A few months ago , I did this same thing for the 6.5 Sherman, and because of all the questions I've received, I thought it might be good to do the SS as well.
The 6.5 SS was designed to be a TRUE short action with magnum punch. When I say "true short action" I refer to a round that will be able to cycle through a short action mag box with the long VLD style bullets and not have to be seated back into the case. This can not only affect accuracy, but also defeats the purpose of a large volume case being able to produce top velocity. In order to accomplish the above criteria, we selected the 7 SAUM case as a parent. By pushing the shoulder back, blowing out the body taper, and sharpening the shoulder, we were able to maintain most of the case capacity in a much shorter case. This shorter powder column increases the efficiency of the cartridge, and I think this has proven out with the performance we are getting. We were also able to produce a much longer neck at the same time. This not only helps with accuracy potential, but IMO, also reduces throat erosion (longer barrel life) by containing the flame point point further back in the neck rather than directly into the throat area. The dimension from the case head to the neck junction is very close to the Creedmore, which establishes the OAL of the cartridge.
As far as performance goes, the SS is everything we had hoped for. With RL33 it appears that 3100' is doable with a 160 in a 26" barrel. With the 140's, 3200'+ is no problem. Accuracy is very good as is case life. This is especially true when we use the 300 SAUM Norma cases.
As far as case prep goes, I like to be right up front with people. The SS is not difficult to form, but by the same token, it is not for everyone. If you don't mind a little bit of fuss, the rewards are there. You will need a 7 SAUM die shortened by about .090". This allows for pushing the shoulder back. I like to leave the expander ball in and "iron" out the case neck with 6-8 strokes of the press. This usually pushes the extra brass to the "outside" of the base of the neck so it can be removed during neck turning. I then trim the case length to spec and use a Hornady hand neck turner to true up the neck wall and create the proper clearance for the chamber. I turn the neck approx. .005-010" farther than the chamber spec which gives a nice clean junction at the neck/shoulder after fire forming. Next step is to run through the SS die to neck down to 6.5. I set the die to leave the neck approx. .010" short of where the new junction will be. This assures proper head spacing when fire forming. You can then either load a bullet and fire away, or use the cow method with shotgun/pistol powder, which is what I prefer.
We think this will make a great light weight carry rifle and/or a very good long range weapon for big game, up to and including elk with the 160's at 3050-3100'.
For anyone wanting to join the party, I have both the reamers and custom dies in stock for a quick turn around on your build.
Feel free to post any questions or comments.......Rich
I just realized that I posted the wrong pics, but you can get the idea.
Very cool concept...what's barrel life look like? Any feed issues with the sharp shoulder? Keep up the great work.
Don't know about barrel life yet as we haven't had them long enough. Having said that, we expect it to be very good as we have a couple 6.5 Shermans (270 parent) that have 1700 and 1500 rounds through them and they still shoot great. They have basically the same design but hold approx 4-5 grs. more powder than the SS. Also, the SS has a little longer neck.........Rich