New Cartridge Load Development, Meet the 6SST

[lancetkenyon]

Many of you know the name Rich Sherman, as in Sherman Short Mag, and the Sherman line of long cartridges (think Ackley Improved on steroids).

You also know Eric Goss, of Axisworks LLC, the gunsmith/artist many of us know and have a man crush on.

Well, these two mad scientists have collaborated and built the first ever (and ONLY) rifle chambered in the 6 SST (Sherman Short Tactical). Based off the 6.5SS (Sherman Short) which is a slightly shortened version of the 6.5 SAUM with body taper blown out and a 40° shoulder.  I have one, and know of a few other guys that do too, and the case design is phenomenal and very efficient.  

Well, the 6.5SST was born off the 6.5SS case first.  From the demand for a shorter case, and with a 30° shoulder for slightly easier feeding for the PRS crowd to push the 140-150 upwards of 3100-3200fps, while fitting in a detachable mag with the long bullets.  Well, naturally, for even less recoil to be able to see your own hits (or misses), the thought of a 6mm version was conceived to push a 105-115 to near 3200fps with lower pressure and better brass life than the 6CM, 6x47L, 6XC with max loads will allow.

So Eric built his second PRS rifle, and chambered the very first 6SST in existence.  This big fat pig weighs in at 22lbs 9oz all in.  Crazy, right? Well, there is a method to his madness.  Weight=recoil absorption.  This rifle kicks like a sub-sonic .223.

R700SA DBM

MPA (Masterpiece Arms) RAT (Rapid Adjustment Technology) chassis w. about 8lbs of weights installed, fully adjustable cheek piece and LOP, barracade stop, vert grip

27" Benchmark 1:7.5" MTU contour w. 5 port self-timing Muscle Mag brake

Trigger Tech Special @ 1#

Atlas Bipod

AIAX magazine w. Axisworks +2 base

Badger Ordinance 20MOA Picatinny rail 

USO 34mm rings

Vortex Razor Gen II 4.5-27×56 w. EBR-2C MIL

I started load development on this rifle/cartridge combo.  Rich Sherman has brass from Norma and ADG available. I have some of both.  They are within 9gr of each other.  They do take a bit of work to prep.  They start out as a .300SAUM or 6.5SST brass depending on what type you get.  

Neck it down from 7mm or 6.5mm to 6mm

FL size

Expanding mandrel

Neck turn

Anneal

Load

The SST takes a lot less fire forming than the SS version, since it retains the 30° shoulder and only slightly alters case taper and shoulder/neck.  

Here is a loaded round, ready for fire forming.  Rich states the SST fire forming loads can be run at full loads since forming to chamber is minimal.

So I loaded up 10 sighters and a 23 round ladder test, and not knowing where starting load might be.  Rich and I talked about what we thought might be a good starting load.  Being a totally new cartridge, we hoped we were on the right track.

Eric and I discussed uses and hopes for this round.  Eric chose what bullet he wanted to try, and we knew what primer to use.  He let me pick a powder, one that is clean burning, temp stable, fairly slow burning, and would have good case fill.  H1000 seemed to fit the bill.  Not the fastest speeds from it, but with a 3200fps cap.on speeds for PRS, that should be very attainable.  We also decided to see what we could hit for a future hunting rifle build too.  

Took it out to the desert and zeroed it at 100 to 1.5" high.  

Cold clean bore shot was the right, then 4 more right at the top of the diamond.  These were mid-range loads, 3256fps average w. 110 SMK @ .0200" jump.

Out to 200 to verify in preparation for the ladder test.  That shows some promise!  

The winds were really whipping today.  18mph L-R w. gusts.  Then swirling later to 10+ R-L.  Making wind holds impossible.  So I just shot holding center.  343 yard ladder test.  I would have gone further, but I had a good depression to lay in to help limit wind blowing on me. 

Here are the results of the ladder test....

We definitely hits speeds better than Rich and I were expecting with H1000.  

Next will be charge weight testing followed by seating depth testing.

The rifle should be a real shooter when load development is complete.  I am honored to be the first person to ever work on a load for this new cartridge and another amazing Axisworks rifle.  

To be continued.....

[L Cazador]

Not impressive and nothing I've never done with a 6.5/284 Shehane. Don't you think that is a pretty wimpy barrel for this caliber?

[PRDATR]

Maybe he should get into building Benchrest rifles. Do they really use rifles that heavy in PRS matches. I don't know anything about PRS how do you win a match? Shoot bug holes?

[Big Browns]

Very interesting read Lance!  Thanks for the info.  Please keep us updated!!!!

 

FYI, You really need a YouTube reloading channel...  I would love watching and learning!!!!

