I have a Savage Model 112 that I just had rebarrelled to 6mm-284. I took Lapua 6.5-284 brass ran it thru the 6-284 Redding FL die and loaded 53 grains of Retumbo with 105gr Bergers to a length of 2.370 at the ogive. At the range the primers backed out on the first firing. Anyone have any thoughts as to why? The resized brass measures 1.797 before firing and 1.803-1.805 after firing-used Hornady Headspace gauge to measure. I measured my headspace gauges I took to the gunsmith for him to install the barrell and the go-gauge measures 1.801, the no-go gauge measures 1.805. The shoulder moved forward .006-.009 and the necks are visible shorter. I don't think this is a headspace issue, I think that maybe I need to turn the necks. A bullet will not slide thru the neck of an unsized case. What do ya'll think? My barrel is a Shilen 8 twist stainless select and I have not seen any markings to say it is a tight neck chamber.