Does any one have any experience with these?

Johnston.
Great concept; they are using a cut off 308 case as a primer holder and gas seal, seated against a nipple, (which I never thought of). Otherwise, it is a bolt action muzzleloader. Good idea; I have been building them on Mauser actions (but I didn't seat the case against a nipple) (and some with nipples for musket caps) since 1980, but not for re-sale.
If you are going this route, why not go ahead and make it for smokeless powder as well. When I started, we didn't have sabots either, so it is a better game now, ballistically.

Yes I own one what would you like to know?

I live in lower MI where it is a shotgun/muzzleloading only area. I have been using the Ultimate for about 10 years now.

Ken uses a bolt action with a Lothar Walther barrel. The barrel has a non-removable breech plug/nipple threaded into it where the chamber would be on a centerfire rifle. A large magnum rifle primer is used in a 45 mag casing. This casing slides over the nipple.

I use 4-50gr Pyrodex pellets behind a 50cal, 300gr Hornady SST. This crosses my chrono a little over 2300fps.

The ballistics are really very close to a 405 WCF. I regularly shoot mine out to 300yds. Beyond that, the bullet is dropping like a stone so your LRF better really be on.

The rifle is very accurate. My pre-season zero check for the last two years have both been within 1" of center on a 300yd target.

The rifle is also very easy to clean. A few patches with Birchwood Casey Black Powder solvent followed by an oiled patch and its done.

The downstoke is that my rifle is heavy. Mine also uses a Howa action. One of my friends has the carbon fiber barrel model and it is nice and light.

So there you have it: accurate, powerful, easy to clean; but heavy.

BTW, my BIL used mine tonight to fill his tag from 181yds.

That pretty much sums it up. The weight, especially forward weight is an issue for me. I am a small guy with a short reach. Any kind of rest to shoot from and your golden. 300 yards and down no problem until you get to inside 30 yards then the trajectory has to be compensated for. Everything is a trade off in one way or another. They do clean easy. I find mine can be a bit picky about whose sabots I use. Still, plenty accurate and more than enough oomph to get the job done. Well made. Not cheap.

I have 2 of Kens Ultimate Muzzle-loaders, and I don't think you can find a better Muzzle-loader anywhere.my loaders are over well over 10 years old and one of the big things that separates these muzzle-loaders from the rest of the pack are the barrels that he uses the raw barrel costs more than the cost of a top-end competitors muzzle-loader. I originally bought this brand because of its long range capability I enjoy primitive weapon/muzzle-loader areas in New Mexico and didn't want to deal with range issues, it is best to put a ballistic type scope on that is matched to your bullet/powder, Ken can help you organize that successfully. I have shot mine at 300 yards many times always grouping well. The older loaders are a bit heavy but very accurate. With all the hi-tec components that are available today they have been able to cut the over-all weight of the finished Muzzle-loader considerably, I am actuality getting ready to order one of his newest model Muzzle-loader soon.

Hope this helps and Good Luck!

I own 2 of the UF muzzleloaders as well. They're awesome and I couldn't be happier. I consistently shoot animals at 300yds with zero problems.

Do not own one but have met Ken. He is a fun to talk to. Some of the stuff that come out of his mouth is PURE Bs but very fun to hear. Clint

Clint......that's an understatement!

yea you do want to wear your boots. laughing
Mine actually has a weatherby rather than a howa action.

Larry, I have a couple. Going to do a ML hunt in New Mexico this October. Call me and I can fill you in.

take a look at the new remington ml.

nipples belong on a woman's chest, not on a man's rifle...