OK, I love this game, I know its old and everything but its still a classic and still has a lot of people playing now. Plus I've not much to do at the minute so why not write a solution for a top game! Plus there will still be people just picking up this game so check it out!
Boomshot KILLS ONLY COUNT FROM EITHER WARZONE, EXECUTION OR ASSASSINATION, NOT ANNEX!
Just so you know maps with the Boomshot on them are:
Clocktower (Middle of the map and across the water
(Middle of the map directly across from the statue
(The 'BS' on the map
Old Bones (DLC)Bullet Marsh
(DLC) (Where the Boltok is on the Gears 3 map
DLC is free by the way for the extra maps and Annex mode!Map Pack 1Map Pack 2
It's up to you which map you choose, most people would go for Gridlock but its more about what your team mates and opponents are doing which decides the difficulty on getting the Boom kills rather then the map.
Whichever you choose just play it clever and tactical, try and have friends with you to help you get the Boom. When/if you get the Boom its easy to get too excited or over confident with the Boom and waste the two shots it has! Then it wont spawn for a minute or two, and by that time the round is over.
When using the Boom, aim for the ground where the player is stood for the best result. In most cases, the splash damage will greatly damage them, kill them or down them. If they do go down (but not out) and you dont want to execute or curb stomp them, finish them off with the last Boom shot but make sure its from at least 6-7 foot away (in game foot lol!), or wait for a team mate of theirs to come and with good timing you can score a double kill as he goes to pick his friend up.
If you have no shots left then unlucky! Just execute them and try again in the next round/match.
These are just a few tactics to try but obviously they wont always work, most players are smart and very skilled and wont fall for the same tricks, thats if you even get them once to begin with! Mix up your tactics and ideas and just try to play smart.
Just a few other tips incase you are being constantly troubled:
Clocktower's Boom is too exposed and the sandbag and small wall before reaching the boom supply useless cover from Snipers, plus most players will run into the middle to begin the shotgun madness straight away so you need to be quick.
Gridlock's Boom is mainly exposed to anyone hiding behind the cars on either side and the hammerburst towers, but precise aim is needed to be downed from the towers.
Mansion's Boom can be a tough one to pick up. The positions of the walls and cover can provide some tough battles, plus the endless chances of being flanked from 2 or 3 different positions. 1 trick that works for me is to have someone go the 'normal' direction for the boom (as in the outside route) while i run through the mansion, through the front door and can end up being right behind the other team... unless one of them goes for grenades!
Mausoleum's Boom i recently had a horrible battle with a Host who was beating me to it everytime running in the direction of the Tourque Bow, so annoying! This boom is in decent cover but be warned when leaving the middle section as people could be hiding behind the walls. Maybe giving this map a miss is also a good option lol.
If you have any questions on the DLC map booms then give us a comment, otherwise i dont really wanna talk about them LOL. Only decent map for an easy boom would be Garden.
If that doesnt help then drop a comment an I'll try an answer your question. Good luck!
EDIT: Just found this on youtube for the SUPER NOOBS if you are really REALLY struggling with the Boom! The vid does have some good pointers, credit to XoADREADNOUGHT