bulk priming

i've had 2 problems:

1) After doing an extract batch (and using top off water), my gravity reading is WAY OFF. Forum people tell me that its difficult to mix my wort with the top off water to get an accurate reading. The yeast will mix it up good.

2) I have had bottle bomb issues with batch priming.

Are these 2 issues related? If it is difficult to mix up wort with top-off water, is it equally as difficult to mix a sugar solution with wort?

The issues are related in that they both are caused from inadaquete mixing.

Not completely mixing partial boils is not a big deal as the yeast will will the wort during fermentation it just prevents you from getting an accurate OG reading. If you really are having problems an option is to measure the OG of the partial boil and then do the math to figure out the OG of the full volume of wort. It's a pretty simple calculation (OG "points" x boil volume)/total volume, i.e. 3 gallons boiled at 1080 would be 80 x 3 = 240/5 = 48 or 1.048 gravity for 5 gallons.

Bottle bombs are a bigger issue as you've probably learned because they lead to exploding glass. Bottle bombs are caused by 1 of 4 problems: unfinished fermentation, too much priming sugar, inadaquete mixing of priming sugar, or infection.

If you used the standard 4-5 oz of priming sugar for 5 gallons we can rule out excessive priming sugar.

How did you mix your priming sugar? Generally adding it to 2 cups of water and racking on top is enough to mix in thorougly, if you're concerned adding a very gentle stir can help. Did you test any of the non-exploding bottles? Were some flat and some overcarbed? Inconsistency between bottles would point towards uneven disbursement of the priming sugar.

Did you take hydro readings 2-3 days in a row until stable to make sure fermentation was complete? If you didn't the beer may not have been done fermenting when you bottled and this could be the problem.

The last potential problem is an infection. Test some of the non-exploding bottles to see if the beer tastes ok, if it does you know the whole batch wasn't infected but its possible one or two bottles may have been.
I guess one final possibility is that you had one flawed bottle that cracked under normal pressure, although this is less likely than the others.

I'd move them all into a plastic container in case they explode again it will be less mess and less dangerous. I'd suspect the most likely cause is an uneven disbursement of the priming sugar. Giving it a very gentle stir next time you bottle or pouring half in the bottom and gently pouring half in when your siphon is half done should solve this problem.

I'm pretty sure my bottle bomb issues are mixing related. My process is to transfer from primary to bottling bucket (don't use secondary) the day before bottling. The next day, I pour the solution on top and then stir (in circles both ways and also across the bucket). I then bottle about 15-20 minutes later. My guess is that this mixing is not mixing sufficiently.

The reason I don't add the solution first and then rack on top is because I'm worried that the sugar will settle overnight. Do you think this is the case? Or will it remain mixed sufficiently overnight. The reason I let it sit overnight is to let anything that got sucked up from the primary settle.

Well it sounds like inadaquete mixing is the issue. Personally I just rack carefully onto the priming solution and then immediately bottle, if you have lots of trub you can wrap the tip of your racking can in sanitized cheese cloth or get a tip for your racking cane. If you really want to let it sit overnight I wouldn't add the priming sugar as this will cause re-fermentation overnight and there will be less sugar to bottle carbonate. If you do let it sit overnight I'd give the priming sugar a good but gentle stir to get the sugar to the bottom.

Ultimately I would say the easier solution is to rack on top of priming sugar, stir gently and bottle immediately, if you rack carefully sediment shouldn't be an issue.