The 6UM

[ThunderMug]

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

What brand of bore scope do you recommend? Or will just any one work?

 

[ThunderMug]

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

I have other brands of barrels that vary 50-100 fps from one to another in the exact same caliber, length, and twist rate. But to be 200-300 fps slower than everyone else is getting in the same barrel length is driving me nuts.

Do you think that the 1-7" twist rate in the 16" and the 1-7.5" in the 20" barrel are proper for the 115 DTACs?

 

[Axlrod]

I have other brands of barrels that vary 50-100 fps from one to another in the exact same caliber, length, and twist rate. But to be 200-300 fps slower than everyone else is getting in the same barrel length is driving me nuts.

Do you think that the 1-7" twist rate in the 16" and the 1-7.5" in the 20" barrel are proper for the 115 DTACs?

I have had excellent results w/7.5 twist and Dtacs.

Before you scrap those barrels, have you measured a fired case neck and compare to the reamer print? Or can you fit a bullet in the neck of a fired case? I have experienced what you are going through a couple times. And it was a tight neck for the brass I was using. Once I turned the necks, I was able to use more powder, without over pressure.

 

[ckleeves]

I have had some slow Bartleins, one was painfully slow so no doubt it happens. The weird thing (or maybe your just unlucky) is getting two of them at the same time and with different twist rates.

Like was mentioned above make sure a bullet can slip into a fired neck and maybe make a call to your smith and ask if he saw anything unusual or if the reamer bushing was on the small side. Would also be worth a close look with a borescope.

You may or may not find anything, the real slow one I had nothing was visually or dimensionally wrong and the reamer was proven it was just a turd.

 

[ThunderMug]

So fellas....

Yes, I can slip a bullet into a fire formed neck easily.

The reamer measures .2785 neck diameter.
The reamer print says .2790
A piece of fire formed brass measures .2775

I also removed the firing pin assembly and the ejector. A piece of fire formed brass allows me to close the bolt farely easy, but it takes some effort. The bolt handle does not fall under it's own weight by any means, but I have found that to be true with most of my rifles.

Then I took a piece of Scotch Tape as suggested by T_Widdy and put one layer on the case head.
With 1 piece of tape that measures .0020 I CAN NOT close the bolt.
Does that indicate not enough head space?
The Go Gauge that I bought from UM allows the bolt to close with ease.

Does all this indicate that my barrels are really just rediculously slow? As in 200-300 fps slow?????

I mopped my barrel with Wipe Out and Accelerator, then rinsed it with brake cleaner, then absolutely scrubbed it with Witches Brew. Hoping to remove a potential carbon ring. (I did order a borescope!)
This cut my groups in half, but I am still getting pressure at very low powder charges.
I can only get around 2,900 fps with the 115 DTACs and 61gr of H1000 or 63gr of N570 before ejector swipes and 1gr more and I have very heavy bolt lift.

As you can see on the Garmin, it's slower than Biden.
That was the 103s with 60gr of H1000.
Pathetic.

 

[PathFinder]

My 24" Bartlein is a little on the slow side. It is at 3330 with the typical 66 grains of N570 at .060 off and a NR, coated DTAC. But it was able to go up to 67+ grains without unreasonable pressure signs.
It's worth bore scoping those chambers first. Probably best to figure it out before having any more cut so it doesn't happen again.

Sent from my Pixel 6 using Tapatalk

 

[Ryan Avery]

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.

So fellas....

Yes, I can slip a bullet into a fire formed neck easily.

The reamer measures .2785 neck diameter.
The reamer print says .2790
A piece of fire formed brass measures .2775

I also removed the firing pin assembly and the ejector. A piece of fire formed brass allows me to close the bolt farely easy, but it takes some effort. The bolt handle does not fall under it's own weight by any means, but I have found that to be true with most of my rifles.

Then I took a piece of Scotch Tape as suggested by T_Widdy and put one layer on the case head.
With 1 piece of tape that measures .0020 I CAN NOT close the bolt.
Does that indicate not enough head space?
The Go Gauge that I bought from UM allows the bolt to close with ease.

Does all this indicate that my barrels are really just rediculously slow? As in 200-300 fps slow?????

I mopped my barrel with Wipe Out and Accelerator, then rinsed it with brake cleaner, then absolutely scrubbed it with Witches Brew. Hoping to remove a potential carbon ring. (I did order a borescope!)
This cut my groups in half, but I am still getting pressure at very low powder charges.
I can only get around 2,900 fps with the 115 DTACs and 61gr of H1000 or 63gr of N570 before ejector swipes and 1gr more and I have very heavy bolt lift.

As you can see on the Garmin, it's slower than Biden.
That was the 103s with 60gr of H1000.
Pathetic.


View attachment 885017

When/where did you buy the reamer? We updated it after the first couple of barrels.

