6mm dasher fireform cases

G

glbreil

Guest
I need to fireform several 6mm dasher cases in a dedicated fireform barrel using 80 grain bullet. I have a bunch of H4831SC. Does anyone know of a safe but effective load for this powder? Thanks Gary
 
To my way of thinking, there's really only one viable reason to go with a Dasher over a std. BR, and that's to get higher velocities out of the heavier (105-115gr) bullets used in mid- & long-range shooting. To that end, I've always fireformed with 105-107gr. bullets, using Varget, N150, or RL15. I tried forming with 85gr. bullets, but got much better results with the heavier bullets. 4831SC is much too slow for the Dasher, especially with an 80gr bullet, even in fully formed cases.
 
I am just wanting to blow out the cases, I am going to shoot them in the dirt through a barrel dedicated just for fire forming. I just thought someone may klnow how much powder will get the job done and not blow up the gun. I am not concerned about anything else.

Gary
 
You need to generate at least 40,000 psi to do a good job of fireforming. Not sure you can get there with 4831. You could always try one and see, then abandon that powder if it doesn't work.
 
Thanks Charles, I didn't really think about it not generating enough pressure, I just didn't want to put to much. I did try one andit formed pretty good, but the shoulder is a little bit round yet, I did have room for a little more, but I will probably just move on to reloader 15. I just have an abundance of 4831SC.

Thanks Gary

Can't figure out c.o.w.?
 
Gary, he means Cream Of Wheat fireforming method. There's a bit written about it on the 6mmBR website under the 6mmBR Improved cartridge guide. Fireforming with 105s and Varget or H4895 using the false shoulder method works for me.

Nate
 
If you just want to blow away the powder and are not worried about carbon and unburnt powder in your fireforming barrel, the jam as much H4831SC as you can get in there. If it doesnt blow right out, at least you might be able to jam a bit more in next time.
Something I found when fireforming Dasher though is that you can get awsome accuraccy while fire forming. You might want to try a normal powder and fireform it in club matches.
 
glbreil said:
I need to fireform several 6mm dasher cases in a dedicated fireform barrel using 80 grain bullet. I have a bunch of H4831SC. Does anyone know of a safe but effective load for this powder? Thanks Gary
Click to expand...

Consider Charles's advise, if you had the Dasher already blown out and fill it to 100% load density (35 grains) with 4831 it will generate only about 31,300# with an 80 grain bullet. Yhis is according to QuickLOAD.
 
Gary, a couple of the replies touch on what I was talking about - you can't generate enough pressure with 4831 - even with heavier bullets - to do a good job fireforming. I understand wanting to use 4831SC if you don't currently have a better use for it. But when you consider how well most Dashers shoot with fireforming loads of Varget or RL15 & a good 105-108gr. bullet, why waste barrel life & even a cheap bullet (if there is such a thing in today's market) fireforming when you can shoot good FF loads in a match?
 
Good advice. I use 30.0 grs. Varget under a 107 SMK. Also, jam the bullet about .010" for good fireforming
 
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I use 30 gr of h-4895 and 115 bullets, false shoulder method (jumping .020):eek:--- yes jumping
 
Quote from BR Central:

"The first, and simplest, method for forming 6BR Improved brass is to seat a bullet long into the lands, with strong neck tension, and then fire the case with a near full-power load. Make sure the bullet seats firmly in the lands so the case can't move with the firing pin strike." To each his own.
 
Useing the "false shoulder method," I found by jumping the bullet that my blow lengths were longer and more consistant. :D

By useing a 115 bullet you need to push it way in to the case to jump, which in turn causes more case pressure.
 
tenring said:
Quote from BR Central:

"The first, and simplest, method for forming 6BR Improved brass is to seat a bullet long into the lands, with strong neck tension, and then fire the case with a near full-power load. Make sure the bullet seats firmly in the lands so the case can't move with the firing pin strike." To each his own.
Click to expand...

There are lot of old wives tales out there. Here is the point:

Premise: Unless there is no head clearance (space between the boltface and cartridge head, sometimes called "headspace"), you will not do the best job of fireforming.

Test: If you think you have sufficient neck tension to achieve this, seat a bullet a bit long and close the bolt. If you can close the bolt, then there wasn't enough tension.

No one I know has ever been unable to close the bolt.

But consider a false shoulder: If you get it too "long" you cannot close the bolt. You have to push it back a bit more until the bolt will close.

Now if anyone doesn't agree, they are essentially claiming the premise is wrong. That's really what most arguments are about, one person makes an assumption, often unstated, that the other disagrees with.

If you disagree, I consider the following:

We all know that the energy in firing a primer will move the case forward in the chamber -- that is, if it can move. Take a case with a bit of excessive head clearance. Fire it. The primer looks flat and a bit uneven.

