Alright so you want to check your grain crush, you want to check the CONVERSION efficiency. Don't sparge, don't mashout. Just do a single infusion and check the mash gravity and strike volume to determine the conversion efficiency.
Do you have a large-ish thermos, say 32+ oz?
Take 0.4 lb (6.4 oz) of grain, and strike with 0.15G (19.2 fl oz) of water at 160.79F to get mash temp of 152.
Mix up with a whisk or fork thoroughly. Then close the thermos, check the crap out of it to make sure it's mixed up well just incase the small diameter didnt make mixing difficult. Leave for an hour.
Assuming grain yield around 36 points, with 4% moisture...
90% conversion = 1.0615. 92% = 1.0627 94%=1.0639 96%=1.0652.
If it's below 90% then you definitely need to tighten the mill gap more.