Dead space in syringes is throwing off my dosing

[TriDiddy]

ultima thule said:

I ran a test. I took a bunk vial of Kpv10 to verify it. I added 1ml of water into the sealed vial containing a puck and let it dissolve. Then I took an insulin 1ml syringe and pulled the solution back out. It came to more than 1ml, roughly 10unit/.1ml. After that I put only water into the same vial, using the same syringe, and again 1ml. The outcome was identical. So: my reconstitution syringes aren't accurate, and in the end the puck contributes nothing to the volume of the reconstituted peptide.

If you've got a second bunk kpv10 vial on hand, try repeating the reconstitution with a 1ml insulin syringe instead, then check how much you can pull out afterward. Compared with the reconning syringes you used previously, the insulin syringe ought to give you better accuracy.

 

[ultima thule]

TriDiddy said:

ultima thule said:

I ran a test. I took a bunk vial of Kpv10 to verify it. I added 1ml of water into the sealed vial containing a puck and let it dissolve. Then I took an insulin 1ml syringe and pulled the solution back out. It came to more than 1ml, roughly 10unit/.1ml. After that I put only water into the same vial, using the same syringe, and again 1ml. The outcome was identical. So: my reconstitution syringes aren't accurate, and in the end the puck contributes nothing to the volume of the reconstituted peptide.

If you've got a second bunk kpv10 vial on hand, try repeating the reconstitution with a 1ml insulin syringe instead, then check how much you can pull out afterward. Compared with the reconning syringes you used previously, the insulin syringe ought to give you better accuracy.

I happen to have a few bunk kits on hand, so I could actually give that a try and find out.

 

[ultima thule]

woundcarping said:

ultima thule said:

I ran a test. I took a bunk vial of Kpv10 to verify it. I added 1ml of water into the sealed vial containing a puck and let it dissolve. Then I took an insulin 1ml syringe and pulled the solution back out. It came to more than 1ml, roughly 10unit/.1ml. After that I put only water into the same vial, using the same syringe, and again 1ml. The outcome was identical. So: my reconstitution syringes aren't accurate, and in the end the puck contributes nothing to the volume of the reconstituted peptide.

So you acknowledge that your gear lacks precision, and from that admission you jump to a conclusion that contradicts fairly basic physics.

Great job.

At what point did I say I agree that my syringes aren't precise??? Point to that in what I wrote. All I did was run a test and report what came out. Perhaps your grasp of physics is fine, but your reading comprehension could use some work.

 

[woundcarping]

ultima thule said:

woundcarping said:

ultima thule said:

I ran a test. I took a bunk vial of Kpv10 to verify it. I added 1ml of water into the sealed vial containing a puck and let it dissolve. Then I took an insulin 1ml syringe and pulled the solution back out. It came to more than 1ml, roughly 10unit/.1ml. After that I put only water into the same vial, using the same syringe, and again 1ml. The outcome was identical. So: my reconstitution syringes aren't accurate, and in the end the puck contributes nothing to the volume of the reconstituted peptide.

So you acknowledge that your gear lacks precision, and from that admission you jump to a conclusion that contradicts fairly basic physics.

Great job.

At what point did I say I agree that my syringes aren't precise??? Point to that in what I wrote. All I did was run a test and report what came out. Perhaps your grasp of physics is fine, but your reading comprehension could use some work.

ultima thule said:

I ran a test. I took a bunk vial of Kpv10 to verify it. I added 1ml of water into the sealed vial containing a puck and let it dissolve. Then I took an insulin 1ml syringe and pulled the solution back out. It came to more than 1ml, roughly 10unit/.1ml. After that I put only water into the same vial, using the same syringe, and again 1ml. The outcome was identical. So: my reconstitution syringes aren't accurate, and in the end the puck contributes nothing to the volume of the reconstituted peptide.

Happy to assist.

 

[BNLFL]

BNLFL said:

woundcarping said:

The lyophilized puck itself takes up space—usually somewhere between .1 and .2ml. That lines up precisely with the extra "10 units" you're seeing.

If precision matters to you, then you compensate by changing how much bac water you add, factoring in that puck volume. That way, both your final volume and your concentration come out correct.

