How much clearance when trimming brass?

[fatelvis]

I just purchased the Sinclair case plugs to measure your actual max case length of your chamber (mine is 1.58”) and my current Lapua 6BR brass is at 1.56”. How much “clearance” should I allow from my actual max, before I trim? I assume I am good now with 20K clearance, but I was looking for my target size to trim at. Thanks!

 

[Bill Norris]

.005 to .010 clearance should work well.

 

[fatelvis]

.005 to .010 clearance should work well.

Thanks Bill. Would you just let the brass “grow” another 10-15K before trimming them all to the same length, or even them up now? (They have 2 firings on them and have never been trimmed)

 

[Bill Norris]

Thanks Bill. Would you just let the brass “grow” another 10-15K before trimming them all to the same length, or even them up now? (They have 2 firings on them and have never been trimmed)

I would just let then grow more for now. Watch them as you F/L size as they will definitely grow.

 

[One Eye Pete]

Normally I don't like to go less than 10K on the clearance. (I always like to err on the safe side) As far as I know more clearance is not detrimental and a 6BR has a nice long neck anyway so normally you have plenty of bullet in the neck.
On match loads I like to have all my case lengths equal, even if they are a little shorter (more clearance). On match loads I trim them every firing. (but then I do a lot of case prep on match loads that wouldn't be necessary with hunting or plinking loads)
If you started with 20K and have 2 firings on them then a good compromise might be to set your trimmer for 15K clearance and run them through to see how well they even up.
5K clearance may be OK but to go that close you better be really careful that you don't let any carbon ring build up.

 

[Kracken McGraw]

https://www.6mmbr.com/6brfaq.html

 

[LHSmith]

Normally I don't like to go less than 10K on the clearance. (I always like to err on the safe side) As far as I know more clearance is not detrimental and a 6BR has a nice long neck anyway so normally you have plenty of bullet in the neck.
On match loads I like to have all my case lengths equal, even if they are a little shorter (more clearance). On match loads I trim them every firing. (but then I do a lot of case prep on match loads that wouldn't be necessary with hunting or plinking loads)
If you started with 20K and have 2 firings on them then a good compromise might be to set your trimmer for 15K clearance and run them through to see how well they even up.
5K clearance may be OK but to go that close you better be really careful that you don't let any carbon ring build up.

Actually, there is a downside to having excess clearance - the more you expose the chamber area between the case mouth and the step left by the reamer just forward of the throat, the more likely carbon will get a foothold and build up a carbon "ring". Once started these can be quite difficult to remove. Also there are instances in competition Benchrest where the absolute maximum case volume is sought and shooters go to great lengths in sizing die, reamer selection and fireforming methods to achieve this goal to net them a few more precious fps velocity they believe necessary to win tournaments.

 

[Bill Norris]

Actually, there is a downside to having excess clearance - the more you expose the chamber area between the case mouth and the step left by the reamer just forward of the throat, the more likely carbon will get a foothold and build up a carbon "ring". Once started these can be quite difficult to remove. Also there are instances in competition Benchrest where the absolute maximum case volume is sought and shooters go to great lengths in sizing die, reamer selection and fireforming methods to achieve this goal to net them a few more precious fps velocity they believe necessary to win tournaments.

This is where my head was when I was replying to the question as well.

 

[Mikemci]

If you are using this in BR competition, trim after every resizing, to 1.56. .020 short of the reamer trim length. If you are looking for maximum accuracy, you will be cleaning the barrel and brushing the chamber very regularly and carbon will never get a foothold.

 

[JFrank]

I just purchased the Sinclair case plugs to measure your actual max case length of your chamber (mine is 1.58”) and my current Lapua 6BR brass is at 1.56”. How much “clearance” should I allow from my actual max, before I trim? I assume I am good now with 20K clearance, but I was looking for my target size to trim at. Thanks

IIRC my trimmer is set at 1.55 with a chamber of 1.570