Rechamber a American Derringer M-7

[Patton]

I have an aircraft aluminum American Derringer M-7 in 380acp.  While this gun is a sob to hang onto at 7oz, I really wish it was a larger caliber. So I would like to have it rechambered in 9mm or 38spl.  I would prefer the 9mm and I believe it would be the easiest to do.  The chamber walls are pretty thick, AD chambered this same size stainless barrel and frame in magnums, 44, &45.  The aluminum barrels were 22,32,380,38, and 44spl.  So none of them were as high of pressure as a 9mm but I believe it can handle it, the walls are about .25"

So can anyone recommend a gunsmith for the work or know about what it would cost to rechamber the upper and lower barrel?  Anyone see an issue since this is aluminium?

[RED333]

380 max pressure 21,500 psi (148 MPa)

9mm max pressure 235.00 MPa (34,084 psi)

38 spl max pressure 17,000 PSI

With ALU the more you work it the harder it gets and becomes brittle.

 

The 38 "might" be OK, but you are extending the chamber into the barrel.

I carry a 25 ACP, it is a "get off me" pistol.

380 is enough to do the job.

[Patton]

I have studied those pressures, kind of makes me worry. Truthfully I can't imagine ever putting more than 100rds through it ever. I know the 38 would work, the aluminum barrels came chambered in 38. What intrigues me is I would most likely have the smallest lightest 9mm in the world, not to mention bullet selection. Also, I am going to try to carry a 9 all the time, this being a BUG.

[Joe357]

JMHO, I think you will be hard pressed to find a gunsmith that will do what you are requesting because of liability issues.

What you are looking to do could cause the gun to blow up even on the first round. If it has a steel barrel maybe but not aluminium.

[Jonnin]

I think you are looking at a barrel replacement instead, I would not trust this.  Which probably would cost the price of the gun.  They make stouter derringers --- buying one would be the answer IMHO.

 

Another issue is the closing mechanism may not be sturdy enough for the 9mm.  

 

If its a try it once, load it, and hope you never use it again,  MAYBE you could get away with it.   It would probably take a *few* standard pressure 9mms without blowing up after modification.   But even shooting one box might be enough to cause a failure and certainly +P is out.  You could have him bore the chamber extra deep so it does not engage the rifling right off, that jump would help a little with the pressure, or heck, even make it a smoothbore, that would probably do it.

Edited November 24, 2013 by Jonnin

[Patton]

I am afraid you guys are right, which has been my thought for awhile as well. While the American Derringers are over built I still suspect the 9mm was never chambered with a M-7 intentionally. What is the strength of a pot metal cobra compared to my aircraft aluminum AD? That is what has made me interested in the chamber reaming anyhow.

[Jonnin]

not easy to answer without exact materials used and thickness.  And the process used to make it could even have an effect.   It would take some doing to determine a comparison. 

[Patton]

And of course hard to do that without testing and destroying the weapon to begin with.

[peejman]

That's a nearly 60% increase in pressure/stress. That sounds like a lot, but one could assume the gun was originally designed with a safety factor of at least 4. Calculating the stress is pretty straightforward, you just need the geometry.

That said, I doubt you'll find a smith that'll do t because of the liability.

You do realize that the .380, 9mm, and .38sp are all the same diameter, right?

[Patton]

You do realize that the .380, 9mm, and .38sp are all the same diameter, right?

That's the only reason I think it may be worthwhile, the chamber would need to be lengthened and slightly widened for a 9mm to headspace. Truthfully, the 38 could be done but it's not worth it. Not much gain and extra work over the 9mm to accommodate the rim.

I reload and could actually reload 124gr in a hot .380 casing, but I would rather it be a designated 9mm gun.

Changing the barrel is an option but barrels are $250 and appear to be machined into the hinge. plus the barrel will be stainless making it a 10oz gun over the original 7oz.

[peejman]

It's your gun to do with as you please, but I guess I don't see the point. You've stated that it's a bear as a 380, anything more powerful is just going to be worse. I view a derringer as a "get off me" gun at best and I see little advantage in moving up to 9mm.

[Patton]

While 9mm wouldn't be a huge improvement over a .380, I would like the most powerful two shots possible if that is all that I had. The 9 would use same rifling as the .380 so it would make the most sense, otherwise two shots of 44spl or 45, or some other big low recoiling bullet would do best. Part of it is just wanting to tinker but I would venture to say I would have the lightest 9mm pistol in the world. And the recoil I was not looking forward to, with the .380 it is snappier than a LCP. Accuracy is pretty good for a derringer, basketball size groupings at 15yards.

I am curious if anyone has shot the same gun in .380 and then the exact same gun in 9mm? Something like a LC380 and a LC9. Just curious how much more recoil is in a 9 over a .380. I know a 9mm revolver feels closer to 357mag then 38spl.

[Jonnin]

Ah!  A custom 380 IS the way to go.  The top 380 PSI is much higher than most load data and most american 380 ammo is super weak.   You can make some that is much better than off the shelf 380 and it is still safe to shoot.  You can even exceed that a little bit safely, as the saami pressure is "safe" which means there is a margin of error over and above that before things start to go wrong.   You cant go all 9mm+P on it but you can get it "pretty close" to standard pressure 9mm, probably 85% of the way or more.

 

380 pressure is safe to AT LEAST 23k (top end of the tested ammo saami pdf)   My load data sheets for 380 have 21k as the max pressure on their top loads.    25-26 seems to be toward the top best I can tell but you should read their pdf yourself to be sure, I just did a quick look. 

 

Its not easy to measure pressure though....  

 

I am not recommending blowing the thing up here.  Be very careful if you go this route.  The reason the load data and off the shelf ammo are weak is to avoid damage to pot metal pocket rockets of yesterday, but even so,  yours was designed to some maximum and beyond that lies danger.

Edited November 25, 2013 by Jonnin

[Guest Bonedaddy]

Someone explain to me why 9mm pressure is so damn high, please.

[peejman]

Someone explain to me why 9mm pressure is so damn high, please.

 

Because they wanted the bullet to go really fast.

[Jonnin]

Someone explain to me why 9mm pressure is so damn high, please.

 

Or, you might ask why so many "modern" pistol rounds are so weak compared to their potential if they all were shot at 9mm pressure levels...? 

[Patton]

I have decided to just leave it the way it is at least for now. While it may be capable of handling the 9mm pressure I don't really know if it worth any expense to do the modifications. It is actually a sweet gun the way it is, a slight hair bigger than a NAA mini mag and weighs abou the same.

[tnhawk]

It would be difficult to find a gunsmith to do the work.  The difference in pressure for the 9mm is too great for me to want to trust it.