do you ever end up with way less velocity than is published?

[Dake21]

I'm interested about why certain barrel gives faster or slower muzzle velocity. Is it in the design of the barrel or it's random?

 

[Chilly807]

To the OP's question, the brand of brass you're using can have quite an effect on velocity. My .243 Tikka shows noticeably lower velocity with Winchester brass than with Federal, with Lapua being slightly slower than Federal. All cases have had the primer pockets uniformed and deburred, however the volume of the cases is also different. My Winchester cases have the largest volume, with Lapua and Federal having lower volume.
I'm experimenting with loading different brands of brass with different powder charge weights to get the same velocity. Once the Federal and Winchester brass is gone, I'll probably use Lapua exclusively if it is available. Nice stuff.
I've also noticed lower than book velocities with the Tikka, part of which I attributed to the shorter barrel. The only book that's given me roughly what I expected from a given load was the Sierra manual. Hodgdon wasn't too far off either as I recall.

 

[RePete]

Comparing manuals will fry your brain. I've been cross referencing Hornady and Lyman. Some Lyman 150gr 30-06 loads show 4 gr more RL19 than the Hornady does for RL17. IMR4064 very close though.

Look at the equipment used to obtain those numbers. Hornady use a 300 yard indoor range and dopplar chrono. They may use a pressure gun or an actual rifle.

 

[dan belisle]

I've been in the hornady test cell. Underground range (pretty cool set up, actually). They had a pressure gun set up off to the side, but were using actual rifles while I was there. The 30-378 was a new factory round at that time, and they asked me if I wanted to take a few shots. Got a tour of the factory, it was a nice experience, very nice people. - dan

 

[jethunter]

I'm loading my t3 lite 300 win mag with 185 berger classic hunters. I loaded them over 72.6 grains of h4831sc and each was measured on a calibrated gempro 250 my chronograph tells me 2785fps with little spread. Hodgdon lists the starting load for 190s as 69.0 grains producing 2795fps, the max is 73.0 for 2923fps. with a barrel that's 24 3/8" I wouldn't expect to be slower than the published start load with a near mac powder charge.
I also shot some factory 9.3 through a 20 inch barrel and got 2250 so that's about what I was expecting, just the 300 seems off
do you guys find you are way under book values for seemingly no reason.?

Usually published data is close but sometimes not so close to individual rifles. Seems like there was more discrepencies with older data. The advent of low cost personal chronographs about 30 years ago might have had some bearing.

Getting a chronograph and checking some of my "best" loads years ago was eye opening. Notably a 30-06/H4831/180gr load that was 250 fps lower than the Lyman book said it would be. every 30-06 I tried that load in was 200+ fps lower than Lyman's numbers. In hindsight it should have been obvious H4831 wasn't well suited to that load.