This is my first time here to post.  So here goes I traded for vulcan arms 9mm ar-15 rifle It has the carbon fiber upper and lower. I started firing it with 115 gr fmj and it would jam about every 8-10 rounds it would throw empty case on top of bolt and it jam between top front of bolt and front end of charging handle. I then changed to 125 gr fmj and there was no difference. I then took buffer and spring out of a car stock i have and replace it with the one in the 9mm. I then fired more 125 gr fmj with no difference in operation. I then started holding the mag which is a sten mag up in the mag well and the problem seemed  to get better. I started getting happy again I fired another 20 rounds and then it  jammed and It was bad!!! The bolt was to the rear and would not go forward
I then noticed the rear portion of the lower were the buffer tube threads in was busted and the
bolt was back to far and plunger to keep the buffer back was jammimg the bolt. What Happened??
and were should I go from here???
 

Thanks
Ed

Vulcan is Hesse arms. I've never owned any of it but on every board and most guys I've talked to say it's horrible crap.  TAKE pictures and post them.

I would call vulcan and explain to them what has happened.  If they won't work with you, without charging you for repairs,  I would simply try to salvage the barrel,bolt, and small parts and replace the stripped upper and lower.

I've never seen a Vulcan 9mm set up, but believe it is the same as the one Model 1 used to sell. A Colt bolt assembly useing a Socom type Sten mag block with a Colt style ejector in the mag block.

With the Model 1 9mm upper I have the feed angle to the chamber was far to steep and caused stovepipes because the Sten magazine sat to low.

I figured the magazine had to sit higher to allow the rounds to have almost straight shot into the chamber because theres no front feed ramp like a Colt set up.

I milled the bottom of the bolt assembly narrower so it would clear the narrow feedlips of the Sten mags. Next I marked where the Sten magazine over insertion tabs contacted the lower recievers magzine well on the bottom when seated. I then plunge cut 2 relief areas with a 5/8 end mill about 3/16'' deep. Last I made a longer mag catch for the block out of 1/4 keystock.

Now it'll even feed an empty 9mm cases most of the time because the round is just about a straight shot into the chamber with the magazine setting 3/16'' higher.

Save a little more and get something worth buying, with Hesse/Vulcan you are just throwing your money away