You took the right (correct) path in choosing a TVM rifle from Jack Garner. Way better rifle & ALL AMERICAN parts; reliable, good back-up from the shop. After the demise of the Hatfield Company, anther company tried to resurrect the company, but with a new name, Upper Missouri something-or-other. Not to be confused with "Doc" Carlson's fine establishment, Upper Missouri Trading Post.
They lasted about two years, I think (Correct Me, if longer) before going belly-up. Then, another company arose call Austin & Halleck. They brought out a traditional half-stock rifle, but I don't think it was a "Hawken" design. I think it was call a "Mountain Rifle". They also brought a couple of inline rifle designs to balance the business. Think A & H went under a few years ago.
I have seen a couple of A & H Mountain Rifle come up for sale on the www.muzzleloadingforum.com
classified section for sale in the past month. There is one now on page 3 of the classified section posted by "Smoky289, highlighted in pink(?). Still for sale, but got a couple of folks wanting to trade.
The price on the Hatfield sounds about right. I think when we switched from Hatfields to Jack Garner the price for a Grade 3 stocked rifle was $700-750 American. I think Hatfield spent more on slick advertising and less on quality of construction.
Matt & Toni Avance have the helm now at TVM (Tenn Valley Muzzleloading). Jack still has his operation, TVM (Tenn Valley Manufacturing). Confused yet?
I wouldn't want to wish anyone a Hatfield now, unless they're going to put it over the proverbial mantle for people to marvel at. However, I'll buy any used TVM rifle with Jack's name or Matt's name on the barrel in a heartbeat if the price is right.
I just bought a like-new TVM rifle last month. I sold it for $600 ten years ago. Bought it back for $750 last month, and sold it for $1000. Everybody was happy with that deal.
Its hard for me to explain, not be a machinist or gunsmith. Others may have to pitch in. Look at Nate McKenzie's post, reply#3. He was aware of the breechplug design.
"Picture" a breechplug with a thread-length of 1", instead of 1/2" long. Then, looking at the breechplug from the right profile view, drill a hole into the side of the breechplug threads for the vent liner to be installed.
Bear in mind that a hole has been drilled from the center of the breechplug face all the way down to the position of the vent liner. This hole is about the size of a .22 caliber bore brush, which is how we instructed customers to remove the fouling, when the gun failed to fire.
This how we found out about the design of the breechplug, when we tried to remove one from a Hatfield barrel, and ended up shearing off half (the length) of the vent liner. At that time (no one at Hatfield told us),
the correct procedure would have been to remove the vent liner first, THEN the breechplug.
So, outwardly, the lock position will be the same.
Sorry, have no photographs to replace these "thousand words".
Hope this helps.