I don't even know where to start, I am so frustrated. I have a six-year-old gelding who I've had for about a year and a half. I train with a wonderful trainer, and we have taken it very slow with my horse. He is more than fancy broke. Very soft in the mouth in general riding, Very respectful, if you think stop he will stop. He looks amazing, coat is gorgeous, very well muscled. Is a very very happy horse. Our first barrel has never really been our most wonderful barrel. The issue with his first barrel is getting worse. We use the Connie combs method for barrel training, using the square method. And points. We head in to our first barrel and he feels great, ears are forward, listening to me, and I think we're going to have a wonderful first barrel. Once he gets to the back side of the barrel he blows by it by multiple multiple feet. And then the rest of our run isn't the best. He smokes his second barrel and third barrel. And he pretty much always head shakes on the first barrel. I use an equine dentist and he was just done in May with no issues. I also had one of the best racehorse vets in New England come out a month and a half ago And adjust him and he found nothing wrong. Checked his stifles, hocks, said there was absolutely nothing wrong. I also had a performance vet come out before the racehorse vet, And he thought his right stifle needed to be injected. The performance vet is our usual vet. You can slow work the pattern all day long and his first barrel is perfect. When we get to the back side of the first barrel he doesn't pull me or anything it's just like he's running off, and he takes it so wide that it's like we will duck our second barrel but we never have. He was treated for ulcers with omeprazole. I know this horse like the back of my hand. And I know for a fact he loves running barrels. Every time we run home his ears or forward and at the end of our run when we are done he is so happy, licking his lips. I know he loves his job. We have a very special bond together. I can always usually tell if something is not right with him and my trainer and I cannot put a finger on this. He will ride around in any bit, including a Snaffle and he is perfect. He never logs on my hands and he is a fancy broke horse. The past week we have tried switching him to the left barrel first and his two right turns he blows by them. I am starting to wonder if my performance vet is right about him needing his right stifle injected. The racehorse vet said he didn't feel in his opinion he needed that injected. I do not have any videos to post as I go by myself. His left hand turns are wonderful.  He rates them beautifully and I don't have to do anything for him to turn them. He does it pretty much by himself. It's just the right hand turn that is a huge issue. Any advice would be appreciated, please be easy on me my mind is fragile right now. He and I never fight. Even when we don't have a good first barrel we are not out there fighting with each other. I mean I am very frustrated at the end of my run but we are two peas in a pod.

I would inject the stifles if you trust that vet. 

If you already have or if you still not sure what to do go get a bone scan.  I wish I had done alot sooner than what I did!  It would have save quite a bit of money!  My horse worked perfect but he fought at the gate and he never felf off or anything.  He had a bone cyst in left tibia above hock. My vet said that God was watching out for us bc he could have easily broke it while we was running!

Before the scan I took him to several well known vets and they couldnt find. 

I know how frustrating it is! I had to pay out of pocket, I have no insurance but it was worth it bc I got an answer!

Prob inject hocks and will be fine.Thats what I would do. All four joints

sounds like stifles and if you've already had one performance horse vet tell you as such, I'd personally start there. Also, if they're sore in the stifles the liklihood is they're probably sore in the hocks too. "Peel the onion" and figure out what your horse needs and then fix it, you'll have a whole new horse:)

Inject. To be honest I learned a long time ago to let the horse tell me when it's time to inject. I also just had one that was baffling because she passed many lameness evals with flying colors, several with phenomenal lamenss/sports medicine vets. She had a fractured spine and we all had no clue. Only found out with a friends thermal camera app on her phone. Took her back and said hey xray this spot & sure as hell there it was. So I don't put much weight on lameness evals for diagnostics anymore. My gelding would tell me when he needed hocks done also, he'd swap to his right lead in the back between 2nd and 3rd. So when I saw him do that in a video, off to the vet we went 

I had a horse that for the first few years of competing we struggled with his first barrel. I'd go into it like you, thinking in the first part of the turn we were going to nail it, this time, then he would pop off the back side, head up, lose momentum and make a big arc to the 2nd barrel - 2nd and 3rd were beautiful. (he did not shake his head, though, like you say your horse did)

Drills, injections, different bits, breaks.

Finally figured it out. Saddle fit.  Especially with him, being smaller on right side than left, saddle would tilt further down on his right side, digging into the back of his shoulder, also dropping me in to the inside of the turn, adding even more pressure on the front right part of the tree, making it impossible for him to flex and turn back the other direction smoothly and quickly. 

It started his 4 year old year, futurity year. I bombed Ft Smith.  He's 24 now, taught me tons about saddle fit, and to this day, has no problem nailing the first since I got it figured out.

I had the same thing happening, on a very honest horse. He was misdiagnosed twice, by same vet.

Long story short, I took him to a great vet I have used for decades. After a very thourough lameness exam, he injected his stifles.

 Im so glad i " listened" to my horse and continued searching for the right answer. I had actually asked the first vet to check his stifles {signs told me thats where the problem was} 

Inject.

He is very clearly telling you that turning to the right at speed hurts.

When I was training my Red, I was having issues with his barrels too - especially to the right. It took THREE trips to the lameness vet to finally discover he had a fusing right hocks. (On flexions, his hocks flexed fine. Vet was shocked when we finally decided to do x-rays. Very advanced fusion.)

And he had a catchy right stifle on top of it.

Injected hocks and stifles and I had a new horse on my hands. Was a bit frustrated that it took so long to figure it out. Now, if I think anything is wrong with their hind end on turns, we x-ray those hocks and stifles and do ultrasound of the stifles. I don't mess around. I want to know what's going on and what needs attention and take care of it.

I would inject hocks AND stifles. When one gets sore, often the other does too due to compensation.

As far as the racehorse training saying you don't need to inject, no offense, but he works on racehorses. Not barrel horses that turn, LOL. You are having a very big performance problem. That means you have to do something.