Another Dasher fire forming thread.

[jsimonh]

I've read everything I can find and just want some reassurance that I'm going in the right direction based on my numbers.

I went through and found 3 pieces of new Lapua brass that all measured the same at 1.5560.

After necking up to 264 and then sizing back down to a nice "crush" fit with a whidden die my brass was 1.5470 for 2 and 1.549 for one.

After firing they measured 1.534 for 2 and 1.531 for the last one.

I used 30gr SW Precision and a Barnes 112gr jammed hard.

I'm okay with the shorter brass but I've seen where most say 1.54x and some claim to stay in the 1.55x.

The shoulder line measured with a whidden comparator was 1.246 on 2 and 1.2455 on one.

What say you?

Also, this is a follow up to my stuck case issue I had posted about earlier, finally got the new brass in.

 

[CaptainMal]

Curiosity got me as I had fire formed some new Lapua Dasher and have them in a rack waiting for another barrel. All I did was stick some cheap 100 gr hunting bullets jammed .030" with 30 gr. of IMR 4166.

Just measured maybe 10 of them. They ran from 1.545" to 1.555". That's ONE simple fireform. Now when I actually shoot them a second time with a real Dasher load, they will stretch a bit and get closer in length.

What you are doing is a lot of fussing to get sketchy results.

 

[RegionRat]

Sounds like you may need to see what they look like after another cycle before you can draw any conclusions.

The real question is, how did they perform while doing the fire forming? Then, how did they shoot after a full Dasher cycle?

 

[LRPV]

I've read everything I can find and just want some reassurance that I'm going in the right direction based on my numbers.

I went through and found 3 pieces of new Lapua brass that all measured the same at 1.5560.

After necking up to 264 and then sizing back down to a nice "crush" fit with a whidden die my brass was 1.5470 for 2 and 1.549 for one.

After firing they measured 1.534 for 2 and 1.531 for the last one.

I used 30gr SW Precision and a Barnes 112gr jammed hard.

I'm okay with the shorter brass but I've seen where most say 1.54x and some claim to stay in the 1.55x.

The shoulder line measured with a whidden comparator was 1.246 on 2 and 1.2455 on one.

What say you?

Also, this is a follow up to my stuck case issue I had posted about earlier, finally got the new brass in.

You’re doing it right. That’s all the longer blue box gets when forming dasher brass unless you stretch the web. They’ll grow a little with subsequent firings but not a lot as long as your die fits your chamber pretty close. You will get consistently better brass by false shoulder and or hydroforming.

 

[Ccrider]

You’re doing it right. That’s all the longer blue box gets when forming dasher brass unless you stretch the web. They’ll grow a little with subsequent firings but not a lot as long as your die fits your chamber pretty close. You will get consistently better brass by false shoulder and or hydroforming.

This is informative. I was wondering why most of my hydroformed brass had not grown much past 1.534 or so after 4 firings. Presumably, stretching the web is not a good thing.

 

[johara1]

One more reason to turn necks when shooting a Dasher, necking up and back down shortens the case even more. Use where the neck turner stops for the shoulder..... Clean the loaded f.f. cases off with non chlorinated brake cleaner and do the same with the chamber. I only shoot 5 then let it cool and clean the chamber again, plus seating the bullet in real deep is hard on the lugs and you gain nothing. Using the shoulder formed by where the neck turner stopped and backed up by a bullet is far more effective. You should be able to hold a blow length of .003, 1.547 - 1.550...... if not you may need to look at the chamber, if it is too polished ruff it up and get a nice cross hatch finish with 320 ..... jim

 

[LRPV]

One more reason to turn necks when shooting a Dasher, necking up and back down shortens the case even more. Use where the neck turner stops for the shoulder..... Clean the loaded f.f. cases off with non chlorinated brake cleaner and do the same with the chamber. I only shoot 5 then let it cool and clean the chamber again, plus seating the bullet in real deep is hard on the lugs and you gain nothing. Using the shoulder formed by where the neck turner stopped and backed up by a bullet is far more effective. You should be able to hold a blow length of .003, 1.547 - 1.550...... if not you may need to look at the chamber, if it is too polished ruff it up and get a nice cross hatch finish with 320 ..... jim

ok Jim, you come up with this on every thread ever about fireforming dasher brass and later state that you’ve never used blue box brass which is what 99% of people have to work with now. Have you gotten these blow lengths with blue box brass?

Another question, what neck diameter are you running and how thick are turning your necks, if you don’t mind sharing?

 

[jsimonh]

Johara1's theory was one that I kept seeing as I searched. It really is kinda confusing when reading all the threads. I would expect it to shrink some do to the shoulder moving up and out. If it stayed the same length but added volume it would make since that something is getting thinner.

I messed around more tonight with neck expansion and false shouldering by not running the mandrel all the way through the neck. By only expanding far enough to get a false "ring" after resizing I found my brass doesn't shorten up as much.

I aslo noticed that no matter what my length was after creating the false shoulder the fired case was exactly .011 shorter on the 5 cases I fired tonight. Ive got a 257 mandrel coming tomorrow to play around with.

This new method gave me lengths of 1.536-1.538

I also called Peterson cartridge and they confirmed their brass is 1.530 +-.006

 

[johara1]

ok Jim, you come up with this on every thread ever about fireforming dasher brass and later state that you’ve never used blue box brass which is what 99% of people have to work with now. Have you gotten these blow lengths with blue box brass?

Another question, what neck diameter are you running and how thick are turning your necks, if you don’t mind sharing?

I use all blue box brass, and when I shot a Dasher it was .266 and now with the Br imp. it is .268...... jim

 

[johara1]

BTW, Blow length of 1.550 are a lot easier to get with the Br Imp. It is nice to be able to trim after fire forming on 95% of the brass, When I ran out of the old Lapua and went to the Blue box brass I had a reamer made at 1.560 length from the old 1.570 length. Now I see the Blue box brass is getting a little longer, not much but a little...... jim

 

[tsyarnall]

You’re doing it right. That’s all the longer blue box gets when forming dasher brass unless you stretch the web. They’ll grow a little with subsequent firings but not a lot as long as your die fits your chamber pretty close. You will get consistently better brass by false shoulder and or hydroforming.

Are you sure.........

 

[jsimonh]

Are you sure.........

Great clip! Could you elaborate though? I used a 257 mandrel this weekend to create false shoulders on all my brass. The 257 mandrel would make the overall length shorten right about .008 very consistently. Sizing the neck partially back to 6mm gained me back .003. Overall creating the false shoulder caused my cases to shorten by about .005-.006 with very few outliers. Im anxious to see how much more they shorten after firing.

 

[tsyarnall]

Sorry, nothing intended except I was just keeping it lite. When I read the first line of Jason’s comment, immediately this came to mind. I’m trying to learn the Dasher, too, and I read everything that touches on the cartridge.

Have a great day,

Scott