Im not that comfortable with backfilling.
I built a little holder custom with padded grippers to hold the bottle and syringe upside down and stable, I warm the oil, let it fill. Took about 20 minutes and a few little rubber grippers and a stand for electronics work.
With a 29 half incher it takes about 3-4 minutes to fill a full mL.
I go do something else, come back and shoot. Shooting takes about twice as long mL per mL as a 25 or 23 gauge.
But you should not be shooting fast anyways, and really for everyday injects your not shooting 3 ml usually, a 29 half inch feels like nothing compared to a 1 inch 25g, the ammount of scar tissue/pain/damage with a 29 is just not even close.
If I need up to 2ml's everyday ill load two 29's and shoot both into two different sites on rotation, or use larger needles and shoot quads, glutes, etc, if more than ill use a 3ml syringe with a normal needle on it, usually a 25g.
I was worried at first that a half inch isnt deep enough for even delts, tris, pecs, which are usually lean on most guys, but I trusted Bill, and sure enough, no issues at all. I still do deep on quads and such even though I know Im likely lean enough. Big muscles just dont bother me in the slightest with a 25g, cant feel it, so its a non-issue.
Do it, dont cling to nonsense. Dont rape your shoulders and pecs with huge pins, your just damaging the tissues.
I use 29 half inchers for every upper body injection site, and I dont really use my bis or tris or even lats often, just delts and pecs, better reach, Im steadier, with smaller needles you really have to work at it to abuse a site.
I use 25 1 inchers for quads, or 1.5 inchers based on mostly whim. Most often the 1 inch.
And always 25, 1.5 inchers for glutes.
I used to be all gung ho like every-other guy, thinking a little injection pain was just a tickle, a part of the game, using 23's for lots of stuff, 1.5's in quads, 1 inch needles in delts and pecs, I always just thought deeper is better, but it doesn't seem to matter as long as you play it smart, that extra half inch isnt worth anything but scars.