The local association I was raised in (Texas) was organized in 1857. They adopted the New Hampshire Confession. It is a modified document that drastically waters down the Calvinism of the Philadelphia Confession. On the other hand, in 1868 this Missionary Baptist Association made peace overtures to the local Primitive Baptist Association -- even invited one of their preachers to preach for them in 1869. So they must not have thought a strict 5-point Calvinism heretical, or even all that odd.