05-22-2020, 01:02 AM
MT
With enough neck tension in an auto-loader you don't need the added step of crimping, and without the Lee design mangling your cases every time your cases will last longer and your group sizes will be no worse, probably better.
Enough neck tension is at least .002", especially if there a reasonable jump to lands. Your bullets can shift a tiny bit but as long as they don't come up against the lands there's no difference in start pressure to cause the classic split vertical group on the target. Another way of ensuring the bullets are less likely to shift is by having enough shank in contact with the neck. It helps if there's at least the diameter of the calibre in contact with the neck - so with Grendel at least 6.5mm of shank. You can check all this by measuring the before and after OAL of a round loaded into your AR when the BCG slams it into battery. If it doesn't shift or only slightly then you are good-to-go without needing to crimp.
Rounds loaded for the military and even factory rounds for civilian auto-loaders (e.g. Gemtech's 300BLK 220SMK subsonic) typically use cannelured bullets. This permits crimping into the void without damaging the bullet like in your photo. It's all about guaranteeing bullets won't budge with any amount of abuse, in any rifle. In your case you have the luxury of loading for one gun with known conditions. You don't need to be so severe.
FYI, Redding makes a taper crimp die for Grendel which covers more surface area of the neck and is a tapered effect. This means it is more forgiving on case length. It is also a lot less severe on the neck and the bullet.
With enough neck tension in an auto-loader you don't need the added step of crimping, and without the Lee design mangling your cases every time your cases will last longer and your group sizes will be no worse, probably better.
Enough neck tension is at least .002", especially if there a reasonable jump to lands. Your bullets can shift a tiny bit but as long as they don't come up against the lands there's no difference in start pressure to cause the classic split vertical group on the target. Another way of ensuring the bullets are less likely to shift is by having enough shank in contact with the neck. It helps if there's at least the diameter of the calibre in contact with the neck - so with Grendel at least 6.5mm of shank. You can check all this by measuring the before and after OAL of a round loaded into your AR when the BCG slams it into battery. If it doesn't shift or only slightly then you are good-to-go without needing to crimp.
Rounds loaded for the military and even factory rounds for civilian auto-loaders (e.g. Gemtech's 300BLK 220SMK subsonic) typically use cannelured bullets. This permits crimping into the void without damaging the bullet like in your photo. It's all about guaranteeing bullets won't budge with any amount of abuse, in any rifle. In your case you have the luxury of loading for one gun with known conditions. You don't need to be so severe.
FYI, Redding makes a taper crimp die for Grendel which covers more surface area of the neck and is a tapered effect. This means it is more forgiving on case length. It is also a lot less severe on the neck and the bullet.