1X fired 6 Dasher brass not sealing

[TackDriv3r]

Fireformed all 6 Dasher virgin brass, annealed and full sized with the SAC modular sizing die, used a .263 bushing and a .242 mandrel and loaded 105 Hybrids. First time I seen carbon on the shoulders of each 1X fired brass.
Prior, on my virgin brass, I used a .265 bushing and I did not see any carbon on the shoulders at all after fired.. My loaded neck is a .268 and the chamber is a no turn .275
What should I look for to prevent this from happening? Seems that the neck is not sealing off the gases when fired.

 

[Fast14riot]

Generally that's too low of a charge

 

[Gray420]

Is it alpha brass? I feel it takes 3 or 4 firing on the alpha brass before the brass is fully formed. Clean it, reloaded it and resend it. I would second fast14’s comment as well.

 

[C BOSSE]

strongly agree= low charge / or too slow powder, or both, that is also a very loose neck .275 that will not give you a lot of case life stretching that far, I most likely am wrong but last i knew .272 was plenty big enough for no turn necks

 

[C BOSSE]

i have not used alfa brass in a dasher / but most likely to go light loadings will help save the primer pockets

 

[Ccrider]

With .007 clearance, the neck may not be sealing well allowing carbon to get to the shoulder. That is more clearance than I would be comfortable with.

 

[TackDriv3r]

Generally that's too low of a charge

Loaded from 31.6 to 32.2 grains of Varget. 32.2 grain velocity was at 2980 fps. On the virgin brass prior, I loaded it at 31.6 grains, and velocity was at 2920 fps and there was no carbon on the shoulders. Barrel is a 4 groove and 30 inches.

 

[TackDriv3r]

Is it alpha brass? I feel it takes 3 or 4 firing on the alpha brass before the brass is fully formed. Clean it, reloaded it and resend it. I would second fast14’s comment as well.

Yes, its Alpha brass.

 

[JFrank]

.001 neck tension is extremely light. That would be disaster in my Dasher or Br-a

 

[TackDriv3r]

.001 neck tension is extremely light. That would be disaster in my Dasher or Br-a

What do you suggest?

 

[JFrank]

What do you suggest?

with a .268 loaded round I would start with a .265 bushing giving me .003 bullet hold for my initial load work then test different size bushings as part of the load development.

Just me of course…

 

[TackDriv3r]

with a .268 loaded round I would start with a .265 bushing giving me .003 bullet hold for my initial load work then test different size bushings as part of the load development.

Just me of course…

No mandrel?

 

[JFrank]

No mandrel?

Nope..
The only time I personally use one is to relax brand new un-fired brass necks, after that first time I haven’t found the need.

Not advising , just sharing..

Jim

 

[TackDriv3r]

Size 1/2 of the neck with the bushing. The unsized part will fully expand to the chamber, after 3 high pressure firings.

The photo looks like the head to datum has gotten shorter. Allows more gas leakage. This can happen on a low pressure loading.
As the case body expands outward, the shoulder is moved back. Shorter head to datum.

Shoulder looks rounded. Not fully formed? View attachment 1668612

That is what I do with my Redding dies for other rifles, but for this Dasher I have the Short Action Customs modular die where the bushing and mandrel sizes in one step. Unfortunately the bushing is in a fixed position where it sizes the whole neck to the shoulder junction. It's not adjustable, so I would need to get a different sizer, what die brand is best?
I was shooting high 2800 to 2970 fps, its not low pressure , isn't it?

 

[Webster]

Fireformed all 6 Dasher virgin brass, annealed and full sized with the SAC modular sizing die, used a .263 bushing and a .242 mandrel and loaded 105 Hybrids. First time I seen carbon on the shoulders of each 1X fired brass.
Prior, on my virgin brass, I used a .265 bushing and I did not see any carbon on the shoulders at all after fired.. My loaded neck is a .268 and the chamber is a no turn .275
What should I look for to prevent this from happening? Seems that the neck is not sealing off the gases when fired.

I thought a no turn neck was less than .275? Just looked up 6mm no turn. .272 is std special request is .271. ..275 doesn't sound normal? Your saying you have 7 thou clearance? Did you gun smith tell you it was a .275" neck?

I have a no turn 6BR. Don't know the reamer spec. Kelbly chambered the barrel and I asked for no turn. A loaded round o.d. is .2695. The necks were turned to 0.0125" many years ago and never did a cleanup pass. So I probably have about 0.002" clearance on each side. Never had soot below the neck. Same on my 6BRX.

Looks like .002" is tight 0.004" is no turn after reading several articles. That's split over both sides. I would verify these numbers to be sure the clearances I stated are correct. Another website says .272" is the PTG STD no turn. Are you using a bump gauge after the cases are fired twice.

I always had black soot yours is gray? Your soot deposit looks very thick?

 

[Webster]

.001 neck tension is extremely light. That would be disaster in my Dasher or Br-a

More neck tension might allow the pressure to build higher before the bullet leaves the neck giving a better seal? I use a .265" bushing with a 0.125" thick neck.

 

[JFrank]

IDK ~That’s a little above my pay grade

 

[Jerry Snyder]

The neck portion on the JGS reamer for my 6 dasher says 272.5

 

[243winxb]

Short Action Customs modular die

I have not used one. Using Redding type S fl bushing die on 243 win & 6.5 CM.

Their video said the shoulder may be set back .015" when shell holder contacts the sizing die? About 4 minutes 15 seconds in to video.
If i understand video correctly?? To much set back of shoulder??

 

[243winxb]

Shims- .001" to .025"
Looks like another way to adjust the shoulder bump??