18 inch Barrel makers

I am going to be building a 6.5 Grendel with an 18 inch barrel to accompany my 24 inch Overwatch model.

Can members reading this thread please let me know who makes barrels that would fit my project? So far, I have found Alexander, Sabre Defense, and Satern as the makers.

Does anyone know who actually makes the 18 inch barrels for Alexander Arms?

For what it is worth, I went with the Lothar Walther 18" CSS. The throat is tighter than my AA 24 inch overwatch, but that isn't a problem as both rifles really like the same load...30.3 of W748, 123 grain Scenar, Lapua brass, Remington 7 1/2 primer. Seated length has to be a bit shorter to accommodate the shorter throat of the Walther barrel, but again, that isn't a problem with the AA barrel.

Overall, the AA chamber isn't as picky as the 6.5 CSS chamber. I am told that the 6.5CSS was more made for accuracy shooting, while the Grendel chamber was designed to be less picky so that it would work better for military and LE applications. Too tight a chamber for military rifles has always been a problem. And, the Grendel chamber appears to be more forgiving of variances between different lots of ammo, while still giving satisfactory accuracy.