Yes, a bobs-only 720 of Original Minor is possible - singles are not necessary!

Why is this the case? Firstly, a course of Original produces an equal number of positive and negative changes, as can be seen here:

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214365 --

241635 --

426153 +

462513 +

645231 --

654321 --

563412 +

536142 +

351624 --

315264 --

132546 +

123456 +

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This means that the negative changes are not sealed off, as they are in the plain courses of some other methods like Grandsire Doubles.

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720s of Original Minor can be made up by leaving the treble unaffected by most of the calls, leaving it to plain hunt as if it were a Plain Minor method.

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Why are singles needed in 720s of Plain Minor methods? In the diagram above, you can see that for every place that the treble occupies, the parity is always the same. So, both of the treble's blows in 6ths place are odd changes, both blows in 5ths place are even changes, etc. Singles are needed so that the treble can reach the even changes in 6ths place, the odd changes in 5ths place, etc.

 

But in Original, the treble can be affected by doing a dodge in 5-6, which allows it to access the alternative parity.

 

Though singles are needed for a 720 of Bob Minor, it is very important and noteworthy that a bobs-only 360 (the in-course extent) is possible, but so too is a bobs-only 300. This is interesting because the 360 is one course longer than the 300, and both touches use q-sets, yet it is still possible to get a one-course difference without singles.

 

This can be used to produce a bobs-only 720 of Original. We start off by partitioning the hypothetical 720 into three separate round blocks. Each round block keeps the treble unaffected, leaving it to continuously plain hunt just like in Bob Minor. The first round block is an in-course 360. The second round block is an out-of-course 300. And the third round block is an out-of-course touch of 60 changes - the 60 changes that are missing from the out-of-course 300.

 

We now have a true 720 partitioned into three separate round blocks. And a q-set of bobs, luckily, has three members. We then add a q-set of bobs to affect the treble - one bob causes the treble to make 4ths and hunt back down, the other two bobs respectively cause the treble to dodge in 5-6 up, and 5-6 down. These latter two bobs change the parity of the rows, allowing access to the out-of-course blocks.

 

This then sweeps up all three blocks into one, and makes us a bobs-only 720. And the added bonus of having those three bobs affect the treble is that the touch can be pedantically classed as Original Minor, and not some Plain Minor method!

 

Here is the bobs-only 720 that I came up with on this plan in 2013:

 

720 Original Minor

RBP

                         (a) 125463

1.3.6 (7 divisions) 136425

                         (a) 132456

                       (3b) 164532

                         (a) 163524

                       (4b) 156432

                         (a) 153426 

                       (4b) 145632

                       (2a) 142653

                       (4b) 164325

                         (a) 162354

                       (3b) 143562

1.2.3 (4 divisions) 143256

                       (4b) 124635

1.4.6.7 (7 div.)       156342

                         (c) 164235

                       (3b) 152364

                       (2c) 163542

                       (2b) 142356

                         (a) 145362]

                       (2c) 163425]

                       (3b) 154263] A

                       (2c) 162534]

                       (2b) 134256]

                         A   123456

(a) = 1

(b) = 1.5

(c) = 1.5.6

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Composed 16th March 2013, this isn't actually as complicated as it looks (sorry if the notation is a bit wonky.)

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To put things into context, (b) is the same as a plain lead of Single Court Bob Minor, (a) is (b) with a bob left out, and (c) is (b) with an extra bob. (4b) is therefore like most of a plain course of Single Court. The three other courses are the ones in which the treble is affected. I've underlined sections where there is some repetition - particularly the last bit which is almost a three-part.

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The reason that (c) only occurs later on is because this is the in-course 360 part of the touch - and it is based on the Bob Minor 360 Wrong, Home, Wrong. The bobs at 5 and 6 are like the consecutive Hs and Ws in Bob Minor. The section at the start is the out-of-course 300, and is analogous to the Bob Minor touch 3Ws, 3Hs. For this, the extra bobs in (c) aren't needed. The middle section is the missing out-of-course touch of 60 changes, and we can see the (4b) squeezed between the two turning courses.

 

I highly doubt that I was the first person to come up with this 720 plan. Frank Blagrove jokingly used to claim that he had a 720 of Bob Minor with no singles, until he revealed that it used a bob to affect the treble. My 720 is probably a variation of Blagrove's, and there may well have been others before him.

 

And there are other bobs-only 720s of Original on different plans to this one. A fine example is this extremely neat 9-part by Ander Holroyd, which looks very easy to call. The part ends are three bicycle three-parts. While you're at it, do have a look at some of Ander's other compositions, which include many more ingenious and novel extents of Doubles and Minor.