best type of horn to use..

this would be recreation of a medieval composite prod/lath.. trying to source and gather material.. looking at the grooved laminated sections laid at 90 degrees to the bow face..

I'm sure some of the others will chime in on this but here is my twopenerth. Do not fall into the same trap as me. I bought a box of offcuts, 16 water buffalo horn ends. This yielded a huge amount of scrap and an amount of usable horn, but all in small pieces that are an enormous struggle to scarf together and multiplied my work load.  Invest in good quality horn. Large sheep or ram horn is what I would use next time but water buffalo is seen as most cost effective.  I cannot comment on gemsbock or other exotic antelope species. 
You can only use the side strip, the top and bottom plates won't straighten no matter how hard you try.  
You will need to saw and resaw into strips 5mm thick, any thicker and it won't straighten for you.  Straighten with dry heat and fix when straight with cold water.  The longer the strips the easier the work.  A crossbow takes surprisingly little horn, 1 good size water buffalo horn might be enough. You need maybe 9 strips of horn 11mm wide 75cm in length to get a 300lb bow. I cut mine much too wide and lost a huge amount of good horn as I reduced the eventual thickness .  The work is not too difficult but there is an awful lot of it. For instance, you will have to groove at least 12 yards of horn...

Water Buffalo horn is the de facto standard for all wood-horn-sinew bow construction, with a mixture of fish and hide glues to glue them down.  You want the absolute longest horn you can find, with the pieces just touching or slightly overlapped at the center of the prod.   Horn on the belly and sinew on the back, of course.

is there any update of making Horn sinew  prod?  I am very curious!

Mmm, it’s harder than it looks. Experiment on scraps until you get the glue the right consistency. I had many failures. Use the longest strips you can get. I suspect goat horn is better and more authentic than water buffalo but no-one I know of has tried that yet.

don't we have pictures during the development of a prod?

The couple of cross-sections published on the internet and that I have found in books show horn that is not black.  Water buffalo horn is black.  Talking to other makers there is a theory that European Ibex were hunted to the edge of extinction partly because their magnificent horns are the perfect shape for making crossbows and goat horn is the same colour as the horn in the cross-sections.

The only person to have mastered horn bows currently is Andreas Bichler, his work can be found in an image search.  You might be able to contact him through the historical society he is part of

Not all water buffalo horn is black, or even gray.  European cattle horn which is white to gray has also been used,  also Ibex and wild Sheep horn. 

If you want to learn how to use and properly glue wood, horn, and sinew to make a composite prod, I strongly suggest seeking out the Asian Traditional Archery Network on Facebook and a website.  These archer-historians have been recreating wood/horn/sinew archers bows (including several that I know of less than 48" long) from many different cultures, for thirty years or more.  They know how to properly prepare, shape and glue the specific kinds of woods, horn sinews and glues to successfully make composite bows.  It's not easy and it's not fast, but it is doable.  You might even be able to find a craftsman willing to make an appropriate prod for you, but it probably won't be cheap.

Good advice from Kenh, just keep in mind wood composite archery bows are an entirely different technology from crossbows, which usually don’t use wood at all

Early medieval wood-horn-sinew crossbow prods developed after the West was introduced to composite bow technology by various invasions from the East -- Huns, Magyars, Avars, Mongols and others -- as  as far back as Roman times, and as late as the late 1200s incursions by the Mongols.

I'm not sure where the OP got the idea of " grooved laminated sections laid at 90 degrees to the bow face".  Small grooved or ungrooved plates of horn simply aren't going to work.  The grain (and grooving if any) of the horn MUST be down the length of the prod, just as the grain of the wood must be. 

Of the hundreds, if not thousands of cultures who made w-h-s bows throughout history, only the Western Scythian people managed to make bows from a number of short pieces of wood and horn bound together with sinew to make their bows -- and those did NOT have the grain of the horn or wood at 90 degrees to the length of the bow.

Because you are both correct, the long lengths of horn, the longer the better, are assembled on edge into a block with all the horn strips at 90 degrees to the belly/back of the bow

kenh wrote:
I'm not sure where the OP got the idea of " grooved laminated sections laid at 90 degrees to the bow face". 

Holger Richter, "Die Hornbogenarmbrust", chapter 4 pages 73, 77, 80 and chapter 5.

kenh wrote:
Of the hundreds, if not thousands of cultures who made w-h-s bows throughout history, only the Western Scythian people managed to make bows from a number of short pieces of wood and horn bound together with sinew to make their bows -- and those did NOT have the grain of the horn or wood at 90 degrees to the length of the bow.

Except Angermuseum Erfurt inventory number 10208,
Stadmuseum Köln inventory numbers W821B, W828B, W827B and W827A - just to mention a few.

Hopefully I attached an image

Nope that didn't work, here is a link to the met museum.  It should also trigger some related images that might be useful

https://www.google.com/imgres?imgurl=https%3A%2F%2Fimages.metmuseum.org%2FCRDImages%2Faa%2Foriginal%2FDP214785.jpg&imgrefurl=https%3A%2F%2Fwww.metmuseum.org%2Fart%2Fcollection%2Fsearch%2F35675&tbnid=zAK8oSXxQgIWUM&vet=12ahUKEwi7svCVkcb4AhUIhxoKHXu8DiAQMygdegUIARD6AQ..i&docid=HjZJqG9RqwuSxM&w=4000&h=3494&q=horn%20sinew%20crossbow%20section&ved=2ahUKEwi7svCVkcb4AhUIhxoKHXu8DiAQMygdegUIARD6AQ

We need to be comparing apples to apples not apples to oranges or bananas or strawberries!

There is a class of crossbow built from asiatic archery bows, one strip of horn along the belly, thin wood core, sinew back. These Chinese type used standard archery bows with a long draw length and sophisticated trigger

There is an (early) class of horn crossbow with a wooden lath - sometimes yew, sometimes other wood.  Die Hornbogen Armbrust discusses brown oak as a core.  This was actually used as a shady practice to make bows using too little horn look like they were made of lots of horn - people complained and there are Guild records of makers being reprimanded for dodgy dealing! (Bichler, paraphrased)

The last of the hornbows used huge horn cores with enormous amounts of sinew.  Bichler has made several of these, they do not take set as the huge amount of sinew keeps pulling them back into line, or even into reflex.

a 74cm long prod with (at centre) 11mm thickness of horn and 9mm thickness of sinew produces between 120kg and 150kg of force (Bichler) .  Wood complicates the production process and is very likely to fail.  Crossbows are bent into very tight arcs and kept cocked for long periods of time