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Discussion Starter · #1 ·
Unfortunately I live in Massachusetts and here we can only get the Sig P320 in 9mm or .45 and only in the compact model with the thumb safety. If you want any other version you need to source parts and make it yourself, including cutting a notch for the mandatory thumb safety and finding only 10 round magazines because anything else is a felony.

So here is my question I have the 320 9mm compact and would like to change over to the .40 S&W caliber, can I just change the barrel and magazine or do I also have to find a slide and recoil spring set? I have not found different recoil springs to order anywhere and the sig site doesn't have different ones in the shop only one available. I would rather pay the $189 and $44 for magazines then $407 for a whole setup and end up with an extra grip and slide if I don't need it...
 

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You will have to switch slides as well, as the breech face of the 9, where the cartridge base slides upward going into battery, will be narrower on a 9mm slide than on a 40 slide.

I don't own a P320, so the forgoing is assuming the breech face is made like most every other SIG pistol.

With guns like the P229 40, one can do the caliber switch with just a conversion barrel going to 9mm, as the cartridge doesn't care if the breech faces is wider than need be. But one cannot go from 9 to 40 without getting a 40 slide.
 

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Unfortunately, the 40SW barrel will not fit into the 9mm slide.

If you want to avoid paying $407 you can try and assemble it from individual parts from different sources. Barrels and slides are relatively easy to find. You can check the classifieds section of this forum, or places like ebay.
 

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Well that is sorta correct. As explained by bumper above - its really about breech face size.

A 9mm barrel will fit into the larger 40SW slide. Not perfectly, but it will fit and some say if shoots fine that way. Others say it causes extra barrel wear and accuracy issues.

Also, there may be a marking somewhere on the inside of slide that denotes which caliber it was made for - but Im not certain.
 

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Aah. The People's Republik of Massachusetts. It's amazing that the birthplace of our nation (New England - CT, MA, NY, NJ) have devolved into such tyranny. You are better off with a complete slide assy., since the 9mm and .40 shoot to different POA/POI and the sight may or may not be regulated properly for the ammo you are using in .40, and you will need a different recoil spring for .40.
 

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Why is the 40 not available to you in MA? The 9 will work in a 40 slide but the 40 won't work in the 9. I haven't had any issues with the former in full size 40 320s.
 

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Aah. The People's Republik of Massachusetts. It's amazing that the birthplace of our nation (New England - CT, MA, NY, NJ) have devolved into such tyranny. You are better off with a complete slide assy., since the 9mm and .40 shoot to different POA/POI and the sight may or may not be regulated properly for the ammo you are using in .40, and you will need a different recoil spring for .40.
Add Kalifornia to the list. We aren't even allowed to buy a new gun like the P320 because its not on the California DOJ List. We can purchase them from a Private Party face-to-face so a gun that normally cost $500 is $1,300-$1,500 if you can find one.
 

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Discussion Starter · #11 ·
Add Kalifornia to the list. We aren't even allowed to buy a new gun like the P320 because its not on the California DOJ List. We can purchase them from a Private Party face-to-face so a gun that normally cost $500 is $1,300-$1,500 if you can find one.
That is how mass is with anything newer than a gen 2 glock. The only ones we can get newer are private sale from LEO.
 

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Discussion Starter · #12 ·
Aah. The People's Republik of Massachusetts. It's amazing that the birthplace of our nation (New England - CT, MA, NY, NJ) have devolved into such tyranny. You are better off with a complete slide assy., since the 9mm and .40 shoot to different POA/POI and the sight may or may not be regulated properly for the ammo you are using in .40, and you will need a different recoil spring for .40.
Yeah, as of June 20th 2016 we cannot purchase AR-15s and Aks as well as a few other "assault weapons" because our AG Healey decided on her own that even though they have been sold legally in the state for years we are all wrong and they are too dangerous so no new sales. Technically you can't even build one because you have to register it on a fa10 form and none are allowed after 6-20-16.

When did we get so stupid as to hand over the rules of what equipment we will use to defend ours selves from our government to our government???
 
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