My .300 AAC build would cycle supers just fine. Subs would fail to eject. I changed to a yellow spring from Sprinco. Now subs will eject but jam next round. This is all factory ammo.

I know i can try different ammo. Or handload to achieve desired effect. I'm also thinking lightweight BCG and / or lightening the buffer. It's a 3 oz, don't know if anybody ever goes lighter than that.

Thoughts???

Sounds like you need more oomph to get things working properly. You might consider a heavier projectile. What is the bullet weight that's causing the issue?

 

Would the gas system or the gas setting be a factor? I know some rifles people can increase or decrease the pressure based on ammo or if they run a suppressor?
Just spit balling ideas here.

 

What kind of AR are we talking about here? 6", 16" or something in between? Is it a PSA , S&W, Colt, etc., or custom build? How are you trying to run subs/supers - both with a suppressor, subs with and supers without or both without a suppressor?

I've got an 8" .300blk I built and went through the same problem when I added a suppressor. It took some tweaking but I now have it running subs and supers from 110gr up to 220gr consistently with and without a suppressor. I built mine and it has a pistol length gas system with a non-adjustable gas block.

I'll spare you all the troubleshooting I did, but in a nutshell I started with a captured spring H2 buffer that ran flawlessly with supers and subs without a suppressor. Then I got a suppressor and it was a disaster. More fails than success. Did a bunch of troubleshooting and wasted a lot of money chasing a problem that I thought could be fixed adjusting the buffer. The buffer did need tweaking in the end, but ultimately it was the BCG that was the real problem. I ultimately got it running consistently with supers/subs with or without the suppressor using a Sprinco Yellow, an Odin Works Lite adjustable buffer that I run slightly heavier than carbine weight (3 oz) at 3.3 oz and a KAK Industries down vent BCG.

Every AR is different, so my fix probably isn't going to be your fix, but what I found was that the BCG I originally had was just cheap and not fully to spec. As for a lightweight BCG, I personally wouldn't as the lower end ones are about the same price as higher quality mid range standard BCG. Unless then entire build uses parts designed to reduce weight, you won't notice any difference and the weight taken from the BCG will definitely require buffer spring/weight adjustments.

 

After twice using OSHA equipment with tech to operate...the port noise is louder than the bullet....So I used a KaliKey to turn it into bolt action and I have a bolt action upper---I don't care about semi-operation---I want QUIET...

 

If you have a spring that works for the supersonic loads and another spring that works for the subsonic loads then just use the appropriate spring for the ammo you want to use. Changing a recoil spring in is about a 1 minute or less procedure. Not at all a big deal, IMHO.

There is such a big difference, ballistically, between the sub-sonic and supersonic loads that it will likely be difficult to find a single spring that works well with both cartridge variants. Probably better to use an adjustable gas block. YMMV of course.
-Bob

 

Opened up the gas port to 0.125. Problem solved. Cycles subs without fail. 4 o'clock ejection. Locks open on empty.

All I ever wanted to do with this rifle was shoot subs. Saving up for my suppressor. If the suppressor adds a new problem of being overgassed due to back pressure I will add an adjustable gas block and tune it down. If I don't have to that would be just fine.