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Big'r Brother
(patent pending)
The MSRx-258 Big'r Brother is a special purpose system, designed to enable forced reset safety devices and inhibit bolt bounce.
Rifle Spring
The MSRx-258 (when paired with an A5 style buffer) allows use with an AR-15 rifle spring, and a combination of this duet proved to have the least recoil of all of the systems tested.
The total length of this combination is 6-5/8".
For AR-9 blowback PCC's with AR-15 rifle receiver extensions.
If you already own an AR, you may have the buffer and spring.
Carbine Spring
When maximum mass is the goal, a 9mm extended PCC style buffer (when paired with the MSRx-258) may provide the most potential, 13 ounces or more.
The total length of this combination is 6-5/8".
The 411 about FRS/SS
The MSRx-258 (buffer and spring) has been tested and proven to function with the Atrius FRS and G.M.R. super safety devices when paired with A5 style companion buffers (weighing from 3.8 ounces to 7.2 ounces) and an AR-15 rifle spring, as well as the AR-9/PCC extended buffers (weighing from 6.4 to 8 ounces) and an AR-15 carbine spring. The cheaper solid steel buffers that we tested as companion buffers performed no differently than the buffers with sliding weights of similar mass.
When total buffer system mass in the rifle length tube approached 11 ounces in testing we began to see failures with the forced reset devices. The weaker ejection pattern indicated that there was just too much mass for the system to operate, therefore it is recommended that total buffer mass be kept to 10.8 ounces or less (MSRx-258 + companion buffer) combined.
The sweet spot in the rifle receiver extension appears to be right around 10 ounces total mass, but we have had 100% function with combinations as light as 6.6 total ounces, with the only significant differences being rate of fire and felt recoil. As a rule, the heavier the companion buffer, the slower the rate of fire and the softer the recoil impulse.
Sliding Buffer Weights
The MSRx-258 Big'r Brother buffer contains a pair of steel sliding buffer weights, which satisfies that requirement of the forced reset selectors and super safeties. Testing has shown that we can use a (cheaper) solid buffer rather than fork out the big bucks for tungsten.
The abbreviated carbine spring is approximately 1.5x the length of the tail, which allows the Big'r Bro to become one with the companion buffer when compressed in the buffer tube behind the bolt, while providing an added measure to inhibit bolt bounce.
When fully compressed, behind the bolt, both buffers act as one unless there is a bolt bounce occurance.
Rifle Receiver Extension
The rifle length receiver extension gives us the most room to operate in, so let's make the most of it.
The MSRx-258 buffer and spring can be paired with either an AR-9 extended PCC buffer and AR-15 carbine spring (center image) in a rifle length receiver extension, or any A5 style buffer and AR-15 rifle spring (bottom image), as desired to affect felt recoil and enable FRS.
As illustrated, the two buffers in tandem will operate as a single unit, until/unless there is a reversal of energy upon impact with the breech face, as in bolt bounce.
Bolt Stop Clearance
Both the L'il Helper and Big'r Brother system buffers are designed to provide ~3/16" of clearance behind the bolt stop when the bolt assembly cycles fully to the rear of the buffer tube. This may vary slightly depending on buffer tube and lower receiver.
One can fine tune the total package weight simply by changing the companion buffer.
A solid steel A5 style (H4) buffer (7.2 oz) paired with an MSRx-258, which allows the use of AR-15 rifle springs, is tested and proven with the Atrius FRS and the G.M.R. super safety.
The MSRx-258 Big'r Bro and spring will add 2.8 ounces to the total mass of your recoil system. Combine with the A5 style or PCC buffer of choice (with appropriate spring) to achieve the desired weight.
An AR-9 extended PCC buffer (7.5 oz) with the MSRx-258. This pair is tested and proven with the Atrius FRS as well as the G.M.R. super safety, with carbine spring in a rifle receiver extension.