Pros and Cons of UBR Gen 2+A5 buffer weight in SR-15 Mod 2

[BallisticHarmony]

I've read threads on here about combining an SR-15 with an A5 buffer, as well as other threads asking about putting a UBR on a 5.56 carbine, but never these two features in combination. This is probably because the original UBR, of which almost all UBR discussions are referencing, was not A5 compatible. While solely adding one of these features to an SR-15 could be argued as an unnecessary improvement, I believe there's a case for adding both features in tandem. I'll try to explain my reasoning for wanting these upgrades to what many consider to already be a more than exceptional rifle, which is the 14.5" Mod 2.

Before automatically discounting the UBR Gen 2, remember that it is 20% lighter than its predecessor. When using front-end attachments such as a powerful white light, IR device and possibly a can, rearward weight may actually not be as detrimental as many think for a general purpose carbine. I think of it like a weighted scale, where the UBR in the back allows the gun to be rotated on its axis so the muzzle can be raised with less strength. The uninterrupted cheekpiece of the UBR also allows it to be used in a variety of shooting positions without compromising cheek weld, and to my knowledge it's the only collapsible stock available that can be safely used as a door-breacher. Additionally, the UBR Gen 2 is the A5 length.

It's widely known that SR-15 gas systems are finely tuned to the rifle's supplied buffer weight, resulting in superior recoil mitigation and reliability compared to a more standard pairing. This is why many folks advise against running alternative buffer lengths or weights because why try to fix something that isn't broken? On the other hand, many other people have reported mild handling improvements from their SR-15 when using an A5 buffer, and depending on the weight used reliability doesn't seem to suffer either. In the case of the UBR Gen 2, which accommodates the A5 length, it almost seems like a waste (to me) to not utilize this feature and instead use the standard buffer and spring with the "buffer spacer" provided with the UBR. The KAC intermediate Mod 2 gas system combined with this added recoil mitigation could just about make it worth the trouble.

So here are the pros and cons to running the UBR Gen 2 and the A5 buffer in an SR-15 as far as I can see them.

Pros
1. Potential reduction in recoil allowing for faster followup shots and more accurate impact ID
2. More consistent cheek weld
3. More robust collapsible stock
4. Potential counterweight to front-heavy attachments

Cons
1. Increased weight in the rear
2. Potential reliability reduction in adverse conditions
3. Negligible improvements to an already finely tuned system

What are your thoughts on all this? Do you consider it a pointless thought exercise or something worth exploring? I'm hoping that one of our many SMEs could weigh in and let me know if my ramblings are onto something or not worth the forum's time. Thanks a lot for reading!

[crosseyedshooter]

In case there's super secret sauce in the KAC buffers, you might want to open one up and confirm. Otherwise, just match the same weight with an equivalent A5 buffer and off you go!

[Clint]

Stock selection is a user choice and does not affect function.

The buffer system may and has been covered extensively.

https://www.m4carbine.net/showthread.php?203447-KAC-SR-15-Mod-2-w-VLTOR-A5-Buffer

[Falshooter]

In simple terms, with the vltor A5 system allows you to maintain the benefits of the rifle length buffer system while having the ability of having adjustable LOP. I currently runs 2 A5 setups in an 18 in SPR and a 10.3 short barrel set up. The system works great, only con I can think of is cost. Also the buffers are proprietary. Certain stocks while fully collapsed dont cover the buffer completely. If I could afford it all my ars would use the A5 system.

[Hammer_Man]

Put your original KAC buffer on a scale, and match up the equivalent weighted A5 buffer in your brand new UBR stock, then shoot your gun a lot and report your findings to the group. Thanks in advance.

[Renegade0100]

Maybe it's just me, but KAC's rifle already have enough proprietary Stoner magic going on that makes them what they are. I don't really see the point in putting an A5 system on one; that's just screwing with an ecosystem that's already vetted and proven to be ultra-reliable. Especially when the rifles are as expensive as they are too.

[BallisticHarmony]

Maybe it's just me, but KAC's rifle already have enough proprietary Stoner magic going on that makes them what they are. I don't really see the point in putting an A5 system on one; that's just screwing with an ecosystem that's already vetted and proven to be ultra-reliable. Especially when the rifles are as expensive as they are too.

Well put. Maybe I'll just add the UBR and leave the rest as is. Setup is 1-8 ATACR, Scalarworks mount, M600DF, MAWL

[Renegade0100]

Well put. Maybe I'll just add the UBR and leave the rest as is. Setup is 1-8 ATACR, Scalarworks mount, M600DF, MAWL
I think that'd be a good move. What you listed is a solid setup.

[Alpine2k3]

I did try my SR-15 MOD1 16" upper on a lower equipped with a A5 system for funsies one time. It had a weird muzzle dip to it when firing it.

[masakari]

https://i.ibb.co/LkTy27H/20181007-102600.jpg (https://ibb.co/gj08BKh)
https://i.ibb.co/YTgJVDK/20190205-171143.jpg (https://ibb.co/93PBdwf)

I own both the original UBR as well as the second generation. The original was definitely built better, but yes it is heavier. My recommendation to you would be to buy the newer one and try it with the A5 spring and buffer. If there's no improvement or if you have problems, you can just go back to the original buffer set up with the spacer. You'll still have a far superior stock and better handling characteristics.

