Dasher chamber question for the experts

[Carl Ross]

I screwed on a fresh 6 Dasher barrel today from a new gunsmith I haven't used before. In the course of getting it set up I noticed the base of the chamber seems REALLY tight. So I started taking some measurements.

At the .200" line here's what I've got:

New Lapua 6 BR Brass: .4693"
8x Fired Lapua Dasher brass from previous barrel: .4712"
8x Fired Lapua Dasher, sized in either a Forster FL die or Whitley's Redding FL die: .4708"

The fourth decimal place is an eyeball measurement off my micrometer, but they were all pretty repeatable numbers.

FWIW, the sized Lapua Dasher will chamber and extract with zero resistance in my current (old) chamber, the bolt just falls open and closed.

Chambering the sized Lapua Dasher brass (.4708") in the new chamber will shave brass off the base and require aggressive tapping of the bolt beyond the primary extraction cam to remove.

Chambering the new, unfired Lapua 6 BR brass (.4693") in the new chamber will take a little sharpie mark off the base, and will require a little extraction camming action (tiny click).

Is this a situation a Harrel's D4 die could help with, or am I going to fight this for as long as I use this chamber?

Appreciate it guys,
Carl

 

[dkhunt14]

First off, I don't think a chamber should shave off brass. It must be really sharp on edge or something.. You can try a small base die and see if you can get a little more size on case. Or you can send Harrels a fired case and they should have a die to size it. They have multiple sizes. Call them and see. Matt

 

[avidflyer]

What are the specs on the neck. Ive seen a very tight neck cause issues like this... Guy couldn’t chamber new brass and very stiff

 

[Carl Ross]

Neck is .272”, so no turn. Also I confirmed the base is the only place touching via sharpied cases, both formed Dasher and new BR.

 

[nmjwolf]

Ask for a reamer print. The 200 dimension could be too tight for your sizing dies...

I had a dasher with a .4700 dimension and needed to use a small base 308 die every firing even when sizing with a D4 from Harrells....it was sucky.

 

[dmoran]

When you say "the base", do you mean at or near the .200" line or some where else?
Would like a better description or picture of where your getting brass shaving/swiping off the case(s).

Brass swiping on the base of the case-head, the length to the shoulder is culprit = more set back is needed.
Brass swiping of the webbing/expansion line, the diameter is culprit = a smaller diameter die will be needed.
Donovan

 

[Carl Ross]

I mean the .200" line Donovan. This is where I am measuring and also where I'm shaving brass. I suppose I can order a tight die and see how it goes...

 

[Sheldon N]

Dang that's a really tight chamber if even virgin brass at .4693 is having issues. I can't imagine someone would spec a reamer that small. Agree with the comment above to ask for reamer specs from your gunsmith.

Any possibility that your gunsmith was using an overly worn reamer?

 

[KenOath]

I would also recommend seeing the smith about reamer dimensions.. seems tight.

 

[22DASHER]

Just a thought from what I have seen and heard.... just because the reamer was spec’d out at a certain dimension does not mean that is the actual dimension. This has happened more than once. Take those numbers with a grain of salt.

 

[swd]

Chambering the new, unfired Lapua 6 BR brass (.4693") in the new chamber will take a little sharpie mark off the base, and will require a little extraction camming action (tiny click).

Is this a situation a Harrel's D4 die could help with, or am I going to fight this for as long as I use this chamber?

Appreciate it guys,
Carl

That chamber is too tight at the back end, no way around it. Yes your always going to fight it. Pull the barrel and have a reamer with correct dimensions run in it before you pull your hair out in frustration.

 

[Dusty Stevens]

No chamber should ever be sharp enough to shave brass even if it was so small it rubbed

 

[Carl Ross]

That chamber is too tight at the back end, now way around it. Yes your always going to fight it. Pull the barrel and have a reamer with correct dimensions run in it before you pull your hair out in frustration.

This is what I was thinking. Just wanted to make sure I wasn’t missing anything. Thanks for the input guys.

 

[Mulligan]

Just a thought,

Isn’t the Norma dasher brass a bit smaller at the base? Could your smith have used a reamer designed for the Norma brass?

CW

 

[Carl Ross]

My 1st run Norma Dasher brass (I’ve got both Norma and Lapua but this barrel was slated for Lapua) measures around .468” at the .200” line. I discovered last night that if I trim a piece of Norma it chambers fine. The barrel is stamped 6 L-Dasher (for Lapua) and the neck also isn’t cut deep enough for untrimmed Norma, so I don’t think it was a Norma reamer mix up.

Does anyone know of a tighter base die meant for the Norma brass?

I’d normally contact the ‘smith, but it was such a pain to get the barrel from him in the first place that I’d honestly rather pay someone else to fix it if I cannot find a workable die/brass solution.

 

[3dogs]

Carl
Take it over to Alex
Jim

 

[tclaunch]

or am I going to fight this for as long as I use this chamber?

^^^
This, get it done right with a reamer with same base @ .200" as your old one .4714"

 

[Carl Ross]

I sense a consensus, thanks again for the input guys.

 

[Tim Singleton]

Is the scrape place on the brass uniform all the way around?
Deeper or heavier mark on one side than the other?

 

[Tim Singleton]

Does it scrape virgin 6br lapua brasss? If not
Its worth fire forming a couple new pieces of brass in it to see how it does
If the brass never blows out at the base with the tighter chamber it should resize and work fine.
you just cant use the brass blown out in the larger chamber in it