As far as primers go...Look at the top of this forum. There is a link to primer cup thickness under tips for new and old reloaders. Read the whole article, it is very informative about small rifle primers. The 221 FB is a high pressure round. I have found less primer problems with BR4 and Remington 7 1/2 primers than any other primers I have tried in my 222 family of cartridges (221 FB, 222 Rem and 223 Rem). When you look at reloading manuals, you will see Remington 7 1/2 is the most popular primers for the small rifle pocket (except Speer of course). I personally like the Remington 7 1/2 because of this...I have found that they shoot well, are generally cheaper than the CCI primers and they give me no primer related problems; but as in any load development, you have to try different things to find out what works best. If you have Winchester primers on hand, that is what I would try. If you do not get satisfactory results, like blown primers or pierced primer, when you have not reached full pressure loads or you get fliers and erratic results, then you can purchase and try other primers. If they give you satisfactory results, be happy and do not change a thing. I am not even inferring that you push the pressure limits of this fine cartridge, it just that some times even with out pushing the pressure limits the thinner primer cups can pierce, flatten severely or give you erratic results. Some have found that the thicker primer cups do not reliably fire, they switch to a thinner cupped primer and they have no ignition problems. I have not found this in any of my guns, but some have. One more thought - the CCI BR4, Remington 7 1/2 and Fed 205M are bench rest primers and specially constructed for consistency not only from primer to primer, but lot to lot. Good Luck and Good Shooting.