Carbonation Inconsistency

I'm new to all grain brewing. I recently brewed an Irish Red and there seems to be inconsistency with carbonation from bottle to bottle.

To give a background I did 7 days primary fermenter at 70
7 days secondary at 70
14 days secondary at 50
after bottling went back to 68 for 21 days

When I've opened my bottles, I've had some beers overflowing with head spewing out of the bottle when I opened it and others that don't have any head at all. I thought at first maybe the yeast went dead so I shook some of the bottles prior to putting in fridge. My only other thought is I syphoned too much trub into some of the bottles.

Anybody else know what may have caused this?

You gave a bunch of information about fermentation but that's not going to help us figure out your uneven carbonation problem

How did you go about adding your priming sugar? Did you boil it in a little bit of water first, put it at the bottom of your bottling bucket, and rack your beer on top of the priming solution making sure to create a whirlpool?

correct, exactly as you decribed.

Hmmm...

What are your cleaning and sanitation practices like during bottling?

Welp, the night before I wash the bottles in a dish washer using a non-scented detergent. Prior to bottling I shoot easy clean sanitizer into each bottle and hang them on a sanitized bottling tree.

Well jeez man, I don't know then unless there were just some rogue buggies that didn't quite get the full treatment.

Gently stir after racking to the bottleing bucket,if that doenst help maybe you have some kind of infection.Do you rinse your bottles after drinking out of them or do you let them crust up then just throw them in the dishwasher? I always rinse immediatly,use a bottle brush in them,dry,store,sanitize on bottleing day.
Are you chilling down your bottles completley before drinking them?
I think it was you shaking your bottles prior to putting them in the fridge. You want your yeast to settle at the bottem and generally avoid it in your glass.Its best for a clearer,less yeastie tasting beer to avoid stirring up the yeast you want to settle firmly at the bottem.It makes for good conditioning.

Definitely stir the brew in the bottling bucket with a racking cane after moving it over. I also put in half of my priming sugar when I start siphoning out of the carboy and rack onto it, and then add the second half once there's about a third left in the carboy. My first batch came out with most of the bottles being undercarbonated, and one bottle that wouldn't stop gushing because of poor mixing on my part.

Give it another week. You may JUST be at the point where the bottles are starting to carb, but everything's up to speed yet. Since every bottle is it's own microcosm they don't all necessarily come up at exactly the same moment. And 3 weeks at 70 degrees tends to be the minimum most beers take...You're probably just on the cusp of them carbing up.

Personally I think the idea of needed to extra stir priming sugar is bunk.....The movement of racking 5 gallons of beer onto 2 little cups or priming solution is going to mix it up fine on it's own.....

I used to agree with this Revvy, but then I found several batches where there was definitely uneven carbonation and I had conclude that the priming solution had not mixed.

I was thinking about it, and just because you are racking 5 gallons of beer on the sugar doesn't mean that its mixed. Think about it like as Italian soda - if the syrup is poured in first, and then the mineral water, the soda is going to be drastically sweeter at the bottom. In the case of bottling the sugar solution isn't as dense, and the ratio isn't as high as a soda, but I think the illustration still applies. I think how the racking tube is positioned may have a big influence as well. If its pointed straight down at the bottom of the bucket, it may well mix. But for me that is rarely the case - it usually curves to the side or even upward, which I feel can allow a sweeter beer layer to exist leading to uneven carbing.

To make sure this doesn't happen, you don't need to stick any kind of instrument into the beer, but as it is racking just gently swirl the bottling bucket to encourage mixing.

I just rack on top of the priming soultion, then give it a a swirl or two with the racking cane, and then bottle ... I am pretty sure that gets it well mixed ... i think uneven carbing can happen for many reasons though ... my biggest problem was waiting the 3 weeks ... it actually still is .. haha