Remingtons and their "mile long freebore". Mine has even more jump but shoots great at "mag length" of 2.810". For what it's worth, the freebore is the same size as the groove diameter so if you shoot a bullet with a fairly long bearing surface it's not so much the "jam", it's the fact that the bullet's centering better in the freebore. A good excuse too to keep the carbon ring out of the front of the chamber, just behind the second shoulder.