Part of my cunning plan was to get a mould for casting PP bullets in dia .400". I could then use these bullets for my knurling experiments, and if those experiments did not work out as planned, I would still  have the option of paper patching them and trying that.
Frankly I'm surprised that it seems not anyone on this site has not been down this rabbit hole and posted their results, this is a bit worrying. I was hoping to learn from others experiences, rather than my own.
Finally, in order to save money, I was wondering if anyone has a mould that  they would like to sell that casts a PP bullet of .400" dia. This could either be a cash deal or an exchange for one of my many .40 cal moulds that I don't use. If anyone is interested in such a deal please PM me and I can provide a list of the moulds I no longer use, all of which are in perfect condition. If this is not possible then I will just have to grit my teeth and buy a new one.
Mike.

MickB I admire thinkers and doers and I believe you have your intentions very well thought out. I hope it turns out to be the same as you have it figured out in your head. Might be time to just go for it I would really enjoy hearing about your results. Buy chance do you have a lathe and a milling attachment and or a mill. If so I might be able to help you in regards to making your own bullet mould.

Craigd I prefer to leave that up to each individuals own preference and especially when it's of his own thoughts on what it is he is wanting to try. But I would add if making a cherrie to cut a mould the rule of thumb for shrinkage would be to add .002 to anything from 25 cal up to 32 to end up with the right as cast finished size to the diameter of  the cherrie itself. For anything larger than 32 cal then add .003 and it too being the general rule. Alloy used also makes a difference but either way it will be within a few tenths and it should not make a big difference from 30-1 up to 20-1. At least it has always worked out very well for myself as well as opening up the baseband diameter for some other folks such as Vall on this site.

Oops, I forget  to ask what would be the best length for the bullet to be as I know there is some sort of formula for calculating this. 
My barrel is 16-1 and .400" bore if that helps.
I checked Buffalo Arms web site and it seems that any PP moulds that they have, in the size I require, are out of stock at present, looks like a custom mould will need to be ordered.
I was thinking of getting a nose pour mould if possible, could anyone provide me with the email address of a good manufacturer please ?.
Mike.

So that would make the bullet 1.224" long , right ?. As to a good mould maker who is available to make me a nose pour mould and what would be their contact number please.
Mike.

MickB in regards to a mould maker that would be able to fill your request. Contact Steve Brooks at the below link he does make nose pour moulds and he also does one of a kind work. He is a bit pricey but the quality of his work is well worth it.

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buffalo arms will make any out of stock mold at no xtra charge and ship very soon  hard to beat the quality   art

Just to clarify a couple of points from my previous posts. I thought that if I was going to splurge on a new mould I would try a nose pour for two reasons. I was led to believe that with a NP mould that any voids that might be in the cast bullet would be more likely to be at, or near, the point of the bullet and have less affect on accuracy. This may just be BS for all I know, quite some years ago I did have a NP mould for my 45-90 and one thing I did notice however was that the bullets all had perfect bases, and this is generally accepted as being a good thing.
On the subject of bullet length relative to the groove diameter of the barrel, the bullet I'm currently using is from a BACO mould ( JIM409400M4 ) this bullet is 1.4" long which seems to go against  the formula of bullet dia x by 3 times the groove dia of the barrel. I might add that of the 8 or so designs I have tried so far this one has given the best results at the distance our club usually shoots which is 100m. 
Mike.