Semi-automatic rifles - Full length resizing only?

[Fossil4Life]

Apparently, Lee does not sell a collet sizing die for semi-automatic rifles, only the full-length sizing dies. I was told by Lee that when reloading for semi-automatic rifles, that the brass should always be full-length resized every time, and not neck sized.

Why is this the case, if I am going to be using the brass for one specific rifle only?

[knight0334]

Semi-auto's should be FL resized. The resizing issue isn't just with the chamber, but also feeding. Sometimes just a couple thousandths of an inch difference can mean it will feed or not.

I'm not saying that neck-sized only will not work, but FL will improve the odds of it working properly. Semi-auto's are more sensitive to feeding issues than any other gun(couple exceptions).

The only real advantages to neck-sizing are more consistent ballistics if the neck-sized ammo is used in the same gun, and slightly easier reloading.

[daschnoz]

Yes, go full length resize for semi-autos. Here's why....

As the case starts to extract, the chamber pressure is still pretty high (relatively speaking). The case moves back say 0.125". The case diameter at the head is larger than it is 0.125" forward of the head. The chamber pressure will push the case outward into the chamber wall - increasing the OD of the case. If you try to rechamber this case in your semi-auto, your rifle will not go into battery.

In bolt guns, you don't have this problem. The case doesn't move until you operate the bolt - which is well after the barrel pressure has dropped.

[Fossil4Life]

Thanks for the info, guys. Another question: I have a Lee Pro 1000 reloader. Should I use the Lee-branded dies for my 300 Blackout, or are there other dies that would work with this reloader that are better than the Lee's?

[busa dave]

I prefer Hornady Dies. I feel they are higher quality.

[knight0334]

About the press - as long as the dies fit the press they should work. Some of those quick release type dies, will of course, not work.

I've used all sorts of dies in my Lee Pro1000. RCBS, Lee, Redding, Lyman. The 300Blackout should load without issues in the Pro1000 even though that press is designed move for pistol length cartridges. Lee, themselves, sell a .223 Pro1000 package - so the 300 is within working lengths.

I tend to stick with Lee dies for straight-wall pistol cartridges, and Lyman/Redding/RCBS for rifle or bottle-necked stuff..

[saleen322]

I prefer Hornady Dies. I feel they are higher quality.

+1 on this. The Hornady new dimension dies are made with a physically longer overall die body to give more adjustment range in progressive presses.

[tabasco_joe]

The only real advantages to neck-sizing are more consistent ballistics if the neck-sized ammo is used in the same gun, and slightly easier reloading.

I think you might agree that case life is often extended as well.

[knight0334]

I think you might agree that case life is often extended as well.

That might depend on the case design. In some situations full sizing will prolong, in others neck sizing will. If the case has a strong taper to it, neither type of sizing will really change much. (one reason Ackley tried to straighten the taper out on his "Improved" designs)

Straight wall cases would probably be prolonged by full sizing, where as bottleneck would likely see an advantage with neck only.

[dkf]

Semis don't have the cam over effect like on a bolt gun which pushes the case into the chamber. The extra resistance from a neck sized only case will most likely not function in a semi.

I use an RCBS Small Base X-Die set for .223/5.56. Lee dies are good but I did have some issues with a .380 set that worked poorly with jacketed bullets.