So Bear Creek had some uppers on a pretty good sale and I had a lower laying around....

I used an Anderson Lower, Palmetto complete lower parts kit, and Bear Creek 450 bushmaster upper. I took it out this weekend and I get 2 shots and then jam. Tried slow shoots and fast shots and it was the same thing each time. A few months back I built a 300 BO (radical upper) for my daughter and it works flawlessly.

I know its a loaded question, but any ideas on how it fix it, or do I try and send the upper back for them to look at?

What buffer are you using in the lower?

Did you try multiple magazines?
What buffer is in the gun/what caliber was it built for originally?
What angle is it ejecting at?

Should be some people more knowledgeable than me along shortly.

What type of jam are you experiencing? Feeding, extraction, ejection, not picking p cartridge from mag...

Also simple question have you tried another magazine?

Possibly overgassed or buffer/spring issue.

Need more details on the exact happenings of the failure. The more detailed you can make it the more useful the info will be. I've built a few and came across some issues. I personally feel like you're not giving enough info. There's a chance it can be a few different things culminating into on jamming.
"Jammed" is not as universal of a term as you think.

All that said, there was another thread about a 6.8spc ruining someone's rifle becasue it was overgassed. I, like many others, believe you should just get a simple adjustable gas block regardless of what else you do.

Thank you for the responses.

I the buffer tube is whatever comes with the Palmetto kit, it just says "Mil-Spec Buffer Tube Assembly: 7075 aluminum with buffer springs"

I had 2 magazines that I bought from CDNN that say 450 Bushmaster on them and both of them did the same thing. A buddy handed me a magazine that he uses flawlessly in hiss 458 socom and I tried it and the same issue happened.

Yes, I should have put more details in the post, you all are correct. As far as "jam" it seems to be a feeding issue. The first round loads fine, after firing the second round loads, after shooting it, the third round will be stuck between the magazine and chamber if you will. I drop the magazine, help the round into the chamber, put the magazine back in and fire, chambered round fires, next round fires and third round hangs up..

Great, i actually think that's a great level of detail to work with but some may ask for me.

My layman's perspective:
1. i still think getting a simple adjustable gas block is a must, but probably won't solve your problem by itself. It will for sure make much more options available to you. p.s. be aware of those who simply say use a heavier buffer. Going back to the previously mentioned 6.8spc thread, nit's a bandaid solution to a stitch problem imho.
2. my guess would be something to do with departure angle of the round because of the round nose of the bullet + that straight walled cartridge. i want to say opening up your feed ramps on the barrel extension may resolve this. if it had to be a gass issue, then it sounds more like under gassing than overgassing.

good luck.

Try a heavier buffer. Doing that will frequently solve FTF issues.

Is the bolt catching the new round on the base, or up on the middle of the brass? Might not be enough gas to run the bolt far enough back, or to heavy of a buffer if the bolt is hitting the middle of the case. Are you running reloads, 223, or 5.56 ammo.

It's factory ammo, 450 bushmaster.

Where is the bolt face hitting the brass?

I saved the brass, I will take a look tonight when i get home and see what I cam determine

A friend of mine bought a socom a few years ago, he ditched the metal mags and bought Nagpur versions and the room was not sufficient so the round took a slight nose dive and wedged it’s self in a fail to feed manner.
We got a metal mag and it fixed his issue. I also noticed that the plastic mag didn’t have the same relief in the front as the metal mag. Might try to open the front up of the mag so the bullet has no choice but to hit the ramp when it’s latched in.