Short throat issue, rifle wont chamber anything with a COAL over 2.245

[Fess]

This really seems to be a problem with this chamber. I had one that was replaced under warranty. Same thing, Sierra 120gr hpbt would jam in the lands at mag length.

I wonder if the "compound" throat is hard to get right because this problem seems to be epidemic.

I should also say the head space on this barrel was fine.
TTF

Here is a link to see the Grendel's SAAMI chamber. http://www.65grendel.com/forum/showthrea...l-Drawings

The compound throat makes the Grendel unusually sensitive to reamer wear. Typical modern rifle chambers have a section of straight freebore before the angled throat. The walls of the freebore are parallel and the diameter is greater than the 0.264 diameter of the barrel's grooves. The tapered throat starts at the diameter of the smooth freebore and gets smaller, intersecting the base of the rifling and continuing until it is smaller than 0.256" diameter of the lands. The angle of taper varies from cartridge to cartridge, but often is commonly 1-1/2 degrees per side. The sides of the bullet can't touch any rifling until it is past the freebore. The .264 LBC and "Grendel II" chambers are like this.

The SAAMI Grendel chamber does not have typical freebore. Instead, its throat starts with a gentle 1/2 degree-per-side taper, then increases to 1-1/2 degrees-per-side. The starting diameter is again larger than the grooves, but the rifling begins somewhere before the taper steepens. Exactly how far down the barrel the rifling begins depends on the wear of the reamer. If the reamer is at max spec (0.2644 +0.002"), the rifling begins farther down the barrel, almost at the place where the taper angle increases. If the reamer is at the minimum spec (0.2644"), the rifling begins sooner. If the reamer is too worn, the rifling starts even sooner, giving the infamous "short chamber." The unusually shallow taper angle increases the movement of the intersection with the rifling due to a given amount of reamer wear when compared to that of a steeper taper angle.

In practical terms, with the SAAMI Grendel chamber, the distance to the beginning of the rifling is variable and can be very short, depending upon the condition of the reamer. With a "standard" chamber, the distance to the rifling still varies somewhat, but it is always longer than the freebore.