[jerrysimons]

If I had a SR15 I’d put an A5H0 buffer in it with either a springco green or VLTOR mil-spec rifle spring. Your mid-length gas 14.5” KAC is not as proprietary as their intermediate gas 16” barrels (I am dying for somebody to tell me
gasport sizes on KAC barrels). I think the supplied buffer with the KAC is a 3.0oz carbine buffer. A5H0 is 3.8oz. I would go A5 at least for the rifle spring rate and VLTOR’s patented spring pre-loaded weight stack inside the A5 buffer. These are improvements over the KAC configuration. If in the unlikely event you have issues with the slightly extra .8oz of buffer weight you could swap one of the middle steel weights in the A5H0 buffer for a deriln weight spacer to get the weight down to match a carbine buffer. VLTOR is even soon rolling out a user configurable A5 buffer where you can mix and match weights and buffer body material.

I like the gen 2 UBR, it does indeed counter balance the rifle when you start hanging stuff off the front. I wouldn’t have got one either if I couldn’t use a A5 buffer system in it. Personally my favorite stock is a Magpul MOE-SL, which also pairs nicely with A5 length buffer tubes but it is not much of a counter balance if that is what you are going for.

Edit: my bad 14.5” SR15s come with HH (H2) carbine buffers: 4.7oz. The A5H1 at 4.56oz is the closest match, standard A5 buffer is H2 at 5.33oz.

[jerrysimons]

I did try my SR-15 MOD1 16" upper on a lower equipped with a A5 system for funsies one time. It had a weird muzzle dip to it when firing it.

Here is the down side to running heavy buffered systems, especially with the A5H3 and A5H4. The extra mass is good at delaying unlock and plowing through dirty gunk but you feel it too when it hits home into battery and the muzzle dips.

[1911-A1]

A few weeks ago I got some new tungsten buffer weights, and decided to mix and match the A5 weights in my SR15. I think the weight combos went from 4.5ish to 7.6oz or something close. All weights worked fine in my SR15, and there was almost zero difference between the weights when it came to cycling, performance and felt recoil. I was expecting SOME difference, but I could barely tell them apart. I could feel SOMETHING felt different, but it wasn't better or worse, just a slightly different impulse.

[Tigereye]

If I had a SR15 I’d put an A5H0 buffer in it with either a springco green or VLTOR mil-spec rifle spring. Your mid-length gas 14.5” KAC is not as proprietary as their intermediate gas 16” barrels (I am dying for somebody to tell me
gasport sizes on KAC barrels). I think the supplied buffer with the KAC is a 3.0oz carbine buffer. A5H0 is 3.8oz. I would go A5 at least for the rifle spring rate and VLTOR’s patented spring pre-loaded weight stack inside the A5 buffer. These are improvements over the KAC configuration. If in the unlikely event you have issues with the slightly extra .8oz of buffer weight you could swap one of the middle steel weights in the A5H0 buffer for a deriln weight spacer to get the weight down to match a carbine buffer. VLTOR is even soon rolling out a user configurable A5 buffer where you can mix and match weights and buffer body material.

I like the gen 2 UBR, it does indeed counter balance the rifle when you start hanging stuff off the front. I wouldn’t have got one either if I couldn’t use a A5 buffer system in it. Personally my favorite stock is a Magpul MOE-SL, which also pairs nicely with A5 length buffer tubes but it is not much of a counter balance if that is what you are going for.

Edit: my bad 14.5” SR15s come with HH (H2) carbine buffers: 4.7oz. The A5H1 at 4.56oz is the closest match, standard A5 buffer is H2 at 5.33oz.

I recently picked up a new SR15 14.5". It came with the carbine buffer.

[jerrysimons]

I recently picked up a new SR15 14.5". It came with the carbine buffer.


Thank you, I thought so but apparently misread read one of Jack’s post in the linked thread to indicate HH. So only the 11.5” comes with the HH?

[kerplode]

I dunno, man...If I paid $3k for an SR15, I'd expect to not have to screw around with buffers and all that noise.

lol @ HH :-) Reminds me of Mitch Hedberg:


I was gonna get a candy bar; the button I was supposed to push was "HH", so I went to the side, I found the "H" button, I pushed it twice. ****in'...potato chips came out, man, because they had an "HH" button for Christ's sake! You need to let me know. I'm not familiar with the concept of "HH". I did not learn my AA-BB-CC's. God-god dammit-dammit.

[jerrysimons]

I dunno, man...If I paid $3k for an SR15, I'd expect to not have to screw around with buffers and all that noise.

lol @ HH :-) Reminds me of Mitch Hedberg:

I dont think you “have to” but I am convinced VLTOR has a superior buffer configuration to the standard carbine set up.

[1168]

I dont think you “have to” but I am convinced VLTOR has a superior buffer configuration to the standard carbine set up.

Something I’ve wondered about: If the A5 is superior to other systems, why doesn’t Knight’s, LMT, Colt, other top tier mfgr’s use them?

[jerrysimons]

Something I’ve wondered about: If the A5 is superior to other systems, why doesn’t Knight’s, LMT, Colt, other top tier mfgr’s use them?

Licensing. Brand identity. Profit margin. And probably thinking it is only marginally better than their set up anyway.

[Tigereye]

Thank you, I thought so but apparently misread read one of Jack’s post in the linked thread to indicate HH. So only the 11.5” comes with the HH?

I have a 16 and 14.5 and both have the carbine buffer. However, I will add a Surefire suppressor in the future along with the HH buffer. I will also tell you that both rifles shoot very smooth with the carbine buffer. I have the A5 system in my other rifles and like the system.

[Pappabear]

I had issues with my SR-15 not locking back when running suppressed, so I added the A5 and my issues where resolved. A5 is never a bad thing but I admit-tingly drink A5 cooled.

Drink up!

PB