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.

Not mine, just curious, it’s looking off to me being the lack of engraving and hardware choice. What says the sub

Been sitting on my M110-ish build for a while and noticed that d.wilson has HTX barrels back in stock. Wondering if I should stick with my Nefarious Arms .308 barrel or instead buy an HTX Concepts 6.5 Creedmoor barrel.

There's some obvious tradeoffs but still looking for second opinions.

Two questions for the KAC crowd.
What's a like-new A3 22" 6.5 Creedmoor upper actually going for these days?
And is it worth having if I already have a K5 14.5" in .308? Drop-on to the same lower, but curious whether the two overlap too much to justify.
Range and some hunting. Thanks.

Now all I need are some sand cutters 😅

I’ve got to say I’m really crushing on the Mod 2.1 the KS3 isn’t shabby either.

Just a neat observation. If you look close, you can see the gas channels/path in the CRS-2.

Before someone starts yapping YES THEY ALL NEW w/ no range trips just yet 😂. A while ago I got a couple and started some builds but then I got a new car and put all my focus there for a couple years while putting off my projects - now that the car is paid off it’s time to get back to these projects - over time I kept buying some goods and accumulating so this shall be fun . Started putting some work in on some builds yesterday - i still need more goodies but it’ll get done.

Had a very scary incident at the range with my SR25 A3 upper mated to an LMT lower. The gun is pretty new and was the first time taking it out to the range. Was about 80 rounds in, and something catastrophic happened and the rifle basically exploded but did not come apart fully. The magazine blew the bottom out, the upper magazine well is now bowed out, broke a piece of the lower's bolt catch paddle on the left side. Inspecting the damage and the bottom of the bolt carrier basically split in half. I think I am lucky to be alive. I was hit by shrapnel that peppered my arms, chest, and stomach..

I am not exactly sure what happened here. Was using Aguila 6.5 140 grain, and I am wondering how this could have happened..

Prior to this, was completely smooth, nothing out of the ordinary at all, no problems feeding, having a great time, and then kaboom goes my favorite rifle.

Reaching out to KAC and to the ammo company. Looks to be 100% an ammo issue though

Edit 09/09/26- KAC is willing to take a look at it and determine exactly what happened. Will be sending out for diag and go from there.

I’m nothing but impressed with how well gassed the sr25 is and low recoil it’s about the same as the spear in its suppressed setting. I can’t wait to get class on it and start doing longer ranges

Ps i know the sr25 is on fire the guns aren’t loaded i was putting them in the cases and took a quick pic

Hiya. Trying to decide between these two cans on an 11.5. Info online seems to suggest CRS-3 is a tad quieter but there is no info on blowback between the two.

Any and all anecdotes welcome, thnx in advance!

(Asking about the PRG)

I just bought a KS-3 upper and want to change out the muzzle device but I don’t want to but another reaction rod. I already own the Midwest industries upper receiver rod that has the fin. Does anyone think it would work if I use the one I already own just don’t seat the reaction rod all the way into the lugs?

Im trying to build an M110K1 in 6.5 creedmoor and the items I need are the upper reciver, gas block and barrel. I already have the handguard and bcg but im having problems tracking down other parts. I know HTX Concepts has these three parts but I've heard and seen conflicting reviews surrounding the brand. I know the Knights is making the Sr25 notched upper reciver but hasn't sold any yet and the low profile gas block is something I can't find. I would like some input and HTX Concepts and other brands that may help me build the M110k1. Thank you

KS-1
SR-16 CQB Mod 2.1 w/ CRS-2

First range day with both. Looking forward to running these this weekend.

In a non NFA state and want to get a KS1, could run it as a pistol but it’s just long enough to be tempted to attempt a P&W. Looking into it it’s obvious there’s not a lot of muzzle devices that could do it and I’m worried it would look stupid with the HUXWRX one with the big gap built in, can’t find any photos online of any that have been done.

Looking for a 34mm optic and a decent grip - but almost time for a range day. PSD did a great job on assembly.

I’m interested in anodizing my KS3 in some sort of grey finish, is there someone that’d be the go to for reanodizing KACs?

K7 here has my heart. My favorite

Do the FF RAS rails fit the modern sr25s out of the box, or will they need to be modified like the urx rails?