In an effort to stay on a node, optimize powder burn, and stay within design pressure I find that some loads that qualify are compressed.

I have one that is 111.9% case fill.

Is there any rule about how much compression is to much (re- changing burn characteristics of the powder), I know at some point the bullet won't seat fully.

It's a 9.3x62 and H4350, 286gr bullet.

If you bulge the case while seating the bullet, it's too much compression....and yea, I have done this....but I like slow powders and long barrels.

I measure the loaded cartridge, write down the OAL and wait a day. If it doesn't grow in length, it's not compressed too much. (Only with extruded powders). I don't compress ball powders.

If you bulge the case while seating the bullet, try shaking the loaded case with a barely seated bullet, (to orient and settle the powder), before seating the bullet fully. (I hold the case against my tumbler.)

Compressing a powder charge generally happens near the top of the charge rather than all the way through. A powder charge is more evenly and less dramatically compressed if you help it 'arrange itself'.

^^^ Like this, there loaded now with no drama, like to get an accurate 2500 or so fps out of it.

Since I've been shooting a lot more the last few years, particularly 308 Winchester, I've shifted to different powders that don't fill the case as full when thrown directly into the case.

I don't like much compression for a couple of reasons.

This is what I do as well.

With the powder selections available today, with some exceptions, it's not hard to get performance w/o overly compressed loads.

MM

Holding the case against a tumbler for a few seconds is a good idea. I only load compressed charges in a couple of rifles. I mostly hold my fingertip over the case mouth and tap the rim on my bench.
Rechecking C.O.L. after a few hours is a good idea...

Seems many have forgotten how to use a drop,tube,or even make one.

I haven't.

If you have to use a drop tube and a vibrator then too much trouble for me unless it was a really outstanding load or I had a lot of powder that needed to be used.

In addition to the cartridge length growing you could see a greater spread in velocity if it is really crunching the powder. In general I look for the 95 to 105% or less case fill range to start with.

I wonder how the newer powders with the retardant blended through out will react to compression?

I don't see the value when one can touch the case to the vibrator quicker.

A drop tube attached to the side of powder measure is a lot less space and quieter than having a tumbler running besides. I would also say it is a tad faster. Have you ever used one?

It's rare to find a "most accurate" load that requires any compression, and if you "need" more velocity you probably need a bigger cartridge

Charge all the brass, cases in loading block, and put the block with the cases on the running tumbler for a few seconds and your extruded powder settles lower in the case. Effective and doesn't take longer than a few seconds.

I've had trouble with holding the bullet in place making consistent depth seating challenging.

I have had good success around the 100% mark for consistency.

A lot depends on what people think is "compressed." Many handloaders I've run into think compressed means what I would call "crunched," meaning extra effort is required to seat bullets, and the powder charge can push the bullet back out, and even deform the case to the point where the round is difficult or impossible to chamber.

In general, a little compression with extruded powders doesn't hurt anything, and can result in a very accurate load. Compressing spherical powders is more difficult, and can result in erratic pressures and velocities, especially after the ammo isn't shot when reasonably fresh, due to clumping of the powder.