I use Purina Flock Raiser because it available to me with 
fresh mill dates and consistently high enough turn over in 
my location and at the same price as Dumor or Nature Wise. One store had feed more than 6  months old on the shelf and since nutrients diminish over time (normal turnover time is formulated into the equation), and depending on storage conditions (heat or humidity) could happen rapidly. I no longer shop there. Generally aiming for not more than 6 weeks past mill date is preferred. According to the person who orders feeds at TSC.. I believe they are *technically*  alleged to be good/best by.. within one year of milling. But topping the confusion is the difference of how they label those dates. If I had Kalmbach feeds available I might try them again as when I did, it smelled so good. BUT it's a regional feed, to the midwest I think that I got on Amazon and not available to me on a regular basis. If you're interested please check out the feed comparison charts, someone has worked really hard putting together.. For me brand doesn't matter, nutritional analysis and ingredients do. And I cannot personally afford to go "organic".. So it (Purina FR) may not be my #1 pick if my resources were different.. (location, funding, etc) But it has been a very good product with acceptable and reliable consistent results.
https://www.backyardchickens.com/threads/➡-feed-comparison-spreadsheet.1275920/#post-20524932
Yes, I have stated the POSSIBLE down sides of feeding a rooster "layer" feed. I personally choose not to feed it as the savings of doing so is outweighed by other factors and the risk just isn't worth it to ME. As I've seen many state they never NOTICE any problem.. and there IS a genetic factor (which is the unknown part to us) that is largely at play. So I would probably get the flock raiser (or other low calcium formulated ration)... and feed out the layer, mixed with the FR to spread around the nutrients. But YOU should do what feels best for your flock, with what you are currently thinking and understanding, with what resources (funds) you have available. You can always switch things up if you change your mind,
I NEVER switch my feed. I start my newly hatched chicks, the boys I'm raising for the freezer, my active layers, breeders.. EVERYONE only gets the FR, ever.
I realize you are asking about a 
hen only flock. My personal thought with my current understanding means I would NOT feed layer to a hen only flock either.. Maximizing the micro-nutrients in my eating eggs (all eggs are 34% protein and 64%, fat according to their energy aka calorie content with half that protein and a good portion of the nutrients being found inside the yolk) benefits MY long term health. Plus the hens having more reserves on board and seeing who different the personality withdrawal was when going through molt was telling to me. The extra amino acids.. make the birds stronger, more resistant to internal/external parasites, ultimately predation.. according to MY anecdotal evidence.. 
That being said.. we do all we can and ultimately we are not in control. For Orpington.. not less than 18% protein is preferred. They however can SOMETIMES be genetically prone to fatty liver hemorrhagic syndrome.. be careful not to feed them 
excess high energy low nutrient treats.. like cracked corn, scratch, left overs. Just be sure to keep it under 10% of the total daily ration for best results.
Thinking maybe "hatch" was meant. 
While I'm here sharing my thoughts on feed let me touch on another subject many will tout.. FERMENTING, aka.. FF.. I bought in for a while and did it.. I mean all the rage.. increase protein, add probiotics, decrease feed cost, increase health, increase eggs size, the list goes on and on..
All those things equaled chicken math. If it's saving me this much plus I free range I can add this many more.. RIGHT?! Right. 

 I did it for a flock of 72 including some ducks.. I did ONLY FF for 2 whole years. I didn't save ME a dime.. NOT one! My birds weren't healthier, eggs weren't larger. Nothing. I wasted a lot of time doing it for a flock that size in a large plastic trash can, and had a lot fun seeing the layers and bubbles, stirring with an oar. I even fermented dog food, don't. 
 
FF 
might help some birds that are in need or save some very wasteful flocks.. but ultimately.. it's unformulating a formulated ration and many feeds already have probiotics added to them even when they don't spend money to advertise it on their fancy label. Looking back just this moment I found myself wondering if it actually decreased my hatch rate?! 
Solutions not problems! 
