I have some new Peterson Brass 6mm Creedmoor. After the first firing the cartridge length was shorter than the case was when it was new is this normal?
My other issue is I purchased some new Nosler Brass. For my 17 Remington. I loaded it with my normal load The cartridge would not chamber. I had no issues with new Norma brass. This is my first new brass from Nosler. I was wondering if I ran the brass through a FL die that would solve the problem.
Advice would be appreciated
The laws of physics tell us the case can only lengthen when fired. Part of the case hangs out the back of the chamber and is engaged by the bolt head. The spring-loaded ejector button (on Model 700 type rifles) pushes the case forward so that the case shoulder is fully chambered, leaving a small gap at the rear, and pushes the bolt rearward, so the bolt lugs are pressed against the lug recesses. The firing pin crosses the tiny gap, the cartridge goes off, the case wall engages and grips the chamber wall under high pressure from front to rear, and the length of the case increases at the rear where the case is unsupported by the chamber. This stretching is cumulative and is why cases fail at the web. The process is described in great detail in the book "Ammunition Demystified", by Jeff Siewert. See pp 87-90.
If the case mouth has not been trimmed and chamfered, it may be possible to melt part of the rough end of the case mouth when it is fired. The hot gas and unburned powder are extremely erosive on barrel steel and brass and I can imagine a scenario where a small amount of brass melts at the case mouth when fired. This could appear to be a shortening of the case when it really is not.
A second explanation may be that the case is substantially smaller in diameter at the shoulder than the chamber dimension. Think of firing a standard case in an Ackley chamber. Since energy that could be used to push the bullet through the barrel is being used to expand the case to the Ackley dimensions, you will see lower velocity when fire forming than when firing the same powder charge in the formed case. Fire forming can also result in a slightly shorter case.
I suggest full-length resizing, trim to length, and chamfer inside and outside the neck before loading cases the first time. Trim to the length specified in your reloading manual, which is usually about 0.005" - 0.010" shorter than the SAAMI maximum length. In general, not every piece of factory brass is exactly the same length from base to case neck, even if the manufacturer claims it is pre-processed.
You didn't describe the chambering issue completely. Will some cases only chamber part way, or is the issue the bolt won't close or is hard to close as you lower the bolt handle? The former problem is likely an out of round case solved by full length resizing; the latter may be a too long case, solved by sizing, trimming, and chamfering.
