Seating depth and Velocity

[ArtP]

Just curious. Has anyone measured, with a chronograph, the difference in velocity related to seating depth, or distance to the lands?

On paper, closer to the lands should create higher pressures, but does this translate to higher velocity. Also, longer cartridges may produce less pressure inside the case. There might be a trade-off.

Am just wondering if anyone has conclusive evidence they were able to prove to themselves with a chrono.

 

[USSR]

In my load development with my 6.5x55 Match Rifle, softseating bullets into the lands required about 1 grain less powder to attain the same velocity as seating the bullets .012" off the lands.

Don

 

[Walkalong]

You need good start pressure for good consistent burns which helps equate to small ES & SD numbers.

Neck tension is one way, seating into the lands is another, or a combination of both.

In 6PPC we used very light neck tension, which makes it easier to have a smaller variance percentage wise, and seated bullets at or into the lands. One rule of thumb we had was to seat bullets until the lands made a "square" mark on the bullets as a starting point. Tweak as needed.

If you are going to seat against or into the lands, work up the load like that from the beginning.

If you change and seat the bullet against the lands after working up a load, reduce the charge and work back up, just like we should do with any change.

 

[gamestalker]

I've had some really good results by seating up into the lands to the extent that an indication of contact is clearly visable, and then backing off .002". This has produced super consistent velocities. I do however use common sense regarding my starting charge, in that I start at the lower end of the data.