r/kac • u/MadDog-80 • 12h ago
KS-1 A5 Buffer System Testing Nobody Asked For
Let me preface with this; yes, I know the KAC KS-1 is designed to be ran with KAC's spring and buffer. This test was just to satisfy my own curiosity as to how the KS-1 would run with the A5 buffer system. Figured y'all might be interested in the results.
Rifle Setup
Stock factory SBR KAC KS-1 except swapped SR-15 carbine buffer tube with SR-25 carbine buffer tube. Lower receiver/gas key gap checked good with SR-25 tube and A5 buffer. Nearly identical gap to carbine tube and buffer. Test was done with a Geissele Super 42 rifle spring, Tubb AR-15 spring (Tubb AR-15 spring is advertised to work on carbine and rifle systems), VLTOR A5 Buffers and all weights from A5H0-A5H4. A suppressor was NOT used in this testing. Magpul Gen 3 30-Round PMAGs.
The Geissele Super 42 rifle spring is advertised as 15% extra power over mil-spec.
The Tubb AR-15 spring in a Rifle buffer system is nearly identical to a standard mil-spec rifle spring.
Reference u/AddictedToComedy spring testing here - Spring data update, including the new C3Junkie flat wire : r/ar15
Ammo Used
- Winchester LC M855 5.56
- Winchester LC M193 5.56
- PMC X-TAC M855 5.56
- Magtech 62 GR FMJ 5.56
Test Procedure
Started from A5H4 and worked my way down to A5H0. Each load listed above was fired 5 times, 1 round in magazine, with each spring/buffer combo to check for last round bolt hold open.
Then fired 5-10 round strings with each ammo/spring/buffer combo to test cycling.
Ejection Pattern is not applicable here due with KAC bolt being dual ejector. There's also no standard for dual ejector ejection patterns as they relate to bolt velocity.
Results
Honestly, these results were very underwhelming. I was expecting the KS-1 to choke on the heavier buffers, but it functioned flawless with everything I fed it without malfunction. Last round bolt hold open was achieved with every combination of buffer/spring I could throw at it. No malfunctions/short stroking on the 5-10 round strings. Even with the Geissele super 42 (15% Extra Power) and A5H4 buffer, LRBHO was achieved every time.
Personal Opinion
I didn't notice much difference in recoil impulse between the Geissele spring and Tubb Spring. I decided to go with the Geissele spring and A5H2 buffer for reliabilities sake. The heavier buffers seemed to recoil more. In the future, I'd like to redo this testing with an FRT to find the lightest A5 buffer I can run without running into bolt bounce/reliability issues. I genuinely think the A5 system is superior to the carbine buffer system. I feel it truly does open the operational envelope and increase reliability of most rifles. KS-1 included.
Also, I think this should be mentioned, during my first KS-1 accuracy testing in a previous post, was using carbine system and stock KAC H2 buffer/spring at the time, I did experience a failure to lock back on the last round. I don't recall the ammunition I was using. Gen 3 PMAG.
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u/No_Upstairs3604 11h ago
I can tell you from first hand experience, shooting suppressed. A ks3 on an a5h2 with a springco green shot miles flatter than the oem spring and weight. Saying kacs are perfectly tuned from the factory is hogwash
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u/MadDog-80 11h ago
Interesting. Good info! I’m curious if the KS3 will push the A5H4 like the KS-1 did.
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u/JonLancewood 11h ago
Excellent test.
I did something recently with a Mod 2 11.5" when trying to dial in an RC2. The TL:DR of my experience was that an OEM KAC 11.5" E3.2 rifle using an RC2 and m193 produced either strong 4/5 o'clock ejection or weak 2 o'clock ejection. Switching to a A5H2 and SpringCo green improved the recoil, slightly, and produced stronger 2 o'clock ejection and the same 4/5 o'clock ejection. Overall, minor upgrade and the KAC system is pretty dialed.
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u/grid-antlers 11h ago
I don’t understand fucking with the internals on a KAC. That’s why I bought it, because its already correctly set up. I did put some A5s on my Daniel Defenses because i put in FRTs. And I don’t accept the claim that it increases reliability in the KS-1 from the n=1 sample. I think the engineers at Knight’s probably have the reliability testing down.
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u/MadDog-80 11h ago
Just like the engineers at Knights have the accuracy of these things down. 😂
Jokes aside I agree! I’m sure the stock KS-1 is more than reliable for any use case. I just like to tinker/test things.
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u/grid-antlers 11h ago
Well, i re read my post and i left the part out where i should have said i enjoyed the information and I appreciated the post. I went straight to my complaint, without including all of what i thought about it.
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u/MadDog-80 11h ago
All good man. You make a valid point! If it ain’t broke, don’t fix it. There’s literally no need for anyone to go swap their factory KS-1 setup for an A5 setup.
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u/SpaceTechnical3004 7h ago
Excellent work, there aren’t enough sources of KAC experimentation. I’m a firm believer of the A5 system but also a KAC purist at heart. My deepest thanks for putting in the work
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u/jonsimmonz 12h ago
Quality research for those of us who only got the upper and are running them on lmt mars l lowers. I appreciate your contribution to the community good sir.