Dasher FF "BLOW LENGTH"

[4xforfun]

I decided to FF my brass the old fashond way....no COW, no pistol powder, no dedicated FF bbl....just expand and reduce to crush fit and jam bullet and shoot in the gun they are intended for. I swab the chamber and wipe the brass with brake clean before each shot (I am still in the shoot, clean, shoot mode)

Now, I have heard of guys talking about "optimum blow length".

My virgin brass is 1.554.

My brass is 1.553 after I neck up to .257 and back down to .243.


My FF brass is 1.541. It is the same with 29, 29.5, and 30 RL15 and 30 Varget and 105 vld. Absolutly NO signs of PSI. I am sure I could go up a couple of more grains.

Is there any point or advantage to hitting them as hard as I can the first time? Is there a "blow length" I should be shooting for (no pun intended)?

I still have 195 left!!!!

 

[rcw3]

Your hitting an OAL for fire formed brass just about exactly what mine was/is - it seems to me you are doing fine (although I don't swab the chamber after each shot - just load them up and shoot them). I typically run with a moderate to higher 6BR loading for Dasher fire forming and that is what you have. I don't feel you need to hammer it real hard to fire form the brass the first time. There's some info on this web page on what I did:

http://www.6mmar.com/6mm_Dasher.php

Robert Whitley

 

[flatlander]

I agree with Robert, and can't really think of any advantage to cleaning the chamber after each shot. I've fireformed over 1200pcs of Dasher brass for five different barrels over the years, and have done as much of it as possible during matches - primarily, 600yd prone any/any matches. In my experience, the only thing you're giving up while fireforming is 100-150fps of velocity - the accuracy with a good bullet is very close to what you'll see with formed cases.

As another example, one of the guys in our club shot the winning score in one of our BR Varmint Silhouette matches (200m-500m) with fireform loads in his Dasher. Considering that it's best to shoot 105-108gr bullets to get fully-formed cases, and that Dasher FF loads are running velocities equal to or exceeding std. 6BR LR loads, why not get some good out of your FF ammo?

 

[4xforfun]

Like I said...I am in the middle of BBL break-in so i clean EVERYTHING...The last thing I clean is the chamber....and I ALWAYS wipe off my loaded rounds after I get them loaded...my loading "environment" is not as sterile as it should be!!

 

[alf]

Tod,

You're in the ballpark with OAL after fireforming.

No matter how sharp the shoulders look, I've found I need to shoot the cases a second time before I trust them to match duty.

 

[johara1]

The new blue box brass is short at 1.555 or less and my average blow length is 1.550.a clean chamber and i clean all lube off the cases and i adj. the load to get my length. FF. the one gun shot in .3 tens.......jim

 

[rcw3]

The new blue box brass is short at 1.555 or less and my average blow length is 1.550.a clean chamber and i clean all lube off the cases and i adj. the load to get my length. FF. the one gun shot in .3 tens.......jim

johara1

I do not understand your results as I have never found my Dasher "blow length" to be dependent necessarily on how hot a load I fired in fire forming (i.e. with different loadings I have only seen a couple thousandths variance in "blow length" at most). Where I have found "blow length" to vary significantly (longer) is if the case gets seated into the chamber more than it should so that the case body also stretches on firing instead of just the shoulder being blown forward with some of the neck brass pulled back. The fact that you come out with such a long "blow length" and don't seem to lose any case length when you fire form leads me to believe that may be what is happening in your situation.

I also saw a posting on another thread where you were using a 6BR resize die with your Dasher (and I do not understand how that could possible work at all) so I am wondering if that has something to do with the results you are getting.

Robert

 

[Bkluke]

;D Hi Tod,

I'm with Al, your numbers are what I have been getting on an average. I have yet to see any thing past 1.550 with any consistantcy, trying all different methods powder bullets ect. I also shoot 2 cycles before I bring'em to a match. hope this helps.

