I know this is a month old, but I thought I'd offer my experience, and maybe open your mind to exploring different aspects of reloading.
A few preliminary statements to be made:
There is more than one way to skin this cat. I really don't care to participate in a BS argument where a bunch of guys drop in their 2 cents about "I've reloaded for 50yrs and never owned a chronograph," nor one about the legitimacy of different principles behind different methods of optimal barrel time, OCW, Ladder, velocity flats, etc... Different methods can work, and further different methods can work "WELL ENOUGH" for their respective shooter. Some folks don't have very high demand of their loads, so they can live with lower expectations, and when they get a 3/4" group at 100yrds, nothing else matters, as the load does what it needs. Some guys might not be aware of the BLISS that is found in shooting within a node, vs. at an anti-node, and those guys will live a life EITHER ignoring the "flyers" in their groups, or one of despair where their loads just don't shoot well - some of these guys even go back to factory ammo and don't reload any longer... Alternatively, any variable distance competitor NEEDS to know their velocity, and how environmental conditions change it. I competed in Service Rifle for a few years without a chronograph, and I burnt far more cost in ammo trying to find a load with low vertical dispersion at 600yrds than I would have paid for a chronograph. Bought the chrony, and my scores were better. So the value of a chronograph became obvious for me. See the end here for my newest experience in how spending money on a chronograph is saving me even more money...
I'm debating on getting a chronograph to check some loads and wondering how often you guys use it?
When I only had an optical chronograph, I despised the burden of setting it up, lining it up, running cable back to my position... I'd take my chrony along a lot, and rarely actually shoot over it. Now I have a Magnetospeed and a Labradar, and there's rarely any excuse to not chrony every shot I take in practice.
If I change lots, I chrony. If the environmental temp changes, I chrony. Change primers, bullets, brass, changing neck tension, etc... If you chrony along the way, you'll be able to see when your barrel life starts fading - you'll lose velocity as your throat erodes.
For this reason, despite the higher cost, I REALLY recommend either the Magnetospeed or Labradar, preferably the Labradar, since the POI shifts with the Magnetospeeds, except of course for the high cost of the Labradar. I did fine with a Prochrony Digital for many years, a Beta, and a couple others, but the set up really puts me off, so again, I just don't use them as much as I want because of it. The Magnetospeed Sporter is competitively priced against skyscreen optical chronographs, but it does come with the POI shift. The V3 has more adapters, which is an advantage to some guys, and it stores more strings, so you can do your data transfer when you get home instead of writing at the range... Labradar lets you set up easily on the bench and doesn't affect POI, but it does cost a lot more, and it's a bit bigger to haul around. I keep my Magnetospeed Sporter in my range bag at all times and use it when I'm casually shooting, whereas I use my LabRadar when I'm doing development, but it does mean I own more stuff....
Say you have your good load and it checks in at say 3200fps with say 10 shots do you call it done and that's all the testing you do for that load?
This isn't how I develop loads from the start, so no, I don't get 10 data points and call it good...
Do you chronograph for each lot of powder?
Yes. When I'm diligent and responsible, once I find a proper load for my barrel, I'll buy enough powder of the same lot to last the entire life of that barrel. Otherwise, I chronograph again any time I change lots.
Say I'm doing a load workup for a rifle do you chronograph each load first or find what's most accurate first then see if your pushing it too fast?
Don't worry about specific velocity. There should be a ~100fps window where your round will perform the task needed, so your task is to find a consistent, precise load in that velocity window. If it's 3250 or 3350, it won't matter, as long as it's CONSISTENTLY 3340 +/-5fps and it groups nice and round, and small, you're groovy.
Do you try and keep it under book max fps or right on?
Book velocity is irrelevant. Nothing more than a guide post. Kinda like saying an American man should weigh 170lbs and be 5' 9"... Not many actually hit that number.
I guess another question is as long as you have an accurate load what's the point of chronographing?
Accurate load, precise load... What are you using to determine precision? For your upcoming 300yrd matches, all you need is a load which shoots tiny at 300yrds, so keep your mind in that context. But... What happens inside 300yrds is often very different than what happens outside of 300yrds, but 300yrds is far enough for the little details to matter. At short range (300), a guy might see a half inch group with a 40fps ES, and a half inch group with a 10ES. At 1,000yrds, 40fps spread will reveal itself as vertical dispersion, no matter how small a round shoots at 300 (40fps ES is over 6" at 1,000yrds in my 6 creed, would be a lot worse in your 223!).
Chronograph data should accompany all of your OCW or load work up. Don't focus only on finding small groups - you need to find a forgiving powder window, find a "node." If you find a nice, round group, AND it has little to no velocity shift across 3 or 4 charge weights, you know you're in the hunt.
I've also used this load development method of late. It does work. I started with loads I'd developed the old fashioned ways, then tested this method below to see if I could replicate my loads with so few shots. Sure enough, I found the node in the same place, but in 10 rounds instead of 100. I haven't fully converted, but I'm certainly a believer in saving barrel life, and starting with velocity flat spots does let me get to the end point with fewer rounds fired. For a round like 6mm Creedmoor where barrel life will likely be 1500-2000rnds (800 before it starts falling), it's nice not wasting 10% of my barrel life on load development.