partial fill), than top off with water till it's full before dumping . . . saves a little. Also when dumping the keg it's recommended after the first cup or two that you do several burbs . . . trying to dilute that pesky air that was hiding in the posts.

 

Food grade silicone tubing isn't expensive and just about everyone carries it. I recently "re-hosed" my entire brewhaus . . . and kept extra for spares. Pretty sure if you search around you can find a 1/2" to 1/4" stainless reducing barb which would be perfect.