Chamber length, trimming & carbon ring

[Shooter Mike]

I don’t know what I don’t know. I’m reading that it’s best to measure your chamber length and trim your brass to no more than 0.005” shorter than chamber length to help reduce carbon ring. It’s said that carbon ring can prevent rounds from properly chambering, and increase chamber pressure. I get that. Make sense.

Here’s what doesn’t make sense. If brass is trimmed to 0.005” shorter than chamber length- that smaller area between the case mouth and the throat, wouldn’t the development of carbon in that area result in change sooner than if the space was longer?


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[Rich M]

Carbon ring? So if the brass is too short it will cause a carbon ring?

I been reloading 3-4 calibers for 20-25 yrs and havent heard of that til today. Some ML guys have issues w that.

Not trying to be an ass here. Very curious.

Most calibers recommend casing lengths.

 

[ddowning]

I don’t know what I don’t know. I’m reading that it’s best to measure your chamber length and trim your brass to no more than 0.005” shorter than chamber length to help reduce carbon ring. It’s said that carbon ring can prevent rounds from properly chambering, and increase chamber pressure. I get that. Make sense.

Here’s what doesn’t make sense. If brass is trimmed to 0.005” shorter than chamber length- that smaller area between the case mouth and the throat, wouldn’t the development of carbon in that area result in change sooner than if the space was longer?


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This is true, but you're in the weeds pretty deep. That is why the gentleman above responded the way he did.

 

[SloppyJ]

This sounds like it was stemmed from a Backfire video. That DB said he cleans his 7PRC every 40rds to prevent a carbon ring and that the 7prc is a finicky cartridge due to the tight tolerances.

OP, I think you're too far into the weeds man. Make sure your brass is within trim length spec and you're good to go. When I trim, I trim every single piece of brass I'm shooting in that gun back to the same length for consistency.

If you haven't seen it and feel how I do about the Backfire TV guy, this is worth a watch. Sometimes these dudes make me laugh and this was a good one. In more recent events, they have a video where the backfire dude responds.

 

[BBob]

Problems with or the existence of a carbon ring is more of a thing on the internets than in real life. Sure it can and does happen but not nearly as much as you’d think it does.

 

[Shooter Mike]

I wouldn’t say ok too deep in the weeds on this; rather I disagree with the idea of trimming brass based on chamber length, as it relates to the development of carbon ring.

It was Blake from The RelaodingAllDay YouTube channel who I first came across, that mentioned it.

As I mentioned above, my thought is, the tighter the space (0.005”) the more detrimental a carbon ring would be. Blake (and others) who say to trim brass based on chamber length state this small area will reduce carbon ring. They didn’t say eliminate. That leaves me to also believe that you would see any ill effects of a carbon ring sooner.

Me …. I trim my brass to book length’ish. My new 7 PRC, I had 148 rounds through it. It is shooting fine. I now have 148 fire-formed cases ready to reload. I trimmed the fire formed cases I shot today to 2.268. I cleaned the barrel to bare steel, and removed the carbon ring. I shot 5 foulers and then 21 rounds through it today to find the load I’m moving forward with. It shot the same as it did today, as it did last week.

That’s enough for me. I’ll clean it again when I see its performance degrade.


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[TaperPin]

, wouldn’t the development of carbon in that area result in change sooner than if the space was longer?

That’s a good question - questioning most reloading practices makes sense, at least to me.

Every 6 months someone someone posts with an accuracy or pressure problem that is clearly carbon ring related, so it seems relevant.

For those of us that clean regularly and verify any carbon fouling has been removed with a borescope, it’s a solution to a problem that doesn’t exist. To suggest it instead of simply cleaning, seems like poor practice.

Even if .005” under chamber length reduced carbon build up, how many firings does it take to grow brass that long? It complicates an otherwise simple trim dimension that has worked well for a very long time. My fixed length trim pilots would no longer work - so that would add even more complexity.

Extra slop in the chamber dimensions will dramatically cut down on carbon ring issues - make it sloppy enough and someone might never have a carbon ring issue (and the gun will never shoot as good good as it would have with tighter tolerances).

 

[Weldor]

Problems with or the existence of a carbon ring is more of a thing on the internets than in real life. Sure it can and does happen but not nearly as much as you’d think it does.

I agree, I have seen it more in 6.5 prc than most others. That's through a borescope. I just looked at a barrel for a friend (just like op stated won't chamber a round) It would not chamber. Took alook and there it was. 20 minutes later after removing it it chambered just fine. I can't remember when it was ever talked about except the long range bench shooters years ago.

 

[Shooter Mike]

I agree, I have seen it more in 6.5 prc than most others. That's through a borescope. I just looked at a barrel for a friend (just like op stated won't chamber a round) It would not chamber. Took alook and there it was. 20 minutes later after removing it it chambered just fine. I can't remember when it was ever talked about except the long range bench shooters years ago.

