I am loading a 300 Win Mag with a 165 grain Hornady Interbond with 76.5 grains of R22. The loading manual (Hornady 6th Edition) gives this load approximately 3080 fps. The trajectory of my bullet suggests that my actual velocity is around 2950. How typical is this?

My rifle is as Savage 116 FSAK. I has a 24" barrel, but he last two inches are a factory installed muzzle brake. The brake can be turned off, by twisting it to keep gas from escaping. The bore of the brake is slightly larger than .308, so I'm assuming that even if the brake is in the off position the gas is not really pushing the bullet forward. Does this effectively give me a 22" barrel? Should I consider a faster powder to make sure it burns completely in my barrel?

Differences between velocities published in loading manuals can easily differ over 100fps from those that you might see in your gun.

I can't ever remember matching listed velocities with any of my handloads.

I concur with the other two posts, i.e. "Actual results may vary".

To answer your muzzle brake question, you don't count the brake in your barrel length.

I'm trying to think very hard, here, but I do not recall a SINGLE instance where my velocity was HIGHER than that in a manual.......

I do recall a 35 Whelen load with RL15 that was 250 fps SLOWER. Quite a surprise.... FWIW, Dutch.

The velocity listed in the manual is EXACTLY the velocity obtained with the specified load, fired in the specified gun. The results with a load that replicates (as closely as possible) the load in the manual will always be somewhat different when fired in a different gun. Add to that the differences in lots of powder, capacity of brass, heat of primers, etc., then you have even more variance.

Some manuals use ordinary rifles for their velocity testing while others use universal receivers and SAAMI-standard chambers. A factory rifle chamber, even when barrel length is the same, tends to produce lower pressure and velocity than a SAAMI chamber simply because it is usually bigger, the larger capacity translating into a lower expansion ratio.

Do you need a faster burning powder with your 22" (effective) barrel? No. All of the powder will burned in the first few inches of barrel, so the velocity loss as compared to a longer barrel will not be particularly different with a faster powder; and as tests have shown time and again, the optimum powder burning speed for a given caliber is the same with any barrel of legal length.

If you go to Table #1 on my pages, you will see some of the results I have obtained with some of my favorite loads. At the bottom of each is the data from different reloading manuals, and the data I personally measured ... there is a great deal of difference in many of them.