This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted answer.
Adding the measurement that post #30 says would settle it.
Needle length: typical lengths for subcutaneous injection are 4-6 mm (short), 8 mm (standard), or 10-12 mm (longer). Longer needles are needed for deeper tissue or if you have abdominal adiposity.
Worth separating Dead volume across syringe as a question about the compound from Dead volume across syringe as a question about the documentation. They get answered by different people and only one of them is answerable here.
For anyone finding this later: the short answer on Dead volume across syringe is that it depends on one thing, and the rest of the thread is people identifying which thing.
Dead volume: residual liquid in the hub and needle after withdrawal. Typical residual is 0.01 to 0.02 mL for an insulin syringe with a fixed needle. Accounting for it matters if precision matters.
Anyone with a larger sample, please post it.
Syringe barrel size: common sizes are 0.3 mL, 0.5 mL, and 1.0 mL. Smaller barrels are more legible for small doses. Larger barrels hold larger volumes. Choose based on your dose.
This is where my knowledge stops and I would rather mark the edge than blur it.
Acknowledging rather than arguing. The reasoning holds as far as I can follow it.
I disagree with the framing of Dead volume across syringe above, and I think it is a substantive disagreement rather than a terminological one. Setting out why, so it can be checked.
The reasoning depends on an assumption that is doing a lot of work and is never stated. If the assumption holds, the conclusion follows. I do not think it holds generally.
On Dead volume across syringe I would separate what is worth knowing from what is worth acting on. The first list is long and the second is short, and conflating them is how threads get heated.
No disagreement from me. Posting only so the question does not look ignored.
Answering the question post #41 raises rather than the one it answers.
Insulin syringe graduations: U-100 syringes are marked in units where 100 units = 1 mL. Always confirm your syringe is U-100. Confusion between insulin units and milligrams is the most common syringe error.
Safety-engineered needles are worth using if you have children or anyone else in the house, and the retraction mechanism occupies dead volume that ordinary syringes do not.
Filing this under things that are true until someone shows me otherwise.
Post #45 describes the usual case. This is about the unusual one.
A note on how Dead volume across syringe gets discussed rather than on Dead volume across syringe itself: the confident posts get the replies and the careful ones get ignored, and the careful ones have been right more often.
Fixed versus detachable needles: insulin syringes usually have fixed needles (no dead volume loss to the hub). Luer-lock syringes use detachable needles (more dead volume). Fixed needles are preferred for small doses.
Drawing through a wider needle and injecting through a thinner one is a reasonable approach for a viscous preparation and pointless for an aqueous one.
That distinction has done more work for me than anything else in this category.
Taking post #48 at face value and following it one step further.
Fixed-needle insulin syringes have the least dead volume of any common configuration. At small doses that difference is a measurable fraction of what you meant to deliver.
It is worth checking rather than assuming, which costs nothing.
Needle gauge: smaller numbers (30G) are finer and less painful. Larger numbers (25G) are courser. For subcutaneous injection, 27-30G is typical. Finer needles take longer to draw up but hurt less.
This has been discussed before and I could not find the thread, so, again.
A detachable luer needle plus hub can retain enough volume to matter. Whether it matters to you depends on your dose, and the arithmetic is worth doing once.
Needle length for subcutaneous delivery is a question about tissue depth and injection angle together. Short needles at ninety degrees and longer ones at an angle reach comparable depths.
It is worth stating the boring hypothesis before the interesting one.
Dead volume across syringe was covered in the wiki last year and the page has a review date on it, which is a better starting point than my memory of a thread.
Answering the question post #54 raises rather than the one it answers.
Coring the stopper is a real phenomenon with repeated entries at the same point and blunt needles. Varying the entry point slightly and using a fresh needle prevents it.
The thing about Dead volume across syringe that took me longest to accept is that a plausible mechanism is not evidence of an effect. It is a reason to look, not a result.