Meet The 6SST

lancetkenyon

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

Many of you might 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.....
 

elkaholic

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Very nice work Lance! Looks like Eric picked the right man for initial testing.
You'll be happy to hear that the new run of brass which will be available in a couple weeks will not need turning providing you use my new reamer to clean up the chamber neck. Subsequent builds will be good to go.
I have dies in stock now also so this baby is ready to roll! I can't wait to see some more data with better conditions and a little tuning.
 

lancetkenyon

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Got some rounds loaded up for tomorrow. I sure hope it is not windy like last week.

Hitting the range for some 200 yard groups with the 110s, and headed to the desert for two ladder tests if the wind is not ridiculous.

Top left 3 round groups with the 110 SMK for the PRS loads between 3130-3200 hopefully.

Top right row is a ladder test w. 115 Berger HVLD over RL23 to see if we can get a bit more speed out of them.

Bottom row is a ladder test with 87 VMax over RL19. Hoping to be between 3200-3600 for the charge weight range.



110 SMK seated @ 2.223" CBTO



115 Berger HVLD seated @ 2.223" CBTO



87 VMax seated @ 2.168" CBTO



To be continued...
 

AZShooter

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Tucson Az
Lance,

What is the case capacity in grains of water? Based on the velocities you are getting it would appear to be very similar to the performance of a 6mm-284 win. Perhaps the 6mm SST has slightly more case capacity?

I realize using H1000 was to not surpass the velocity limit of 3200 for PRC competition. I think you can get more velocity by trying slower powder for hunting applications.

In my testing with a 28" 6mm-284 1 in 7.5 twist 5R bartlein and 115 DTACs .010" into lands, got best velocity with Retumbo. Highest velocity with good but not excellent groups was with 57 gr for 3265 fps

Was discouraged with accuracy and switched to the new at the time 105 Berger hybrids. Retumbo was velocity king 57 gr was most accurate velocity 3363 till RL-33 came out. Got 3485 fps with 64 gr of RL-33 and 28" barrel. Drop tube and significant jump to lands in the package setup as a repeater. This load proved to be too hot for some rifles.

Using another barrel in a 24" sporter:

a moderate load with 51 gr of RL-17 was very accurate with the 87 gr V-max 3375 fps

RL-17 was very accurate and fast with the 95 gr berger classic hunter 54 gr 3465 fps

Just saying if you wanted to really crank up the velocity for a hunting round, I mentioned these powders as I believe they would work similarly in the new 6mm SST.

Looking forward to reading more of the results of your testing.
 

elkaholic

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Capacity is 70 grains at 6.5 mm so I suppose 69.5+. We have reached near 3500' with Retumbo behind the 110 and I suspect N565 would push it past. I'm sure Lance will have some more data soon. He was kind of focusing on a PRS load.....Rich
 
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Capt RB

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Dec 1, 2014
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The new tubb rebated 115 has a touch more bc than the 110. Really easy to get to shoot also. My worn out 243 ai came back to life with them. Should get me through the winter coyote season before a new pipe goes on.
 

AZShooter

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Thanks Rich,

284 Win is 66 gr. I learned plenty with that original bartlein 6mm-284. First and foremost and I am sure it applies if your 6mm SST is loaded near top.....don't experiment with too many bullets, barrel will die right around 1000 rounds even it is never rapid fired.

I only have the sporter barrel in 6mm-284 which is one of a line of Rem 700 takeoffs in 243 rechambered to 6mm-284. When it gets burned out I will rechamber and install another for under $75. Currently shooting a 55 gr nos bt @ 4100 with varget. It shreds the varmints.

Look forward to reading more on this new cartridge
 

lancetkenyon

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Back from the range and the desert. Shot some amazing groups with the 110 SMKs staying within the PRS speed cap range. Recoil is very mild, as can be expected with a 22+# rifle with a 5 port brake shooting a light bullet at moderate pressures.

Shooting a few different Axisworks rifles today. 6SST, 6.5SS and 6CM.



Here was the best group, but all were in the .1-.2 range.



3 shot group @ 100 yards



After the range, I went out to one of my LR spots to shoot a couple more ladder tests since the winds were pretty clam, and the air was cold and humid.

115 Berger over RL23. Had a bit better speeds than I anticipated with lower charge weights. So only got 5 rounds in the ladder test. Rich figured we would max out about 55.0, I was hoping for a bit more. Too bad Rich was so far off....



Shot the ladder test @ 404 yards.

Not bad for 5 different charge weights spanning 120fps @ 404 yards. About 1.1", or .26MOAish.



On to the 87 V-Max.....
Results were not what I had hoped, until I figured out why....and witnessed something I have only heard of.

I loaded the 87 V-Max over RL19. Did a very broad charge weight gain of a full grain just to see where we could expect speeds to end up. I started at 50.0, figuring that would be plenty low, and went up to 59.0gr of RL19. Bullet was seated .020" off the lands for testing purposes.

Shot #1 @ 3300 to shot #7 @ 3530fps

Shot a ladder at 404 yards again. Results were less than spectacular......



.....until shot #8. My Labradar gave me an error "could not track bullet". I studied the target through my spotter, and could not find the bullet hole on target. No way I missed a 12"×18" target @ 404 yards.

So, shot #9, I watched. Let me set this up. I was shooting northnorthwest. Time was about 10:00am. Sun at my back almost directly. Got set up prone again, got on target through the scope w. my right eye, but kept my left eye on the distant frame I had set up. When I touched off the shot, I witnessed it for the 1st time ever firsthand.
About 20 yards out, I saw a very brief flash, like the sun shining off 1000 tiny pieces of lead about 5' in diameter. A tiny dust cloud about 20' wide appeared below it. The bullet had vaporized when it left the barrel. I guess a thin jacketed varmint bullet cannot withstand 340,800 RPM. (3550+fps from a 1:7.5" twist).

So I guess we are going to play with a 95TMK and some sort of lighter all copper bullet to see how fast we can get them going and hold together. Sure wish I would have had a super slo-mo video camera going. I laughed so hard I almost had tears.

I wonder how fast I could get the 88 or 101 Hammer Hunter going? I know those would stay together out of a 1:7.5" @ 3500+. I had easy bolt lift and not a single sign of pressure (except the bullet vaporizing) with my higher loads. Last recorded velocity was 3530 that stayed together. So I am betting we had MV of over 3600 with at least 2 more shot that I didn't even record. I have always said "You can't over spin/stabilize a bullet". Guess I proved that wrong.
 
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Capt RB

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With the 6mm competition match most are loading at around 50 grns of H1000. Your probably going to be able to increase your barrel life by 20% over them. That is really impressive. All of the benefits of running a 6mm without the barrel wear associated with it. Would love to see what the Dtac115 would do. They don't need more than 8tw and they have a .620bc
BTW some pretty awesome shooting seeing how your slumming in the glass department:D
 

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