In 2017 CMMG released the CMMG Banshee. It was at that time I was testing various buffer setups to smooth it out and achieve the full auto cyclic rate I was after. The end result of the ‘ARS‘ is below.
- A5 length buffer tube (some buffer tube info here: https://c3junkie.com/?page_id=97)
- Tubb 300BLK or Tubb 556 spring (both are flat springs). I go into detail regarding the springs here: https://c3junkie.com/?page_id=977
- Kynshot RB5007 buffer (comparison of various buffers here: https://c3junkie.com/?page_id=325)
I haven’t updated the links above in some time. So some quick comments on all 3 components:
- Several companies make A5 length buffers not just Vltor, several 308 tubes are also the same like ones from Griffin are nice.
- Flat springs – Not all the same. Some like the Strike Industries are too tight for the RB5007. I like the Tubb 300BLK for getting the full auto cyclic rate down for 9mm/40SW CMMG RDB configurations. It is like 30RPM slower, however the spring is typically too weak for reliable operation for a 5.56 mag fed configuration. The Tubb 556 will work with both but is a little fast for my tastes when used with the CMMG RDB 9mm/40SW configurations. I have found that the Neverwear Warthog flat spring is a good compromise between the Tubb 300BLK and Tubb 556 where it seems to work fine with both my 9mm/40SW CMMG RDB configurations with just about the same cyclic rate as the 300BLK spring but still work with 5.56 mag fed uppers.
- I had been trying to get away from the RB5007 thinking it was a little on the heavy side and wanted less reciprocating mass but with all my testing, I kept going back to it. Read what I did here for more details: https://c3junkie.com/?page_id=1403. In particular, look at this high speed video below from Kynshot. Notice how they say, ‘Slight Initial Bolt Energy Absorbed’.
Now if you look at my live fire video which is in the link above and I have pasted below for convenience and watch the first 5 seconds you can see the buffer body move forward on that initial recoil impulse. The RB5007 is heavier than say an RB5005 but that heavier mass helps with that initial recoil impulse. Likewise, I have always said, I didn’t like the RB5000, original Enidine or the RB5015HD as all of those take like 10lbs to compress vs the RB5007 that take 5lbs to compress and this is all slowly compresses with my thumb. Obviously during live fire and being hydraulic is different. I think the RB5015HD or the RB5000 are probably better suited for applications where you have something that is overgassed or straight blowback, neither of which I mess with anymore.
‘Clicker58’ on AR15.com coined the term ‘ARS’ – Amphibian Recoil System here: https://www.ar15.com/forums/AR-15/Kynshot-RB5007-9mm-buffer-in-5-56-AR/118-790950/
I thought that was a good idea as a lot of people seem to get what I did confused with what Blowback9 is doing here: https://blowback9.wordpress.com/ He reached out to me years ago saying he didn’t see the benefit in using hydraulic buffers and later told me it was only when combined with the flat springs where he saw the benefit. Ultimately, he came to same conclusion I did for his ‘GRS’ – Gentle Recoil System which is very similar to what I’m doing but he has to add more mass since he is dealing with straight blowback which again I don’t run anymore.
It was Blowback9’s posts that informed me about the JRC buffer tube. I had searched for some time for tube longer than an A5 that would still accommodate a collapsible stock and I gave up. Using the JRC buffer tube allowed me to use the RB5007 for the benefits I described about in conjunction with a carrier that can do ‘extended stroke’ like the Surefire OBC pictured below.
All that said, I’ll add another permutation…. ‘ARS-EX’ = Amphibian Recoil System Extended – this lower configuration is just one piece to the puzzle to achieve a state where the carrier isn’t bottoming out. I detail this for gas operated 556 here: https://c3junkie.com/?page_id=1403 and I’m doing it with my 9mm CMMG RDB hybrid Dissent here: https://c3junkie.com/?page_id=1733
This ‘ARS-EX‘ consists of:
- JRC buffer tube
- RB5007
- Flat spring – typically Tubb or Neverwear Warthog as discussed above
- A carrier that allows extended stroke. Could be pistol caliber with my hybrid Dissent or gas operated.
- Spacer is most likely required so that either the carrier key doesn’t slam into the lower or so that the hammer doesn’t slip in front of the carrier as discussed in the last link I pasted above.
For people that don’t want to tinker, I think the ARS is where it’s at as you can just swap uppers and make no changes to your lower with no thinking about it or worrying about having an invalid configuration that could potentially damage your lower or other parts. However, it will most likely result in your carrier bottoming out. It isn’t the end of the world, especially with the RB5007 that is only 5lbs to compress and is a softer impact than say the RB5015HD which is stiffer. As a side note, yes, I know you can most likely add mass to your carrier so it doesn’t bottom out but again my goal is not add more reciprocating mass.
For people that do like to tinker, the ARS-EX is definitely noticeable especially when you compare the two side by side. The plus is you can always add a 3/4″ spacer int the JRC tube and have the same stroke length as the standard ARS…but of course you have to remember to do this.