Velocity & Pressure Spike

[Mikecr]

Orch describes the basis of my input, and what I think is happening to live2huntmt.
Once brass has been fired in his chamber it will never be what it was before.
He'll size it X-amount, it will spring back Xa-amount, and now it's unique to his gun, and in this case probably tighter than new brass fit.
Not a problem, just a difference. It's what I head straight for.

Some see fire forming as wasting barrel life, but the truth is we will all fire form our brass eventually. Right? Just like we all break-in our barrels eventually. Nothing to sweat about.
With a new barrel I use fire forming as my opportunity to do both break-in and full seating testing.
So that I don't have to do a lot of fire forming, I do a deep body lead dip anneal beforehand, and my planning all along allows for brass lasting the life of each barrel, at least.

The last gun I built is on it's 3rd barrel with the same 50pcs of brass(~80 reloads each now).
But you can't do that without a plan to do that..

 

[Rich Coyle]

Mikecr,

What caliber, primer, powder, and what velocity are you running. I guess this is your quiz for the day. You get an "A" for answering and an "F" for not answering. In addition to an "A" you get your name on the board with a star beside it!

 

[dsculley]

I just can't buy the difference is because the brass is now fire-formed to his chamber. My 6.5x47 shoots the same load in the same group whether with virgin brass or fire-formed brass. I have tested this and there is no difference.

He had to reduce his load a full 4 grains, or about 4.2%. That is a large difference. If the difference were 0.4 gr I could accept that the difference is due to the brass being fire-formed. The brass is not smaller now that it is fire-formed than when it was virgin. The chamber has not changed dimensions. If expanding the virgin brass to his chamber absorbed the energy from 4.0 grains of powder, that must be one large chamber. His brass would now have lots more capacity than before.

Live2huntmt, perhaps you could measure and compare the capacity of your virgin vs once-fired brass? I don't think there will be enough difference to explain this, but would be one more bit of information.

It will also be interesting to see what you find when you inspect and clean your rifle. It would be interesting to be able to run a bore scope down the barrel. I would not expect the Lilja barrel to be badly fouled, but I suppose a carbon ring could explain the pressure spike. Please let us know what you find.

 

[live2huntmt]

I just can't buy the difference is because the brass is now fire-formed to his chamber. My 6.5x47 shoots the same load in the same group whether with virgin brass or fire-formed brass. I have tested this and there is no difference.

He had to reduce his load a full 4 grains, or about 4.2%. That is a large difference. If the difference were 0.4 gr I could accept that the difference is due to the brass being fire-formed. The brass is not smaller now that it is fire-formed than when it was virgin. The chamber has not changed dimensions. If expanding the virgin brass to his chamber absorbed the energy from 4.0 grains of powder, that must be one large chamber. His brass would now have lots more capacity than before.

Live2huntmt, perhaps you could measure and compare the capacity of your virgin vs once-fired brass? I don't think there will be enough difference to explain this, but would be one more bit of information.

It will also be interesting to see what you find when you inspect and clean your rifle. It would be interesting to be able to run a bore scope down the barrel. I would not expect the Lilja barrel to be badly fouled, but I suppose a carbon ring could explain the pressure spike. Please let us know what you find.

I just did a H2O capacity test...the fired brass has 3.6% more case capacity than the virgin brass. I had to reduce my loads 4.2%. the .6% difference could be the energy used to fireform the brass. I tried virgin brass yesterday and it shot approximately 22 fps slower than the once fired brass in my reduced load of 92grains. I completely cleaned the rifle and did not notice any difference in velocities or pressure after I fired 3 fouling shots.

I have come to the conclusion that I was more than likely over pressure when fireforming the virgin brass, but the fireforming process helped mask the pressure signs. My reduced loads are producing the same accuracy at the same velocity that I had before..maybe even better. My ES and SD have reduced when using the reduced load in the fireformed brass.

I appreciate everyones input!

 

[Mikecr]

What caliber, primer, powder, and what velocity are you running.

The example cartridge is a 6.5wssm Imp. 139Laps, 215Feds, 47.4gr IMR4350, 28" barrels, 3025fps. QL shows this right at SAMMI max 65Kpsi.
Fitted chamber, turned brass has never been body or neck sized. Just 35deg 1thou shoulder bumping. No trimming or further annealing(beyond initial).

 

[Rich Coyle]

A!