Virgin to FF load changes

[Phys86]

When going from Virgin brass to 1x fired, just a regular chamber, if you use the same powder charge I know that velocity will increase on the FF round.

Does that mean pressure is greater as well? It seems that programs like quickload and grt only take into account fired brass h20 cap rather than loaded cartridge dimensions.

 

[David Christian]

IMHO, 2nd firing is faster as more energy is moving the bullet versus expanding the brass. I think the pressure would be higher in the 2nd firing as well as less gas escapes ahead of the bullet due to a better case to chamber fit.

 

[Phys86]

I was thinking it would be higher as well, but thought it would be from the measurable pressure exerted on the chamber wall being decreased because there's less brass expansion soaking up the energy

 

[K22]

I do not know the answer to your question and could only speculate which I won't.

However, from a practical standpoint, in my experience, some load adjustment may be necessary in load development to establish a "qualified" load, even at the varmint level accuracy standards for which I strive.

Also, the one reloading area that I am very meticulous about is case sizing. I consider it essential to allow virgin cases to fire form before bumping the shoulder. Even after that, I monitor case head space and only bump, when necessary, often after several reloads. Of course, this assumes a set of virgin cases dedicated to a specific rifle. I also full size every time but set my die with Skip shims to control and vary the amount of sizing.

 

[JFrank]

I would think a fired case having slightly more capacity to have less pressure, I have not seen much difference on paper at short to mid range from virgin to fired.

 

[Phys86]

I would think a fired case having slightly more capacity to have less pressure, I have not seen much difference on paper at short to mid range from virgin to fired.

This is also something I thought about.

I typically don't see much difference from Virgin to fireformed.

I recently did some pressure testing with virgin brass and saw slight ejector mark at the highest charge. I dropped a grain and also seated 0.020 deeper to get the cartridges to fit in my box and figured it would be fine with 1x fired. Loaded 25. Then at the range I got progressively worse pressure signs over 7 shots and quit. I was just trying to figure out if it is pressure due to load or if I have a carbon restriction built up in the throat.

All brass prep I did for these would not cause it. So it is either over charge that for some reason didn't show up previously or i need to clean the barrel. Only 125 rounds through the barrel so I'm not wanting to clean it if I don't have to.

I dropped the charge another 1.5gr from where I was last and seated to the original longer length, so we'll see what those do next time.

This is a 243 22" factory Tikka throated longer to seat a 112 match burner at ~2.97coal. cci200, h1000, starline brass. Charge that recently gave high pressure signs was 48gr and 2.950 coal and temps were about 10F higher, at about 75F. In some previous primer testing I did I was getting 3030 with cci200 and 48.5gr seated at the longer coal I think I had a slight ejector mark one 1 round out of 12.

I think it is likely just high pressure that wasn't showing up consistently.