Starting load for Berger 68s in a Dasher?

[jrm850]

I stuck my Dasher reamer in an old 14 twist br barrel for my wife and I'm going to start load development tonight. I have a good supply of Berger 68fb and for appropriate powders I have some h335, 8208, Varget, and Rl-15. After setback her barrel is only 21" long. There is a lot of info on this site for heavier bullets but not much for a Dasher with the light bullets. What I am thinking right now is just working up from 30gr of 8208 for fireforming with a false shoulder and the 68s, but would love to hear some of your recommendations.

Thanks,
Jeff

 

[JEFFPPC]

I am not sure if this translates to the Dasher but I have an idea it might. When I started shooting BR I had a pair of 14 twist 6BR's built. I shot 68 gr Hammonds with excellant results. The powder for both guns was VV135. Nothing else was close in consistancy and/or performance. Good luck. Lets us know how you make out and what velcoity you can get with good accuracy.

 

[Chuckhunter]

Jeff, I used the 68Gr. Berger FB's to form my cases shooting a load of 31.4Gr's.of H-322. Bullets were seated +.010 into rifleing. Five, 5-shot groups were fired for a total of 25 cases. All formed perfectly and the agg. was .247. Not to bad for fire forming. I'm sure the 8208 would work also but I would probably start with 31.5 to 32Gr. According to QL you'll be well below max. pressures. I like to keep pressures between 49,000 and 50,000 psi to form. I was shooting an 8twist barrel so with a 14 twist, your pressures should run even lower. Good luck and let us know how it works out.

 

[jrm850]

Well it was an interesting day at the range... I was in a hurry and made a pair of assumptions that backfired. The first was when I assumed that the 68s would not reach the lands in my .110" chamber if they were seated deep enough in the case. I moved the seating depth I use for the 105s down another .040" but the 68's wouldn't chamber. Luckily I brought an arbor press and my seating die so I fixed that at the range. The second poor decision was when I didn't measure the finished cartridge necks. The 68s are a bit fatter than the 105s and I ended up with only about .0015" total clearance.

I started out with 31.6gr of 8208 which should be a mild load in a 6br and was suprised to see a pretty flat primer with it in the Dasher. The velocity was less than expected at 3247fps especially considering the flattened wolf primer. I could get that velocity out of this barrel when it was a plain 6BR. I'm going to chalk it up as a neck clearance issue and start over. The loads tested went from 31.0 to 31.6 and velocities ranged from 3161- 3247. The groups were horrid at 31.0 and 31.2 but tightened up considerably as I approached the pressure limit. All in all, I learned nothing other than not to let 25 years of reloading experience get in the way of basic procedures.

What I did find which may be of interest to many struggling with Dasher blow lengths is that a light polishing of the neck/shoulder junction in the chamber gave me very controllable lengths that ranged from 1.540" at 31gr to 1.550" at 31.6gr. This is the same reamer I used in my other Dasher which consistantly blows 1.532". The only difference is that I left the neck/shoulder junction sharp on the first chamber.

 

[Hal]

Jr

That was very interesting about "rounding the shoulder/neck juction"

Thats for posting that info.

Hal

 

[SDDasher]

Well it was an interesting day at the range... I was in a hurry and made a pair of assumptions that backfired. The first was when I assumed that the 68s would not reach the lands in my .110" chamber if they were seated deep enough in the case. I moved the seating depth I use for the 105s down another .040" but the 68's wouldn't chamber. Luckily I brought an arbor press and my seating die so I fixed that at the range. The second poor decision was when I didn't measure the finished cartridge necks. The 68s are a bit fatter than the 105s and I ended up with only about .0015" total clearance.
I started out with 31.6gr of 8208 which should be a mild load in a 6br and was suprised to see a pretty flat primer with it in the Dasher. The velocity was less than expected at 3247fps especially considering the flattened wolf primer. I could get that velocity out of this barrel when it was a plain 6BR. I'm going to chalk it up as a neck clearance issue and start over. The loads tested went from 31.0 to 31.6 and velocities ranged from 3161- 3247. The groups were horrid at 31.0 and 31.2 but tightened up considerably as I approached the pressure limit. All in all, I learned nothing other than not to let 25 years of reloading experience get in the way of basic procedures.

What I did find which may be of interest to many struggling with Dasher blow lengths is that a light polishing of the neck/shoulder junction in the chamber gave me very controllable lengths that ranged from 1.540" at 31gr to 1.550" at 31.6gr. This is the same reamer I used in my other Dasher which consistantly blows 1.532". The only difference is that I left the neck/shoulder junction sharp on the first chamber.

I think you are exactly right with this statement. I too have experienced the same with too little neck clearance in my Dasher.

 

[jrm850]

Jr

That was very interesting about "rounding the shoulder/neck juction"

Thats for posting that info.

Hal

I'm going to pull the barrel off of the first dasher and polish that junction to verify. I'll let you know how that turns out.

I think you are exactly right with this statement. I too have experienced the same with too little neck clearance in my Dasher.

It was definitely a dumb mistake. I cut the necks of the remaning cases back to .012" last night and will try again. Trimming the cases on the once fired is a bit of a chore because all I have are the bushing dies that don't go all of the way down the neck. I'll run a slightly oversized expander in them and make a new pilot to match for the turner.

 

[SDDasher]

How are you polishing the neck/shoulder junction?

 

[jrm850]

How are you polishing the neck/shoulder junction?

I replied to your PM but for the sake of others, I just polished it with some 400grit wet paper on a wooden dowel and marked the dowel to stop short of the throat ramps. This was done in the lathe immediately after cutting the chamber. I also knocked the sharp edge off the neck/throat junction to see if it stops the early firecraking my other Dasher exhibits. This barrel is a high round count take-off so it's a good chance for me to experiment.

For reference, I have always polished my chambers in the above manner until I read that a well respected accuracy smith recommends not polishing past the shoulder. I've never observed any early firecraking issues using this method (other than a pair of 7STWs) but then again I didn't always have a borescope.