Vihtavuori 3N37
This is a powder to buy if you want higher velocity ammo in 9 MM in all weights.
This is a smaller Stick powder
A lot of powder can fit into the case, for a stick powder..
10 grains fills the case
There is no load you would actually want 10 grains except possibly 65 grain bullets.  Stick powders like this, do not compress that well either
Not super dirty
Left is bullseye middle is 3N37, right is Unique.  Its average dirty.  Cleaner than Bullseye, and many others. 
3N37
A finer extruded stick powder.  A lot can fit into a case.  Since this is a slower burning powder, you need a lot of powder to get higher velocity and it fills the case, causing compressed loads.  This powder is for loading higher velocity ammo.  It can do top tier velocity in most grain bullets, with the exception of perhaps lighter bullets because you run out of case capacity.  For this reason, its not maximum versatile for 9 MM.  Also, many +p or +p+ loads are compressed and will not accept a short overall length.  If you have a barrel that accepts longer overall length, this powder is better overall.
We did not find this powder to be anything except below average accuracy with many loads.  This powder is more picky on what load it shoots near 1 hole with.  However, this is just nitpicking, as even a 1" group at 5 yards is acceptable accuracy in a pistol.
This powder runs a hotter than most.  But this is not a big deal.  At least this powder is not that dirty and doesn't blacken everything. 
Overall, this powder doesn't make our favorite list for several reasons.  The main reason is, you can get many powders that perform similary to this, but are more versatile, don't compress the powder as much, are less expensive, and possibly more accurate.   Just speaking about 9MM only, this powder does not make a whole lot of sense.  N340 can almost match its velocity, reasonably close.   Too many loads with this are compressed, limiting its potential we think.  Its perhaps slightly too bulky and slightly too slow burning to be suited perfectly for 9MM. 
If you decide to use this powder, we would suggest using brass that has the largest case capacity available on the market.  So far, we see that Hornady brass has ~13.80 grains case capacity, generally.  Starline Nickel is around ~13.50 generally, WIN is 13.25 generally, and Xtreme brass is the least we found at around ~12.75.  You want higher, and if brass was ~14 grains capacity, you would want that.  You need all you can get with this powder...
Lets take a look at some of the brass...

10 grains
Lehigh Defense 65 Grain Xtreme Defender
1.100 OAL
Very compressed load
1715 FPS and nowhere near its pressure potential
4" barrel
7.0 grains
Precision Delta 124 grain bullet
Federal Gold Medal primer (pretty flat)
1.107 OAL, compressed.  This is about as much powder will fit at this OAL
1295 FPS
4.5" Barrel
Primer in upper right, red case, is example of Fiocchi primer under low pressure, see how rounded it is?
7.8 grains
115 Grain Speer Gold Dot bullet
CCI500 primer
1.120 OAL, compressed
1310 FPS
4" Barrel
New Starline Nickel 13.5 case fill cap
Primer looks OK.  Firing pin swipe is normal on many, many guns

7.5 grains
115 Grain Hornady XTP bullet
Federal Gold Metal primer (pretty flat & cratered a bit)
1.106 OAL, compressed.  This is about as much powder will fit at this OAL
1380 FPS
4.5" Barrel
Primer in upper right, red case, is example of Fiocchi primer under low pressure, see how rounded it is?
3N37
These are using CX P10c 4" using stock 3 dot sights from rest at about 5 yards.  the ones that have a "4.5" in bottom right of target are using a XD(M) OSP 4.5" gun with VENOM 3MOA red dot. Accuracy was below our tested average, but high velocity but acceptable. Similar to commercial bought premium ammunition in accuracy.
3N37 Loads
Some of these loads, many of them, are above book, manufacturer recommended pressure loads and potentially unsafe.  Loads are all made at your own risk, and we recommend you never load above maximum manufacturer recommended loads.  Here are some of the loads we tried with this powder..
3N37 Loads
As one can see, we shoot this often, trying out all kinds of above book loads. 
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