FL Bushing Dies vs. Honed FL Dies
We were recently asked: “What size neck bushing is best for Lapua 6mmBR brass in a ‘no-turn’ chamber?” The questioner planned to purchase a Redding Type ‘S’ full-length sizing die with neck bushings. The quick answer is that one should probably get both 0.266 and 0.267 bushings and see what works best.
A loaded 6BR round with an unturned neck will typically run about 0.2692-0.2697 (depending on the bullet). A 0.267 neck bushing, after springback, will give about 0.0015 tension which can work well in a bolt gun. However, some bullets prefer more tension than others. And, you may find that it is useful to tweak neck tension slightly if you make major changes in seating depth during load development. In a gas gun, such as an AR15, you probably want .003 or more tension.
Alternative to Bushings — Honed Full-Length dies
Conventional, non-bushing full-length sizing dies can create ultra-accurate ammo with very low run-out. For some applications, we prefer a non-bushing FL die over a bushing die — so long as the neck tension is correct. But many FL dies have an undersized neck diameter so you end up with excess neck tension, and you work the brass excessively. Forster offers a simple, inexpensive solution — honing the neck diameter to whatever size you want.
If you purchase a Forster non-bushing, full-length sizing die, Forster will hone the neck dimension to your specs for about $10.00 extra. This way you can have a FL die that provides the right amount of tension for your particular load. Forster dies are relatively inexpensive so you can afford to have a couple of FL dies with necks honed to different diameters — such as 0.266″ and 0.267″ for a no-turn 6mmBR. The die itself is fairly inexpensive — currently Sinclair Int’l charges $33.95 for a Forster 6mmBR full-length sizing die (item FP6BRFL).
Forster FL dies, necks honed to .265″, .266″, and .267″.
Steve Rasmussen of IowaHighPower.com gave this a try. In fact, he had three dies made — each with a different neck dimension. Here’s his report: “My original Forster 6BR FL die sized the necks down a lot, less than 0.260″, .256″ if I recall correctly. I sent my die in and asked if they could supply two more FL dies (for three total) to have the necks honed to 0.265″, 0.266″, and 0.267″.” In addition to the purchase cost of two more FL-sizing dies, Steve paid $30 ($10 per die) for the three dies to be honed, plus about $12 for return shipping.
The table below shows the neck diameter range of 10 sized cases using each die. Brass springback after sizing is running 1 to 1.3 thousandths. My loaded rounds are running 0.2697-0.2699 using Lapua I bought last year. So far the dies are working well. I sized 80 cases with the 0.266″ necked die. The shoulder is running 0.4582″ and 0.300″ up from the base is 0.4684". I spun 20 of ‘em and 16 had a runout of one thousandth (0.001) and the other 4 at 1.5 thousandths (0.0015).”
|Die Diameter||Sized Brass||Springback||Neck Tension|