See if seating a bullet long takes the splattered look of the primer away. Now try it with a false shoulder, tight enough it takes some effort to close the bolt.

What has happened is the primer has remained against the boltface, whereas the case has moved forward a bit Then when full pressure was reached, the case moved back, fully reseating the primer. But in the intervening milliseconds, pressure has expanded the primer a bit, so the "reseated" primer is enlarged, flattened, distorted, whatever you want to call it.

What those of us who say seating the bullet hard is insufficient are claiming is that fireforming is a dynamic process. How the case reacts to pressure over the time it takes to fully build, can be variable, and the final results show that variability. If you want to take forward movement of the case out of the equation, you can't get there by just jamming the bullet. The case shoulder itself must be used.

Proof comes from firing a set of cases with excessive head clearance (before fireforming) and measuring the clearance after. If one set has less variance after, then that was the better technique.

Benchrest shooters (who rarely shoot at the ten ring) think even, minimal head clearance matters. Whether or not it does is a whole different argument, including getting into pretty much untestable waters, the effect of varying bolt thrust on accuracy.
 
Gary
The hotter your chamber gets the better your results will be with the 4831.As Jerry pointed out with his quickload data you'll be down on pressure but if you shoot the first 10 cases fast to build some heat in your fireform barrel then let a round go it will come out much better.

Robert Whitley (rcw3) has this to say on 6mmbr.com
I don't understand why people bother with the false shoulder method. To expand the neck way up and then size the brass at the end of the neck back down again to load it over works and work hardens the neck of the brass. I just load 6BR brass with bullets well into the lands and then fire form it to 6mm Dasher brass and the Dasher cases come out very uniform and even in length. I cannot imagine how things can be better with the false shoulder method than what I am getting now. It seems like the false shoulder method is a lot of extra work for nothing (and it over works and work hardens the neck brass as well).

Am I missing something here?:eek:

Robert Whitley


Waterboy aka Lynn
 
I'm surprised alinwa hasn't waded in here... I thought he used to be a staunch advocate of the false shoulder method, claiming that the force of the firing pin hitting the primer would be enough to shove the bullet back into the neck regardless of how much neck tension was used... and then the case wouldn't be seated against the bolt face when it began to expand and grip the chamber walls, leading to case stretch, etc.

Anybody here used that hydraulic forming die from Hornady? I've got a 6 Dasher here that has a little more life on it before I have to decide what to rechamber it to, and honestly the whole false-shoulder fire-forming method was annoying enough as compared to my 6-6.5x47L (neck down and go shoot) that I'm starting to lean thataway for my next barrel...
 
hi monte ,yes sir i have the hornady hydro form die for my dasher,it is a lot of work but will at least put a shoulder although not sharp on the case ,after hydro forming i run them in my regular die to bump back the shoulder to fit the chamber,it kind of flattens it back out ,and fits well.be fore warned,dont do this in a room with white walls.lol. tim in tx
 
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milanuk said:
I'm surprised alinwa hasn't waded in here... I thought he used to be a staunch advocate of the false shoulder method, . . .
Click to expand...
I'm sure he still is. Al has a goal of making cases last. His particular fireforming technique is one part of that, but other measures must be taken as well.

And for those of us who post often, it gets tiring repeating what we've already said. 10, 20, whatever times is enough.

In some ways, fireforming is like chambering a barrel. If it shoots well enough for you, it doesn't matter how it is done. In fireforming, if the resulting cases last as long as you think they should, and the rifle is as accurate as you want, why would you change your technique?

Suppose your gunsmith chambers barrels using a reamer without a pilot? Suppose further that barrels he chambers shoot at least as well as barrels chambered by other top-line smiths. What are you going to say? The barrels can't be any good because he uses a pilotless reamer? That all smiths should change to such a reamer?

And yes, I can think of a way to use a pilotless reamer and get near perfect results. So can you if you think about it.
 
On my statement that Lynn quoted, I have also had a good bit of experience with the false shoulder method as well. With the bullet in the lands technique I currently use with the Dasher and BRX, if the head space of the fire formed cases was in any way irregular, or the OAL of the fire formed brass cases showed some significant disparities as to each other (i.e. more so than the standard OAL variances you see with the factory 6BR base brass), then I would tend to agree that there might be a benefit to use the false shoulder method. Usually what I have seen if a firing pin strike is pushing the case into the chamber (or if the extractor is doing that when it snaps over the rim of the case) you then see variances in either the head space of the fired cases or more sizable variations in the OAL of fire formed cases.

Whatever technique you feel works best is fine.

Robert Whitley
 
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