I know, enough with all the URX posts...But I wanted to see if anyone had a line on URX 4 Shim Kits (P/N:30831), I be needing one for my 6.5cm build!

On a side note if anyone has an extra SR-25 URX 4 Rail Shim laying around from their install and a pair of calipers I would love the ID/OD dimensions, wondering if I can't source a replacement elsewhere!

Maybe the Aero Precision shim kit would work.
I don't know for sure though.

Fucking brilliant, I didn't even realize their enhanced barrel nut used shims! I bought a set to test out that should be here this weekend so I will post up the ID/OD and let you know if they work!

Also still looking for the ID/OD on the SR-25 KAC rail shims, would be nice to have something to compare the Aero shims too!

Edit: from first look at the AP barrel nut install the shims should be the correct size to work with the URX4, but i wont have the special black shim that KAC says is needed in the install instructions. I could use the thickness of that black shim and the material/coating if possible, I emailed KAC so we will see if they can help with that.

Cool, please post your results here when you get them.
I was thinking of getting a set to see if they would work, just didn't pull the trigger on them yet.
I really like Knights stuff, but damn, it's always out of stock haha.

The sr15 kit black shim is .025 I'd assume they would be the same.

thank you sir!

just more of an FYI post that we probably already or or assumed but when i emailed KAC about shim kits i got this generic response:

"component parts like shims are all curranty being allocated for in house rifle and upper builds to fulfill our currant back log on those items"

i am trying to see if they will share any more info on the shims, b/c i am sure we can get the correct ones from mcmaster carr!

I sourced out some SR15 extractor springs from a company but they want $3.46 each to produce 100 of them.
Not gonna pull the trigger on that one yet either.
I did manage to score a couple field repair kits from operation parts a little bit ago!
Super excited about that.

Also found this old discussion looking for the same info… KAC didn’t have them and he used the sr15 version and got by.

https://www.ar15.com/forums/ar-15/KAC-URX4-SR25-7-62-shim-install-instructions-NEEDED/121-744370/

Here is the sr15 urx4 timing instructions: https://www.knightarmco.com/wp-content/uploads/2021/06/INST-00105-05-2021-WEB.pdf

“score a couple”

A nice fuck you then if you abused the 1 per household rule he has posted.

___

He couldn't find the SR-25 URX4 rail installation instructions so he used the SR-15 instructions, but he already had a SR-25 shim kit.

I'm like 99% sure the shim kits won't interchange! AR-15 barrel extension/base OD is .985" and AR10/DPMS barrel extension/base OD is 1.205"...but as I don't have both in hand to physically compare I could be wrong!

The .308 BAR Shim Pack from Aero Precision (APRH308950) was delivered today and includes 5 shims but not their thicknesses.... so I chatted with customer service and they indicated that 1 is .005" and 4 are .001".

Whats that old saying, Trust but verify, just by feeling the shims through the baggy I could tell that 1 shim was not .001" or .005" so i pulled my calipers out, here are the thicknesses i received:

1 x .010"
1 x .005"
3 x .001"

Rough ID/OD:1.2550"/1.375"

Not bad, but still no .025" shim to mimic the black "base shim" that KAC says is required with the URX 4 install. Enter Reddit, I must have been too focused on searching for info on the SR-25 shim kits that i overlooked one talking about the SR-15 kit and how 2 redditors successfully used the Spikes Barrel nut shim kit on the SR-15 URX 4 handguard installs! Spikes also makes a .308 Shim Kit (SKU: SARX100) https://www.spikestactical.com/collections/upper-parts/spikes-308-shim-kit/. Their kit includes 8 shims with the below thicknesses:

3 x .001"
3 x .003"
1 x .012"
1 x .025"

Since they include that thicker .025" shim i picked up a set and will hopefully use it to install my handguard when they arrive!

Good info man!

@DHwreckage
Did this work?

just wanted to confirm what you have posted above.  i've used the spikes shims on both 15&25 urx4 installs with no issues.  i prefer the KAC shim kits but the spikes can work if you can't find the KAC shims in stock.

-t

Yup this worked, had D. Wilson do the work/install though since I couldn't find a URX wrench for less then what he charged...or at all.