Yeah - if I was in your shoes I'd still consider it, maybe with a slightly thicker mash at the expense of a bit of efficiency - heck you could mash in 75% of your water and grist in your mash tun and the other 25% in another pot, stir them both so all the grains are wet/no clumps and then transfer the 25% into the tun and give it a churn as desired - that way you could fit everything in there without spilling when stirring. That or scale back the recipe by a half gallon or so.
I have a five gallon cooler mash tun and I typically do 12 pounds or so of grain for most of my recipes. 12 pounds is just fine. I don't think I've brewed anything with 13 pounds, but that is probably pretty close to the cutoff point, depending on your exact water to grain ratio and amount of grains. That being said... I did make my PtE clone-ish thing with the same mash tun, and that one had just shy of 15 pounds of grains. Now to do the 15 pounds I obviously had to fill it all the way to the top, and fudge on some of the volumes and numbers, because beersmith said I needed 5-point-something gallons (and gave the mash volume number in red, because technically I didn't have enough room to mash that much grain). However, I mashed a little thick, and sparged a little bigger and longer than usual. I let the first of two batch sparges sit there for about ten minutes, just to make sure I got as much extraction as I could. The sparge volumes were a bit larger too.* BTW, this is just a musing, but is my five gallon mash tun the reason why I have to double-batch sparge? Can't say this has ever caused me any issues, and beersmith does do the calculations for you. I did not notice any ill effects on my PtE pseudo-clone from the small mash tun, or anything else for that matter. The beer came out great. I did forget to take the OG on that beer, so I can't say if I hit my target or not, or the effects of the smaller mash volume, altered water to grain ratio, or slightly different batch sparging procedure. My guess is that there IS some effect from making these changes, but that these effects aren't going to be very noticeable if you're just out to drink and enjoy the beer. If you haven't dialed in your system yet** you also might not be able to tell what effects the smaller mash tun is having anyway. So... If missing your OG by two points bothers you a lot, get a ten gallon mash tun. Otherwise, you can brew just fine with the five gallon model. I'm going to keep using mine for mini-batches at home, and for smaller batches or test batches when needed. *tho to be truthful, I usually don't worry that much about sparge volume, I just keep sparging till I get the kettle to the desired degree of fullness. This is pretty much within a half gallon or so of what beersmith calculates, but I just quit bothering to actually measure the sparge water. I can do this on many of my beers because I don't care about the exact specifications, and I know it will be pretty close anyway. The difference between a 6.1% beer and the same beer at 5.9% just won't make any difference to me, so I am a little lazy about trying to be perfect every time.. If I were trying to do something very specific, such as clone a specific beer, I would stick to the exact numbers in beersmith. Also, when I start using my new ten gallon system, I will follow all recipes and volumes to the letter until I get the new system dialed into beersmith. ** I would not use the from a beer like my PtE clone as part of dialing in my system. Strictly use data where the grains properly fit into your mash tun, such as a 12 lb or smaller batch.
