I'm looking for a perfect balance of effectiveness (db reduction) with a low as possible length for my 300 blackout SBR (9" MPW). It looks like both the SDN-6 and Sandstorm have very close overall lengths and performance but Gemtech doesn't list the added length openly like AAC does for the SDN-6. Anyone able to measure theirs for me (lol)?

The OAL is 7.8", but the length added will be less because a portion of the barrel of the host has to insert into the supressor...this is what the OP is asking for.

Sadly OP I can't answer that for you, but I can give you some observations that guided me to the 762SDN-6:

1.  The 762SDN-6 is a QD mount can, with a ratcheting locking mechanisim to keep it from backing off during usage and getting a baffle strike.  The Sandstorm is a screw on can, with no locking mechanism.  And if you are going to use it on an AR the host rifle can't have a flash hider or brake.

2.  The 762SDN-6 works with a brake, to act as a sacrificial blast baffle to reduce baffle erosion.  This isn't an option for the Sandstorm.

3.  The 762SDN-6 is Inconel in construction...which while weighing more than Titanium is significantly more resistant to heat based erosion.  Inconel was designed for turbine blades in jet engines...

4.  The Sandstorm is significantly lighter.  Not saying that the 762SDN-6 is heavy, but I definitely notice it on the end of my rifle.

5.  The 762SDN-6 is rated for full auto 7.62 NATO.  Sandstorm is not.

6.  The 762SDN-6 is cheaper.

If I were looking for a suppressor for my bolt gun...that I'd be carrying hunting...I may lean towards the Sandstorm.  Even then it would be a head scratcher.  For anything else I'd go with the 762SDN-6.  That's what I went with for my 10" 300blk SBR and I couldn't be happier.