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Author Topic: Question about case bulging from different powders for you reloading experts  (Read 836 times)

Offline wooltie

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I'm shooting 30/06, m70 w/24" benchmark.

So long story short -- after shooting a load with 4350, there is a slight bulge near the case/head that appears on about half of the case's diameter.  When I say bulge, I'm referring to where this section of the case has expanded beyond the remaining section of the case.  You can run your finger from the case shoulder down to the case rim at one point you'll feel a bump and you can see the case has expanded from the bump to the case rim.

The kicker is that the bulge is not uniform; it appears generally on one side of the case, not "all the way around the case".

I was told that this may be due to how the bolt seats the case in the chamber -- meaning the case is offset from the center of the chamber and case expansion is not uniform as a result.  Don't know if that's accurate.

However -- I don't have this issue when I shoot 4064; I only see this issue when I shoot 4350.  I can shoot the same bullet/case/primer but vary the powder (and of course charge weight) to achieve the same velocity, and the cases do not bulge with 4064.

any thoughts as to why?

Offline Stein

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I assume it happened more than once, not just a bad or worn out single case?

Different powders lead to different pressures for the same velocity, so that could explain it.

Were you using IMR or H4350 and how much?

Offline bobcat

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Not sure but I'm curious how much 4350 you're using and is it IMR or Hodgdon? And what bullet?

Offline wooltie

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I've shot a few hundred rounds with IMR4350 and a few hundred with IMR4064.  The issue has always occurred with 4350 regardless of bullet and charge.  I stick within book regardless of bullet/weight e.g. SGK, NP, accubonds, IL, 165g at 55-57 grains IMR4350 seeing 2700-2800 fps.

My load for this year is H4350, 55.3g, 180g SGK seeing 2700 fps.

I've resized and fired these cases without any problems, it's just interesting why one powder seems to cause the bulging while another doesn't.

Offline Yondering

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One of your loads is obviously higher pressure than the other. Achieving the same velocity with two different powders doesn't mean the pressure is the same, not by a long shot. The faster burn rate powder generates higher peak pressure to achieve the same velocity. Along with that, the burn characteristics can be different, causing different results in the brass, one of the reasons why reading traditional "pressure signs" is unreliable.

The "bulge" you describe is because the chamber is a bit oversized at the rear compared to the diameter of the case head. The extractor generally holds the case to one side, so you see expansion on the side of the case that had more gap. It's a pretty normal thing to see on a lot of rifles and nothing to be concerned about.

Offline wooltie

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One of your loads is obviously higher pressure than the other. Achieving the same velocity with two different powders doesn't mean the pressure is the same, not by a long shot. The faster burn rate powder generates higher peak pressure to achieve the same velocity. Along with that, the burn characteristics can be different, causing different results in the brass, one of the reasons why reading traditional "pressure signs" is unreliable.

The "bulge" you describe is because the chamber is a bit oversized at the rear compared to the diameter of the case head. The extractor generally holds the case to one side, so you see expansion on the side of the case that had more gap. It's a pretty normal thing to see on a lot of rifles and nothing to be concerned about.

ahh okay, thanks!

Offline Bushcraft

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Hmmm...I'm not convinced that the issue has anything to do with the extractor. Let's think about this a second...

The pressures from the primer and powder ignition are FAR more than anything the relatively small amount of side leverage pressure that the extractor or extractor plunger spring is imparting.

I'm not a gunsmith by any stretch of the imagination, but I suspect your chamber is slightly out of round.  I have two Remingtons with production barrels that have this issue.  Well, did...I had a friend screw on a custom barrel and that issue went away.  I would be somewhat surprised if Benchmark reamed it that way though. Who did the gunsmithing?

Is your Winchester M70 a CRF or a push-feed?
« Last Edit: July 17, 2019, 11:26:00 AM by Bushcraft »
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Offline Eric M

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One of your loads is obviously higher pressure than the other. Achieving the same velocity with two different powders doesn't mean the pressure is the same, not by a long shot. The faster burn rate powder generates higher peak pressure to achieve the same velocity. Along with that, the burn characteristics can be different, causing different results in the brass, one of the reasons why reading traditional "pressure signs" is unreliable.

