I'm having some minor issues with a JP SCS behind a M6A2 upper.  

The upper runs flawlessly with the H2 buffer that came with it.

initially with the JP SCS, I had left the buffer retainer pin in place. the bolt would fail to lock back after last round.  Swap to a DI upper and had same issues with the addition of frequent light strikes, I think due to battery lock up failure.


So I take out the buffer pin and spring.  Left the buffer tube one turn out from the depth it will hold the buffer pin,   this makes no change in the performance of the LW upper, but resolved the issued with the gas upper.  


I see that JP now offers an H2 SCS, they list for use with piston uppers.  Any idea the difference?  I'm assuming it is the buffer weights.


My question is can I just change the weights and/or spring in the SCS that I already own to resolve these issues with the LW upper.

Any insight would be appreciated.    I do not have any gas adjustments available on this upper, so that's not an option.    

Have tried multiple magazines that work great in other AR's.  

These lowers are set up with a Strike Industry's carbine tube.  These are my two 3gun AR's so I need solid reliability through rapid fire, barrel dumps, etc...

Thanks,

Definitely sounds like a mismatched buffer/spring setup.  I've had a complete factory LWRC upper in M6A2 and M6A2-S (mid-length gas).  Both came with a supplied buffer from LWRC.  My buffers were standard carbine weight buffers and not H2...which made me wonder why they even bothered to package them together.  Both uppers ran flawlessly with no issues and perfect 3-4 o'clock brass ejection pattern.  Still, if your upper ran perfectly with an H2 buffer, you need to run an H2 buffer.  

Sounds like the JP buffer you have is an H or H1.  If your upper likes an H2 buffer and you try to run a lighter buffer, you can usually get one of two issues.  More likely I think you'd get more aggressive cycling, but you would get full cycling.  In your case you describe that you're not getting full cycling...no bolt lock back.  I can't comment about the performance of the gas upper you tried, as that throws a whole other list of variables into the mix...barrel length, gas length, etc.  The other thing your "too light" buffer could cause, but not as likely from your description, might be "too early" an attempt to extract the fired case.  However, this should be somewhat evident by the condition of your fired brass.

If your rifle likes an H2 buffer, then you run an H2 buffer...period.  I'm assuming that your M6A2 upper is still totally OEM.  You don't mention how many rounds have been fired through this upper.  Sometimes a new rifle needs a good many rounds fired through it to "smooth-up" the BCG and barrel extension interface.  With a factory LWRC this usually isn't the case, as the NiB BCG and manufacturing tolerances are pretty much spot on out of the box.  My LWRC was my first exposure to full NiB BCG, and I was quite impressed with how smooth the BCG cycled in a brand new gun.  I kind of doubt you're experiencing a break-in issue with that upper.

Edit:  Due to another currently running post about LWRC piston rifle buffers, I just discovered my M6A2 buffer that came with the factory upper is unmarked but appears to be H2...kind of odd.  I just inspected my M6A2-S buffer, and it is marked H2.  Both buffers weigh just over 4.5oz, so they're both clearly H2 buffers.  Not sure why the M6A2 buffer wasn't marked since both uppers were brand new factory uppers and had a buffer shipped with them.  The unmarked buffer has been etched "H2" to avoid confusion in the future.  I'm glad these posts caused me to check and realize the issue.  I'm sure this is not common practice for a mis-labeled buffer to make it out to the public, but in the future it will cause me to throw any buffer on the weight scale regardless of markings just to be sure.

Thanks for the feedback.  

This LW is all stock with probably 500 rounds through it;  and yes, it runs great with the H2 buffer that came with it.  

I know the enemy of 'good enough' is better.    but honestly this is used for a local matches and my life doesn't depend on the reliability of this weapon.  


I spoke with JP and the basic difference between this SCS and their H2 SCS is all three weights are Tungsten on the H2.  The springs are the same between the two.

Just sharing the info, while I wait on parts to arrive...