6mm BR / Dasher - uniforming flash holes

[memilanuk]

I purchased an extra box of 100 6mm BR cases to make an even 300 in anticipation of using the gun @ some upcoming matches. I was fire-forming the cases using 31.8gr IMR 4895, and some 105 A-Maxes I had sitting around collecting dust,as well as a few 107 SMKs to round out the 100 bullets necessary). I had measured the seating depths for each and adjusted the seater die accordingly - both were seated 20 thou off the lands. I had fire-formed 200 rounds previous to this with 107gr SMKs and the same load with no problems noted.

A couple observations from this last batch kind of worried me:

1) When running a Russ Haydon PPC-sized flash hole tool into the cases, each and every one of the new batch needed a fair amount of material removed before it would pass through freely. I did check w/ my regular-sized Sinclair flash hole tool just to be sure I did indeed have a PPC-sized tool in the first place; it would not pass. I have not uniformed 6 BR flash holes in the past,not sure what possessed me this time specifically) but I've never seen a flash hole deburrer remove that much material just to get through the hole.

2) The fire-forming loads suddenly exhibited relatively high pressure - flattened primers, and a fair number of either smoked / leaky primers, or ones that just flat fell out of the case in the gun! There was no indication of cratered primers, but I just had the firing pin hole bushed and the pin turned to fit by Gre-Tan Rifles, so one can only guess at how high of pressure it would take to crater primers now. Bolt lift was also a bit stiffer than I would have expected, although no 'click' to open.

I'm not entirely sure if these two are related - opening up the primer flash hole and potentially letting more pressure into the primer pocket area, followed by leaky and loose primer pockets after just fire-forming loads. My gut instinct is that I may have just permanently ruined 100 cases of 6mm BR / Dasher brass by uniforming the flash holes.

What do you think?

 

[AckleyImproved]

Mate

I do not know the answer to your openning up the flash hole and pressure, but I think I can say your cases have at least halved their life, if not stuffed.

I have ran into the doughnut issue with my Dasher, and it did some funny things to the primer pockets, and the primers. I ditched brass and started again.

Just tonight I have loaded up some fireforming rounds for the Dasher, necked to 6.5 and false shoulder made. I have not touched the flash holes or the primers pockets, and the chamber is unturned.

I will be fireforming with 31grains of Varget and 87Vmax.

Maybe the 31.5 grains of powder wit the 105/107's is just a little to much?

In my BR Dasher I fireform with 28 grains of varget and a 107??

I did find that a tapered button is not good for necking up and back down. The concentricity goes to shit, and if I had to neck turn I would be buggered. This problem has been a PITA for my BR Dasher.

CHeers
AI

 

[flatlander]

Monte,
I've been using a Sinclair PPC flashhole deburring tool on Lapua 6BR & 6x47 cases since 2004 when I got my first Dasher bbl. I've had no issues with pressure that I could lay off on use of the deburring tool, but don't recall that it removed all that much metal.

As an aside - I tested deburred vs. out-of-the-box 6x47L cases over the chrono while group shooting at 600yds. last spring, and found that ES, SD, & groups at 600 with the deburred cases were no better than that of the un-worked brass. Sorta makes me wonder about all the time I've spent deburring flashholes on many thousands of pieces of brass over the past 15yrs. However, let's not forget that Lapua & Norma flashholes are usually pretty uniform to begin with, while your average U.S.-made case may indeed benefit from the work.

 

[NorCalMikie]

Monte: Seems like your loads might be a "little" on the hot side?? In a "savage" action we run 30.0 to 30.5 max grains of powder with a 80 grain bullet and are "just shy" of hitting pressure signs.
31.8 seems a little stout to me pushing a 100 + grain bullet.
But that's just my humble opinion.
I don't think the flash hole situation is related. Sounds like you brass might be on the edge of being junk now.

 

[memilanuk]

Oh crap. 'Tard alert.

Found the problem...

31.8gr IMR4895 is a hair on the warm side, but not unduly so.

32.4gr, on the other hand... :nono:

Powder measure got used w/o re-verifying the setting. Entirely my fault. Well, there's 25 cases down the drain,the ones fired w/ the heavy charge.

Still had some leaky primers in the first 50,when the measure was definitely still set on 31.8gr) which I had not had from the previous 200 cases @ 31.8gr.

Sometimes I'm my own worst enemy.

 

[Woody]

milanuk:
Sounds similar on the leaky primer possibly as I had going on. I went longer on the OAL. Took care of it. My length,not that you want to go by mine) using 105 Amax is 2.345". Just so the bolt is a smigdeon tough on the closing. Get them in there and they fire form just fine for me.

FWIW,

Woody

 

[Flybuster]

I am going to fire-form up 40-50 more 6 Dasher for the Pacific Northwest International.

This lot of br brass a few of them have burrs I can clearly see when held up to the light. I am afriad to open them up, I just want to clean some of the junk off. I think I read about using a drill bit, on this site.

I might try some IMR-4895 with A-Max, I have been using H-4895. How's the velocity in yours Monte?

 

[memilanuk]

31.8 behind a 107 SMK was giving about 2980-2990 fps. Actually about the same as 32.7gr of RE-15 was in fire-formed cases I was hoping for a bit more - 3050-3080 or so.

 

[Forum Boss]

1. With the 6BR, I have observed that, after reaming the flash-holes with a K&M flash-hole tool, the pressures DID rise, as evidenced by higher recorded velocities,over chron) and bigger primer craters.

2. The issue with flash hole reamers is that often, the cutters are too wide in diameter. The K&M tool is spec'd to cut a .0625 hole,1/16"). We've seen examples that will ream as large as .068. The Russ Haydon tool uses cutter tips from K&M so you have same problem.

The specs on the Sinclair tool that comes in from the outside have been better, but some will cut more than the .062 claimed.

---

I think it you can find a flash hole reamer that really cuts .062 or .063 you should be fine. Lapua's spec is 1.5mm or .059" The problem is that so many of the tools cut bigger holes.

 

[techshooter]

Monte:

What was the barrel length on that Dasher again?

Chris

PS: The new 6.5-284 did GREAT at 600 today,Cascade 80 prone match). The bullets went where I pointed them, I just didn't always point them in the right direction.

 

[memilanuk]

Chris,

30" if I recall...

I've been busy getting Kathy set up a rifle that works,since the Dasher has had some hiccups) so she's using my 10FP w/ the 24" LW .223 barrel... shot a 200-12X @ 300 a couple days ago using B80VLDs. Hopefully today we stretch things out to 600.

Monte