I wanted to to do the turkey spatchcocked on the grill after using a dry brine on it. This was my virgin flight with all the qualifications above. I did a dry run last week with a 5 pound chicken just to get the logistics figured out a bit, but this bad boy was big. I got an 18 lb heritage turkey (Bronze) from Good Shepard farms. http://www.goodshepherdpoultryranch.com/
I'm posting what worked for me, because I really found nothing much to guide me online about this with all those qualifications above.
First, I dry-brined it using 4 tablespoons kosher salt (Mortons) and 1 tablespoon rubbed sage. Rubbed it in, inside and out. Turkey sat in disposable aluminum pan and was covered with plastic wrap. 24 hours covered, then overnight uncovered. Overall about 36 hours total before hitting the grill. I noticed about 6 ounces of juices in the bottom of the pan at the end of that time. I did not rinse the bird, just wiped it off a little. I did the dry brine rub before spatchcocking it, frankly because I wasn't sure I would succeed in getting it cut and thought I might have to bail out and just roast it the regular way after I felt that bone structure.
The biggest challenge was spatchcocking it. This bird was big but also since it was a heritage breed it had different heavier bone structure. These guys spend a life running around outside on a farm, and I could tell by feeling it that my regular Cutco kitchen shears were NOT going to make it. I started with my trusty Cutco shears from the neck end first. They did OK through the ribs, but about half way down I hit the pelvis. It was like trying to use a scissors on concrete, so I needed something else. First I sliced through the skin with a knife to expose the bone. I then used a Japanese-style pull saw with a 14 inch blade to saw through the pelvis. It worked quite well actually and with a bit of effort I sawed it apart and repeated the process on the other side.
I did not tackle the keel bone at all. The pointier breast structure of the heritage turkey along with stronger bones did not make it possible to squash it down appreciably. I did manage to get the legs and thighs splayed out akimbo. I tucked 1 onion in the neck cavity as well as fresh sage, thyme and rosemary. Tucked same herbs in the legs area too.
Bird went on grill at 3:30. I was expecting at least 3 hours for 18 lb bird. I used Kingsford Competition briquettes. Fire was banked at 1 end of basic Weber kettle. I put the oval disposable pan on the lower rack and added about 1 quart water in the pan. The pan worked well also to keep the fire banked and indirect. I placed the turkey with the butt end closest to the coals to give the dark meat extra heat. I was surprised to find that at 2 hours the thighs were already at 155 degrees while the breast was only at 118, so I rotated the bird 180 degrees to put the breast end closer to the fire. By 2 hours 45 minutes the breast was at 157 degrees and the thighs were at 168. I also began brushing on an apple cider glaze (cider reduction and butter) during the last hour.
I must say, it came out great! I was worried the breast would be a bit dry at that temp, and I admit I overshot slightly, but maybe due to the dry brine it was very moist and juicy anyway. I used the back, neck and giblets on the stove to make gravy. The pan under the bird accumulated too much crud, ash, etc to use.
So my summary is- first, dry brining is great! I don't miss sloshing around with loads of icky turkey water at all. Second, to spatchcock a heritage breed turkey takes some different tools because they have stronger bones, but can be done if you plan it out. I really recommend the Japanese style pull cut saw, which worked very well. Finally, between the spatchcock cut and grilling, the bird was done faster than I expected. It had to sit nearly an hour while my other dishes caught up, but was still delicious. Next time I will time it differently.