View Full Version : 9x18 ammo in a sten gun

November 13, 2008, 06:33 PM
First off this is an intellectual question only, I do not own, plan to purchase or want to test this theory. This is just the sort of mechanical 'what if' that sticks in my craw. To avoid repetive posts I'll lay out some givens, please reply if you disagree.

1. 9x18 Mak is .01 shorter than 9x19 parebellum/luger. Since the Sten is an open bolt design/fixed firing pin design where the bolt is actually still in motion at the point of firing, I dont see where the case length diff. would matter.
2. 9x18 bullet width is around .09 more than 9x19. .364 vs .355. This would certainily be unsafe in a modern firearm made to close tolerances but in a plumber's nightmare sten? Loose tolerances and a shot out barrel would negate this concern in my opinion.
3. The 9x18 generates about 10,000 PSI less force in chamber than the 9x19 so cycling may be an issue. Since the majority of the Sten's resistive force comes from the weight of the bolt I dont see where lighting the recoil spring would be productive and could cause light primer strikes.
4. I'm not even sure if com block ammo and Stens have ever come into direct contact during conflicts but if anyone has ever heard of a 'combat tested' story please post, I'd be interested in hearing it.

Again this is just a 'what if you had to'. I am not going to attempt this even if I had the means.

James K
November 13, 2008, 09:48 PM
First, the STEN was NOT made by plumbers and the tolerances for the barrel are the same as for any other barrel in 9mm Parabellum. In fact, STEN barrels are very well made and the gun is highly accurate, shooting around an inch at 25 yards when fired semi-auto from a rest.

The STEN fires from an open bolt, feeding the round into the chamber and then firing the primer as the cartridge stops on the chamber shoulder. Since the 9x18 would be too short (if otherwise OK), it would not stop at the time the bolt closes and would not fire. But the main problem is that the larger bullet of the 9mm Mak requires a (surprise!) larger case that will not fit into a 9x19 chamber. So you would need to either rebore and re-rifle the barrel and ream the chamber or have a new barrel made. Then you would have to open up the bolt face for the larger case head. I don't know if the blunt bullet of the 9mm Mak would even feed, but IMHO such a conversion (if you were serious) would be silly when 9x19 is a lot easier to get and cheaper than 9mm Mak.


Jim Watson
November 13, 2008, 11:12 PM
I dunno, Jim. I think if you promiscuously slipped a 9.2mm Makarov round into a Sten magazine, it might well stop with the oversize bullet wedged in the tapered 9mm Para chamber and fire. Possibly with a good deal of exposed case wall and some fireworks out the ejection port and down into the magazine.

Dumb idea.

B. Lahey
November 13, 2008, 11:20 PM
4. I'm not even sure if com block ammo and Stens have ever come into direct contact during conflicts


I think Stens and commie ammo have been around each other in just about every conflict in South America, Asia, Africa, and the Middle East for the last 60 years or so.

November 14, 2008, 08:07 AM
The 9mm Makarov uses a unique shape for the weapons chamber as well. Rather than being straight walled the chamber is 'belled'. The 9mm Mak is pretty hot for a blowback weapon, thus the slightly belled chamber slows down the slide when the pistol is cycling. Unique, cheap and effective, gotta love those commie engineers!

November 14, 2008, 02:22 PM
I admit the STEN was a great engineering accomplishment and fufilled it's purpose exactly as designed. It was designed to be built in low tech shops, be inexpensive, reliable in less than ideal conditions (read: loose tolerances.. although I admit this may not apply to barrel dimension) and put a lot of rounds down range. The .09 difference in bullet dimension should not necesarily prevent a sten from firing a 9x18. Although, it is an excellent point that the case would be oversize also. I would think that the case would chamber but would be slowed considerably by being slightly oversized, this may cause premature detonation and case failure or simply prevent extraction once fired. Just my .02

I know this a stupid argument since nobody in thier right mind would ever have a reason to try this but it's better than discussing 5.56 vs 7.62x39 all over again.

James K
November 14, 2008, 10:22 PM
Hi, bwogle,

Have you tried putting a 9mm Mak in a STEN gun chamber? If not, why do you persist in the idea that the STEN is so "sloppy" that it would fit, and that the barrels were so poorly made that a few millimeters here and there wouldn't be noticed. And what makes you think STEN guns were made in village blacksmith shops? The gun could have been ASSEMBLED in small shops if necessary, but in fact they were all made in well equipped factories, on government provided tooling.

Just FYI, before I wrote what I did, I tried putting a 9mm Mak round into a STEN chamber; it won't fit and its case won't fit in the bolt head.

You had an interesting idea, but put it to rest. It is not as if we had a shortage of 9x19 or a surfeit of 9x18 Mak; there is just no earthly reason for anyone trying to make something like that work.