Not enough shoulder bump resizing 6.5 PRC? (SAC Modular Die + MEC Metallic Press)

[thirdeye462]

Hi everyone,

I'm calling upon the collective wisdom after searching online about not getting enoug shoulder bump from my press/die set-up. I'll start with my scenario then go on to the problem:

Scenario

I'm very green at reloading. I have a long way to go yet. Up till recently, it's been all study and theory for months and months. Just this week, I've been actually starting to use my gear.
I'm running a new 6.5 PRC rifle (Cadex R7 XS with Bartlein, 1:8, 26") - so now I have a chamber to test on.
I purchased a box of once fired brass (Hornady Precision Hunter) to start learning how to prep brass correctly (taking measurements before and after, die set-up, resizing, cleaning, lubing, trimming, etc.). This brass will not be refired; they will be for dummy rounds I'm making.
My set-up includes a MEC metallic press with Hornady Lock n Load bushings, and a SAC modular sizing die with .288 neck bushing and .2625 expander mandrel.
I've positioned the sizing die to kiss the RCBS #38 shellholder at the top of the stroke, plus somewhere around an extra 1/2 turn. This means I am beyond feeling cam-over; it's straight up hard stop.

Issue

The brass was correctly sized at the .200 line (according to SAAMI); case length was coming out a bit longer after sizing in some cases but still within tolerance - except for a couple pieces, which I trimmed to eliminate this variable because they wouldn't chamber.
For the cases that I had to trim down, their shoulder geometry was longer than SAAMI (greater than 1.6517 at the .420 line) (I'm using a Derraco headspace comparator)
I kept resizing the brass and after adjusting the die down and down until I couldn't anymore. The shoulders were just not sizing below 1.653 or so. I also confirmed they would not chamber at all at this length

I ended up sticking a piece of tape between the ram's shellholder plate and the RCBS shellholder I'm using.

Bingo.

Shoulders went back about 2.5 thousandths or so (I think I ended up at 1.651 or so (slightly under SAAMI spec). They also chambered just fine.

So, with the measurements I took and the feedback I'm getting from my process, I'm coming to the conclusion that I've been left with a common problem: a shellholder that is likely impeding shoulder bumping such that resized brass won't chamber and is way too tight.

So, what now?

Here's are the asks:

• Have I missed anything in trying to determine what's going on or in my explanation?
• Anything else I can do to test or to bump that shoulder back?
• Is it better to find a different shellholder or sand/lap my existing one?
• Has anyone tried shimming a shellholder in a MEC metallic press like I did with tape to get your shoulders correct? (See photo). If so, what did you use? Or, is this a bad idea?

Ready, set, go! (And thank you!)

 

[Beater]

try a diff shell holder. or remove some from the top of it to get it up in there that last 2 thou

 

[OldDude]

If I were inclined to use a shim, I'd look for some brass or stainless shim stock; the tape might compress under load.
As was mentioned, taking a bit off the top of the shellholder might be a better option.
After a shellholder shave, I'd be inclined to mark the shellholder somehow.

 

[Deathrawt]

Yup take a bit off the top of the shell holder
I use emery cloth taped down to a glass table and use circular motions keeping the top of the shell holder square to the table
Take a little at a time and retest until you can chamber the brass

 

[I Dont Care About You]

I've positioned the sizing die to kiss the RCBS #38 shellholder at the top of the stroke, plus somewhere around an extra 1/2 turn. This means I am beyond feeling cam-over; it's straight up hard stop.

Thats too far. You need press cam-over to ensure consistency in the sizing dimension.

I totally don't get the explanation that you aren't getting sufficient headspace out of your setup, which is so far down that you don't get cam-over on the press but then you "shimmed" the shell holder with tape and that worked to shorten the headspace on the case? None of that makes any sense.

I would suggest you go back to the die setup instructions and follow those.

Then I would suggest that you stop massively overthinking it all and just fire some rounds in your rifle. Measure your fired cases, ignore SAAMI and size the cases to fit your rifle. THAT is the only thing that matters.

The brass was correctly sized at the .200 line (according to SAAMI); case length was coming out a bit longer after sizing in some cases but still within tolerance - except for a couple pieces, which I trimmed to eliminate this variable because they wouldn't chamber.

What does OAL and neck trimming have to do with the sizing operation?

For the cases that I had to trim down, their shoulder geometry was longer than SAAMI

You overlooked the fact that OAL has nothing to do with headspace and thus has nothing to do with cases that won't chamber.