Double feed problems Ar-15 40 caliber

[Aceofpyro]

So this is a brand new build. I have a 40 cal ar-15 built on a spikes tactical glock lower. It has a 7 inch barrel with a linear compensater. It's gas blow back only. Im using and Ar-10 buffer spring and a 9 oz buffer.

I took it to the range and it would randomly double feed (about every 3 to 5 rounds) the bolt slammed pretty hard at one point pushing the bullet into the casing. Anyone have any ideas

-Thanks

[mellino19]

I used to have this happen with my AR9. I installed a taccom feed ramp to my upper and it hasn’t happened since, could be part of the issue.