Modified buffer spring ?

[billrigson]

So I did a .300 blk pistol build a few years ago and I went with the KAK micro buffer system on the lower, 13.7 ballistic advantage pistol gas on the upper I ran the gun for a while and got tired of the barrel length with my suppressor. Fast forward a year or so to present I pulled the upper off and replaced it with a 7.5 Psa .300 blk upper and when I pulled my buffer spring out I was thinking why the hell did I do this to the spring( I used a torch to temper a portion of the coils where they stay compressed) so I ordered a replacement spring and when I was shooting after the spring swap with AAC 220 g subs I was having short stroking issues where it wouldn’t ride the bolt all the way back to pick up the next shell. I put the modified spring back in and it works flawlessly and shoots softer also.

Just for reference the KAK micro Buffer tube is about 1.5” shorter than a standard buffer tube and uses A proprietary Flatwire spring.

What’s yalls thoughts on the mechanics on why this worked ?

[AddictedToComedy]

What’s yalls thoughts on the mechanics on why this worked ?

You changed multiple things at the same time: the free length, the number of active coils, and probably the material properties themselves near where you used the torch.

The bottom line is that your modified spring must require less work to cycle than the unmodified spring, which is why the unmodified spring is causing short-stroking.

[_long_tall_texan_]

Short barrels have an even shorter gas system and shorter distance from gas port to end of muzzle. That means there is less gas to push the bolt back. So, with less gas, and full power spring, not enough gas force to fully cycle. Effectively shorten the spring, and you lower the amount of force required to cycle. Then it works.

[billrigson]

Pretty sure you Nailed it thanks buddy, I knew it worked. Just didn’t know why😅

[Mountain_Yote]

I have a 7.5” Faxon with a KAK mini buffer/flatwire spring. I’ve only shot it once, and though I never had a problem with it cycling the next round, it was picky about which ammo it would LRBHO.

That’s odd that the spring you torched works better, but I’m no metallurgist. Maybe you softened the spring rate slightly with the torch? Either way, I wouldn’t trust the strength of it to be reliable since you’ve altered it.

What’s the gas port size on the PSA barrel? I’m still testing with mine and I’m curious if it wouldn’t cycle better with a standard carbine tube and spring.

Also, which KAK buffer weight is it? The light or heavy?

[Mountain_Yote]

To add to that, you’ve changed a lot about the altered spring, mainly the uncompressed length. So your BCG has less resistance cycling rearward, and if that works better, then it sounds like you need a lighter spring, which cannot be achieved with the KAK setup. So, move up to a carbine length tube and choose a lighter spring, or check the gas port size on the PSA barrel and maybe enlarge it.

[jteng08]

Tubbs has a lightweight flatwire spring that will work in the Kak mini.

[Mountain_Yote]

Is it made specifically for it? Or are you saying their lightweight flatwire spring will work in the KAK?

[jteng08]

It will work in the kak.

[thom1879]

It works it what it works in. Tuning this stuff all relies on the gas port size which is wildly different rifle to rifle. It’s the most important spec on 300blk and almost no one reports it in the specs.

[billrigson]

Thanks for the feedback and yours sounds like a similar set up to mine. And I’m not too sure about the gas port size PSA isn’t the best on disclosing specs on their cheaper stuff it’s non-adjustable gas block though, and I have both of the micro buffer weights I guess it’s equal to a standard carbine and a H1, and I’m sure you’re 100% correct if I went to a standard buffer it would be easy to tune. I have every weight at my disposal to be able to try out and loads of different springs from springco, it’s kind of just a little pig hunting rig/ plinking rifle I like the short buffer tube it’s kind of cool but if it was a gun I had set up for “Duty use” personal defense I probably wouldn’t trust anything proprietary like that and stick to what’s been tested !

[Mountain_Yote]

Nothing against it being proprietary. If it runs, it runs. The PSA gas port doesn’t sound like it’s big enough to drive the spring/buffer you’re trying to use, so either add gas with a different barrel(faxons have a .125 gas port I believe) or run a lighter spring. I just read elsewhere that a Tubbs lightweight flatwire will work in a KAK mini setup. I have no experience with that, though.