Consistently Poor Efficiency

I've brewed 6 AG batches so far on my new equipment, and have consistently been getting 55% efficiency. I've tried different sparging methods, sparge times, mash times, and each time I only get 55%. My mash tun is a 15 gallon megapot with a false bottom, and initially I thought that my efficiency was low because there was a good deal of dead space underneath the false bottom and only about 3.5 gallons of water above it with the grain. I tried the same recipe with a bazooka screen, but got the same preboil OG. I thought it might be the grain crush, but I've now bought grain from 5 different online shops and have not seen any difference in my gravity readings between them. I'm not too familiar with water chemistry, and the first 2 batches I did not tamper with it and used spring water from the grocery store. Used the same water with 5 Star PH buffer, and no change in my gravity reading. I'm doing a batch now that had 16lbs of grain, and my preboil was 1056 after a 2 hour mash. Same reading before and after sparging. Second time doing this recipe, exact same preboil gravity. Water to grain was 1 to 1.33. Besides a consistently poor grain crush between stores or poor water PH I am really at a loss at to what could be effecting the efficiency so dramatically. The beer I'm making is fantastic beer, but I'd like to be getting 75% efficiency so I don't need to buy extra grain to account for the poor conversion. Any help would be very very appreciated.

How accurate is your thermometer? Are you possibly not hitting 152-154 degrees?

How much water are you using per pound of grain?

How are you sparging?

My thermometer is quite accurate, got it from my friend who works in a lab and I calibrate it with another thermometer before brewing. I'm using 1.3 quarts per pound of grain. I fly sparge with a sparge arm, usually sparging for about 45 minutes for a 5 gallon batch. My big issue is that even before sparging I'm getting these low numbers. I wonder, since the pot is pretty wide compared to it's height, that it could be effecting it.

I am pretty vigilant with my temperatures, though for this beer I mashed at 150 so it would be a bit drier. Typically I'm around 152, and holding it there consistently.

I see nothing wrong with your method. How did you arrive at a 55% efficiency?

That is what bothers me. When I put my recipes into my brewing software they say that at the gravity I'm reading I am getting 55%.

I see you mention pre-boil gravity. how about posting the recipe along with post boil gravity. Also are you using a hydrometer or refractometer? if hydrometer what temp is your sample when testing? if refractometer are you calibrating before use?

Recipe:
14lbs 2 row pale
.75lbs Crystal 15
.75lbs Light Munich
.5lbs Crystal 40

Preboil reading: 1040 at 155 degrees farenheit = (by my calc) 1055
Postboil: 1068

Using a hydrometer, which I calibrate with tap water and a thermometer before using it.

hydrometers in liquid over 90F are very very very inaccurate. always cool to below 90F (preferably to as close to 60F as possible)

I have done that, and I've found that the calculator I have used is pretty accurate (within 2 points) of what I get from cooling it down. I will definitely cool it down from now on, though, as it will be more accurate overall. I'm sure that is changing my reading somewhat, but do you think that would make me 15 or so points off?

if your hydrometer readings were correct, you'd be getting 65% efficiency, not the 75% you're looking for but better than 55%. Have you bought grain from Brewmasters warehouse? I know that with them I normally get 72-74%. also what is your post boil volume?

Of course bigger grain bills can cause your numbers to go down a bit. One thing to look at would be to get a grain mill and grind your own grain.

the reason I ask about post boil volume is.. at 65% and 5.5 gallons you get 1.068. at 6 gallon to hit 1.068 you need 71%... just that half gallon makes a huge difference

Post boil volume was exactly 5 today, not quite the 5.5 I was going for.

That makes sense, I guess I need to use a different calculator/do my own equations. I've been in the market for a grain mill, just waiting for the funds and the moons to align. Thanks for the help, glad to see I'm not that far off.

pssst.. make a mill for $20 bucks.. look up pasta mill