Question about seating the bullet straight

[CPorter]

Since you mentioned your weapon is an AR-15 you will need to full size resize to insure rounds will chamber in semi-auto mode. As far as runout goes there are a few factors that come to mind. The more you work the brass the more likely you are to increase runout. This applies to the neck mostly but affects the other parts as well. Bananna shaped cases seldom function well. On your necks, measure a few fired cases and figure out what size the chamber neck is. Then measure your loaded rounds. Info I have from the die manufactures say that .001" is optimum for neck sizing and concentric ammo. This is for bolt actions and hand feed. For semi-autos you will probably need .003" for reliable feeding. Not using the expander ball can cause the neck to push into the shoulder IF the neck is too small and/or too thick. You may also get ring marks around the nose of the bullet. It also depends if you are using flat base bullets or boat tailed. Boat tails are easier to seat in smaller neck sizes. Flat bases will get you crumpled necks if you are much more than .002" under sized. I imagine you can get the neck of you full length die opened up a bit so you aren't working the brass more than you need. Might be better to get a body die and neck die to make it easier to adjust. Also if your necks are not uniform in thickness then you can't expect a bullet to seat straight. Neck turning will help this but can be a pain for a semi-auto that you loose a lot of brass with.

How much does it affect accuracy? Well, other mentioned benchrest shooters and long range shooters. They will be different because most of those seat into the lands. If the bullet gets jammed into the lands crooked then it will gouge slightly and deform slightly then precess as it flies. You can't seat into the lands and get ammo to feed from the magazine. The jump into the lands will always insert a bit of random skew so it's not nearly as critical in your application. Keep your brass work to a minimum and then work on uniform neck tension to insure consistant powder ignition and burn. That should get you repeatable accuracy and reliable function from your AR-15.

 

[abinok]

They are ok...
Far superior to the standard seating dies that are basically a cup on teh end of a bolt like the RCBS and others, inferior to the various inline seating dies... redding foremost among them. If you are seating longer bullets for caliber, they work well, and since this thread has TIR (total indicated runout... as I have never heard of RO before) in the title, in this regaurd they do well. Not as precisely adjustable as the micrometer inline seating dies for sure, but ive loaded some very precise ammo on them... under .002 virtually all of the time, most under .001"... when seated by rotating the case as the bullet is seated as above. Though, I don't usually go 4-5 steps in seating. Usually 2-3, and if a spin on the Neco goes well, I get to cranking the handle.