Reloading Rifle Cartridges and Seating Depth

The final step of reloading is to seat the bullet in the case. A crimp can be applied, but it’s not always necessary and is often rare in cartridges intended for long-range shooting. My first handloads were made to feed my Ruger Model 77 MK II.308 Winchester. My dad, dear Ol’ Grumpy pants, had been shooting his.308 Winchester ever since he left boot camp in 1968. There was a stack of brass and we sat to choose a bullet. The Badlands Precision Bulldozer 2, 140-grain,.277″ bullet responded well to a small change in seating depth. This resulted in 1/2-MOA groupings. Massaro Media Group. After some deliberation about cost, we settled for the 165 grain Hornady InterLock Spitzer. That bullet came with a swivel, and seating depth was not an issue. Seating depth became a major issue when I tried to get the Barnes X bullets to shoot. Looking back, none of my rifles printed any groups worth a damn with those bullets, but the effects of seating depth were shown, as the groups opened and tightened from minute-of-lemon to minute-of-cantaloupe.Shortening CasesThe bullets of 30 years ago were certainly not the same as those available today; the dimensions of many of our classic cartridges will quickly show that they were designed to use bullets with shorter ogives, and therefore a lower ballistic coefficient. It can be frustrating trying to mate an old cartridge design with a new bullet while maintaining a cartridge length that fits in the magazine. For example, the.350 Remington Magnum is designed to fit in a magazine with a short action, but uses the bullets from the 1960s. Try to fit a Nosler 225-grain AccuBond (or 200-grain) in that case at a C.O.L. The.300 Winchester Magnums’ shoulder was pushed forward to allow for more powder capacity. As a result, bullets longer than this Swift Scirocco II are pushed down into the case. Massaro Media Group. The same thing can happen with a.300 Winchester Magnum, which uses some of the longest bullets. The case was lengthened, and the shoulder was moved forward compared to Winchester’s belted magnums. This is presumably to make more room for powder. The goal was achieved, but it did compromise the amount of space left for the bullet to exit the case. The Battle of C.O.L.Many of today’s cartridge designs have a case that is shortened to allow enough room to use those long projectiles with the best ballistic coefficients. The 6.5 Creedmoor comes to mind, as well as the 6.8 Western or the new 7mm PRC. The 6.5 Creedmoor is gaining ground on the.260 Remington despite the latter’s greater case capacity. This is because the Creedmoor allows for a longer-range bullet to be loaded in the same magazine. The 6.8 Western is a shortened version.270 WSM with a faster rate of twist to use bullets that are too heavy for.270 Winchester or.270 WSM. In both cases, the powder capacity is sacrificed to allow the highest B.C. Bullets with a higher B.C. will perform better in cartridges that have a higher capacity. Four cartridges that were specifically designed to handle long, sleek bullets with high ballistic coefficients. From left to right: 6.5 Creedmoor (left), 6.5 PRC (7mm PRC), and.300 PCR. Photo: Massaro Media Group.With Hornady’s new 7mm-PRC, the case is designed to propel 175- and180-grain bullets at speeds comparable to the 7mm Remington Magnum. But the case geometry allows the long bullets to sit so that the base shank of bullet, where it transitions into a boat-tail, sits at the base neck of the case. This reduces the amount space taken up by a long, deep bullet. This seems ridiculous to me and I’ve not seen any evidence for this phenomenon. As long as there is enough neck tension and good chamber concentricity I don’t have any problem with a bullet extending in the case. The rule of thumb says that the further out of the case your bullet is seated, resulting in a larger C.O.L., the lower the pressure will be. However, I’ve seen instances where it was the opposite. Seat SafelySometimes the reloader will be able to take advantage of additional space by increasing the powder. Seat the bullet as far out as possible, but not so far that it rests against the lands of rifling. This can cause dangerous pressure spikes. The C.O.L. dimension is usually found in your reloading guide. Some shooters choose to skip the magazine restraint, and instead load a cartridge that is too long to fit in a mag but safe to load into the chamber. In fact, some bullet companies market single-feed projectiles: the Cutting Edge Bullets Lazer, for example.Experimenting with seating depth can be a sound means of turning a good load into a great load. I’ve been working on a load using the Badlands Precision monometal 140-grain Bulldozer bullet. The 6.8 Western’s C.O.L. My initial load was seated at 3.000 inches with groups printing 0.75 inch at 100 yards. Photo: Massaro Media Group. Massaro Media Group. My initial load was seated 3.000 inches with groups measuring 0.75 inches at 100 yards. I’ve found, after a full circle of the Barnes X modern iterations, the TSX, TTSX, and LRX, that these bullets like a little more jump. They give their best accuracy if seated at SAAMI spec…or even a little deeper. Seating depth, like powder charge weight, is one of the easiest adjustments to make when reloading. Keep your caliper close by, record the seating depth of each bullet/cartridge combo, and experiment to see if it can improve your group sizes. The target grids and bullseyes are measured in MOA. Subscribe to the Gun Digest newsletter and we will send you your print-at home target pack immediately. Enter your email below.