When you pack harden, the carbon absorbsotion occurs when the steel reaches a certain temp that it will absorb carbon. The absorbed carbon is in the form of carbon monoxide and carbon dioxide, this is the by-product of carbonaceous materials, which, when heated,  off gas these compounds. 

For any practical sense, increasing the carbon content will not increase hardness..   Machining annealed 1095 (spring steel)  is not much different than machining 1020. 
But, what the additional carbon has done is increased the steel’s ability to be hardened. 

Taking both 1095 and 1020 heating to 1400 deg F, then quenching , there will be no difference in machining the 1020 than in it’s annealed state. But the 1095 will be “file hard’ and a true bugger to machine without carbide. 
Heat back up to 1500 deg, and allow cooling slowly, once cool, they both again, are easily machined. 

Additional carbon in the steel does not greatly reduce wear resistance when the steel is in the annealed state.
 
As to blocking:  I used to use blocking quite often when I first started doing CCH. Nice blocks beautifully machined out of stainless steel.  What I have found over the years, is that blocking is not 100% necessary.  If the steel is going to move, it will move no matter what, if there is a block in there it will “spring” once the block is removed. 

BUT… The great aspect of case hardening is that you have an hard outer surface and a soft inner core… so the parts are easily tweaked. 

Mike Hunter
Hunter Restorations

Thanks for the info Mike.
This might be an area to leave to the professionals when you got lots of money tied up in a frame. If you make your own as a hobby and this is a learning process then by all means do it your self.

Joe,

Agree with your thoughts. 

Most of what appears to be too difficult comes from not having tried to do it. Duplicating a process that was regularly performed a century ago takes some thoughtful experimenting with proper tools and equipment, but it's not modern day rocket science. And it couldn't have been too onerous otherwise the major arms producers would have shied away from it to prevent a high materials scrap rate and a waste of labor. 

One reason I asked about blocking is because after having examined the interior of a lot of old frames that were originally pack-hardened (along with some junker frames that were only good for skeletonizing or sectioning), and some that were blocked during recent re-color hardening, I've come to doubt that blocking was regularly done way back when.

The only way to sort the facts from the often repeated BS (and no offense intended to anyone who's posted on this thread) is to experiment. And as that old saying goes...  nothing ventured, nothing gained... or learned.  

Joe,

First, Mike Hunter gave a really good description of the pack hardening processes, and I agree with his thoughts on the hardened and annealed state comparisons.

I don't think there's much to be gained by packing tight enough to put mechanical pressure on a receivers sidewalls. Think more along the lines of a cartridge that has been drop-tubed full of Fg , but not yet run into the compression die. Good kernel/grain contact without crushing.

You want a fairly firm pack for two reasons:
1st, you don't want the parts to move around in the can and end up against each other, or the container walls. Leave room between the can walls and between the individual parts.
2nd is you don't want the top surface to settle down and drop below any portion of your parts as slag could develop on the exposed surfaces of those nicely polished pieces.

At first I sealed the lids to the containers with fire clay, but found it was a waste of time and money as the media degases long enough to move it from the oven to the quench. My oven is inside and my tank is outside. The lids are slip-snug and on there to keep the red hot char in the can during the move. The red heat of the can and lid makes them stick together and a couple taps knocks the lid off. I wear leathers and gloves, helmet and face-shield when quenching.

Something else I found is that the different medias (bone-char, wood-char, and mixs of the two) degas differently at different temps, so you'll want to experiment with temps and soak times to get the results you're after with your media.

I normally anneal just after quenching as the ovens already hot from hardening. I place the parts in a packet made from stainless foil with some paper towel in it to burn up the oxygen from any air in the packet. I open the door, set the packet inside and turn off the oven controller. Then I pull it out the following day.

Joe, you got a good machine case on your Hoch with the kasenit. 
Keep on experimenting!  

I have always heard that warpage is caused by internal stresses built up during quenching. Sort of agrees with Mike that if the stresses are there it is going to spring whether you block or not. Uniform heating and quenching would seem to be one of the keys.

Never the less, I have always blocked alloy (4340) receivers with close fitting, clamped mild steel blocks before giving it to the heat treater. He says it is probably not required. No warpage problems so far, but a very limited sample.
Chuck