5906 and 4006 compatibility

I have read here many times that there is very limited compatibility between the two models, but that the slide from a 9 should fit on a 40 but not vice versa... well, I found that to be not quite true... Bought a 4006 recently and then a 5906 came through the shop so it was... serendipitous and I tried to mix and match.

No, the 5906 slide will not fit on a 4006 frame. The reason for this is the locking lugs on the 9 barrel are wider than the slot in a 40 frame. They can be filed down I expect - in fact I intend o try at some point in time when I get my hands on a spare 9 slide.

The really amusing part for me was that the mags are not interchangeable - minor changes in geometry so 40 doesn't fit in a 9 magwell and vice versa.

Took some pictures of the differences - hope it helps someone in the future. (4006 is always on bottom or right)

ltkatz said:

The really amusing part for me was that the mags are not interchangeable - minor changes in geometry so 40 doesn't fit in a 9 magwell and vice versa.

Click to expand...

The 59 series mags won't fit in a 4006 magwell?
I had used 59 series mags many times way back in the day when 11 round 40 mags were 1) very hard to find and 2) very expensive due to the AWB.

ltkatz said:

Click to expand...

Nope, won't fit on mine. It looks like the magwell on 4006 is more beveled and the 5906 mag ends up being too wide at the edges for it.

No problem with 5906 mags fitting in my 4046TSW with a PC9 upper.

You are all three correct, but you have just scratched the surface.

S&W tried hard to make the 4006 series look like a twin to the 5906 series.

The barrel of the 40 ended up being slightly larger in diameter than the 9, so S&W needed to enlarge the slide by a commensurate amount.

The 40 slide is slightly wider and taller than the 9 slide.

That is why the 40 slide needs that oval plate under the rear sight to retain the springs and plungers for the firing pin and mag safeties so as to keep the same geometry on the action parts.

The 40 and 9 slides both have front and rear rails, but the front rails on the 40 are wider spaced than the 9.

That is why the 9 slide will fit in to the 40 frame, but will not engage the front rails.

Obviously, the 40 recoil spring tunnel is wider on the 40 slide than the 9 so consequently the front rails are too wide to fit in to the 9 frame.

Another slide difference is the pressed in barrel bushing.

Because the 40 barrel is larger in diameter, the belled area at the muzzle is larger.

Consequently, the 40 bushing is larger in diameter.

The 9 barrel is loose in the 40 slide and the 40 barrel won't fit in to the 9 slide's bushing.

Because the unlocking cams needed to be stronger on the 40, they widened them, leaving the area in the frame between the cams (lugs) narrower, where the corresponding area of the barrel slides.

So as to not widen the 40 frame, S&W narrowed the underside of the 40 barrel.

The 40 barrel will fit into the 9 frame but the 9 barrel must be narrowed to fit the 40 frame.

All of the fire control parts interchange with the exception of forged spur hammers.

S&W discovered during live fire testing of the 40 that the forged spur hammer was striking the underside of the slide in a vulnerable area.

It was determined that the mass of the forged spur hammer was to blame and S&W was forced to substitute a lighter hammer.

So while the fire control parts will all fit and function between the 9 and 40, the 9 forged hammer should not be installed in the 40.

Working our way down to the magazines.

Obviously, the 40 mags have the "pimple" on the front to preclude their insertion in a 9 magwell.

If you closely examine the rear corners of the mags, you will notice the 9 mags have square rear corners and the 40 mags have rounded rear corners.

The front to back and side to side dimensions are the same.

On very early production 40s, S&W rounded the rear corners of the magwell so the 9 mags could not go in.

For reasons unknown to me, S&W later changed the production spec on the 40 magwell to squared rear corners.

That's why most folks will tell you that the 9 mag fits 40 pistols.

It does, on later production 40s.

S&W tried pretty hard to make the 9 and 40 models look alike, so much so that it has prompted some of the uninitiated to scoff and say the engineers just stuck a 40 barrel in to a 9mm pistol.

On the "drill down", that is obviously not so.

John

John, your depth of knowledge on S&W's development of the .40cal pistols is fantastic and so specific, it almost seems like you were on their team when it was all happening.

Sevens said:

John, your depth of knowledge on S&W's development of the .40cal pistols is fantastic and so specific, it almost seems like you were on their team when it was all happening.

Click to expand...

I'm not sure I was there with them, but I do have a vague recollection of serving under General George Patton when, in a previous life, he was Hannibal of Carthage and we were crossing the Alps.

I was the guy with the pail and shovel, following behind the elephants.

John

Your Hannibal memory made my day.
Thanks for the info and for taking time to instruct us. It really is appreciated.
BrianD

Brian Parrish said:

Your Hannibal memory made my day.
Thanks for the info and for taking time to instruct us. It really is appreciated.
BrianD

Click to expand...

It is gratifying to be of service to my fellow enthusiasts.

John

JohnHL said:

It is gratifying to be of service to my fellow enthusiasts.

John

Click to expand...

So you're saying that you finally -DO- wish to buy my 2001 Concours?!

Come get it!

Sevens said:

So you're saying that you finally -DO- wish to buy my 2001 Concours?!