That scope is TALL

 

[ckleeves]

Tape the go gauge and then trim the edges with a razor blade and try chambering it. The fired brass isn’t really telling you a whole lot taping it because it’s already expanded to the chamber unless I miss understood what you were saying. It sure doesn’t sound like a headspace issue but worth double checking.

Measure the go gauge before and after tape to see what the difference is. If it closes on one layer add another.

 

[ThunderMug]

Tape the go gauge and then trim the edges with a razor blade and try chambering it. The fired brass isn’t really telling you a whole lot taping it because it’s already expanded to the chamber unless I miss understood what you were saying. It sure doesn’t sound like a headspace issue but worth double checking.

Measure the go gauge before and after tape to see what the difference is. If it closes on one layer add another.

I removed the firing pin assembly and the ejector.
I am able to add one layer of .002 Scotch tape and the bolt closes very easily.
With 2 layers it closes, but it takes a fair amount of pressure on the bolt handle.
I measured the 2 layers of tape at .004
I assume that will give us the data that we are looking for.
So does that mean that I have somewhere between .003-.004 headspace?

 

[ckleeves]

I removed the firing pin assembly and the ejector.
I am able to add one layer of .002 Scotch tape and the bolt closes very easily.
With 2 layers it closes, but it takes a fair amount of pressure on the bolt handle.
I measured the 2 layers of tape at .004
I assume that will give us the data that we are looking for.
So does that mean that I have somewhere between .003-.004 headspace?

Ya you’re basically just adding length to the go gauge to turn it into a no-go to make sure you don’t have excessive headspace. Sounds like it’s right about where it should be. Taping it isn’t a perfectly exact method but you’re just making sure headspace isn’t .008+ or something crazy over a go.

 

[greyghostnw]

What brand of bore scope do you recommend? Or will just any one work?

Teslong anyone who has firearms should have a bore scope. Its a cheap simple way to evaluate your barrel when new and your cleaning efforts and process, handy to look inside brass to look for early signs of case head separation, list goes on. Good luck

 

[ThunderMug]

When/where did you buy the reamer? We updated it after the first couple of barrels.

That scope is TALL

I bought the reamer from UM as soon as they were available.
I bought the Go Guage from UM on 11/13/2024.

That TALL 50x scope is just for group testing.

 

[ThunderMug]

When/where did you buy the reamer? We updated it after the first couple of barrels.

That scope is TALL

Reamer was purchased from UM on 05/24/2024

 

[wind gypsy]

I mopped my barrel with Wipe Out and Accelerator, then rinsed it with brake cleaner, then absolutely scrubbed it with Witches Brew. Hoping to remove a potential carbon ring. (I did order a borescope!)

Assuming you used something that would get in the neck/freebore of the chamber? Can miss that carbon ring area with standard bore guide and bore cleaning procedures.

 

[Tx_6UM]

I got out and shot with the rebuilt scythe today. It didn’t blow up so that’s a plus. I shot 20 rounds with the 115’s and 67.5 grains of 570. That only got me to 3154 with a heavy bolt lift And swipe. I think I’m just gonna back off to 66 and run that for the rest of this barrel. Doesn’t have the speed I was hoping for but it was accurate and will get me to further than I’m comfortable shooting right now anyway.

When this barrel is toast I think I’m gonna step up to a 20 or 22”.

 

[ThunderMug]

Assuming you used something that would get in the neck/freebore of the chamber? Can miss that carbon ring area with standard bore guide and bore cleaning procedures.

I did use a bore guide and what I would call a standard cleaning process. Both barrels had 110 rounds fire formed in them with 57gr of H1000 and I did not clean either barrel the entire fore-forming process.
Then I scrubbed them before working up loads with the fire formed brass.

I unscrewd my barrels. Here are some crappy iPhone photos until I get my borescope.
I can't see a carbon ring. I assume it would be before the lands?

 

[greyghostnw]

I like to wet a patch in boretech c4 around a brush 2 cal larger let it sit for 10 minutes or so where ring is then take patch off and give it 30 spins then check with cam till gone. Letting a patch sit with ring usually gets it gone first go at it.

 

[fraz01]

Any idea how much the throat has eroded ? May be worth cleaning the throat with bore paste to see if that helps. Does your fire forming load still fire ok with no pressure signs? I did see you are using a barrel cooler so it looks like you tried to keep the barrel cool while fire forming. As over bored as this cartridge is it's going to be hard on barrels. Is this barrel the 400MODBB steel? Broke in a Bartlein SS 7prc barrel a couple weeks ago with factory Hornady and Federal ammo, Shoots lights out and no issue with velocity.

 

[BBob]

I assume it would be before the lands?

No, it will form between the end of the neck and where the case ends. If there, it builds up and can cause a constriction to the end of the neck driving pressure up.
1) your chamber, 2) case in chamber, carbon ring, 3) case in chamber, cleaned

 

[Bassy88]

I bought the 115 NR deepcut dtachs for a 6UM-30, 24” barrel in a 7 twist. Is that ok for shooting the dtachs?