Seating depth and pressure?

[SHOOTER]

I have been told and read as long as I can remember. That if you seat your bullets "too deep" you will "rob" case capacity and increase pressure which logically  seems like it would be true but my experience always seems to say this is B.S. 

Everything my chrono, cases and drop at distance has told me is that the deeper that I seat the bullet the slower less pressure I have. The closer I get to the lands the faster and hotter the load. I've seen this in all my rifles that i have played with seating depth in. 

Example from this weekend loading for a 7 rem mag 

180gr Berger Vld hunting

69.7grs H1000

.030" off lands 2910fps 

.020- 2920 fps

.010-2930 fps

.005"- 2940 fps 

I've seen this over and over again. With my 338 edge. I can cram a 300gr smk down to an oal of 3.690" (ogive about to go below case mouth)  (90grs H1000) shoots great sub .5 moa at 2800 fps then I can hang it out to .010 off the lands at 3.850" oal (90grs H1000)  and shoot sub .5 moa at 2885 fps.

So why do people always get so set on worrying about seating depth and pressure?  What have you guys seen ? 

Thanks

 

[Couzer]

I’ve personally seen it, but different powders burn at different rates. All depends on what you are loading, so many variables.

[muledeerarea33?]

Some bullets are more accurate depending on how far they have to “shoot the gap” 2910-2940 isn’t much of a difference or a deal breaker either way. If your are consistently accurate at different depths then I’d personally shoot the higher velocity. But only if that consistency is out past the 3-500 range.

[recurveman]

changes in velocity can be caused by a TON of variables.   New barrels get faster for 50-75 shots.   If the load is compressed it opens up even more variables and they get extreme really fast.  cleaning the barrel during the session.  It has been my experience that if the only thing I do to my load is make it longer then I will be a bit slower.   Not a ton but a few feet per second.    The more I put the bullet into the case the more velocity I get.   Normally I don't care about the cause an effect that much.    I just want to make sure that the load is super accurate and that I'm not showing a bunch of pressure.  Honestly I follow velocity more for accuracy that anything else.    Once I find a certain speed for a bullet out of my barrel I want to make sure that I stay right at that same speed to get great results.    

[MMACFIVE]

Seating deeper gives more freebore thus reducing Pressure. Wheatherby has make a fortune this way. 

[L Cazador]

I think you may be misinterpreting this. Seating bullets with more jam or more into the rifleing will increase pressure. It's rare getting more pressure off the rifleing but it's possible with certain powders. In my 45 years of reloading this has always been the case. This is why I feel it's important to find bullet touch first and then work on seating depth.