Ok, I know they are supposed to be a bullet hose, and in the same class as a sterling type sheet steel Kiss carbine. The one I chose uses the Modified Sumoi stick mags. 9mm. Came with four of em, and I am competent to make more fit. It is in great shape. I have been told to not use the mag as agrip, and to keep it clean. This is one of the folding stock / 16in brl versions. Looks grey, and has no blemishes.
I will post picks when I get it home.

I don't know about the SW760 (Valkrie Arms or Special Weapons?), but the SW76 (real bullet hose ) was supposed to be pretty decent.  You could modify Tec9 mags to make it work with the SW76.  There's a guy in Shotgun news with replacement parts, although I don't know what fits over to semi versions.

Anything?

Well the SW760 is a Special weapons Knockoff of an MK Arms MK760, which is a rather good copy of a Smith and Wesson Model 76, a Copy of the Carl Gustav M-45 "K" SMG which was manufactured at the behest of the U.S. Navy as for how good or bad the SW760 is I do not know I have not handled one, I have handled at different times a S&W M76 and an MK 760 Both of which were nice for Tube guns. All I know really but I will take a look on Google and see what I turn up.
S&W76
"When the Swedes cutoff export of their M45 series SMG to the Americans as a result of our involvement in the Viet Nam war, special operations operators cast around for a replacement. What they found was a U.S.-built, reengineered version of the Karl Gustav M45D called the Smith and Wesson Model 76. Smith and Wesson marketed the SMG to both the U.S. military and civilian law enforcement agencies. Limited numbers were used by Navy SEAL Teams and by other special operations forces. However, the gun did not sell well and was eventually dropped from the S&W line by the mid-1970s. S&W did not copyright the M76 and another series of private manufacturers marketed the gun in both 9mm NATO and .45 ACP as the MK 760.

If a close comparison is made by of the Karl Gustav M45 and S&W M76, the similarities are striking. The cocking handle is on the right for both; both have rear sights protected by "ears" that are welded to the receiver; both have their front sights welded to a perforated barrel jacket; and both have a folding stock that is very similar to the other except that the stocks fold in opposite directions. Like its predecessor, the S&W M76 uses the same box magazines as the M45. The form and shape of this 9mm magazine is peculiar to the M45, M76, Egyptian "Port Said", and no others. The M76 or MK 760 can be found fitted with the very effective SG9 suppressor ("silencer") manufactured by AWC (Automatic Weapons Company).

Specifications:
Caliber: 9mm NATO (9x19mm)
Length (stock extended) -- 31.8 inches, (stock folded) -- 21.7 inches.
Barrel -- 8.4 inches
Weight (empty) -- 8.6 lbs. "

The MK-760 was first introduced in 1983 by Mike Ruplinger. He registered the corporate name as MK Arms Inc. He purchased the rights to the Smith&Wesson Model 76 and with Kenneth Domenick opened a factory in Fruithurst, Alabama. As Phoenix Firearms, doing business as, MK Arms Inc. The range of serial numbers started from MK1001 through MK1094. As a result of MK-Arms making copy of S&W 76, Soon the US Navy was placing orders for replacement parts for the earlier-made S&W Model 76's still in the military inventory.

Mike Ruplinger and Kenneth Domenick went there separate ways in 1984. Kenneth moved his operations to Pamama City, Florida. And opened Southern Machine Tool & Die Co. in 1984. With the trade name of Global Weapons. Here Kenneth produced a copy of the S&W Model 76 with a model designation of M76A1. Also produce were suppressors with matching serial numbers. The serial numbers, I have so far are 71001 to 71038.

Mike Ruplinger also moved to Irvine, California in 1984 and started producing  this copy of the S&W Model 76. Under the MK Arms Inc logo. The serial number range for this submachine gun was S082 through S450 so far. MK Arms also made pistol and carbine configuration. MK owners have e-mailed me with P and C serial numbers. These guns may have been converted to full auto. The Gun Owners Protection Act of 1986, eliminated further manufacture of automatic weapons for civilian ownership. MK-Arms was awarded certification to produce a respectable number of submachineguns before the provisions of the 1986 law went into effect.

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TECHNICAL SPECIFICATIONS FOR BOTH SMITH&WESSON M-76 AND MK-ARMS MK760:
Cartridge: 9x19mm-Parabellum
Type of Operation: Blowback
Type of Fire: Selective (Full-Automatic and Semi-Automatic)
Cycle Rate: 720 rpm
Barrel Length: 8 inches
Length:
Stock Folded: 20.25 inches
Stock Extended: 30.50 inches
Weight:
Unloaded: 7.25 lbs
Loaded: 8.75 lbs
Magazine Capacity: 14 rounds, 24 rounds and 36 rounds mags
Front Sight: Protected Blade
Rear Sight: Fixed Aperture