Saw on the net where this HST load was tested in a 3" Kahr and came up with 970 fps +/-.

I just shot ten loads in my 3.5" C9 and only came up with 955 fps.
One test had it running at 990 in a 3" !!

I will put it across the chrony again to make sure of the low readings but has anyone else had low readings with the +P factory load in a barrel of 3.5 or less?

Just that the low on one was at 944 fps.............not a good thing. That is a standard HST load reading.

Major ammo cos. load to pressure & not velocity. YMMV.

Just remember the 147 grain 9mm bullet is preferred with suppressors. The heavier bullet travels slower, and through a suppressor it will make less noise than a faster, lighter bullet.

For a 3-3.5" barrel look at 124 grain rounds. +p may give you more FPSs, but the bullet may exit the muzzle before all of the powder is burned. If you're going to use a 3" or 3.5" barrel, then consider Speer Gold Dot's short barrel rounds. Speer makes a 124 grain +p 9mm round for short barrels. Here is the ballistics table for that round.

Honestly, 955 vs. 970 is no more than I would expect for a normal shot-to-shot variance in the same gun, let alone between two guns. Their chrono results came from their test gun, whatever it may have been. It was not your gun or any other, similar gun, and the velocities will vary not only shot-to-shot but gun-to-gun. Either 955 or 970 fps is stepping out pretty good for a short barrel.

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Pisgah

I haven't tried that round, but FWIW, my CW9 shoots 115 gr Critical Defense right at 1000, and I get 1100 from my standard M&P.