Buffer weight for SBRs?

Sharing a recent experience/email with Geissele CS.

Recently acquired a URGI 10.3 which came with the Super 42 and H3 buffer. Pretty much immediately replaced one of the tungsten weights with steel to make the buffer an "H2". Installed with a LAW adapter, I was finding operation to be sluggish with .223 ammo and that the bolt wouldn't lock back even with some 5.56 options, primarily 55gr. I did experience a couple short stroking malfunctions especially in cold weather.

I've been exchanging a few emails with Geissele CS, but the TL;DR is that the LAW adapter adds 2 oz to the BCG and changes the recoil dynamics. Currently running with the Super42 and a "Carbine" buffer (removed all three tungsten weights and replaced with steel), and now cycles all ammo I've tried so far. Curious if others have had similar experience.

From Geissele CS:
Thank you for the update. The law tactical folder does have a space that adds a few ounces so It would not be a true H1/H2/H3 and additional tuning would be required. Would you be able to tell me if it is now running in the H1 configuration?

My latest response:
Thanks for following back up. I did exchange one of the tungsten weights with steel to make the buffer a "H1" with the super 42 spring. I found that function was improved, but that the bolt would still not lock back consistently on the last round, depending on ammo. Federal M855 worked without issue, but cycling was sluggish and locking back was inconsistent with 55gr Wolf Gold .223, 55g Federal AE .223, IMI M193, CBC M193, Speer Gold Dot 62gr and Gold Dot 75gr. What surprised me most was that Federal Mk318 62gr OTM would not consistently lock back. I am running unsuppressed and brass ejection is somewhere between 4:30 and 5:00.

According to LAW Tactical's website, the buffer extension weighs 2 oz. Exercising some google-fu:
Carbine buffer weighs approx. 3.0 oz
H1 buffer weighs approx. 3.8 oz
H2 buffer weighs approx. 4.6 oz
H3 buffer weighs approx. 5.4 oz
H4 buffer weighs approx. 6.8 oz

So with the LAW adapter the overall weight of the cycling system (less BCG) is:

Car + LAW = 5 oz (between H2/H3)
H1 + LAW = 5.8 oz (>H3)
H2 + LAW = 6.6 oz (~H4)
H3 + LAW = 7.4 oz (>H4)

Since the Super 42 is an extra power spring, I'm guessing that an H1 buffer plus extension at 5.8oz, heavier than an H3 - is causing the issue. Next step is to try to replace the last tungsten weight in the buffer with steel to make it equivalent to a standard carbine buffer, which would put the total weight of the buffer and LAW extension between a typical H2 and H3 weight, which would be within the recommendations for a 10.3" with carbine-length gas system. Unfortunately I don't have a suppressor to test, but I wonder if the 5oz combined weight would be a pretty sweet spot between suppressed/unsuppressed.

If you like I'd be happy to report back after the buffer swap and range trip.
Hi I recently had the same issue with my MK18 . Before shooting it for the first time I installed a Geissele h3 super 42 and SDE trigger. First clip ran flawless I don’t recall the brand but was 223 bolt locked back as should . Next clipped was 5.56 M855 it would not cycle the next round. casing ejected but no bullet In chamber just click . I then installed the factory Daniel defense h buffer and the thing ran like a champ. Dumped like 200 rounds without an malfunctions. As you stated the law adapter adds extra buffer weight preventing it from functioning properly with heavy buffers. Atleast Geissele ones…
 

Farmboy20

Regular Member
This is a little off topic but what does the group here do for ar10s (.308) far as buffer springs combos. I bought pws mk216 earlier this year and I’ve been trying to get it smoother recoiling. I understand it’s going to have more, however suppressed and on setting 3 for the gas, the bcg is still coming back fast and hard. I have changed the buffer out from the factory to pws suppressed buffer. While that did help some i hope to still smooth it out some more. Any advice be very much appreciated.
 

Greg "Sully" Sullivan

Established
Vendor
VIP
What we see when teaching Armorer courses is that the AR308 type rifles are all over the board, and nothing is standardized between manufacturers or builds, unlike the AR15 which tends to be more standardized. So we see a lot of AR308 type rifles that are cycling too fast.

I have seen a LE Agency that had a large amount of AR308 type rifles in their agency, and they were experiencing slam fires upon loading and while shooting. After they agency starting experiencing issues on the first few rifles, they sent them back to the manufacturer, who stated that it was an ammunition issue, and suggested they use different ammunition. So the agency changed ammunition manufactures several times, and still experiences the same issues, to the point that the rifle manufacturer came out to the agency to see what the issue was, and didn't get the problem fixed as the agency still experienced more problems. These rifles showed up in a class, and upon inspection I found that they had a very long and heavy action spring (buffer spring) installed with a standard weight buffer. It is my determination that the heavier spring was slowing the action during the unlocking/extracting/ejecting/cocking cycles, but the heavier spring was pushing the action forward with more force which in turn was causing the slam fires. Upon my suggestion to go to a standard type action spring (buffer spring), and a custom heavier buffer, the rifles started working correctly. In this case and similar ones, my suggestion is to run a custom heavier buffer like a 10-oz from HeavyBuffers.com

Another great option that we have found is the gas control system from https://www.riflespeed.com/, which we like as it is adjustable with a quick turn by hand to one of the 12 different settings, and is well built for durability. We have found that this system is great on the .308 type rifles, as it allows the shooter to fine tune to the load being shot, and all the variables like altitude issues and hot/cold weather issues.


CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123
 
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