Gas blowback ?

[jwfire25]

Hello,

Quick question. I am using Winchester brass for a 308 load. I am using a 168 SMK, with the last load being 44.5 grains of Varget. For some reason I can not get the brass to fully seal. I am still getting blowback around the neck. The brass in the picture has been fired 4 times. I am curious if it's the brass? 44.5 grains of Varget should definitely be building enough pressure to fully fire form. I am curious on your guys thoughts!

Thanks!

John

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[kcheung2]

Has that brass been cleaned or is that how it looks immediately after firing? It actually looks more like annealing than soot.

[jwfire25]

Has that brass been cleaned or is that how it looks immediately after firing? It actually looks more like annealing than soot.

This is how it look immediately after firing. This brass has not been annealed

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[devster55]

Looks pretty normal to me. Is it a gas gun? The factory xm80 rounds look just like this out of my M1A. From my understanding it’s ok to have some on the neck. You have problems when it starts going below the shoulder.

[jwfire25]

Bolt action. Oh ok. None of the factory ammo I use ever has any soot around the neck. As long as it's normal. I'm just making sure I'm not doing something wrong. These particular loads were pretty hot so I figured everything should have been sealed up tight.

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[rsrocket1]

The important thing is that the case body is clean. You are NOT getting gas blowby unless you think there is a gas path from the neck of the chamber out to the open air. Sooty necks are the result of the neck not completely expanding to seal the chamber before the body. Your load of 44.5g Varget looks like it will generate over 56,000 psi peak (Quickload). That's pretty hot.

The brass is fine. Make sure you aren't seeing any extractor imprints on the bottom of the cases.

[smoothy8500]

None of the factory ammo I use ever has any soot around the neck... These particular loads were pretty hot so I figured everything should have been sealed up

That is normal soot with almost every reloading powder available. As you noted, that's a pretty hot load. If you had good performance around 41-42(ish)gr, that will provide adequate velocity to maintain accuracy at 600yds.

[fguffey]

A reloader in the neighborhood came up with 80 7 Remington mag cases (4 boxes). All of the cases had a black glaze around the necks, I expressed a concern and suggested we visit the reloader/ shooter he got the cases from. He said it was too late, he said he purchased the cases from the wife after he died. And then I expressed concern about the rifle.

My concern had to do with the carbon on the necks, I had to cut the carbon off with a knife. There was no way the neck was expanding when the round was fired; and the neck of the chamber was no different. Problem, the rifle was no longer in the family.

I suggested the using a faster powder, I suggested the bullet could have been moved closer to the lands, I suggested the throat of the chamber could be shot out, the shot out throat could delay the build up of pressure. And then there was the possibility the shooter/reloader was oversizing his cases.

Time is a factor.

F. Guffey

[jwfire25]

The important thing is that the case body is clean. You are NOT getting gas blowby unless you think there is a gas path from the neck of the chamber out to the open air. Sooty necks are the result of the neck not completely expanding to seal the chamber before the body. Your load of 44.5g Varget looks like it will generate over 56,000 psi peak (Quickload). That's pretty hot.

The brass is fine. Make sure you aren't seeing any extractor imprints on the bottom of the cases.

No ejector Marks. I loaded it that hot to see if the soot around the neck would stop. I plan on backing it off to around 41-43 grains. Once I figure out what the rifle likes.

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[jwfire25]

I am trying to replicate the results I get with 168 grain gold medal match. I shot this 4 shot group at 100 yards. With my Bergara HMR. I also just picked up some 4064 to try out. I was messing with seating depth also but so far the SMK seems to be best at the overall length of 2.800.

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[divingin]

The neck soot is normal. You'll get a bit of gas leakage before the neck seals to the chamber, and that's what you're seeing.

Saw a guy last weekend with a 300 WinMag; his cases were sooty from case mouth to belt. That was a sealing problem.

[fguffey]

Too slow? Or low pressure? The bullet can be too light. The pressure never got high enough to expand the case enough to seal the chamber. There are time the gas trapped between the case and chamber can collapse the case when the pressure inside the case drips.

F. Guffey

[smoothy8500]

I am trying to replicate the results I get with 168 grain gold medal match. I also just picked up some 4064 to try out. I was messing with seating depth also but so far the SMK seems to be best at the overall length of 2.800"

I use IMR4064 and get good results with either 168's and 175's.

[jwfire25]

I use IMR4064 and get good results with either 168's and 175's.

How many grains do you use?

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[rsrocket1]

I tried to find some cases with soot but no blow by and this is about as good as I could get. They are 45ACP loaded with a +P charge of Titegroup. You might be able to see a "U" shaped mark of soot that goes about 1/4 the circumference of the case. This shows that the gases made it below the case rim but not all the way out to the breech. The case did its job by expanding and sealing off the gas.



Early in my reloading career I used Lee dippers to load what I thought was about 4.0g Unique in a 45ACP cartridge. It turned out to be only about 3.5g. It wasn't until my kids were watching me shoot and told me they saw my hair being blown back when I shot the gun. The cases were sooty the entire length. That was ture blow by.

If you don't see soot all the way down to the case head, don't worry about it.