The song of the week is the old bluegrass standard 'Roll In My Sweet Baby's Arms' in the key of A.
The chord progression I use for this song is:
This is the progression that is found in row B column 2 of the Basic Chord Progressions chart. Notice that only one of its measures differs from the progression located immediately above it (row A column 2). Some people prefer to use this latter progression (A2) instead of progression B2 for Roll In My Sweet Baby's Arms. This is one of those songs in which one should therefore pay extra close attention to the person who is leading the song the first time that they play through the progression in order to see whether they end the progression as 5511 or as 1511. Other songs on the suggested song list that can vary in the same manner as this - depending on who is leading the song - are:New River Train, Red River Valley, and Mountain Dew.
In the key of A: 1=A; 4=D; 5=E
(For those who capo to the 2nd fret to play in the key of A - that is, nearly all bluegrass banjo and guitar players - so that they can use the same chord shapes and fingerings that they would use for playing in the key of G, the chord shapes are: 1=G; 4=C; 5=D)
The A chord consists of the notes: AC#E
The D chord consists of the notes: DF#A
The E chord consists of the notes: EG#B
Together, these three chords contain all 7 of the notes that make up the A major scale. This is the reason why most bluegrass songs do not require the use of any chords other than the 1, 4, and 5, For, most bluegrass melodies contain no notes other than the notes that make up the major scale, and many of the melodies that do contain non-major scale notes do not linger on these notes for a long enough time to require a changing to a chord that contains the note in question.
If you listen to a lot of different recordings of Roll In My Sweet Baby's Arms, you may notice that the vocal melody for this song tends to differ from singer to singer to a greater extent than what is the case for most other songs. The melody sheet that I have included in the attachments reflects more or less the way that I tend to sing the song at present. (For those who only read tab, I have included a sheet music to tab conversion chart for the melody notes that the song contains for mandolin, guitar, and banjo. With the help of this chart, some of you may find it useful to write out a tab of the melody for yourself. )
If you know a different version of the melody and wish to use that as the basis for your break there is no problem in doing that, for all the different versions of the melody that I have heard work just as well as the one that I use with the chord progression that I use for the song. Also, this song lends itself quite well to playing an improvised break that is lick-oriented rather than being directly based on any version of the vocal melody.
Here are a couple of youtube links to listen to:
Flatt and Scruggs - key of Bb
Ricky Skaggs, Earl Scruggs. and Doc Watson - key of A