See you boys in May ;D ;D

 

[johara1]

Robert, All i can tell you is after talking at length with Dmoran about this, the load is where the length comes from. I am running a .266 neck so i neck tun to make my shoulder to a tight fit and i have found that the 115's give me the longest length,and i adjust the charge for the longest length. I make sure the chamber is clean and cases are degreased and i use a vary soft primer. My average is 1.550 out of 100 cases the longest 1.552 and the shortest 1.548. The old brass I could get 1.555 but not any more.
I have one barrel that makes the longest brass and thats the one i use for the rest of them......jim

 

[RenoMD]

Good Sunday Morning, before I head out to the range... I had been reading obsessively on blow length, and it appears the consensus is to make sure the chamber and bore are dry/oil free. I've seen Johara1 use chlorine free brake cleaner, others say they used it too. My question is would there be any harm in using regular old rubbing alcohol which isn't as toxic? Also how frequently do you guys clean between strings of fire-forming? I see others saying they shoot a match with their fireforming ammo but most matches I go to don't allow you to clean b/c there isn't time.

Clean every 10-20 rounds? Clean every 20-30 rounds? I would think the moment you get brass that is fairly off in blow length from the others, to clean and Dry the chamber out. Anyone use anything else aside from brake cleaner to degrease the chamber/bore? Thank you!

Today is the day!

 

[Phil]

Reno,

This thread is almost 6 years old.....

Send Jim or Donovan a PM and ask away, you might get a quicker response from one of them....

 

[22DASHER]

Don't fret over case length. Whether it be hydroforming or fireforming.... trim them to the same length after forming. Some of the best shooting Dashers in the country right now are shooting Dasher brass that is formed "short" through hydroforming. I do have a method for longer blow lengths in the 1.550" range and I mostly shoot the shorter hydroformed brass now.

 

[lloydx2]

Chamber reaming depth can also change blow length average. As long
as cases are clean with no case lube left overs. I have never had any need
to clean between shots. My lengths have been 1.540-1-2. I don't worry about
over-all length as much as length from base to the shoulder .350 datum line
Knowing my exact chamber head spacing I then know how its matching up with my chamber.

 

[RenoMD]

Ah excellent thank you for the info guys... I was just trying to do the right thing on forums, use the search function, and not create another thread on the same topic, and continue on with a good topic someone created already on blow length. But I appreciate the advice! 22dasher, that makes very good sense to just form them all then trim them all to the same length to maintain consistent neck tension between piece of brass.

 

[reubenski]

I just read thru this thread and found it pretty helpful!

 

[Cool Tool]

@4xforfun

Ancient thread,(2011) but since it's been resurrected.... How did that short brass end up working out for you in 2011?

Tom

That's funny I don't care who you are good one Tom

 

[lloydx2]

Benchrest Central

 

[4xforfun]

That's funny I don't care who you are good one Tom

Are you refering to the above post where my blow lengths were short, or the fact that I had a MAJOR brain fart and trimmed them to 1.500 the week before the nationals!!

 

[Cool Tool]

Are you refering to the above post where my blow lengths were short, or the fact that I had a MAJOR brain fart and trimmed them to 1.500 the week before the nationals!!

Well if I recall you shot pretty damn good that year that's why I thought what Tom said was funny. LOL

 

[RenoMD]

I'm going to write a full write up with details and lots of pictures which I have been taking on my technique... to close the loop on my questions.
I expanded to 264 w/ a 21st century expander mandrel and expander die, necked down with a FLS forster w/o the internals, then re-expanded to 243 with another 21st century expander mandrel. (I'll put my measurements in the full write up)

Load specs: Hornady 105 vmax, 30 gr varget, CCI 450, false shoulder for a full crush on the entire bolt close with a 0.015 jam for good measure.

I shot 5 cleaned, shot 5 cleaned shot 5 cleaned, then shot 20 cleaned, shot 20 cleaned, shot 20 cleaned, then shot 40 cleaned, shot 40 cleaned, shot 40 cleaned, then shot 50 cleaned for a total of 245 (5 of the rounds did not ignite...good primer strike too).
My method, I tested blow length of each cartridge for the 5 shots then clean technique, comparing not cleaning with ETOH to degrease the chamber and bore vs. cleaning WITH ETOH to degrease the chamber (after I cleaned that is). Then did the same thing with 20 shot clean, then 40 shot clean.

Guess what... you guys were right. It made absolutely no difference in my chamber degreasing. My lengths 1.531-1.535, with the great majority 1.532-1.533. Meh... I'm still going to use them for a competition. FYI only 1 split neck out of the 250 rounds I fired. AWESOME sharp shoulders all the same datum line measurement 1.2510 using the whidden 0.350 bump gauge and mitu calipers, give or take 0.001 on occasion.