Looking to the past when pistols and rifles (Carbines) shared the same caliber ammunition I now want to accomplish the same goal.  My first choice is an AR in 357 Sig but my research found problems with pressure and discussions on whether this round should be gas operated or blow-back.  Not the same issues with the 40 S&W, done all the time and blow-back system is standard.  But, I still keep coming back to the 357 Sig....  FYI: It will NOT be suppressed.  I DO want a carbine and not a pistol so a 16" bbl is what I'm looking at.  

Questions for you guys (gals?):

I can have a custom bbl turned down for this project.  What is the ideal rate of twist for 124 - 147 grin bullets?

It seems like an easier way to go is to go the buy an already contoured 9mm Para barrel and have it re-chambered?  40S&W bolts are not hard to find and all a 357 Sig is basically is a 40 necked down.  

A heavy buffer "might" mediate some of the pressure issue and allow me to do a blow-back design, but I just don't know?  A gas system might be the way to go, but, that complicates the build.

All in all I'd like a 357 Sig carbine but would settle for a 40 S&W if I can't have the reliability I require from all my builds.

What advice do you talented people have?  No use reinventing the wheel.

Thanks in advance,
Bill

My advice would be to contact RonaldMWilliams of RMW Extreme.
He builds custom DI pistol-cal uppers.

+1 to what echo said.
I would also only do it in DI as it will shoot better  with less recoil. I have shot one in FA and it is amazing the lack of recoil.

RonaldMWilliams of RMW Extreme

Good idea.  I'll contact him for advice.   I have so many spare parts on hand I like the idea of building it from scratch...plus it would give me a winter project.

Thanks,
Bill

ADCO opened up a 9 MM bolt for my 40 S&W build.

Good to know, thanks.  How about a good source of 9mm bbl blanks?

How long a piece you want...... just got a pallet in truckfreight yesterday...........9, 40, and 45......

I think an 18" should machine down to a 16" blank quite nicely!

shoot me an [email protected] know I have a 17  x 1.250 9mm 1/10 twist I can spare.....

I have built DI 357sigs for the Air marshals service & 40S&Ws for the FBI along with the Boarder patrol.

Very good.  Can you send me along a price list for an upper?  PM Sent with email address attached.

Bill in OR

im doing one in 357 auto cut down 223 brass to 357 lenth load as 357mag
making a plastic block to fit in ar mag a 20rd steel mag and useing a spring from a m1 carbie .mag
the plastic bit works as a feed ramp .
still working on placement of gas port .
load useing 223 shell plate and 357 mag dies
shooting 158 gr

Will a 6.8 bolt work for 40/.357 sig DI uppers?

It should..... .002 difference in max case head diameter........




Check out the .357 AR thread on weaponsguild.......

A 6.8 bolt makes that part of the build pretty easy and readily available.