The "bulge" you describe is because the chamber is a bit oversized at the rear compared to the diameter of the case head. The extractor generally holds the case to one side, so you see expansion on the side of the case that had more gap. It's a pretty normal thing to see on a lot of rifles and nothing to be concerned about.

ahh okay, thanks!
Even if this is normal isnt it ruining his brass?

Offline Yondering

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One of your loads is obviously higher pressure than the other. Achieving the same velocity with two different powders doesn't mean the pressure is the same, not by a long shot. The faster burn rate powder generates higher peak pressure to achieve the same velocity. Along with that, the burn characteristics can be different, causing different results in the brass, one of the reasons why reading traditional "pressure signs" is unreliable.

The "bulge" you describe is because the chamber is a bit oversized at the rear compared to the diameter of the case head. The extractor generally holds the case to one side, so you see expansion on the side of the case that had more gap. It's a pretty normal thing to see on a lot of rifles and nothing to be concerned about.

ahh okay, thanks!
Even if this is normal isnt it ruining his brass?

No. Unless it's very excessive. A picture would be useful to determine that.

Offline Yondering

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Hmmm...I'm not convinced that the issue has anything to do with the extractor. Let's think about this a second...

The pressures from the primer and powder ignition are FAR more than anything the relatively small amount of side leverage pressure that the extractor or extractor plunger spring is imparting.

I'm not a gunsmith by any stretch of the imagination, but I suspect your chamber is slightly out of round.  I have two Remingtons with production barrels that have this issue.  Well, did...I had a friend screw on a custom barrel and that issue went away.  I would be somewhat surprised if Benchmark reamed it that way though. Who did the gunsmithing?

Is your Winchester M70 a CRF or a push-feed?

Pretty easy to determine for yourself with some experimenting, no need to go by imagination. It can happen from extractor pressure or from laying at the bottom of the chamber from gravity (if the extractor doesn't push it to the side). Mark your cases and try it; it's pretty repeatable.

Offline Crunchy

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Hmmm...I'm not convinced that the issue has anything to do with the extractor. Let's think about this a second...

The pressures from the primer and powder ignition are FAR more than anything the relatively small amount of side leverage pressure that the extractor or extractor plunger spring is imparting.

I'm not a gunsmith by any stretch of the imagination, but I suspect your chamber is slightly out of round.  I have two Remingtons with production barrels that have this issue.  Well, did...I had a friend screw on a custom barrel and that issue went away.  I would be somewhat surprised if Benchmark reamed it that way though. Who did the gunsmithing?

Is your Winchester M70 a CRF or a push-feed?

Benchmark is not going to cut an out of round chamber.  Not sure what the issue is though. 

Offline hogslayer

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Maybe this has already been covered. But measure the web if the fire case before and after sizing.  If itís not getting sized this can happen. 

Offline wooltie

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Hmmm...I'm not convinced that the issue has anything to do with the extractor. Let's think about this a second...

The pressures from the primer and powder ignition are FAR more than anything the relatively small amount of side leverage pressure that the extractor or extractor plunger spring is imparting.

I'm not a gunsmith by any stretch of the imagination, but I suspect your chamber is slightly out of round.  I have two Remingtons with production barrels that have this issue.  Well, did...I had a friend screw on a custom barrel and that issue went away.  I would be somewhat surprised if Benchmark reamed it that way though. Who did the gunsmithing?

Is your Winchester M70 a CRF or a push-feed?

It's a CRF built by FN.  I had another smith install the barrel.  He is local, well known and has been gunsmithing for decades.

The bulging isn't noticeable to the naked eye.  You have to closely inspect the brass and even run a finger alongside the case to feel the 'bump', but it's there.

I'm using winny brass and cci primers.

