Having used Federal 711B and 900 / 900B rimfire ammo for smallbore silhouette for a few years, I ordered 2 cases of 711B from the supplier who visits the Nationals at Ridgway this past July, where I picked up the ammo.
Well, I opened the cases a couple of weeks ago and discovered that the cartridges no longer had the dimpled head used in the past. Having smelled a rat, I decided to test the ammo, hoping it would still give similar results out of my Remington 40X and Sako 78 rifles. The older 711B ammo with the dimpled case heads consistently produces groups of just under 1 inch at 100 meters. The 900 and 900B ammo produces groups around .750 inch.
Sadly, the "new" style ammo can only be politely classified as "trash". While shooting 10-shot groups, it would put 5 or 6 shots in one plce, and the other shots about 1 inch away, forming another group. Since I observed this with both rifles, I took 200 rounds at random and weighed them (Yes, there is nothing better to do on cold nights in Wisconsin). I found that 123 cartridges weighed between 51 and 53 grains, and 77 weighed between 53 and 54 grains. I will be test firing to see if there is any correlation between weight and point of impact.
If I do find a statistical correlation, I will have a new passtime for the long winters up here, and I will have decent-grouping ammo, segregated by weight that I'll be able to use next spring and whe I move back to Arizona.
On the other hand, if segregating by weight solves nothing, well, I'm really screwed!
Bottom line, STAY AWAY FROM THE TRASH BEING MADE BY FEDERAL THESE DAYS, and save yourselves a lot of grief.