Westerado: Double Barreled

The achievement leads up to the "Dapper Deputies".

This is a solution I found in the depths of the Internet after failing way too often with the Beefheads - I added some notes to clarify the steps.

Start with a new game and go to Clintville

1. Help the concerned woman to get her husband from the saloon
2. Talk with Miss Tressabell in ALL LOCATIONS (Sheriffs Office, Saloon, Ranch and Oil Tycoon), so you won't see her again at the Rancher's house
3. Again talk with the Sheriff
4. Now go to the Oil Tycoon and when you ask him for a job, take your gun out
5. Talk with the Beefheads (in the train tunnel) and hire them to do the buffalo ride
6. FAIL the buffalo ride letting the buffalos getting to Fort Motors
7. Talk again with the Beefheads and go with them to kill Rancher Bob (the first option and tell them you know where he lives)
8. Go back and talk with the Oil Tycoon (I just delivered the message to the tycoon and didn't ask for a new job)
9. Then go talk with the Beefheads but DO NOT CLICK ON : "Have you got a job?"
10. Go to the Sheriff. He'll ask you to kill or arrest 5 wanted criminals (yep, you need to go through with that - easier to just find criminals to kill but use the bolas if you need some alive)
11. After that the Sheriff will ask you for help finding some Deputies, go to the Beefheads and convince them with the option for more "Bugjuice", then lead them back to the sheriff

Here the "Magnificent Seven" Achievement should pop

12. He will not hire them right away, convince him to accept them as deputies by drawing your gun

I took out the gun at the follow up after he refused, he said something around "What where you thinking bringing them here". And don't worry if you screw it up - just dashboard exit the game and restart. The Beefheads don't follow you on screen but as soon as you enter the Sheriffs Office they will appear and you can do it all over.