Thread: ? Head Space

Originally Posted by 6x47

I thought the shoulder/ neck junction length were the same on both a std and AI?

For those with QuickLOAD, the dimensioned drawings supplied may be used to compare; say .257Roberts/.257AI, 243Win/.243AI, 30-06spr/30-06AI and so on. This comparison will find that officially the improved cases are all 0.004" shorter at the shoulder-neck junction, plus or minus maybe half a thousandths depending on the particular pair of designs.
There will be plenty of barrels out there in improved chamberings that will have been fitted to "feel right" on a sample of a few parent cases supplied at the time. As Moa Hunter has said above, within reason it doesn't matter so much, as long as the full length or body die being used is set up to keep the cases snug in that particular chamber. I have had one improved chamber where the initial crush fit was a set up a little enthusiastically, and I needed to grind a bit off the base of the die to make it usable. With some variation it just means your improved or wildcat chambering is a little more wild. A good rule for long case (and personnel) life with AIs is probably to not mix rounds between rifles unless they are a standardised design – of which only the .280AI comes to mind.