Horn 75 is the way to go for price.
Keep an eye on www.snipershide.com. Guys over there occasionally organize group buys for components. Several will get together and they end up doing a drop ship deal where they order many thousands of bullets and/or many lbs of powder in 8lb jugs and they get good rates. I’ve used this for powder and it was good deal. You won’t see group buys for plinking bullets, but good match bullets, yes.
Regarding trimming, frequency required will always be dictated by case length. You are correct, if you trim to the recommended “trim-to” length, you ought to be able go a couple of reloadings between trimmings.
Your trimming frequency will be a function of your rifle’s chamber, how hot your loads are, and probably most importantly, how you have your resizer set up. Most of the case growth experienced occurs from resizing moreso than firing, so once you get your resizer set up you’ll need to take some before and after measurements to see how much growth you experience.
Having said that, what I’ve done based on many recommendations from Dillon owners is, I got a Dillon trimmer and it will be mounted it in a separate toolhead. Toolhead #1 will have the Dillon trimmer/trim die combo in station #1 and station #3 will have my FL sizer mounted in that position. Cases will then be run through the tumbler afterwards to remove lube.
I plan on taking care of priming off the press, using a hand held, tray-type primer (Lee Auto Prime).
Toolhead #2 will be dedicated to charging, seating and crimping (you would also include priming with this toolhead if you intend to use Dillon’s priming system). I may end up putting a flaring die in station #1 if I need to debur the neck interiors. From what I gather, the Dillon cutter spins so fast and makes such a clean cut that you don’t get a cut with a bunch of burrs that need chamfering/deburring. What minmal burrs there are, the post-sizing tumbling session reportedly takes care of them. Some guys use a Lyman M-die to re-set the neck dimension and basically iron out any remaining interior burrs that might be there, others just live with them and proceed straight to charging and seating.
Another option is a bench mounted trimmer like either a Gracey or Giraud that simultaneously trims, chamfers and deburrs, or a lathe-type trimmer but those are a royal PITA when you start talking .223-volume production requirements.
Regardless, my philosophy is you should always trim after resizing so loading bottle necked rifle cartridges is a bit different than loading pistol cartridges which don’t grow near as much (I can’t remember the last time I trimmed a pistol case). That’s why I separate my loading process into two processes – a sizing/case prep phase and a final loading phase. I’ve done it this way for years on my turret press, but it would take four pulls of the handle to get one loaded round. That’s why I went progressive, and just yesterday I mounted my new Dillon to my bench so I’m kind of in the same boat as you. But I researched long and hard regarding how to take care of trimming, and what I’ve described above is a pretty popular approach among more experienced Dillon owners. Plus it’s much cheaper than a Giraud.
The only downside may be noise. I understand the trimmer (and hookup to a vacuum cleaner) makes things noisy so I’ll have to wear earpro when using the trimmer. I may set the vacuum cleaner outside between my garage and shed or I may rig a long run where it’s at the other end of the garage. But Gracey’s and Girauds use big electric motors so they have a noise signature to contend with. If you need quiet because of your setup/situation, you’re going to have to trim by hand or use something that you can hook up an electric screwdriver to, but production will be S-L-O-W. I know this from experience because up until now I’ve used Lee’s trimming system, and while effective, it is S-L-O-W.
The last option – I haven’t ever used one of tehse but some guys do. They use a RCBS X-die. With these you trim the cases .010 shorter than the recommended “trim-to” length (1.740 instead of 1.750), and then from that point on, you never need to trim again. The X-die is supposed to have some built in stop in the mandrel that limits case growth length. I’m not sure though if you have any way to adjust for headspace and neck interior dimension using this die. You might want to look into this.
Lots of HP guys use Varget, RL-15, either 4895, VV 140/540 or TAC for their heavyweight loads. Just use a manual and work up loads. Powders which are appropriate for 55 grain pills are a tad too fast for the heavier bullets.
Dillon’s powder measure will have some variation with extruded powders – don’t be surprised by a maximum spread of .7 grain, with most of the variation falling in the + .2 grain range. For this reason, take a look at TAC, it’s a ball powder.
You probably know, but if not, you’ll need to either ream or swage primer pockets for mil-sourced brass (e.g., LC).
Good luck.
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