I picked up 2k of 165 FMJ .40 S&W bullets at a good price just for practice use and am doing a big run of .40 on my 650 to build up a good supply of match and practice ammo.  What do you guys find when you are using identical powder, primers and cases & only dropping down to a lighter bullet.  With the same charge, are you getting close to the same velocities?  I've noticed in all of my manuals that with everything else being identical, the lighter weight bullets are indicating a heavier charge of powder.  If the OAL and powder charge stay the same, how close would velocities be between a 165 & 180 grain load?

I'm using Titegroup and I don't see any info for titegroup and 165 & 180 loadings for FMJs

Thanks for any experience you can offer before I start to do a work-up

Bueller? Anyone with any experience with this?

I reload .40 for competition, but I use 180s exclusively.  You may have to work up some loads and test them to get the answers you want.

Look at Hodgdon's website for data for Titegroup and your bullets. To get the info you need, you're probably going to have to load up your bullets and use a chrono to test them yourself.

I shoot .40 S&W in USPSA Limited.

.40 S&W is a high pressure round with very little margin for error when it comes to charge weights, OAL, and the powder you are using.  I primarily only use Vihtavuori N-320 and Accurate Solo 1000 when loading for .40 S&W, and only 180 grain bullets to make major power factor.  I first had to find an OAL that would reliably feed in my gun.  I started with a mid range load of powder and the SAAMI OAL, which I believe was 1.135.  Has failures to feed with rounds this short, so I incrementally brought out the OAL (keeping the powder change the same) until I found one which fed with no issues, which for my gun ended up being 1.160".

Because I had brought out the OAL, I increased the internal volume in the case, which dropped the velocity to below where I wanted it.  I slowly and methodically loaded some rounds with incrementally larger powder charges and my new OAL of 1.160" until I started to see the velocity I was looking for.

If you load a 180 grain and 165 grain bullet to the same OAL, the 165 grain cartridge is going to have a slightly greater internal volume, and if you load the 165 with same powder charge/type as the 180, the 165's velocity will generally be less.  This is why you generally see higher powder charges for lighter bullets.

The reason you're not seeing Titegroup in any reloading manuals (and I just checked my Hornady and Sierra books) is it's a little too fast of a powder for .40 S&W.  So is the N-320 I load - Vihtavuori has no 180 grain N-320 load, they recommend N-330, a slighly slower powder.  However if you look at the container of Titegroup, you'll see a MAX load data for .40 S&W.  Lots of guys I shoot with load their .40 ammo for matches with Titegroup.  Just make sure you work up your load!  Don't just start with anyone's interwebz recipe for Titegroup.  I don't know what kind of gun or division you're shooting, but it would really suck to KB a STI race gun with too hot a charge of powder.

Lots of good .40 reloading info here:Clicky

This is why I stated in my OP that it is not listed on their site

This is what I was thinking to be the reason...thanks for the affirmation of what I was seeing/reading/thinking.  In making up some dummy rounds the OAL came out the same between the 165 & 180s.  Figured the velocities would drop off a bit due to the greater internal space created.  I just wanted to load up these 165s for practice & gun break-in without making any adjustments to OAL or powder drops.  I will make up a few to chrony

ETA...I am loading for an STI 2011

I wouldn't imagine much change at all, Ive noticed my powder load is almost identical between .40 and 9mm. Even when I play with bullet weights. I use lead 180gr. 4.4gr of WST or AA2