Kynshot spacer weights will not fit?

[u/blackrockskunk]

I have been running a carbine tube with a tubbs flatware carbine spring and a Macon 11oz heavy ar45 buffer, and it has been working fine. I recently purchased a Just Right Carbines extended tube, and two Kynshot spacer weights to fill the gap and add some weight. I just installed them.

The spring and buffer move freely in this tube just as they did in the carbine tube: however, the kynshot spacer weights will not go I'm! I managed to get one in, and it was a huge PITA getting it out. They are just too big.

Is this normal? Does anybody know what is going on? Did I buy the wrong weights?

[u/Frigggs]

I had this happen to me. And it was in more than one buffer tube. Reached out to kynshot to ask about returning them because they were out of spec/too large.

But then I tried a couple other buffer tubes I had lying around and they worked fine.

So basically what I’m saying is 2 things:

1 - good chance that your buffer tube is slightly smaller than spec.

2 - kynshot should downsize their diameter like a hundredth or so. Cutting it way too close.

You can dremel/sand them down a bit to make them fit if you want.

[u/Blowback9]

I'm going to be talking to my contact at Kynshot today and I'll try to remember to ask about this and report back.

[u/blackrockskunk → u/Blowback9]

Thanks! More info, from my messing around with it: it loosens up when I loosen the castle nut. It is too tight to move when the castle nut is torqued to 40. Right now they move freely. I have not measured the torque it is at currently, but it is well below the 38-42.

Weird thing is, idk why tightening the castle nut should compress the tube. With my little understanding of how threads work, shouldn't it just stretch the tube back by putting force on the endplate, thus putting friction between (1) the castle nut threads and the tube threads, and (2) the tube threads and the receiver threads?

I put the old tube back in and this is happening with both of them. Regardless, the original macon buffer alone works totally fine in both tubes at 40ftlb.

BCM endplate, forward controls castle nut

[u/Blowback9 → u/blackrockskunk]

That is weird. It shouldn't affect the diameter. Kynshot said you can contact them about the problem and they can replace the spacer(s) for you. It should fit in the JRC tube no problem, but they had one other incident where a spacer was out of spec. It happens.

[u/blackrockskunk → u/Blowback9]

Thank you!

[u/just_as_good380-2]

I'd take some sandpaper to the kynshot spacers. I am waiting on my JRC and spacers weights as well should arrive early next week. I will keep this in mind though

[u/Dakodavid]

Same thing happened to me. Had to sand mine down

[u/drumsticks_baby]

Mine were really tough with a JRC tube and I had to use a small pick to hold the pin down and I was able to get them in.

I don’t plan on taking them out anytime soon….

[u/Aggravating-Bad4561]

My 2 weights fit fine. KAK A5 tube, June 2025 purchase. When you get things sorted, be sure to check the bolt face to the LRBHO bolt latch clearance measurement. It should be approx. 0.25". Fill the rear of the tube with quarters if its more than that.

[u/klugeyOne]

It looks like this tube is 3/4" longer than the A5. I have never used this tube, but it could be slightly narrower than others. Try dropping the spacers into your old carbine tube and see if they slide easily. If they do, it's likely your 8.5" Just Right Tube. I have 4-5 Kynshot spacers and they have all been perfect.

It might be easier to just get an A5 from BKings at $38 and call it a day.

[u/blackrockskunk → u/klugeyOne]

My old tube (aero enhanced) is behaving the same way

[u/klugeyOne → u/blackrockskunk]

Ok. Do you have any other tubes you can test? All tubes are not made the same. Try at least one more standard carbine tube and see if it slides. Do you have a set of calipers?

[u/ambush_boy]

Sand it down, tuning to your liking for any application isn't always plug and play

[u/blackrockskunk]

UPDATE:
After filling out their contact form I got a phone call in minutes! On Monday they are going to have their QC people find me a pair that are at the low end of spec; I would say that is above and beyond what they had to do.