The old shooting 40 S&W in 10mm barrel trick...

[arakboss]

I have read about and watched videos of people shooting 40 S&W cartidges in 10mm barrels. Both of these cases are designed to headspace off the case mouth. Why does it work, supposedly the extractor will hold the 40 S&W case against the breech face during firing.

This made me wonder if there is an analog situation that could be done in the AR platform? Assuming you had a bolt that would snugly fit the 9mm cartridge (5.45x39 bolt appears to), maybe it could be fired in the 350 Legend barrel. Both the 350 Legend and 9mm are suppose to headspace off the case mouth and they both share similar dimensions toward the bottom of the case. If the extractor on the 5.45 bolt would hang on tight to 9mm case it could potentially work. I would probably want to test the first one with a string pulling the trigger.

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[arakboss]

I have read that a 223/5.56/350legend bolt can be opened up a bit to accommodate the 9mm rim diameter. I suppose the rim of the 9mm case could be filed down if you didn't want to buy or sacrifice a bolt. It is difficult to know what the 9mm case would look like after being fired in 350 Legend chamber but I would expect to fit the chamber in one firing. Whether or not the 9mm would fully chamber is unkown. I may do a plunk test tomorrow and see. On paper the 9mm is about .001 wider at the base of the case.

 

[arakboss]

I dropped a loaded factory 9mm round in the 350 Legend chamber and it fell into the chamber about 1/4" past the chamber mouth. A once fired case dropped in the chamber right about where it should sit.

 

[DirectDrive]

 

[red442joe]

View attachment 1250732

No.

Joe

 

[red442joe]

I have a Star Megastar 10mm. I have read that it is the only pistol built specifically for hot 10mm, the Bren Ten not withstanding.
I have shot a lot of 40 S&W through it, just for funsies. It does ondeed index/headspace off the extractor. 10mm is only a little above 40 S&W for pressure, However.....there is "more" "places" of higher pressure.......longer case, more surface area....more bunches of pressures...
Same deal with 9mm case vs. 350 Legend case.
Danger = meh

Joe

 

[arakboss]

I have a Star Megastar 10mm. I have read that it is the only pistol built specifically for hot 10mm, the Bren Ten not withstanding.
I have shot a lot of 40 S&W through it, just for funsies. It does ondeed index/headspace off the extractor. 10mm is only a little above 40 S&W for pressure, However.....there is "more" "places" of higher pressure.......longer case, more surface area....more bunches of pressures...
Same deal with 9mm case vs. 350 Legend case.
Danger = meh

Joe

I would have no worries about pressure issues, unless the 5.45x39 bolt doesn't allow the 9mm case to fully chamber.

My main concern would be whether or not the AR extractor would hang on to 9mm case during chambering and firing. If the extractor would hang on for one firing, I believe the 9mm case would fire form to the 350 Legend chamber. Subsequent firings of fire formed brass might make it easier for the extractor to hang on to 9mm cases.




9mm factory cartridge in 350 Legend chamber.




Once fired in some other firearm 9mm case in 350 Legend chamber.



350 Legend cartridge in 350 Legend chamber.






350 Legend vs 9mm cartridges.

 

[arakboss]

@Will_White has proposed using a 5.45x39 bolt along with a 9mm barrel and standard barrel extension to function as a single shot 9mm set up. I like the idea except for the prices involved and messing around with barrel extensions.

I have extra 5.56 bolts and would be willing to sacrifice one of those bolts to try out running 9mm in a 350 Legend barrel, if I thought the chances were high that it would function like running 40 S&W in a 10mm barrel. The advantage of this route for me is that I already have all the components needed. The only real work involved would be to open up the 5.56 bolt to fit the 9mm rim (about .010).

If I wanted to try out the idea before ruining a perfectly good 5.56 bolt, I could file down the rim of a few 9mm cases to fit the 5.56 bolt. That wouldn't be a completely fair test as the rim diameter reduction might impede the ability of the extractor to hang on to the case. If the extractor was able to hang on to the case even with a shaved rim that would bode well for it working with unmodified cases. It would also give me an opportunity to fire form a few cases and see if they get mangled or not. If the brass fire formed well I could try reloading them a few times to see if they continue to hold up.

 

[arakboss]

This is the cheapest entry I have found for a 5.45x39 bolt. I could borrow the assy parts from my extra 5.56 bolt kit. Is it worth $45 to save the labor of enlarging a 5.56 bolt @Will_White ?