In a tight chamber it may have some relevance, but for the majority i don’t think it does. And I absolutely disagree with the methodology Blake, from ReloadingAllDay describes. Trimming ultra short would only exacerbate the problem- it would make the chamber even tighter.


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[BBob]

How does trimming ultra short make a chamber tighter and what is the definition of ultra short? Is it .010”, .020”, or more short???

Practically no one in BR uses tight chambers anymore. Dimensions have opened up both in short and long range. People no longer use really tight necks and there’s at least a couple of great shooters that have tried and have won using no turn necks. For reference typical neck clearance these days is in the neighborhood of .004”. Not long ago it .0015-.002”. Freebore diameters have opened up a bit as well.

 

[Shooter Mike]

How does trimming ultra short make a chamber tighter and what is the definition of ultra short? Is it .010”, .020”, or more short???

Practically no one in BR uses tight chambers anymore. Dimensions have opened up both in short and long range. People no longer use really tight necks and there’s at least a couple of great shooters that have tried and have won using no turn necks. For reference typical neck clearance these days is in the neighborhood of .004”. Not long ago it .0015-.002”. Freebore diameters have opened up a bit as well.

I think you’re missing the point of what I’m saying. The recommendation has been to trim your brass to be no farther than 5000s of an inch from the end of the chamber. I think that is hogwash.


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[BBob]

I think you’re missing the point of what I’m saying. The recommendation has been to trim your brass to be no farther than 5000s of an inch from the end of the chamber. I think that is hogwash.

Ah yes I took “short” as to mean a shorter case. I’d agree that .0005” clearance is too little and silly. Most people would have no way to measure and verify it accurately anyway.

 

[wind gypsy]

5000s of an inch from the end of the chamber

I’d agree that .0005” clearance is too little and silly.

You guys mean 0.005", right?

 

[Shooter Mike]

You guys mean 0.005", right?

Yes. Voice to text spelled it out.


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[E.Shell]

IMO, no matter where the case mouth ends up, that's where any carbon buildup will occur. Cutting the case mouth back just moves the deposit back.

That said, I've been handloading for multiple cartridges since 1971 and the ONLY time I ever had issues with hard carbon in the throat was with a 6.5-300 Wby. I was using large quantities of H-870, which is a very slow powder with a lot of deterrent coating.

The buildup occurred over a 400-500 rounds. The symptom was that eventually, each time I loaded a batch of ammo, pressures ran a little higher than the last batch, even though I was working with the same component lots. I had cleaned the bore regularly, but that hard carbon wasn't removed during normal cleaning.

 

[BBob]

You guys mean 0.005", right?

He said .0005”, it was not my number.

 

[Shooter Mike]

He said .0005”, it was not my number.

0.005” is what I meant. FWIW, I’d be lucky to even measure 0.005” accurately in a chamber, lol.


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[TaperPin]

As a practical matter, how is the actual chamber length to the end of the neck even measured? Blindly trust what it is supposed to be? Is there a tool? Casting the chamber with Cerosafe? Cut half the neck off and add a bullet or something allowing the cut off part to extend out like a sliding plug? With the barrel off I can put a pin gauge in the chamber that will bottom out against the end of where the neck goes and compare that with a headspace gauge, but few people have that luxury.

I doubt most reloaders could even measure it to within a few .001” and at least one out of every fifty will screw it up bad enough until the case is too long and pressures spike. Two thicknesses of scotch tape are like .006”

 

[Shooter Mike]

As a practical matter, how is the actual chamber length to the end of the neck even measured? Blindly trust what it is supposed to be? Is there a tool? Casting the chamber with Cerosafe? Cut half the neck off and add a bullet or something allowing the cut off part to extend out like a sliding plug? With the barrel off I can put a pin gauge in the chamber that will bottom out against the end of where the neck goes and compare that with a headspace gauge, but few people have that luxury.

I doubt most reloaders could even measure it to within a few .001” and at least one out of every fifty will screw it up bad enough until the case is too long and pressures spike. Two thicknesses of scotch tape are like .006”

There is a tool. The Sinclair Chamber Length Gage


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[Rugger7622]

Interesting topic and timing. I'm reloading for 7mm-08 and the suggested trim length is 2.025. I just got the Sinclair Chamber tool and my chamber measures. 2.0645. Following traditional trim wisdom, I would trim to 2.0545 - if they ever grow to that length. I'm trying to wrap my head around why I would trim to 2.025 knowing the length of my chamber? If I didn't measure the length, I get trimming to that length, but knowing my chamber length seem to change the equation for me.

Another question is why doesn't ever reloader buy a chamber length gauge ($15) and measure their chamber? We do so many other measurements, seems like this is one that everyone should know? Am I missing something?