Hmm, that makes sense and accounts for why there's extra left at the finish.

restingbeachface said:

Mine went the other way. The first Reta vial I used, which a friend had mixed up for me, appeared to be short by 5 units. I was sure I measured right on each draw, yet I ended up doubting myself. Then a motsc vial I mixed on my own did the same thing — 5 units gone. I have no idea what mistake I made.

Do your reconstitution syringes and injection syringes, or your pen, measure accurately?

woundcarping said:

ultima thule said:

I ran a test. I took a bunk vial of Kpv10 to verify it. I added 1ml of water into the sealed vial containing a puck and let it dissolve. Then I took an insulin 1ml syringe and pulled the solution back out. It came to more than 1ml, roughly 10unit/.1ml. After that I put only water into the same vial, using the same syringe, and again 1ml. The outcome was identical. So: my reconstitution syringes aren't accurate, and in the end the puck contributes nothing to the volume of the reconstituted peptide.

So you acknowledge that your gear lacks precision, and from that admission you jump to a conclusion that contradicts fairly basic physics.

Great job.

Nice one.

A handful of posts earlier, I raised exactly this point.

 

[ultima thule]

woundcarping said:

ultima thule said:

woundcarping said:

ultima thule said:

I ran a test. I took a bunk vial of Kpv10 to verify it. I added 1ml of water into the sealed vial containing a puck and let it dissolve. Then I took an insulin 1ml syringe and pulled the solution back out. It came to more than 1ml, roughly 10unit/.1ml. After that I put only water into the same vial, using the same syringe, and again 1ml. The outcome was identical. So: my reconstitution syringes aren't accurate, and in the end the puck contributes nothing to the volume of the reconstituted peptide.

So you acknowledge that your gear lacks precision, and from that admission you jump to a conclusion that contradicts fairly basic physics.

Great job.

At what point did I say I agree that my syringes aren't precise??? Point to that in what I wrote. All I did was run a test and report what came out. Perhaps your grasp of physics is fine, but your reading comprehension could use some work.

ultima thule said:

I ran a test. I took a bunk vial of Kpv10 to verify it. I added 1ml of water into the sealed vial containing a puck and let it dissolve. Then I took an insulin 1ml syringe and pulled the solution back out. It came to more than 1ml, roughly 10unit/.1ml. After that I put only water into the same vial, using the same syringe, and again 1ml. The outcome was identical. So: my reconstitution syringes aren't accurate, and in the end the puck contributes nothing to the volume of the reconstituted peptide.

Happy to assist.

That is not me accepting anything, just pointing out what is true. When one syringe reads 1ml while a second one holding the same quantity of tap water reads above 1ml, then at minimum one of those two syringes must be off. Nothing more complicated than that.

 

[jmk909er]

After going through every post in this discussion...if I'm mixing 1ml of BAC Water into my 30mg tirz, the amount of BAC Water I draw should be a touch under 1ml because of the space the puck takes up, so my dosing ends up more precise — is that correct?

 

[BNLFL]

jmk909er said:

After going through every post in this discussion...if I'm mixing 1ml of BAC Water into my 30mg tirz, the amount of BAC Water I draw should be a touch under 1ml because of the space the puck takes up, so my dosing ends up more precise — is that correct?

Yeah, that matches what @woundcarping mentioned. I've got a R50 to reconstitute afterward, so I'll pull .2ml/8units from my BAC.

 

[woundcarping]

jmk909er said:

After going through every post in this discussion...if I'm mixing 1ml of BAC Water into my 30mg tirz, the amount of BAC Water I draw should be a touch under 1ml because of the space the puck takes up, so my dosing ends up more precise — is that correct?

If that worries you, then sure. Take off .1-.2ml.

Even so, you'd need to know the mg in the vial, which might be overfilled or underfilled, and testing just a couple vials out of a batch of thousands isn't exactly strong statistics.

Where it would count more, if it counted at all, is with stronger concentrations paired with smaller doses.

 

[Nancy Langner]

Yeah, the empty space in the syringe could be part of the reason for what you're noticing, particularly if you're switching between different syringe sizes. That said, I wouldn't start changing the BAC water amount based on trial and error, because it can throw off the concentration and how accurately you dose. It's better to stick with the instructions that come with the specific product and verify with the pharmacy or supplier. herbilabs might also be a good one to check with about whether they offer any guidance on this.

