It seems to me that the WCs use of the quote by Cunningham in its report was extremely misleading because the Mannlicher Carcano does eject significant nitrates back onto the persons face as stated by Guinn. This is what Jim DiEugenio is talking about.
However the DPD then proceeded to make a mess of the paraffin casts they took from Oswald. They first subjected the casts to a dermal nitrate test (which was a useless test) which reduced the amounts of nitrates on the casts. So when it came to the second test, the neutron-activation analysis for antimony (which was the more accurate test) the casts were now in a less than desirable state due to the first dermal nitrate test having been conducted on the casts. To make matters worse for this second test, the people handling the casts contaminated the casts making them useless for analysis in this second test (the neutron-activation analysis for antimony test).
So while the WC arrived at the right conclusion (i.e. the parafin tests were inconclusive), it seems to me they inserted a misleading quote by Cunningham.
The Cunningham quote is followed a few lines later by an FBI test conducted after the JFK assassination and says that a test shot from a Mannlicher Carcano left no nitrates on the persons face. The WC report does not say FBI ballistics expert Cunningham was the one who did this test but i'm guessing he did as he was the one testifying before the WC. If Guinn tested the rifle and found it emitted significant amounts of nitrates and Cunningham says it emitted basically none, this raises questions about Cunninghams honesty in my opinion. And DiEugenio is right to raise this issue even if the source he cites is less than perfect.
With regard to the scholarship, from what I can see when Bill Turner phoned up Vincent Guinn after seeing Cunninghams testimony, Guinn mentioned a test he had done which Turner mistakenly thought had been conducted after Guinn had read Cunninghams testimony and had become suspicious. In fact the Guinn test had been done the weekend of the assassination. It seems me that Turner made a mistake as to when the test had been done and DiEugenio is simply repeating this mistake by citing "Letter from Turner to Gary Aguilar, July 17, 2007." as the reference. Yes, DiEugenio should have gone to the original source (Guinns article) but i'm guessing he just made a mistake which is probably difficult to avoid when writing a book on a topic as complicated as the JFK assassination.
Even if the source DiEugenio cites is less than perfect, I don't really feel misled by it to be honest. I think the point he makes is valid.