JBP structural/sacrifice pruning

[Fi5ch]

My ~7 year old JBP pictured is 60" tall from the soil line, 40" wide, and has a 1.5-2" trunk at the soil, but very little taper. It has been in this 9"x15" x18" grow box for 3 years and the vertical sacrifice branch has gotten too tall & too thick (1.25") so I'd like to cut it back in late Sept or early Oct. If I reduce the tree to 18" tall I would have to cut off 44" of linear sacrifice branch; is this too much to take off in one cut? Also, the lowest branch is 3 years old and 22" long. Should I cut back the last two year's growth and make it 9" long?

 

[Fi5ch]

Any thoughts?

 

[Wires_Guy_wires]

I'm not good with US sizing, but I believe the sacrifice branch in this case hasn't had the techniques applied you would normally apply to a sacrifice branch; keeping one shoot and not letting it form any branches.
So in essence, this is just a large tree.

Reducing it to a smaller size would be my first goal. And a drastic one at that, because I would cut it back to the second set of branches and rebuild it from there, applying bonsai techniques from there on forwards.
It will probably bud all over and give you a couple different options to move forward from.

 

[Shibui]

It is not too much to cut at once provided there is still some healthy branches left that can continue to grow. I've never seen or heard of a JBP dying from a reduction, only when they are pruned leaving no viable shoots.
The second branches would be my first choice too. Cut there and wait to see what new options emerge. Can always reduce to that lowest branch the following year if that's the best option after the first chop.

 

[Fi5ch]

Thanks. I think i misunderstood that a sacrifice branch needed to be long but without side branches. My (incorrect) thought was the side branches would add extra mass to the lower trunk, but i
they seem to really add mass only to the trunk under the high branches, which is why the taper is poor.

 

[Deep Sea Diver]

All branches contribute girth to the trunk below their point of attachment.

Cheers
DSD sends

 

[TrevorLarsen]

The problem with having too much on a sacrificial branch is that the tree puts all of the buds up top not where you want them. If you only keep 2 buds on your sacrifice (one is a backup in case one dies) then the chemicals that your tree produces to stimulate new buds will go where you want.

 

[Fi5ch]

Am I correct that the best time to chop this 44" sacrifice in 7a is mid to late Sept?

 

[Shibui]

I chop pine sacrifice branches whenever I get around to it.
Winter and spring chops stimulate new buds for spring growth. Those candles will usually be large and strong but can be decandled or pinched to reduce overly long or over strong new shoots.
Summer chop stimulates smaller second flush growth.
Fall chop - the tree may not respond until the spring growth flush but then it should take off similar to spring chop.
Results are pretty similar in all seasons so I don't see any need to favour one over the others.