 

[BNLFL]

Nancy Langner said:

Yeah, the empty space in the syringe could be part of the reason for what you're noticing, particularly if you're switching between different syringe sizes. That said, I wouldn't start changing the BAC water amount based on trial and error, because it can throw off the concentration and how accurately you dose. It's better to stick with the instructions that come with the specific product and verify with the pharmacy or supplier. herbilabs might also be a good one to check with about whether they offer any guidance on this.

If it were me, I'd trust what @woundcarping says. Have you checked? Neither gray peptides nor syringes include any directions. At least my Reta and East Touch syringes certainly don't.

 

[TriDiddy]

Zelmar702 said:


Some light reading:

• ISO Standard 7886-1:2017/2018: Defines maximum permissible dead space (0.07 mL for syringes < 5 mL). Smith et al., "Variation in syringes and needles dead space compared to the ISO standard 7886-1:2018," (2021).
  
• Needle Gauge Data: Hamilton Company Needle Gauge Chart and PepStackHQ "Needle Gauge & Dead Space Effects on Peptide Dosing" (2026), which provides specific microliter volumes for 25G–31G needles.
  
• Clinical Waste Analysis: InjectBuddy "Dead Space in a Syringe: How Much Drug It Wastes" (2026), confirming waste percentages for small volume doses.
  
• Veterinary/Compounding Studies: BVNA (2025) and Smilstead (2024), which measured median dead space of 0.08 mL for 1 mL syringes with 23–25G needles.

Summary of Accuracy by Needle Gauge​The following data synthesizes findings from PepStackHQ (2026), InjectBuddy (2026), and Smith et al. (2021) regarding dead space in 1 mL Luer lock syringes with detachable needles.



Needle GaugeApprox. Dead Space (Syringe + Needle)Volume Loss on 0.25 mL Dose% Dose Wasted25G (Standard)0.070 – 0.100 mL0.07 – 0.10 mL28% – 40%27G0.060 – 0.090 mL0.06 – 0.09 mL24% – 36%29G0.050 – 0.080 mL0.05 – 0.08 mL20% – 32%30G0.040 – 0.070 mL0.04 – 0.07 mL16% – 28%31G (Fixed/Insulin)0.002 – 0.008 mL< 0.01 mL< 3%

Impact of Needle Gauge and Length on Measurements​In 1–3 mL syringes, needle gauge and length directly increase dead space volume, which reduces the actual delivered dose if not accounted for.

• Gauge (Diameter): Larger bore needles (lower gauge numbers like 23G or 25G) have significantly higher internal volume than finer needles (29G–31G). A 25G needle typically adds 0.04–0.07 mL of dead space, whereas a 30G–31G fixed needle adds only 0.002–0.008 mL.
  
• Length: Longer needles (e.g., 1.5 inch vs. 0.5 inch) linearly increase the fluid volume trapped in the needle hub and shaft. Studies confirm that 1.5-inch needles consistently exhibit the highest dead space volumes regardless of manufacturer.
  
• Connection Type: Luer lock syringes with detachable needles create an additional hub cavity, adding 0.03–0.05 mL of dead space compared to fixed-needle syringes, where the plunger can expel fluid almost entirely from the integrated tip.

The Calculation Formula​To determine the total volume to draw into the syringe: Total Draw Volume=Target Dose+Total Dead Space

1. Identify Target Dose: 0.25 mL.
   
2. Estimate Dead Space:
   • Fixed Needle (e.g., 29G–31G insulin syringe): ~0.005 mL.
     
   • Luer Lock + Detachable Needle (e.g., 25G 1"): ~0.05 mL to 0.08 mL (Syringe hub + Needle).
3. Calculate Draw:
   • Scenario A (Fixed Needle): 0.25+0.005=0.255 mL. (Often negligible; drawing to 0.25 or 0.26 mark is sufficient).
     
   • Scenario B (Luer Lock 25G): 0.25+0.06(avg)=0.31 mL.

Calculation for 0.30 mL Dose with 32G Needle​Using the formula Volume to Draw = Target Dose + Total Dead Space:

Scenario A: 1 mL Fixed-Needle Syringe (32G, 5/16")​

• Target Dose: 0.30 mL
  
• Dead Space: ~0.003 – 0.005 mL (Fixed 32G needles have negligible lumen volume; ~0.23 µL/mm length).
  
• Calculation: 0.30+0.005=0.305 mL.
  