I've resized the brass and fired again with no issues.
« Last Edit: July 18, 2019, 07:48:25 AM by wooltie »

Offline Bushcraft

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Drills don't make perfectly centered holes, particularly the longer the hole and longer the drill bit. Barrels are deep hole drilled before the rifling is cut in them. Accordingly, and most people don't realize this, that drilled hole down the center of your barrel isn't actually perfectly centered throughout the length of the barrel regardless of how much money you spend on one. Reamers  don't always make perfectly centered holes either depending on how they are setup. There could have been different hardnesses in the steel being chambered.  The lathe could be old and have excessive runout. The chamber could have been cut without being perfectly aligned with the bore (as it should be!). Reamers can cut out of round chambers if they aren't set up correctly. The reamer could have been used a lot and had asymmetric wear. Lot's of variables at play.  Really serious shooters will oftentimes buy a reamer cut to their exact specifications and it is ONLY used on their new barrels.

Try this:

Will a perfectly round FL resized piece of brass (use a mic and/or a runout gauge) that you've bumped back one to two thousandths wiggle at all (left, right, up, down) when you push it in the chamber with just the tip of your finger?  Does it wiggle more in one direction than another?

As you are (slowly) ejecting a spent cartridge, try marking the brass with a sharpie in front of the ejector (so you have a reference mark). Mic it and highlight the smallest and largest diameters. Then try slowly slipping that spent marked cartridge back in the chamber with a finger, indexing it 45 degrees each time, feeling for and noting any resistance. Observe how far you can push the spent round back in the chamber with your finger as you turn it. (Use a cleaning rod carefully slipped in from the muzzle to note the different depths and push the case back each time before rotating and pushing back in with your finger.)

If your chamber is out of round (oval) it is going to be expressed on the external dimensions of your fired brass. If you have a perfectly round chamber a fire-formed piece of brass may not necessarily slip all the way back into the chamber and index off the shoulder, but it will slip into the chamber essentially the exact same distance regardless of how it is spun if you are using good brass.  If the chamber is out of round it, a piece of fired brass will not slip into the chamber to uniform depths when it is spun.

Hope that makes sense.

Of course, the other factor could be the quality, or lack thereof, of the brass.  If you get one that's thin on one side, clearly that is going to bulge out more than the thicker side of the brass. Winchester brass is infamous for not having the best manufacturing tolerances.  None of it is absolutely perfect due to the way it's made, but I've had to spend a lot of time working my Winchester .308 Win. and .300 WSM bulk brass over to get them nearly identical and there's always bunch that I just use for foulers or short range practice rounds.



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Offline Yondering

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Drills don't make perfectly centered holes, particularly the longer the hole and longer the drill bit. Barrels are deep hole drilled before the rifling is cut in them. Accordingly, and most people don't realize this, that drilled hole down the center of your barrel isn't actually perfectly centered throughout the length of the barrel regardless of how much money you spend on one. Reamers  don't always make perfectly centered holes either depending on how they are setup. There could have been different hardnesses in the steel being chambered.  The lathe could be old and have excessive runout. The chamber could have been cut without being perfectly aligned with the bore (as it should be!). Reamers can cut out of round chambers if they aren't set up correctly. The reamer could have been used a lot and had asymmetric wear. Lot's of variables at play.  Really serious shooters will oftentimes buy a reamer cut to their exact specifications and it is ONLY used on their new barrels.


While most of those details are technically accurate on their own, it's misleading in the context of this thread and sounds like you know just enough to confuse the issue. For example - it doesn't matter if the barrel blank wasn't drilled perfectly centered, because the barrel's exterior dimensions are machined concentric to the hole afterwards, not concentric to the OD before drilling and rifling. While it's possible for a chamber to be off-center relative to the bolt, the things you list are not the causes, nor do we have any real reason to think the OP's chamber is off-center.

What the OP described is a simple and common phenomenon with generous factory rifle chambers. It's not unusual, it happens more than most people notice, and it's not a problem. No need to make a big deal out of something that doesn't matter.

 


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