Fossil/JJ can you confirm the following?
These striations are a specific type of injury not the same as impressions that could be left by the vest ?(It says it somewhere in your document, but I may have got it wrong.)
As per Interested Bystanders point, I would be very interested to know the degree of force needed to produce these marks and can you get an opinion? There must be a retired forensics specialist with a blog/website, who might have an interest.
For what it's worth - ie. me speculating also IMO the regularity of the tram line dimensions are what is so compelling for me. ( double line, regular gap, double line, regular gap.)
Even if say that was a machine embroidered vest where rigid lines are produced to create rigid lines- as opposed to a machine knitted one,-I can't visualise how the lines left by it could be so regular in their repeat once they are pressed at great force against the curved backbones or concave into dent impressions.
https://cc11313.files.wordpress.com/2015/10/image016.jpg
( This type of fabric is designed to stretch and follow curved profiles, I have quite a few of these vests! ) Please correct me if I am talking nonsense and the striations gaps are not regular in their widths apart.
Despite me saying previously - have you considered the toe end of the bat as the source - for the life of me I can't imagine that one could find any wood grain that is so regular in the repeat pattern of double line, regular gap, double line.
I admit I haven't researched wood grains per se but am assuming they are governed by variables of growth and climate changes so I can't imagine they could appear as per your photo.
( Additionally also, as a complete non-expert, for me the only parts of the mag rack to have vertical end grain would be the upright pieces at either end, not the horizontals, it's just the way a carpenter uses wood..... but that's by the by.)
https://cc11313.files.wordpress.com/2015/10/abrasion-at-t11-showing-striations-post-mortem2.jpg
I think the fact that the handle of the gun is so curved makes this all very plausible and that machine tooling extends right down to the handlle's base
making the apex of that curve liable to make contact.
https://cc11313.files.wordpress.com/2015/10/image026.jpg
Anyway I sincerely hope that your research get's out there, it deserves to be further examined and I see that another book will be published in December after the SCA.