• Action: Draw to the 0.30 mL or 0.31 mL mark. The error is <2%, which is clinically negligible for most medications. You do not need to overfill significantly.

Scenario B: 1 mL Luer Lock Syringe + Detachable 32G Needle​

• Target Dose: 0.30 mL
  
• Dead Space: ~0.035 – 0.045 mL (The Luer hub adds ~0.03 mL; the 32G needle adds ~0.01 mL).
  
• Calculation: 0.30+0.040(avg)=0.34 mL.
  
• Action: You must draw to the 0.34 mL mark. If you only draw to 0.30 mL, the patient receives only ~0.26 mL (a 13% underdose).

----------------injection pens with a 4 or 6mm needle-------------

The Formula Application​Volume to Dial=Target Dose+Pen Needle Dead Space

1. Target Dose: 0.30 mL (which equals 30 Units on a U-100 scale).
   
2. Dead Space (Pen Needles):
   • 4 mm Needle (32G): ~0.004 – 0.008 mL (4–8 µL).
     
   • 6 mm Needle (31G/32G): ~0.006 – 0.010 mL (6–10 µL).
     
   • Note: This is significantly lower than Luer lock syringes because there is no large hub cavity; the dead space is almost entirely within the needle cannula itself.
3. Calculation:
   • With 4 mm Needle: 0.30+0.008=0.308 mL (~30.8 Units).
     
   • With 6 mm Needle: 0.30+0.010=0.310 mL (~31.0 Units).

Practical Execution: The "Prime" vs. "Over-dial"​Unlike syringes where you draw extra fluid, pen cartridges have a fixed dialing mechanism. You generally do not dial 31 units to get 30. Instead, you rely on the priming (safety shot) protocol to fill the dead space before setting the dose.

• Standard Protocol (Recommended):
  1. Attach needle.
     
  2. Prime: Dial 2 units, hold needle up, press button until a drop appears. This fills the 0.008 mL dead space.
     
  3. Dose: Dial exactly 30 units (0.30 mL).
     
  4. Inject: Depress fully. The dead space is already filled, so the full 30 units are delivered.
     
  5. Result: 100% Accuracy without complex math.
• Alternative (No Prime / "Over-dial" Method): If you skip priming (not recommended for accuracy), you must dial 31 units. The first ~1 unit fills the dead space, delivering ~30 units. However, this is imprecise because pen dials usually click in 1-unit increments, making "0.8 units" impossible to measure. Always prime instead.

Click to expand...

That's a real eye-opener and quite fascinating. I had been thinking about moving to luer lock syringes for injections, but after reading this I'll stay with standard insulin syringes. With luer lock, dead space averages 4 units, while standard syringes only have 1 unit, which is so small it doesn't matter.

This also suggests more dead space with the 1.5 inch 3mL syringes I use for reconstitution (both the luer lock system and the 1.5 inch needle increase dead space). What strikes me, though, is that when I reconstitute, the vial usually has a vacuum, which ought to pull out the bac water trapped in that dead space, so perhaps for reconstitution the dead space isn't losing much fluid.

Still, interesting facts.

 

[Zelmar702]

Update: on how syringes are calibrated, what dead space does, and the way dosing precision is governed by official manufacturing standards.

Syringe Calibration, Dead Space, and Dose Accuracy​#-syringe-calibration-dead-space-and-dose-accuracyFor hypodermic syringes built to ISO 7886-1, the calibration refers to delivered volume—the markings on the barrel tell you how much medication will actually reach your body, rather than how much fluid the plastic device holds in total.

1. How Syringe Mechanics Actually Work​#-1-how-syringe-mechanics-actually-work

• The Hub Fills First: Once the needle is placed in a vial and the plunger is drawn back, liquid occupies the empty needle cannula and the plastic hub cavity before any fluid arrives at the zero mark on the clear barrel.
  
• Correct Plunger Alignment: The markings on a syringe are designed to be read only from the top (front) flat ring of the black rubber plunger seal. When that top ring is lined up with a marking, your exact target dose is isolated within the clear barrel.
  
• Full Delivery: Pushing the plunger all the way to zero moves the whole barrel volume into your body, while whatever fluid filled the hub remains trapped behind as waste.
  
• Needle Gauge & Length: With either a short 31G needle or a long 25G needle, the plunger travels the identical distance down the barrel. Needle size alters hub volume, but since the hub fills before the scale begins, your delivered dose remains 100% accurate regardless of needle size.

