I just fired new Lapua brass in my 6creed RPR using ~56,000 psi loads. The fired brass is already hard to chamber before sizing. Is it possible the brass has already conformed to the chamber’s dimensions? I thought it took a few firings to hammer out the brass to fit tightly. Is this common? Thanks!
First firing of brass reflecting chamber dimensions?
- Thread starter fatelvis
- Start date
Did you seat the bullets well into the lands for fire forming? This pushes the case back in the chamber and helps to blow the shoulder forward. Measure the base to shoulder and compare to virgin brass. Many times the case length will shrink as it expands around the mid section and base. If this is the case, you may need to body size and shoot again to expand to full chamber length. If you have other brass that has been through this chamber a few times, you can measure a few to determine chamber length. What tools are you using to measure?
What barrel are you shooting?
What barrel are you shooting?
It's a stock Ruger barrel. The throat was waaaay too short when new, so I fired a complete Tubb's Final Finish kit through the rifle, to push the lands forward. It worked well. I'm seating the bullets with a .030" jump. I'm using Redding's Instant Indicator to measure headspace. The virgin brass chambered easily, and seemed to grow .003"-.004" upon the first firing. Is that amount of shoulder movement normal?
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At 56K psi exerted inside the case the brass will expand in all directions including pushing the shoulder forward, sort of like a balloon, - expand to fit the chamber - then limited spring back occurs. In a very short time, F/L sizing is required to easily chamber the round. I have been told by BR shooters and the gunsmith that did my barrel work that a very limited loose fit headspace is desirable; a F/L die accomplishes this.
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Ned Ludd
Silver $$ Contributor
I prep virgin brass using an oversized expander mandrel (~.001" under bullet diameter), followed by FL resizing using a bushing die with the appropriate bushing. The shoulders do not move detectably with virgin brass, only the necks are effectively sized. After fire-forming, I select 10 cases at random during every brass prep and measure them before/after FL resize. Below is a table with the average (10 cases) cartridge base-to-shoulder (CBTS) measurements for subsequent firings of a recent Lot of Lapua .308 Palma brass, which should be fairly representative of what's happening to the brass in the chamber with subsequent firings. All the loads fired in this brass were running around 60K psi.
As you can see, the CBTS for this Lot of brass isn't really changing at all after the first firing. In the past, I have had other preps that might expand just a tick more on the second firing. For the purpose of determining the effect of subsequent firings on actual case volume, you could measure that as well. However, the results will be limited to the accuracy +/- SD with which you can determine water volume. Chances are good with a load running at ~56K psi, you will achieve well in excess of 95% of the expansion you're going to get on the first firing. Remember, brass undergoes plastic deformation during the firing/resizing process, so you may observe other dimensional aspect of the brass changing over time, such as neck wall thickness/diameter. So it can be argued that the case volume will actually be changing at some level on every firing. Realistically, those changes are probably so small that many shooters will never have to worry about their effects.
As far as chambering 1X-fired brass, I can imagine that could depend on the caliber, brand of brass, "tightness" of the chamber relative to virgin brass specs, and probably several additional factors. I have always just assumed F/L resize was necessary and prepped brass after every firing. Certainly, the closer the dimensions of your resized brass are to those of fire-formed (i.e. minimal resizing), the more likely there might be some resistance when chambering it, even after resizing.
As you can see, the CBTS for this Lot of brass isn't really changing at all after the first firing. In the past, I have had other preps that might expand just a tick more on the second firing. For the purpose of determining the effect of subsequent firings on actual case volume, you could measure that as well. However, the results will be limited to the accuracy +/- SD with which you can determine water volume. Chances are good with a load running at ~56K psi, you will achieve well in excess of 95% of the expansion you're going to get on the first firing. Remember, brass undergoes plastic deformation during the firing/resizing process, so you may observe other dimensional aspect of the brass changing over time, such as neck wall thickness/diameter. So it can be argued that the case volume will actually be changing at some level on every firing. Realistically, those changes are probably so small that many shooters will never have to worry about their effects.
As far as chambering 1X-fired brass, I can imagine that could depend on the caliber, brand of brass, "tightness" of the chamber relative to virgin brass specs, and probably several additional factors. I have always just assumed F/L resize was necessary and prepped brass after every firing. Certainly, the closer the dimensions of your resized brass are to those of fire-formed (i.e. minimal resizing), the more likely there might be some resistance when chambering it, even after resizing.
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Not if they have a wisp of lube on them.....as they should anyway.
I LCD neck size only for my 223 and all reloads have a hint of tight bolt closing and I've seen no sign of galling after hundreds and hundreds of loads like this.
A crush fit when closing the bolt gives a good head to datum measurement. I start with .010" between die & shell holder when fl sizing. Check fit in chamber of 3 brass before loading.
I dont remove ejector or extractor from bolt. . Takes about 3 firings to get the crush fit. You will be sizing the brass in the chamber.
In an Ar 5.56 , the slamming of the bolt sets the shoulder back about .001" or more, if the head to datum is larger then the chamber.
I put 1 drop of Break Free CLP on each lug before shooting for the day. Fire forming or not.
I dont remove ejector or extractor from bolt. . Takes about 3 firings to get the crush fit. You will be sizing the brass in the chamber.
In an Ar 5.56 , the slamming of the bolt sets the shoulder back about .001" or more, if the head to datum is larger then the chamber.
I put 1 drop of Break Free CLP on each lug before shooting for the day. Fire forming or not.
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1st firing I jam the bullets about .005" to make sure the case head is against the bolt face.
Straightshooter1
Gold $$ Contributor
When you do that, do you change your powder charge weight any?
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