5.45x39 Stripped Bolt | Red X Arms

www.redxarms.com

 

[Will_White]

This is the cheapest entry I have found for a 5.45x39 bolt. I could borrow the assy parts from my extra 5.56 bolt kit. Is it worth $45 to save the labor of enlarging a 5.56 bolt @Will_White ?

5.45x39 Stripped Bolt | Red X Arms

www.redxarms.com

I'm not a fan of modifying pressure bearing components so I'd go with the 5.45 bolt, or file down the rim on 9mm to test it out.

 

[arakboss]

I'm not a fan of modifying pressure bearing components so I'd go with the 5.45 bolt, or file down the rim on 9mm to test it out.

Great point. I will test a few cases after taking their rims down a bit.

 

[DLS]

Unless you have a quality lathe or mill it will be very difficult to keep concentric while opening up a bolt, especially considering the hardness of the metal.

Just buy the stripped bolt is my suggestion.

 

[DirectDrive]

No.

Joe

No.
Not the 40 into 10 thing. That's been done many times without the shooter catching on fire or blowing up.
It's in reference to the other potential "experiments".

 

[red442joe]

No.
Not the 40 into 10 thing. That's been done many times without the shooter catching on fire or blowing up.
It's in reference to the other potential "experiments".

Ahhhh

Joe

 

[arakboss]

No.
Not the 40 into 10 thing. That's been done many times without the shooter catching on fire or blowing up.
It's in reference to the other potential "experiments".

I don't believe firing a 9mm cartridge in a 350 Legend barrel is going to be dangerous. It might not work but I see very few avenues that would lead to a kaboom situation. I am open to listening to specific problems with this idea that you believe would likely cause catastrophe.

 

[RX-79G]

I have read about and watched videos of people shooting 40 S&W cartidges in 10mm barrels. Both of these cases are designed to headspace off the case mouth. Why does it work, supposedly the extractor will hold the 40 S&W case against the breech face during firing.

This made me wonder if there is an analog situation that could be done in the AR platform? Assuming you had a bolt that would snugly fit the 9mm cartridge (5.45x39 bolt appears to), maybe it could be fired in the 350 Legend barrel. Both the 350 Legend and 9mm are suppose to headspace off the case mouth and they both share similar dimensions toward the bottom of the case. If the extractor on the 5.45 bolt would hang on tight to 9mm case it could potentially work. I would probably want to test the first one with a string pulling the trigger.

The answer to your question is the difference between controlled round feed and push feed. Most 10mm pistols are the former, all ARs are the latter.

 

[arakboss]

The answer to your question is the difference between controlled round feed and push feed. Most 10mm pistols are the former, all ARs are the latter.

Can you explain this in more detail how and how it might effect the feeding of a 9mm cartridge into a 350 Legend barrel?

 

[arakboss]

The answer to your question is the difference between controlled round feed and push feed. Most 10mm pistols are the former, all ARs are the latter.

This could be a problem I didn't think about. This article explains what you are talking about. I will have to reconsider this idea.

Controlled Feed vs. Push Feed Rifles - What's the Difference?

Chris from the Lucky Gunner Lounge team examines the differences between push feed and controlled feed rifles.

www.luckygunner.com

 

[RX-79G]

Browning tilt pistols must be control round feed because the round extracts in a different place on the breechface than it feeds.

 

[arakboss]

The answer to your question is the difference between controlled round feed and push feed. Most 10mm pistols are the former, all ARs are the latter.

One idea I had earlier that I felt was unnecessary is to run a spacer sleeve up into the 350 Legend chamber. The sleeve would fill the gap between the mouth of the 9mm case and the step where the 350 Legend case normally headspaces off of. The sleeve could be as simple as the top portion of a 350 Legend case. That might serve as a stop for the 9mm case to rest against and allow the push feed bolt of the AR to latch on to the 9mm case? If you wanted to remove the sleeve it would be similiar to removing a stuck case wall that sheared off.

Another method that might work is too remove the ejector from the AR bolt and hand place the cartridge into the bolt under the extractor. This would make for a very tedious loading process and would require flicking out the brass from the bolt after firing the cartridge.

@Will_White idea of using 9mm barrel with standard barrel extension is sounding easier by the minute.