...and a .50 gun that appears similar to the Leman except it has an entry pipe and poured nose cap, this gun is by Walker according to the maker's mark. I've not seen one like it before, perhaps you could shed some light.
The entry pipe and nose cap on your rifle was an extra cost option shown in their catalogs and price sheets. See the "Extras on finished rifles" in the 1979 Price List below.
Not very many customers ordered that option even though it was more correct for a Leman half stock rifle. The standard pewter nose cap with the integral hole for the ramrod is more like what one sees on original Leman rifles that started out as full stock and were cut back to half stock during its working life.
I have one that was stocked by Bill McKay that is also a flintlock and has a fancy wood stock--two more extra cost options. This rifle is .50 caliber.
I have another one with the traditional entry pipe that was made by Neill Fields that is a .58 caliber, but it is what I call an "off-the-clock" rifle meaning that he made it on his own time for a personal sale. It doesn't have the GRRW stamp on it nor does it have a serial number. Any GRRW rifle with a makers mark but without the company stamp and serial number is likely one of these "off-the-clock" rifles.
Here is a picture of the two rifles together. The "off-the-clock" rifle is the top one and the factory rifle by Bill McKay is the bottom one.
Both of these rifles have Siler locks. GRRW typically used a Siler lock on the flintlocks they built as there weren't many choices in flintlocks through most of the 1970s.
L&R came out with their waterproof pan flintlock about 1977 that they initially called a "Hawken flintlock", and Ron Long came out with his similar flintlock about 1978. I've yet to see a GRRW rifle with an L&R lock, but I have seen some late production rifles (like 1980) with Ron Long's flintlock.
Your rifle looks like it has a Ron Long percussion Hawken lock on it. GRRW used that lock on their Leman Trade Rifles from 1975 to mid-1978. Your rifle probably dates either late 1977 or early 1978 based on the lock and the mountings.
Sometime in the 2nd half of 1978, GRRW began using the Siler percussion Mountain lock on their Leman Trade Rifles and the Leman Indian Rifles.
I'm not sure why Fields used the Siler percussion conversion lock on the "off-the-clock" rifle other than he was free to use whatever lock he or the customer wanted.