i found an interesting article and i guess is valid although is written by an ex-Hells Angels member.
http://www.diablomag.com/archives/DM9912/sod.html
it says what you already said,he carried a gun and proved on court. I copy/paste the following from it to "excuse" my mistake.
"Most of the books and articles about Altamont are filled with bull"
It's one of the things you cant speak with certainty if you didnt live then. Let me assume that the claim: Hells Angels were responsible for an unecessary death, was an attempt to give them an end.