[Zeke-BE]

This caliber sounds cool!  Just another itch for Lance to tinker with.   Keep us up to date 

[lancetkenyon]

PRS is Hitting targets at various ranges from awkward positions in a short timeline with a limited number of rounds.  Seeing impacts or missed gets your second shot off quickly without relying on a spotter to make your adjustment calls.  A very repeatable and accurate rifle makes this easier.  Faster high BC bullets helps this.  A heavy rifle let's you see your own shots with much greater reduced recoil, and we all know heavy rifles are easier to shoot well.

The 6SST is meant to do this in a true SA magaazine with the bullet seated no deeper than the shoulder junction.  In reality, the 3200fps cap really limits the cases potential.  But for a hunting round, using different powders, 3500+ is easily attainable.  Even with the heaviest 6mm bullets out there like the 115 Berger, 115 DTAC, 125 Precision Ballistic, etc. this should be possible.  

Are there other rounds that can do this?  Of course.  But like the 6.5CM that has boomed that does the same thing as so many other 6.5mm cases, different options are a good thing.  My new 6CM can push the 105 Hybrid to 3200fps too.  But it is about max charge weight to-do so with H4350.  But not anywhere in the same realm as the 6SST for pushing them way beyond that for a flat shooting hunting round.  Which I think this cartridge will really shine at doing.  How many guys like the .243AI or 6AI?  Or 6-06AI?  Or 6-.284, or......yeah, get the point?    Not a new concept.  Just a new way to get there.  Without innovations and choices, we would all drive the same Chevy 1500...and who wants that???

[Zeke-BE]

4 minutes ago, Big Browns said:

Very interesting read Lance!  Thanks for the info.  Please keep us updated!!!!

 

FYI, You really need a YouTube reloading channel...  I would love watching and learning!!!!

You really should!!!  Reloads, long range shooting, rifle builds, optic reviews, bullet performance on game.  Lots of people make money on youtube.  I would subscribe

[Swivelhead]

Cool stuff Lance.  Lot of work  ....... like the idea of hot .243's

[recurveman]

Wildcats are fun and a PITA.  When everything is all said and done most of the time the wind call is really what makes or breaks the shot at the longer ranges.    

[dse]

1 hour ago, recurveman said:

Wildcats are fun and a PITA.  When everything is all said and done most of the time the wind call is really what makes or breaks the shot at the longer ranges.    

3500 fps and a bc over .600 makes the wind calls alot easier.

[Lazy-H98]

Lance-great write up with data and pics.  I dig this kind of stuff.

Can you sum up in a nutshell what a "ladder test" is and what it tells you?

[lancetkenyon]

Ladder test is one round of each charge weight, starting low and working up, in this case, by .5gr increments.  Looking for both a flat spot in velocity and very little vertical dispersion in point of impact in consecutive rounds, showing a plateau for an accuracy node.  Meaning a forgiving range of charge weights to refine for where you need to finish load workup.

Followed by 3-5 round groups for charge weight testing to find the best weight in that range.  

Then, seating depth testing to refine further.

[Lazy-H98]

1 minute ago, lancetkenyon said:

Ladder test is one round of each charge weight, starting low and working up, in this case, by .5gr increments.  Looking for both a flat spot in velocity and very little vertical dispersion in point of impact in consecutive rounds, showing a plateau for an accuracy node.  Meaning a forgiving range of charge weights to refine for where you need to finish load workup.

Followed by 3-5 round groups for charge weight testing to find the best weight in that range.  

Then, seating depth testing to refine further.

Perfect.  Thank you.

[lancetkenyon]

If you look at the photo of the load book, you can see the charge weights, velocities, etc.  Compare that to the target photo with numbered shots.  Each shot is marked after firing, so you know which shot is which on target.

You will see shots 6 thru 12 are all very close to same POI for 343 yards, if you factor out the wind drift.  Under 1" or so for vertical dispersion.  That shows a lot of potential.  But needing to keep.speeds under 3200fps, shots 6/7/8 ( 52.5/53.0/53.5gr) is the range I will be working in.  I will start .2gr low @ 52.3gr and go up in .2gr increments this time to .2gr over, or to 53.7gr.  Load 3 of each and go shoot them @ 200 yards to see which load shoots best, and has the lowest ES/SD (extreme spread and standard deviation). Meaning most consistent speeds which equals consistency.

[Lazy-H98]

On ‎11‎/‎25‎/‎2018 at 7:34 PM, Zeke-BE said:

You really should!!!  Reloads, long range shooting, rifle builds, optic reviews, bullet performance on game.  Lots of people make money on youtube.  I would subscribe

+1 on that.  A local guy doing whats described above,  subscriber #2.