Posted over in precision rifles reloading, they recommended I come here, which makes sense.  Here's the post from over there.

Just got me a Bushmaster BA-50 and finally found a place to shoot it.

Federal AE M33 runs 2737

My handloads using once fired LC and pulled M33 650gr bullets go like this with IMR-5010:
210gr - 2347
211gr - 2335
212gr - 2347
213gr - 2343
214gr - 2099!!!!
215gr - 2185!

I called the 214 a fluke, but the second seriously regressed load at 215 stopped me cold.

Primers look ok.  Not as good as the Federal rounds, but like I'm just getting warm.

It was 70 degrees out and I was keeping my loaded rounds in the shade.

All of my research led me to 215gr being the sweet spot for this powder, but most were using a heavier bullet.

Ideas?  Any more info I can provide?  Thanks.

How far is your chrono?   You could be getting some flash over the sensor messing with it.

Measuring the powder with my trusty RCBS chargemaster or whatever it's called, the electronic one with the integrated scale and trickler.  

I wrote each load in sharpie on the cases and placed the in order in my ammo box.

I put the chrony at 20 feet to be safe.  I've had it act up at 10 feet with hot .357 loads that make big fireballs.  It seemed ok with the first three factory Federal loads, about 150 fps short of factory specs seems par for the course.

This 5010 is probably very old, I think it's been discountined forever.  It looks fine, smells fine, isn't offgassing, kernels (is that what they're called?) look normal if not pretty large.  I've run HS-7 from the early 70s without issue, and this 5010 has been stored better.

I shot them all on paper, group was bad with both the Federal and my loads, about 3MOA, but Bushmaster says it takes 100 rounds to break in the barrel, so I didn't expect cloverleafs today.

Rifle is "new" to you, but is it a used rifle you bought or new out of the box one?

If used, you won't know how it's been treated, necessarily.

If the powder/chrono doesn't seem to be the problem, find a borescope and check your barrel.  Copper buildup in the barrel, over a lot of shooting, but insufficient cleaning will be squeezing and squeezing the bullets down as each travel thru the fouled area worsening the fouling, until, eventually, a bullet will take some of the rifling with it and you'll need a new barrel.  A borescope should show a LOT of shiney copper concentrated in one place of the bore, as opposed to routine coppering in most other places.

Correction is aggressive copper solvents and considerable brushing to get all of the bore down to bare steel again, if the damage isn't too far gone.

A major supplier of .50 services has told me he's saved far more barrels by deep cleaning than by replacing barrels....rifles sent to him because the barrel is "shot out."  Yet an aggressive deep cleaning in his shop gets it back to match grade performance.

Most people just run a few patches thru their rifle after shooting, with a couple passes with a brush.  That's fine for an end of the day quick clean if you're going to shoot more tomorrow, but at the end of the season or after the end of the competition, a deep clean is necessary especially for the big .50 bullet with all that surface area and it's compounded 2x, 3x, 4x if the shooter has been using solid copper/solid brass bullets regularly.  Those foul more readily.

Your load workups of one grain increments is a total waste of time at 200 plus grains. I'd try loading 5 grain increments. I've had a lot of IMR5010 that's somewhat slow but probably near normal. Takes about 230 grains to get the level I want to achieve and not showing any pressure. Like mentioned 210-215 grains is near a start load. You should see some increase in velocity using 5 grain increments. My loads use CCI primers, LC brass, and 647 M33 FMJ.

Rifle was purchased brand new, has a total of 12 rounds through it.  I do plan to go through it with some Sweets and see what comes out, but I went and bought .500 cleaning products instead of .510, so they don't do anything.

I did see loads up around 230 during my research, so I considered that near the top, but the loss of 250ish FPS is what really concerned me.   Velocity regression is where I hit the brakes hard, especially on a rifle that could fire the bolt through my shoulder if I do something dumb, so I'm being extra cautious here.  I still have 216-219gr loaded, but the range is 1:45 away, so I want to make sure all my ducks are in a row before I make that drive.

The issue isn't the powder, it's the amount of powder your not using.
A 215 grain starting charge is for 750 grain plus projos, not the small 650 grain projos.
I start at 225 and work up in 5 grain increments for the smaller weight projos.
If your shooting a bolt action, you can push it pretty hot.
650 pills are made for shorter distances, plinking or fouling rounds.
Don't expect too much in the accuracy dept, unless you size and weight sort them.

SJC

Yeah, 215 grains of powder is the default safe load for .50BMG, unless you're using an unsuitable powder like Bullseye.

Working up some new loads right now, do you all think a crimp would help me out here, get that powder burning a little better?

A light Crimp never hurts, especially when using milsurp projos and brass, but it shouldn't be needed as long as you feel some tension when seating the projo.
You could also load the magazine and after firing a few, check the OAL of the rounds to see if any of the projos have crept out.
SJC

Would H50BMG be a better choice for these light bullets?  I may have found some.