Come get it!

Click to expand...

Sure, I'd love to have a ZG1000 Concours.

A Ninja motor set up as a shaft drive Sport Tourer.

I've ridden 'em, but I never had to fix one 'cause I've never seen a broken one!

A little more genteel than my last bike, a 2001 Yamaha FZS1000 (FZ1).

An R1 engine in a "Naked" frame.

Big, tough, and fast.

Great fun.

But I sold it probably for the same reason you want to sell yours.

I just wasn't riding it enough to justify keeping it.

When I was working 70 miles roundtrip six days a week with other activities, getting there on a bike was the way to go!

But now that I'm retired and I live in a place where I would want to ride to every day, I wake up and I'm already here.

Thanks for the offer though, because the Concours was one of the hundreds of bikes I admired and I thoroughly enjoyed riding, out of the thousands I've had between these two very fortunate legs of mine.

John

JohnHL said:

If you closely examine the rear corners of the mags, you will notice the 9 mags have square rear corners and the 40 mags have rounded rear corners.

The front to back and side to side dimensions are the same.

On very early production 40s, S&W rounded the rear corners of the magwell so the 9 mags could not go in.

For reasons unknown to me, S&W later changed the production spec on the 40 magwell to squared rear corners.

That's why most folks will tell you that the 9 mag fits 40 pistols.

It does, on later production 40s.

S&W tried pretty hard to make the 9 and 40 models look alike, so much so that it has prompted some of the uninitiated to scoff and say the engineers just stuck a 40 barrel in to a 9mm pistol.

On the "drill down", that is obviously not so.

John

Click to expand...

Your knowledge (and confirmation) is very much appreciated. You described the difference in mags and magwells much better than I did

Do you know where the "early" 40s productions with the rounded magwells ended? If it's not clear in the pictures mine is a TFD 1703 (I don't mind, it is registered with the Canadian government anyway) it came to me appearing unfired in the original box with the spare mag still in the wrapper ...

ltkatz said:

Your knowledge (and confirmation) is very much appreciated. You described the difference in mags and magwells much better than I did

Click to expand...

You're welcome.

I'm glad to help when I can.

BTW, I apologize for "hijacking" your thread, but your comments and pictures indicated to me that you are a serious and scholarly student of these 3rd gen pistols with an eager curiosity (like me) and I had hoped that by sharing information (and perhaps, incentivising other members of this Forum to share theirs), we might increase the dissemination of this historical knowledge before it is lost to time.

Do you know where the "early" 40s productions with the rounded magwells ended? If it's not clear in the pictures mine is a TFD 1703 (I don't mind, it is registered with the Canadian government anyway) it came to me appearing unfired in the original box with the spare mag still in the wrapper ...

Click to expand...

I don't know, but your question is a provocative one and hopefully, other members will contribute with observations of "rounded or square" mag wells, serial numbers (at least prefixes), and ship dates to narrow down when the change occurred.

Based on observations, my earliest 40 is a model 4006 (TFF5442) with a ship date of 02/92 and has the rounded mag well.

My "next oldest" is a model 4043 (VDL4770) with a ship date of 03/96 and has the squared mag well.

Interestingly, according to S&W c/s (when they were still divulging this info) they both went to the Taunton, MA PD, although I got them both in 02/16 (from different sources), so possibly that was when that PD was liquidating a bunch of "older" pistols.

Acknowledging the oft repeated caveats that S&W did not necessarily ship in serial number order and "never say never" with S&W, I can only assume it happened sometime in the intervening four years and might possibly have been (at least partially) in response to the 1994 "AWB" as alluded to by snw19_357 in his post.

All of my other 40s have later ship dates and all exhibit the "squared" mag well.

John

Fascinating info for us S&W semi-auto fans. Years ago, a gentleman at S&W by the name of Jim Rae told me the DPA 5906 guns were built using the .40 S&W frames and slides. He indicated that was because they wanted the 9mm PC guns to be stronger than production 9mms. Something about slide/barrel being locked together during firing for a tiny bit longer than production 9mms too. Been a while since I had a production 5906 and 4006 to compare, and never thought to compare parts back then. I appreciate all the info you guys have provided..

I don't have manufacture dates, but my 4006 has rounded mag wells and 59 mags will not fit. My 4013TSW has square mag wells, and the 59 and 69 mags will fit and lock into it. My buddy also bought a 4013TSW and it to has square mag wells. In fact, he bought some "modified 6906" mags from someone to use in it. Not sure if all 4013TSW are square or not.

Rosewood

rosewood said:

I don't have manufacture dates, but my 4006 has rounded mag wells and 59 mags will not fit. My 4013TSW has square mag wells, and the 59 and 69 mags will fit and lock into it. My buddy also bought a 4013TSW and it to has square mag wells. In fact, he bought some "modified 6906" mags from someone to use in it. Not sure if all 4013TSW are square or not.

Rosewood

Click to expand...

All TSW models were produced after the "round-to-square" magwell production change.

Dr. Jinks is looking through the Engineering Changes files for me to determine when the change was made and why.

He tells me it will take some time.

John

.40 mags fit and function great in all my PPC 9's.
Tom