I printed a 20mm calibration cube.  While I don't have a metric set of calipers I used my reloading calipers and instead of .79" (equal to 20mm), it's measuring between .83 and .85.  So a few hundredths off.  This came about because I'm printing a 308 Hoffman Tactical lower and the mag well is pretty tight.  Not sure if I should dick around with adjustment or just sand the inside of the mag well so long as everything else fits ok upon building.

Any thoughts on what/how I should adjust things?  I have an Ender 3 Pro and use Cura.

Thanks!!

Damn it if you weren't right about the calipers!!  Will pick up a set in the AM.  

From watching this vid it looks like extruder calibration is the telling the machine to extrude 100mm of filament, measuring what it actually spits out and then doing old value x 100 / measurement (of what actually extruded)....and that'll give me my correction to adjust to.....correct?

Is that BOTH of what you told me to do or just one?

Thanks!

On the extruder adjustment....how do I make it stay adjusted?  Seems like once I turn the machine off it resets itself back to 93 (factory setting).  

Thanks

First thing first always calibrate your extruder. Good news is once it's calibrated you really don't have to mess with it. Run it about 5 times after you think it's set right to make sure it's calibrated. It should be good for any filament you run.

Print one of these https://www.thingiverse.com/thing:4108156 to help with the extruder calibration. Those scrap pieces of filament after finishing a roll are great for calibrating the extruder.

Use this website to see what needs to be done to calibrate your z offset to ensure your first layers go on right. Then go to the flow calibration section. He has several cubes labeled that you can download and you can set the flow rate on each one to a different value in your slicer. https://github.com/AndrewEllis93/Print-Tuning-Guide. The rest of the calibrations on that site are more for people running Klipper.

Print the flow cubes from like 90% flow to 110% flow. Use 50% infill, 5 walls, 5 top, and 2 bottom layers. In both Cura/PrusaSlicer/SuperSlicer you can set different flow rates for each object. You're looking for the one that is the most smooth on the top (he has pictures showing what to look for).

I've by far had better results doing this than any other method. It's also much faster to get new filaments dialed in. Once you have it dialed in you can save the profile for that filament.

To calibrate your retraction use this website http://retractioncalibration.com/

I've done TeachingTech's methods and a few others, but that Andrew Ellis Github is 3d printing gold for getting everything dialed in.

Need to save to epprom with M500

Once saved, it'll persist across power cycles.

just to say it since its implied by the other posts but not stated - your cube should be 0.80 not .79 and not .83   - you might not get it exact but the average should be really close.  being up to .85 average means being overextruded by 6.25% which doesnt sound like a lot, but in your lower where the whole width of the pocket might be 12.7mm (1/2") it would now be as little as 11.9mm wide, which means a LOT of sanding and finishing to get that sucker into spec.  I know this for a fact as I made this exact mistake in my newb times on a hoffman AR lower.. beautiful print in every way - ASA with no warp whatsoever, and the rear end of the pocket is 12.5 instead of 12.7.  I could dremel it but then the tolerances go right out the window, so I ended up reprinting.  lesson learned.

I would first calibrate extrusion multiplier (to much or to little filament will change dimensions of printed parts).  A decent guide would be https://all3dp.com/2/ender-3-calibration-how-to-calibrate-your-ender-3/. After that I would print a calibration cross from https://www.thingiverse.com/thing:2484766.  There is an included excel spreadsheet that walks you through what to measure and what fields to fill in to get a good calibration.  This cross uses multiple measurements to get an average calibration vs just a standard cube where you only measure each axis once. The calibration cross is actually 2 separate prints; one for x/y and another for z.