Someone had asked about the 7.62x25 Tokarev as an alternative to the .300 Whisper.  With the help of Randall from AR15barrels I got a 10.5 stub of 1 in 8 .308 barrel blank.  Turned it to a nice barrel, chambered in the x25 and modified a bolt slightly.

The barrel is equipped with a standard extension, the chamber is the standard chamber.  I am considering throating it a bit deeper (see below).  The bolt had to be enlarged a hair because the brass for the x25 is a hair larger than the .223.  You CAN make the x25 from 223 brass but that defeats part of the idea of using this instead of the .300 Whisper.

I used two old Parson's mags, one fitted with the Tromix retrofit that is used with the .50AE, which consists of a new follower and a spacer in front.  The other mag was left untouched.  The rounds fit just fine, I was using 110 VMax and 168 SMK both seated to 1.650 COL.  They DID bulge the mag a bit so inserting and removing was a bit tough  ....  



Set the barrel up with pistol length gas system, mated to MGI QCB upper (ideal test rig for this stuff) on top of a registered lower.

Results:
The unmodified mag did not work. It fed one round, then dumped two in the front of the mag where there was the void space.  The mag with the Tromix spacer fed like greased goose snot.  Mag was loaded with 20 rounds.

110 Vmax load was able to eject (quite far I might add) and reset hammer but would not strip next round.  No recoil to speak of.

168 SMK would not eject fully.  Recoil?  Heck, hard to tell the round fired.  Perhaps with other load it might be enough to eject.

Mil Surp would not eject, nasty corrosive stuff.  Yuck.  Need to find some of the S&B stuff.

Definitely worth working on load development as well as looking at altering the Tromix spacer to allow longer seated length (more powder).  If set up as 16" barrel with pistol gas system it should work just fine.  Going to get the Noveske Krinkov FH and see how that works, suspect it will make it work.  Adding a suppressor to the barrel would make it cycle I am sure, just didn't have one with the right thread handy ....

Considering this round would just about work on gas, it leads me to believe that the 10mm can be done the same way with the PRI 6.8 mags, 6.8 bolt and spacer.  Got a few 10mm barrels that are not working with 10mm MAG so they might get a second chance ....

More pictures and updates to follow

Marty + Randall + Cool Idea = More $$$ out of my pocket!

I want one!

Tom  

Back to the feed problems with the 10mm Mag rifles, have you tried a mag spacer with these?

10mm Mag does not need the spacer, issue is with the long round making the transition from mag to chamber.  This is also why I think 10mm (not the Mag) might work.

Polishing chambers and radiusing the mouth is helping but in this case we may have simply hit the limits of case geometry that will work.  Putting a slight neck on the case like the 35/40 Randall is doing on this case is enough to make it work just fine.  Have considered turning these barrels in to 40-44 wildcats or 40 AMPs but that creates more problems (finding mags that work, dies, etc)

Double tap. whoops.

Quoted: Marty + Randall + Cool Idea = More $$$ out of my pocket! I want one! Tom

I like this guy.
I still can't figure out who he is, but I like this guy...

Randall

Quoted: Considering this round would just about work on gas, it leads me to believe that the 10mm can be done the same way with the PRI 6.8 mags, 6.8 bolt and spacer.  Got a few 10mm barrels that are not working with 10mm MAG so they might get a second chance ....

I fear the expansion ratio problems with as little powder as the 10mm case can hold.
You know this stuff 10x better than me, but run some 'case volume-to-bore volume when the bullet cracks open the gas port' comparisons and see where you come up with the 35/40, 338 spectre, 10mm mag and 10mm.

I'm betting that it's a big step backwards when you cut back the 10mm mag to a plain ole 10mm.

Randall

Marty - What Dia gas port hole are you using?

The fact that the gas port is out about the lenght of some pistol barrels would lead me to believe that gas pressure has allready dropped off considerably. Maybe try for more volume to make up for the lower pressure?

Nah, I got it from a VERY reliable source that 10mm gas operated ARs have been built before ...

If the Tokarev with 6.0 gr A2400 under the 168 will just about do the job ....

I pulled some 10mm loads and put them in the program - the 155 XTP load in the 10.5" bbl had a higher listed "operability factor" than the 110 Vmax load in the Tok .... so using pistol length gas system with a 16" bbl would do the trick I would think.

Quoted: Marty - What Dia gas port hole are you using? The fact that the gas port is out about the lenght of some pistol barrels would lead me to believe that gas pressure has allready dropped off considerably. Maybe try for more volume to make up for the lower pressure?

As big as it gets ... I am running a load very different from the pistol loads, by using fast rifle powder.  The 110 Vmax load ejects almost violently ... the brass goes about 25 ft at my 4 o clock, missing the deflector.  I think that if the barrel were a hair longer it would fully cycle as it already resets the hammer.  Thus my thinking that adding a KFH or can would do the trick.  Adding a can was the whole idea anyway, why else load 168 SMK at 1040 fps?

Quoted: Nah, I got it from a VERY reliable source that 10mm gas operated ARs have been built before ...

Yep.  At one time, Olympic built gas-op 10x25mm and .40 S&W uppers.

Quoted: Yep.  At one time, Olympic built gas-op 10x25mm and .40 S&W uppers.

So then the question becomes...

If they did it "at one time", why DON'T they do it now?
Maybe they know something we don't about functioning or mag issues.
Maybe they did just not sell well enough to bother cataloging them.

Randall