I got some 1680 for my 357 Maximum to use in a single shot rifle. The chamber is long and i have plenty of room to not touch the lands with this bullet shape. Accurate Powder says 27-30gr with a 200gr "rubber tipped" (i forget the name leverution maybe) bullet when set up for a Contender. This has a long 2.5 COL which is great for me. But i need to know what is the min i can set a bullet in the case and still have it gripped OK by the case? 27gr of 1680 does not leave much extra room to seat the bullet. I am sure 30gr is really full. So my other question is it OK to compress1680 some? If i set my COL at 2.3 i have about .135 in the case. I feel like that might be good enough in a single shot where the round does not deal with recoil or feeding pressure. But i still bet 30gr will be compressed at that COL, or can i seat the bullet with it even less in the case? Or just compress the 1680 a little? 27gr might be all i need and i might be fine. But i just want to know this stuff.

Compressing powder is acceptable and safe if there is load data to support the charge, You have that..  Contrary to the internet Myth, compressing powder will not blow up in your face or alter the burn rate and turn a safe load into a potential bomb.

 Compressing ball powders like 1680 does come with a few concerns.  It's not easy to heavily compress ball powders.  To much compression can cause the bullet to creep back out of the case over time.  That's about it, compress away and check OAL for creep.

This "rule of thumb" is not always practical though.

Plus with a single shot firearm where the ammo does not have to withstand the riggers of recoil or cycling/feeding you can get away with a lot less neck tension. My concern would be crimping. Most ball powder pistol rounds (straight wall like your .357 maxi) perform best with a heavy crimp. If you are seating shallow you defiantly are not aligned with the canalure (aka crimp groove)

My Accurate Smokeless Powder manual is the #1, so I admit it is a bit dated ( 1994 ).  But the data in that manual is no where near 27 - 30 grains of 1680.  Top load for a 200 gr jacketed bullet is 21.5 grs.





I load the 357 Max in a Contender with 10 inch barrel.  I use a 200 gr bullet I cast from a LBT mold.  I have done a modest amount of work with 1680 in the 357 Max.  I have gone as high as 25.5 grs of 1680, which chronographs from the 10 inch barrel at 1617 fps.  For best accuracy and comfort of shooting, I have settled on 25.0 grs of 1680, which chronos at 1522 fps in my gun.  It is still a handful, but drops the whitetails just fine.





I would urge some caution in trying to make the 357 Max perform like a 35 Rem.  The Max is a fine cartridge in the single shot platform .

 

Western Powders (Accurate) updates their manuals on a regular basis.  It's best to use modern up-to-date data and leave the old stuff for nostalgia purposes.

http://www.ramshot.com/wp-content/uploads/2010/09/WP_LoadSpec_7-2-13.pdf

Let me double check the weight listing. Like i said, the case is getting full at 27gr.

Edit: Western Powders Reloading and Load Data Guide 5.0 is a PFD i just down loaded. It lists 200gr 357 Maxi (lead) with 1680 at 20.9gr-23.2gr with a COL of 1.930. It hen lists a the same 357 Maxi with a 200gr Hornady FTX (flexi rubber tip) at 27.0gr-30.0gr and a LONG COL of 2.5" for a "contender"  I figure the long COL would not fit in a revolver and that is why it is listed as a "Contender" (single shot) round. The larger case volume obviously lowers case pressure some. I cant get a COL of 2.5 because my flat point is obviously shorter than their pointed round. But if i seat it to the same depth in the case, with the same weight bullet, off the lands i should have the same (safe) pressure.