RDR2 How to get Buell for Arthur so John can have him too. Read the description.

After the first encounter, Buell will be outside the cabin when the second Hamish mission is availeble.
Ram into him and keep him moving by shooting at him, because once he stops, you can't jump on his back no more.
You can't shoot him so don't worry about that.
You can see another Buell who stopped running and i had to try again.
If this happens, ride away from the cabin and after a few seconds the mission is back up and Buell is there again.
Get close and jump on his back whem prompted.
This chasing around can be a PITA.
After you jumped on his back, don't get off, otherwise you can't get back on.
Ride to camp, Beaver Hollow in chapter 6, and hitch him there while sitting on his back.
(taking him to the stables and trying to stable it won't work.)
Save.
Reload the save and you while be able to put your saddle on.
Be carefull, he can still be mad for ramming him and shooting at him........
;-)

Now you can have him as Arthur, but as you can see in the video, after you got on his back, another Buell is waiting by the cabin.
So if you don't finnish the last mission (there are 4 in totall) with Hamish and save that for John, John can also have a Buell.