30br chamber length

[P1ZombieKiller]

If new virgin 6br Lapua brass expanded for 30br is 1.522ish long, and the assumption is that it will only grow to 1.528ish after fired a few times, what is the advantage/disadvantage to having a 1.530 chamber?

 

[RGRobinett]

If new virgin 6br Lapua brass expanded for 30br is 1.522ish long, and the assumption is that it will only grow to 1.528ish after fired a few times, what is the advantage/disadvantage to having a 1.530 chamber?

Presuming nothing much shorter than this length, I wouldn't want chamber length of over 1.520": initial fire-form would be trimmed @ 1.520", then, would trim & maintain @ 1.510". Of course, prior to F-F, the actual chamber length would be determined . . . I have learned and re-learned to never trust a print.

Unless cases can be made longer, an advantage to longer doesn't fit my paradigm. Some F-F methods do accommodate longer brass. RG

 

[SmokinJoe]

What Randy is saying is the "original" standard that we used from way back, but it is intended for brass that is mandrel formed only. Another way to form 30BR brass is to blow it out from 6mm to 30cal by filling the case with Bullseye or similar, and then seating a plug material on top like tissue or wax ( I use 1/4" poly balls) and fire it in a long neck chamber which gives an OAL of something like 1.445 - 1.550. To me this made the best brass I ever made; it was completely concentric for turning and since it moved material forward it thinned the donut area and the neck a little. Key to doing that is having a dedicated FF barrel reamed with an extra long neck chamber which requires a special reamer. I had PT&G make mine, print attached. Also attached is a pic of before (loaded for FF) and after firing. Please be aware that this doesn't work well if you FF in a match chamber because the the neck will be too long and will end up crimped down into the lead area, and it's very difficult to get rid of that afterwards. Something to consider and experiment with.

 

[LVLAaron]

What Randy is saying is the "original" standard that we used from way back, but it is intended for brass that is mandrel formed only. Another way to form 30BR brass is to blow it out from 6mm to 30cal by filling the case with Bullseye or similar, and then seating a plug material on top like tissue or wax ( I use 1/4" poly balls) and fire it in a long neck chamber which gives an OAL of something like 1.445 - 1.550. To me this made the best brass I ever made; it was completely concentric for turning and since it moved material forward it thinned the donut area and the neck a little. Key to doing that is having a dedicated FF barrel reamed with an extra long neck chamber which requires a special reamer. I had PT&G make mine, print attached. Also attached is a pic of before (loaded for FF) and after firing. Please be aware that this doesn't work well if you FF in a match chamber because the the neck will be too long and will end up crimped down into the lead area, and it's very difficult to get rid of that afterwards. Something to consider and experiment with.

Could a guy pre-trim the brass before fireforming, and avoid the special chamber?

 

[P1ZombieKiller]

Let me reask the same question in a different way to get what I am after.

If the above measurements are still true....

Can i get away with never trimming brass? Is this even a good idea?

What happens if my brass never grows as far as the chamber length, or will it always continue to grow and I will always have to trim?

 

[gunsandgunsmithing]

Let me reask the same question in a different way to get what I am after.

If the above measurements are still true....

Can i get away with never trimming brass? Is this even a good idea?

What happens if my brass never grows as far as the chamber length, or will it always continue to grow and I will always have to trim?

I think excess area in front of the case mouth contributes to a more substantial carbon ring and MORE trimming, rather than less, if anything. But theoretically, yes and it you stay on top of any carbon buildup, there ya go. But brass always grows, mostly from the firing, sizing, firing sequence

 

[JoeDuke]

One reason to trim is that all cases do not seem to grow the same amount at the same time. I like to keep mine real close to the same regardless to chamber neck length. They do seem to quit growing much after a number of firings. I have never experimented with the longer clearance you are considering. Seems you will have to spend time controlling carbon ring buildup rather than case trimming.