Chamber length, trimming & carbon ring

[Shooter Mike]

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?

The suggestion has been made that one should trim the brass to 0.005” of chamber length. So in your case, if you were to follow that guidance, you would trim your brass to 2.059, with the theory that the longer trim length which leaves 0.005” between the case mouth and the end of the chamber before the throat, leaves less room for carbon ring to develop. My argument is that the smaller space would still develop carbon, and would have ill effects sooner. I also believe there is prescribed trim lengths for a reason.

If you’re trimming your brass to book spec, what would gain by leaving it longer? More bearing surface? And what’s the value in that?

What can you possibly gain by measuring your chamber? I really don’t know. Maybe someone does.


Sent from my iPhone using Tapatalk

 

[TaperPin]

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?

That’s really interesting - now I’m curious about my chambers. I suppose someone could test it with max length and short brass to see if groups change, although I keep hearing it’s not a significant factor, even in the accuracy community.

 

[Rugger7622]

I think you gain maybe not ever really having to trim brass, don't know why it's not a more popular option. Just would have to continue to inside/outside chamfer. Most people I know don't like to trim brass. It's interesting that more people don't measure their chambers to know their trim length when most reloaders are pretty data driven. It's simple to use the sinclair tool.

 

[huntnful]

I fire 100 pieces of brass. Grab ten of the fired cases, find which one is the shortest, and trim the whole lot to that length and pretty much never touch them again.

 

[Shooter Mike]

I fire 100 pieces of brass. Grab ten of the fired cases, find which one is the shortest, and trim the whole lot to that length and pretty much never touch them again.

I think that’s the best and most reasonable way to go about things.


Sent from my iPhone using Tapatalk

 

[Rugger7622]

Why do you think that? We don't do that with powders, bullet lengths, neck tension, etc. Not being argumentative just seems like an area in a data driven hobby that 99% of the people approach it differently. Maybe in the end, it makes zero difference but it curious to me.

 

[Shooter Mike]

Go test it and report back. If there were any value to it, the recommendation for trim lengths would be based on chamber length. Change the length of the neck, you change the bearing surface. The more bearing surface, the more opportunity for the case neck to affect the bullet. The smaller space between the case mouth and chamber end would also cause ill effects sooner as carbon builds in that smaller space.

But again, go test it and report back. In the mean time …. I’m not fixing what isn’t broken.

If you think it’s going to improve your accuracy, shoot 20-30 rounds with brass trimmed within 0.005” and brass trimmed to book length. I’d be willing to bet there’s no improvement by trimming off chamber length.


Sent from my iPhone using Tapatalk

 

[Rugger7622]

I totally agree, I don't think there will be any difference at all. So, why trim if the brass still fits with .0010 of your chamber length? Again, I'm not being argumentative, just curious why this isn't much of a topic on any reloading forum. I don't plan trim until I need to and I'll report anything back, but I don't think I will have anything to report.

 

[wyosam]

I’ve pretty much stopped shooting cartridges that I have to trim. My Ackley cartridges never get trimmed. I’ve got 223ai brass with close to 20 firings on it. Never even uniformed them after fireforming. Maybe some day I’ll stick a borescope in with an empty case in the chamber and see how much room is left. That would probably make me worry about the throat on a rifle that still shoots great though, so I better not do that.


Sent from my iPhone using Tapatalk

 

[Vern400]

I have not found any correlation between case trim length and accuracy. I use the cheap Lee cutter and lock stud. It's very consistent but it does trim to the minimum spec in my caliber.

I had a horrible carbon ring when I bought a borescope. 3500 rounds and never knew carbon ring was a thing. So I spent hours cleaning it out with free all, Kroil, brushes, patches, and right at the end JB bore paste. The rifle shot the same. It's a 308 and they just run. I can understand that some of the more modern cartridges maybe more sensitive if you're looking for benchrest accuracy.

In the whole scope of things, I found a lot of practices that help improve precision. Case trimming, to me simply determines that the case will actually fit in the chamber. If I have 0.010 variation within a box of ammunition I don't lose sleep over it as long as they all fit and go bang.

There aren't many things in reloading where you can say " good enough is good enough" but this might be a good example.

 

[Weldor]

It's a enigma, I just seen a quality weapon 6.5 PRC maker starts with a C,.Round count unknown. Would not chamber a loaded factory round. Fired brass no problem. Borescoped large carbon ring. Removed it, chambers just fine now? @ smith's looked at it also, both said carbon ring. I know guys are all over the board on carbon rings, I've seen more in the last couple of years than the last 40. It's a enigma wrapped in a mystery. LOL

 

[jaydoc24]

You’re spot on about trimming brass to 0.005” shorter to reduce carbon ring problems. But yeah, that shorter gap might mean carbon buildup could affect chambering a bit sooner compared to a longer space.

Have you thought about how often you’ll need to trim the brass and if it’ll affect your reloads' consistency?