KellerBrauer you asked for some additional information on the recipe and measurement technique.
Not sure if the following adds some clues to help trouble shoot my issue.
I use a hydrometer and a test jar to take gravity readings.
My initial gravity reading was taken after I pitched the yeast.
I am fly sparging using a simple, plastic "fighter jet fly sparge" as seen here https://www.northernbrewer.com/products/fighter-jet-fly-sparge
Recipe:
12 lb 2-Row Xtra Pale Malt - Viking Malt Mash (80.0%) - 1.9 SRM
1 lb Munich I (Weyermann) Mash (6.7%) - 7.1 SRM
1 lb Caramel/Crystal Malt - 40L Mash (6.7%) - 40.0 SRM
8.0 oz Black (Patent) Malt Mash (3.3%) - 500.0 SRM
8.0 oz Chocolate Malt (Bairds) Mash (3.3%) - 500.0 SRM
Add 18.75 qt of water at 163.7 F
152.0 F
60 min
Fly sparge with 15.53 qt water at 168.0 F
1.00 oz Columbus (Tomahawk) Boil 60 min (40.1 IBUs)
2.00 oz Cascade Boil 15 min (15.6 IBUs)
Whirlfloc Tablet Boil 5.0 min
Estimated Post Boil Vol: 5.98 gal and Est Post Boil Gravity: 1.074 SG
I see nothing wrong with this recipe as 15lb of grain should yield 1.074 @ 168° in a 60 minute mash. The additional sparging device may not be necessary, as Denny mentioned, but I don’t believe it would cause a 70 point deficit in your gravity. Also, another contributor mentioned the time/speed of the sparge. I timed my sparge yesterday and it was about 75 minutes for about 8.5 lbs. grain and I hit all my targets, volume and temp. So, if the sparge is 90 minutes, or so, you should be good.
I see four possibilities. 1) pH is off, 2) the grain isn’t milled properly, 3) there is an issue with your thermometers and 4) the hydrometer is off.
How often do you calibrate your pH meter? The calibration buffers you use should be within their expiration dates. If not, replace them and recalibrate. I suggest also calibrating your meter using the 4 and 7 pH buffers for better accuracy.
Milling the grain — if you mill your own, you may consider having it milled at your supplier instead — just as a test. If you buy it pre-milled from the same supplier, perhaps you would consider buying a mill and milling your grain yourself.
You can easily check the accuracy of your thermometer(s) my checking the temperature of boiling water. Likewise, your hydrometer should have calibration information printed on the paper insert. You might consider checking it for accuracy.
It’s clear you’re having an issue if you miss the targets by 70+/- points. That can be very troubling indeed. I hope this information helps.