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6 Dasher Brass--To trim or not to trim

HTSmith

Silver $$ Contributor
My dasher chamber length is 1.555" according to the reamer print. I would have to trim my newly blown out brass to 1.530" to get them all the same. I'm concerned about that .025" gap that it would leave between the case mouth and the end of the chamber. So do I go ahead and trim them all or fire them a few times and let them grow? Appreciate your input.
 
Curious so I measured some that were shot yesterday and have not been resized yet. 1.560" That is my trim length also so I guess they will be trimmed back after I anneal and size. Mine is not your reamer but I would leave them as long as possible.

An issue with Dasher is getting enough neck length to hold the bullet. Some want more contact than others but as the throat erodes and you "chase" it, you may find you need all the neck length you can get.

I say keep them as long as possible.
 
I agree with measuring chamber end length, and I let them grow until within 5thou of end before trimming any. Eventually they will be the same length.

The greater the clearance, the faster/harder carbon builds in the chamber neck.
And since I minimize neck clearance in general, I don't want a bunch of carbon piling up there.
Another issue is with sealing. I want my necks to snap seal quickly, so I don't want pressure getting back between neck/shoulder & chamber to cause variance in sealing/timing/grip.

Don't trim them all to the worst condition.
Best to accept reasonable neck length variance to begin, and let brass make it's way to preferred condition.
 
During firing, when the brass expands, how much longer does it get? Does it hit the end of the chamber if it is too long? If so, does this effect accuracy?
 
https://www.sinclairintl.com/reload...s/sinclair-chamber-length-gage-prod32925.aspx

See the little inset video to learn how to determine your specific actual dimension.

ETA: I was surprised when I found out how big some of my factory chambers were. Back in the day, bore scopes were not always long enough to place an empty case in the chamber and then peer at them from the muzzle. We used this method to determine a better trim length on a case by case basis. If you don’t want to sacrifice a case with this tool method, you can use the long bore scope method to accomplish the same.
 
Last edited:
Ccrider said:
During firing, when the brass expands, how much longer does it get? Does it hit the end of the chamber if it is too long? If so, does this effect accuracy?
Click to expand...
1. Neck expansion does not lengthen necks.
2. Yes the neck can hit the end of the chamber if too long, or with excess shoulder bump.
3. If you run out of clearance the case mouth could swage down against bullet bearing (crimping). This could affect bullet release timing, and is potentially dangerous with a warm-hot load.
 
RegionRat said:
https://www.sinclairintl.com/reload...s/sinclair-chamber-length-gage-prod32925.aspx

See the little inset video to learn how to determine your specific actual dimension.

ETA: I was surprised when I found out how big some of my factory chambers were. Back in the day, bore scopes were not always long enough to place an empty case in the chamber and then peer at them from the muzzle. We used this method to determine a better trim length on a case by case basis. If you don’t want to sacrifice a case with this tool method, you can use the long bore scope method to accomplish the same.
Click to expand...
Back in the day when all I had was my Hawkeye I drilled out the primer pockets on a few cases to look at me clearances. Also made my own version of Sinclair’s tool. Also if I remember correctly a 22 Rimfire case would fit in the mouth if a 6mm case and measured my length that way too

Wayne
 
HTSmith said:
My dasher chamber length is 1.555" according to the reamer print. I would have to trim my newly blown out brass to 1.530" to get them all the same. I'm concerned about that .025" gap that it would leave between the case mouth and the end of the chamber. So do I go ahead and trim them all or fire them a few times and let them grow? Appreciate your input.
Click to expand...
I would fire all 2-3 times and then trim to uniform length. I trim to 1.540”
 
I have never trimmed a Dasher case. I have a 1.555 chamber and my rounds have never grown enough (8 firings) to begin to reach it. Basically ZERO (+.001) length growth since they were formed. Maybe by the time the pockets give out I will be close.
 
HTSmith said:
My dasher chamber length is 1.555" according to the reamer print. I would have to trim my newly blown out brass to 1.530" to get them all the same. I'm concerned about that .025" gap that it would leave between the case mouth and the end of the chamber. So do I go ahead and trim them all or fire them a few times and let them grow? Appreciate your input.
Click to expand...
Let them all grow as you fire them the first 2-3 times. Set your trimmer at 1.545” and trim as needed.
 
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