264 Win Mags - When would the brass cases be considered "Fire Formed" for each individual action?

[Alibiiv]

In my experience with belted magnums (264WM, 7RM, 300WM), the base to shoulder on virgin brass is VERY short. My 264WM grew over 25 thousandths on first firing with Winchester brass. My ADG 7 rem mag brass grew 15 thousandths if I remember correctly. These were both in minimum head spaced X-caliber Savage prefits.

With that much stretch happening, it might be good idea to "fire form" with a jammed bullet for the first firing. I did this using some relatively cheap bullets and a mid-level load. One firing got the brass near enough to its full size, with almost imperceptible growth after the second firing with a "normal" load.

If I were you, I'd at the very least check the growth. Measure a virgin piece of brass from base to shoulder, then fire a couple and measure. If the growth is extreme (>0.010") it might be worth using the jammed bullet method, which forces the case head to rest against the bolt face. Otherwise, the brass will stretch backwards and forwards, instead of just forward, potentially thinning the case walls at the web. If the rifles are good shooters, you'll likely get good accuracy out of the fire forming loads, so use them to plink around, get your scope close, break in the barrel, and just have fun.

After the first firing, you'll be able to adjust your die so that you just bump the shoulder back 0.002" or so, and subsequent firing cycles will result in FAR less case stretching, and therefore considerably longer brass life. A small shoulder bump is also probably better for accuracy and precision.

Would you explain the reasoning behind fire forming by jamming a bullet into the lands when a belt accomplishes the same thing. What is the benefit? Jamming a bullet essentially is like forming a false shoulder, the belt serves to do the same thing??? I load a 300 WinMag, after the first firing I no longer use the belt and bump the shoulder back.002-.003 thousandths. My thoughts are that once a full/heavy load is fired the case is pretty much fire formed. I'd fire forming using the COW method i do not consider that round to be fire formed until I put a full load through it. The difference between a COW fire formed case and a full load fire forming is definitely visible.

 

[entoptics]

Would you explain the reasoning behind fire forming by jamming a bullet into the lands when a belt accomplishes the same thing. What is the benefit? Jamming a bullet essentially is like forming a false shoulder, the belt serves to do the same thing??? I load a 300 WinMag, after the first firing I no longer use the belt and bump the shoulder back.002-.003 thousandths. My thoughts are that once a full/heavy load is fired the case is pretty much fire formed. I'd fire forming using the COW method i do not consider that round to be fire formed until I put a full load through it. The difference between a COW fire formed case and a full load fire forming is definitely visible.

Per post #9 and #10...

Not from my understanding. The belt can only keep the case from going forward into the chamber, and the bolt face doesn't "crush fit" the brass against the belt, so there's some amount of wiggle room.

If I'm reading the SAAMI drawings correctly, it looks like the measurement for the cartridge is 0.220" base to belt with a -0.008" tolerance, and 0.220" - 0.227" for the chamber. That could potentially set up a maximum headspace (short belt, long chamber) of 0.015", though such extreme tolerance stacking should hopefully be rare.

For best consistency, the solid belt should never contact solidly against the chamber or you will have issues resulting from bolt preload. Properly built full custom rifle may not have real issues, most factory rifles certainly will. Because of variations in belt thickness, a belted mag chamber should not be set to true zero headspace. As such, most are 10-20 thou long in headspace. When a round is fired, the brass expands to fill the chamber. Once fired, the loader should only size enough so the case chambers easily and no more so that it headspaces off the shoulder, making the belt irrelevant. Fireformed after one high pressure loading.

 

[Carey Farmer]

How many firings for each brass do I need to have true "Fire Formed cases"? I am assuming the brass type will also make a difference but only a few companies make brass for the 264 Win Mag.

As other posters have commented, belted magnum cases are typically 15 thousandths or more short of chamber length, so the front of the case gets work-hardened a bit upon first firing. I anneal .264 Win Mag cases with the flame pointed at the case wall / shoulder junction (rather than at the shoulder / neck junction) to help soften the front of the case. After the first firing, I anneal and resize but shoot to bump the shoulder back only to the same length it was when it came out of the chamber (resizing the case diameter causes the case to grow a couple thousandths in length).

With this approach, my belted cases are typically fully fire-formed after the second firing. After the second firing, I anneal and resize shooting to bump the shoulder back 1 thousandth.

I don't know how many firings it would take to fully fire-form without annealing after every firing.