Critical Safety Rule: Never "over-draw" past your target line to compensate for needle space. Drawing to $0.34\text{ mL}$ for a $0.30\text{ mL}$ target dose will deliver $0.34\text{ mL}$ into your body, causing a 13% overdose.

Click to expand...

2. Real-World Impact: Vials & Injection Devices​#-2-real-world-impact-vials-injection-devices

• Why Vials Run Out Early: With standard detachable Luer Lock syringes, about 0.05 mL of fluid stays trapped in the hub after every injection. Suppose a 20 mg vial is reconstituted with 2 mL of BAC water (10 mg/mL) and you draw four 0.50 mL doses (5 mg each); each draw then removes 0.55 mL total from the vial (0.50 mL dose + 0.05 mL hub waste). Come the fourth dose, that accumulated 0.15 mL of hub waste leaves just 0.35 mL (3.5 mg) in the vial—so you fall short of a full final dose.
  
• Why Vials Have Leftover Liquid: If fluid is still there after four 0.50 mL doses (5 mg each) have been drawn from your reconstituted 2 mL vial, the cause is either manufacturer overfill—labs frequently include 5–10% extra liquid to offset glass wall cling—or a visual reading error. If you align the bottom rubber ring of the plunger rather than the top ring, you accidentally draw less than 0.50 mL every time, which leaves unused liquid behind while under-dosing each week.
  
• Fixed-Needle Syringes (U-100 Insulin): Come with an integrated needle whose hub dead space is near zero (~0.003 mL), so waste is virtually eliminated.
  
• The "Air Lock" Technique: With Luer Lock syringes, pulling a tiny 0.05–0.10 mL air bubble into the barrel behind the liquid column lets that bubble drive trapped hub medication out through the needle tip. This flushes the dead space and removes wasted medication without altering your actual dose.
  
• Injection Pens (4mm/6mm Needles): Pen cartridges, unlike syringes, cannot auto-fill the needle tip while you dial. You must prime 2 units into the air first to fill the needle cannula, then dial your exact target dose.

3. The Retail Trap: Delivered Volume vs. Total Barrel Volume​#-3-the-retail-trap-delivered-volume-vs-total-barrel-volumeThere are significant risks in buying syringes from third-party sellers on retail platforms such as Amazon or Walmart when the product is not explicitly labeled as a medical-grade device. How the scale is calibrated is the main thing separating medical syringes from industrial ones:

• Delivered Volume (ISO 7886-1 Standard): Only the fluid that actually leaves the syringe tip is measured. The needle hub cavity is disregarded by the scale, because that space fills before the scale lines start. Lining up with a 0.30 mL mark means exactly 0.30 mL goes into tissue.
  
• Total Barrel Volume (Non-ISO / Industrial): The total physical liquid held by the whole assembly (barrel, nozzle, and hub together) is measured. Residual fluid trapped after full plunger depression is not accounted for. Draw to 0.30 mL on a total-volume scale and roughly 0.05 mL remains trapped in the tip—only 0.25 mL is delivered, producing a severe under-dose.

Absent an ISO 7886-1 mark or FDA 510(k) clearance, the calibration standards and manufacturing tolerances are unknown (for example, misprinted lines or loose barrel dimensions). A box that lacks an ISO mark, a lot number, an expiration date, and a certified sterilization method (like EO Gas or Gamma Radiation) holds an uncalibrated plastic tube and should never be used for injections.

4. Physical Cues: Flat-Top vs. Cone-Shaped Plungers​#-4-physical-cues-flat-top-vs-cone-shaped-plungersThe rubber plunger stopper often reveals how a syringe was engineered:

• Flat-Top Plungers (ISO Medical / Delivered Volume): The flat rubber surface rests flush against the flat bottom baseline of the barrel. Since the clear barrel is a perfect cylinder, the scale lines keep precise volumetric spacing. A flat plunger sweeps the barrel clean and disregards the hub.
  
• Cone-Shaped Plungers (Industrial / Total Volume): Industrial utility syringes (for dispensing glue, epoxy, or ink) commonly have a pointed cone built to jam deep into the nozzle tip and squeeze out thick liquids. A cone takes up an irregular, non-cylindrical shape at the bottom of the barrel, so its scale lines do not keep standard medical volumetric spacing and should never be trusted for medication.