How much should I reduce my starting powder charge when working up a load with a bullet touching the rifling?

With drive band bullets, none.

With most Bullets, the Starting Loads in the Manuals are fine.

Best of luck to you.

Seating bullets against the lands are generally not recommended, as it elevates the peak pressure even though you start out with a "start load" since there is no inertia to engage the lands for one, and for another, the engraving resistance of the bullet is higher than with drive band bullets such as those of GSC.

Non grooved Monolithic Solids, such as those made from bronze or brass (being harder than pure copper), have the highest engraving resistance and should have at least a 2-mm jump. Lead core bullets can be seated closer as the benchrest shooter are doing, but it is still not a good idea to touch the lands. Why introduce a planned spike in the pressure curve?

Warrior

Rick
When loading for my 25-06 I make up a dummy round to check my seating depth. The technique I use is to seat the bullet way long, I keep adjusting the seating stem until the round chambers with resistance. Then I start smoking the bullet to check rifling engagement. When the round chambers easily and there is just a minor indication of engagement with the rifling, I lock the seating die down and start loading for testing.

Never had a problem.
Jim

Hey Rick, Are you talking about Match Grade Target Bullets or Bullets in general?

I have a 30-30 Contender carbine that has .010 excess headspace, not a lot but I want the stretch to occur in the shoulder of the case and not the web so I am using a 170 grain corelokt seated to heavily engaqge the rifling to headspace the case on the first firing. I started 10% below the max charge reccomendation using 4320 and worked up to 32.0 grains before the primer seated flush with the case head. I now feel the whole problem was caused by pressure being to low, IE protruding primers.

Not all gun/bullet combinations like to be seated out that close to the lands. My .270 WSM I started at .010" off the lands. As I seated the bullet deeper , the accuracy tightened up. At .060 off the lands, my gun shoots .25" MOA at 100, and shoots .5" groups at 200 yards.

You should experiment with seating depth until you find the "sweet spot".

Hey Rick, You might be right about the Presure.

You might have better luck Over Expanding the Neck with a 338 Expander and then P-FLRing the Cases with your 30-30 Die so they are a Crush Fit when snapping the Barrel closed.

Best of luck to you.

I shot all my loads up yesterday with the 4320, 170 gr. RNCL and accuracy is better than acceptable. I just might hunt with this load and seat the bullets into the rifling until I'm out of the RNCL's.