The 6UM

[Montucky]

HELP! I am lost...

I am not getting anywhere near the velocity that everyone else seems to be getting.

I built a 16" barrel and a 20" barrel 6UM

BOTH:
-6UM-40 degree.
-Bartlien barrels.
-Defiance actions.
-115 DTACs.
-215Ms.
-ADG 6UM brass.

I fire-formed 110 pieces of brass in each. Scrubbed the barrels with Witches Brew before I started working up a load for each rifle.
Bumped shoulder .0005 (I would have done more, but my mild fire form load was 57gr of H1000)
Neck tension .002
2.910 OAL.

I am getting around 2,960 FPS out of the 16" barrel with 65gr of N570 with very stiff bolt lift.

I am getting around 3,150 FPS out of the 20" barrel with 65gr of N570 with very stiff bolt lift.

I am getting heavy bolt lift starting at 63gr with light ejector marks on both rifles.

Everyone else seems to be getting wayyyyyy more velocity.

WTF?

View attachment 883421

I have a 7saum that’s finicky on pressure signs on 3rd firing….I backed off 2gr of powder & let her lay in the weeds with a 180 berger at 2800 with 22in….I’m crossing fingers on my 6UM build with 18in making 3000fps…..you’re damn close but heavy bolt lift leaves a guy frustrated….what chrony you running?

 

[Ryan Avery]

HELP! I am lost...

I am not getting anywhere near the velocity that everyone else seems to be getting.

I built a 16" barrel and a 20" barrel 6UM

BOTH:
-6UM-40 degree.
-Bartlien barrels.
-Defiance actions.
-115 DTACs.
-215Ms.
-ADG 6UM brass.

I fire-formed 110 pieces of brass in each. Scrubbed the barrels with Witches Brew before I started working up a load for each rifle.
Bumped shoulder .0005 (I would have done more, but my mild fire form load was 57gr of H1000)
Neck tension .002
2.910 OAL.

I am getting around 2,960 FPS out of the 16" barrel with 65gr of N570 with very stiff bolt lift.

I am getting around 3,150 FPS out of the 20" barrel with 65gr of N570 with very stiff bolt lift.

I am getting heavy bolt lift starting at 63gr with light ejector marks on both rifles.

Everyone else seems to be getting wayyyyyy more velocity.

WTF?

View attachment 883421

Who built these?

I have encountered velocity turds with Bartlien barrels. The slowest 20" I have seen is Tanya's at 3210 with a Pacnor. But it's also the most accurate 6UM I have shot.

I just tested an 18" Benchmark that was 3130 with 65.5g, and Robbys 20" is averaging 3275 with 66g

 

[Ryan Avery]

So besides supporting Roksliders, why the 6 UM vs a 6 Sherman variant? 6 max already has a 40 degree shoulder. The SST seems to come close as well.


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Very similar, the 6UM has a tad more volume and a shorter neck. There is also a slight difference in case taper.

 

[bubba580]

Wicked!

 

[TradLife406]

Anyone have a UM improved reamer they'd sell/rent me?


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[Harvey_NW]

.006 off the lands. I am shocked that I am not able to get more velocity.
I just got done scrubbing my barrel after fire forming 110 pieces of brass. So I ASSume I don't have a carbon ring.

I am really surprised that I can't get better velocity.

Is that supposed to be .006 off the lands or .060?

If it is actually .006, I think trying .060 would help.

 

[T_Widdy]

HELP! I am lost...

I am not getting anywhere near the velocity that everyone else seems to be getting.

I built a 16" barrel and a 20" barrel 6UM

BOTH:
-6UM-40 degree.
-Bartlien barrels.
-Defiance actions.
-115 DTACs.
-215Ms.
-ADG 6UM brass.

I fire-formed 110 pieces of brass in each. Scrubbed the barrels with Witches Brew before I started working up a load for each rifle.
Bumped shoulder .0005 (I would have done more, but my mild fire form load was 57gr of H1000)
Neck tension .002
2.910 OAL.

I am getting around 2,960 FPS out of the 16" barrel with 65gr of N570 with very stiff bolt lift.

I am getting around 3,150 FPS out of the 20" barrel with 65gr of N570 with very stiff bolt lift.

I am getting heavy bolt lift starting at 63gr with light ejector marks on both rifles.

Everyone else seems to be getting wayyyyyy more velocity.

WTF?

Are you getting bolt thrust? Have you added tape to the back of your cases to check your headspace of your fireformed brass?

 

[Duxnbux]

HELP! I am lost...

I am not getting anywhere near the velocity that everyone else seems to be getting.

I built a 16" barrel and a 20" barrel 6UM

BOTH:
-6UM-40 degree.
-Bartlien barrels.
-Defiance actions.
-115 DTACs.
-215Ms.
-ADG 6UM brass.

I fire-formed 110 pieces of brass in each. Scrubbed the barrels with Witches Brew before I started working up a load for each rifle.
Bumped shoulder .0005 (I would have done more, but my mild fire form load was 57gr of H1000)
Neck tension .002
2.910 OAL.

I am getting around 2,960 FPS out of the 16" barrel with 65gr of N570 with very stiff bolt lift.

I am getting around 3,150 FPS out of the 20" barrel with 65gr of N570 with very stiff bolt lift.

