I've done pewter tips on muzzle loaders. I Swiss cheese the wood with as many 1/8" holes that I can get away with, as many that go "through and through", ie: from under the pewter and into the barrel channel, and I put a small chamfer on the holes that break into the atmosphere (hidden) to provide more mechanical grip/advantage. I too strictly employ cereal box cardboard as a mold and bind it with blue masking tape.

A fella has to have the "courage of his convictions" when he starts the pour, and not stop partway through and re-start. That will surely make for a wrinkle or void. Always melt way more metal than you think you'll need. I like Greg's suggestion of stirring with a wooden stick for temperature control, I gotta remember that.

I prefer my metal to be as lead-free as possible to make it as hard as possible. A soft fore arm tip or inlay will dent easier in use than a hard one - just my theory. I threaten to do the next one with straight tin, if I do another. "Old pewter" will have a high(er) lead content than "new pewter".

Hi Bob
So true on the ramrod hole.  The first one I ever did was my S. Hawken and when everything was ready I pulled the rod and filled er up.  Thought it took a little more than I figured.

Bob, 
It's not an issue and I encourage participation in my posts, even with topics straying off topic- like I never stray... only on days that end in "Y".

Further off topic from "special Ballard parts" - one interesting bit of advice I got for material for this process, the more lead alloy used, causes darker finish, potential for alloy expansion (causing cracking)and corrosion around the edges.

Have any of you done it with Cerrosafe? I've looked longingly at the stuff when contemplating a pewter tip. I also have a big chunk of something imprinted as being "ACA Ostalloy 158", a bismuth alloy that supposedly melts at 158 degrees and is used to fixture parts for machining. I reckon it to behave similarly to Cerrosafe but don't trust it to supplant Cerrosafe for chamber casts but wondered about its utility for a fore arm tip. 

I mainly wonder if a gun barrel could theoretically get hot enough to adversely effect a bismuth alloy fore arm tip?

I also use "pewter" occasionally for decorative butts on knife handles.

In a previous job I had, the rebuilding of babbitt bearings for large DC generators and motors was an occasional job I had, puddling the bearings is what we called it.  If the bond to the bearing shell was still secure, the bearing was built up with a small oxy-act torch and babbitt wire.   
I had some voids on my pour and the edges didn't fill out completely, the jeweler's torch I had worked well for this and there was a little flash-back to those earlier days.  Still have a little more work to finish this nose cap and I may be inspired to do a small pour in the grip cap and a diamond around the forend screw... Like I said, a hack with no direction.

Whenever I do a pewter nose cap or other pewter pour I have an electric soldering iron ready to help fill any voids and pinholes. It just melts a small area and allow me to fill it in without burning the surrounding wood. I fill any voids while the metal is still warm from casting. I use a high tin content babbitt.

Here's the next path of wasted time I'll share - rather than cast a forend cap - of brass, I decided I'd machine one from some scrap lying around... I had a steel casting to model one from.  None of my pics show the current state - I'll try to remember to share that  later.  The butt plate is brass so I thought the other end should be also.