Quote:
Originally Posted by slingshot27
Thanks everyone. I brought all my casings to .010" under. I'd say about 10% were a little more but that should correct its self next round.
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Do you mean .010 under your individual rifle actual measured chamber length, or the SAAMI spec length as found in most reloading manuals?
Many trim cutter gauges (Lee) and I suspect fixed GO gauges, are made intentionally shorter than SAAMI minimum spec, (I suspect for legal liability caution). This causes many loaders to trim too short (which is certainly better than too long), and the same caution causes many rifle manufacturers to cut their chambers to SAAMI maximum chamber spec or longer.
If re-loading cartridges for use in several or any rifles, it is advisable to FL size and trim to SAAMI spec,
but if hand-loading for use
only in an individual rifle, then custom sizing and trimming for best fit in that individual chamber, is better IMHO.
A case that is too long for a chamber will contact the end of the chamber neck at the junction of the throat (I hope I have my terminology correct), when the bolt is closed, the lug ramps will cause the edge of the case mouth to crimp into the bullet solidly and will not provide any clearance for the neck to expand and release the bullet on firing. This can cause a serious over-pressure spike and other effects best avoided.
As Dean2 mentioned some chambers can be cut to shorter than SAAMI spec.
The only way for a hand-loader to know the best or safest trim length is to measure the individual chamber using a simple chamber length tool, which can be easily made from a fired case and a bullet. I have posted links to articles on tool fabrication and to the (IMHO better) Sinclair tool on this forum previously, a search will find them.
Good Luck, YMMV.