I am getting heavy bolt lift starting at 63gr with light ejector marks on both rifles.

Everyone else seems to be getting wayyyyyy more velocity.

WTF?

View attachment 883421

HELP! I am lost...

I am not getting anywhere near the velocity that everyone else seems to be getting.

I built a 16" barrel and a 20" barrel 6UM

BOTH:
-6UM-40 degree.
-Bartlien barrels.
-Defiance actions.
-115 DTACs.
-215Ms.
-ADG 6UM brass.

I fire-formed 110 pieces of brass in each. Scrubbed the barrels with Witches Brew before I started working up a load for each rifle.
Bumped shoulder .0005 (I would have done more, but my mild fire form load was 57gr of H1000)
Neck tension .002
2.910 OAL.

I am getting around 2,960 FPS out of the 16" barrel with 65gr of N570 with very stiff bolt lift.

I am getting around 3,150 FPS out of the 20" barrel with 65gr of N570 with very stiff bolt lift.

I am getting heavy bolt lift starting at 63gr with light ejector marks on both rifles.

Everyone else seems to be getting wayyyyyy more velocity.

WTF?

View attachment 883421

You’re not alone. I found pressure at 62.7 grains of n570 in my ladder test the other day. Shooting 115vlds out of a 22 inch proof. The velocity was there, but not much else. Real heavy bolt lift and ejector swipe. .060 off.

 

[Ryan Avery]

You’re not alone. I found pressure at 62.7 grains of n570 in my ladder test the other day. Shooting 115vlds out of a 22 inch proof. The velocity was there, but not much else. Real heavy bolt lift and ejector swipe. .060 off.

Coated Dtacs NR

 

[ThunderMug]

Are your DTACs coated?

No Sir, would that help or hurt?

 

[IrkedCitizen]

No Sir, would that help or hurt?

Pretty sure the coating acts as a lubricant

 

[ThunderMug]

Did UM build these shortiies…..or did you diy…? I’m just curious….

I had a well known gunsmith in Wyoming build them for me. He has build me a dozen SAUMs, Noslers, and 300 NMIs that shoot great with zero issues.
I bought the reamer, go-guage, dies, and head stamped brass from UM.

I think I might have INSANELY slow barrels. The 16" is 1-7 twist. The 20" is 1-7.5"
I have tried every seating depth, 103s, 108s, and 115s. H1000 and N570. 210Ms and 215Ms.

Anytime I try to push any of the above bullets above 2,900 fps in the 16" barrel I get heavy bolt lift, ejector marks, erratic velocities, and my groups open up.

 

[ThunderMug]

I have a 7saum that’s finicky on pressure signs on 3rd firing….I backed off 2gr of powder & let her lay in the weeds with a 180 berger at 2800 with 22in….I’m crossing fingers on my 6UM build with 18in making 3000fps…..you’re damn close but heavy bolt lift leaves a guy frustrated….what chrony you running?

Garmin.

 

[Montucky]

8 day bear hunt & my 12yr old boy punched his tag….7saum, 180 Hybrid, 360yds…On the hunt We called Alex last Tuesday & ordered an 18in 6UM 40 custom from Unknown Munitions….

 

[ThunderMug]

Are you getting bolt thrust? Have you added tape to the back of your cases to check your headspace of your fireformed brass?

1 layer of Scotch tape I assume?

 

[ThunderMug]

Coated Dtacs NR

Hey killer, what do you gain with coated DTACs?

Should I be ordering the standrd nose ring or deeper cut for hunting?

What twist rate do you recomend for the 115 DTACs? I am going to order another 16" and 20" barrel and throw these barrels that I have in the trash.

 

[ThunderMug]

I’m a newb with the 6UM, but I hit pressure earlier than I expected and I’m pretty sure it was from a carbon ring. I scrubbed the chamber/throat with iosso bore cleaner and was able to work back up. I think my final load is going to be 68 grains of 570 with the dtacs, and that got me close to 3200 with an 18” barrel.

How far are you loading off the lands?

I scrubbed may barrel. I'll do it again.
.060 off the lands.
I can barely break 2,900 fps before I get heavy bolt lift.

 

[T_Widdy]

1 layer of Scotch tape I assume?

Add 1 layer at a time till the bolt doesn’t fall easily then measure with a comparator. Pull your ejector when checking.

 

[ThunderMug]

Who built these?

I have encountered velocity turds with Bartlien barrels. The slowest 20" I have seen is Tanya's at 3210 with a Pacnor. But it's also the most accurate 6UM I have shot.

I just tested an 18" Benchmark that was 3130 with 65.5g, and Robbys 20" is averaging 3275 with 66g

I had a well known gunsmith in WY build both my 16" and 20" 6UMs.
He has built a dozen other rifles for me that are all fantastic.
I think these barrels are just F'd.

I am basically 200-300 fps slower than what everyone else is getting.

 

[Tx_6UM]

Hey killer, what do you gain with coated DTACs?

Should I be ordering the standrd nose ring or deeper cut for hunting?

What twist rate do you recomend for the 115 DTACs? I am going to order another 16" and 20" barrel and throw these barrels that I have in the trash.

That’s a lot of money to throw away. I’d buy a bore scope and take a look first, cheap investment.