Howdy guys;
New here, first post.

I have a P320 compact in 357 Sig. I'm interested in an M18 with the manual safety, but only see them in 9mm.

Is the M18 convertible to 357 Sig with a barrel and magazine swap?

Thanks.

Until someone more knowledgeable comes along my answer is NO. You can convert a 40/357 down to 9mm but not the other way around.

quote:

Originally posted by Itsjustme55:
Is the M18 convertible to 357 Sig with a barrel and magazine swap?

No. The slide and barrel profiles of 9mm and .40/.357 are different. With a 9mm slide, a .40/.357 barrel will not fit. With a .40/.357 slide, a conversion barrel can be used to shoot 9mm.

You can also add a manual safety to your existing P320 in .357.

Really ? How do I add the manual safety ?

A whole FCG swap.

AB Prototype will also do a MS conversion to existing FCU. Includes modifying of grip module.
I had it done to my X-Compact. Excellent job/quick turnaround

first welcome to the forum... P320 compact in 357 sig? damn I wish I could find one....

What I would wonder is the opposite of what you asked... could you convert what you have to 9mm with a barrel swap and 9mm magazine.... it's technically not supposed to work but will on some Sigs.... Like the P239 and I think it will even work on P226s with a 9mm recoil spring.

I don't have any experience with the M18 specifically, but I'm 99% sure that you can take the full upper (slide, barrel, and recoil spring assembly) off of your .357 Sig P320 and stick it on your M18 lower (FCU and grip module). Your .357 mags ought to fit in the magwell of either grip module.

You can swap uppers freely between 9mm, .40, and .357 P320s (Sig even sells "caliber exchange kits")...and the M18 is basically just a P320 Carry in baby barf brown with a fancy name.

Pretty much the above. As far as getting a manual safety, you're better off just buying a manual safety FCU. There's some on Gunbroker in the $250 range that should still stay under warranty and you can sell off the one you have or keep it for a spare.

The USGI M18 is 9mm only but is mechanically identical to the commercial 9mm P320C with manual safety.

BLUF (Bottom Like Up Front): Just go to the gun store and buy the "M18."

To "convert" your .357SIG version requires replacing every part in your pistol: a FCU with manual safety, a grip module cut for the manual safety, 9mm magazines, and a 9mm slide and barrel. I'm trying to see if ANY of your .357SIG parts are retained -- doesn't seen like it.

-- Chuck

quote:

Originally posted by Itsjustme55:
Is the M18 convertible to 357 Sig with a barrel and magazine swap?

If the M18 is equivalent to the P320 “Carry” (as I believe), then it could be converted, but in addition to the magazine, an entire 357 slide assembly would also be required.It’s not possible to switch between 9mm and 357 or 40 S&W with just a barrel change. In addition to other differences, the most obvious one is that 357 and 40 have larger case heads.

SIG does offer 357/40 “Carry” slides:
https://www.sigsauer.com/slide...ight-sights-blk.html
Recoil spring (evidently you could use the 9mm M18 spring):
https://www.sigsauer.com/sig-s...ring-assembly-1.html
Barrel:
https://www.sigsauer.com/p320-compact-357-barrel.html

So, yes, such a conversion is possible with (evidently) available parts.

In further addition:
You could move your present Compact slide assembly to an M18 lower (as mentioned above). You would then of course need to use the 357/40 magazines with the conversion.

quote:

Originally posted by Vette02:
AB Prototype will also do a MS conversion to existing FCU. Includes modifying of grip module.
I had it done to my X-Compact. Excellent job/quick turnaround

And that would be the least expensive option to use your current fire control unit.

From a cost standpoint conversion to manual safety makes little sense and changing calibers makes no sense to me. Just buy a new M18.

The AB Prototype manual safety conversion is just under $300 ($200 plus shipping which is roughly $40 each way) and complete P320 FCUs with manual safety are in the $250-$350 range not counting a grip frame cut for the safety. And to convert from .357SIG to 9mm still requires the complete "upper" and magazines.

AB Prototype converted my (factory upgraded) 2017 vintage P320 to manual safety a while ago and the FCU is indistinguishable from a factory version. Now that new FCUs with manual safety are available I doubt I'd do the conversion again and just buy another FCU.

New M18s are universally priced at $650 on Gunbroker and probably at your local big gun store.

-- Chuck

You don't need to get the M18 to get a manual safety. The P320 Compact has the manual safety in one of it's SKUs. It's usually listed at $549 on Gunbroker.