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Posted: 1/18/2026 2:53:32 PM EDT
[Last Edit: StealthyBlagga][Edited]
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Is anyone successfully running a Maxim Roller Delayed Buffer in their blowback 9mm M16? I am trying to get one working with an FRT but am getting intermittent FTF which I attribute to bolt bounce. Unlike a traditional buffer system, the Maxim RDB does not have free floating weights to create a dead-blow effect. If anyone has had good luck with the Maxim RDB, please let me know what (if anything) you did to make it work. |
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Did you see this old thread?: https://www.ar15.com/forums/AR-15/-ARCHIVED-THREAD-Maxim-Defense-RDB-review/15-780933/?page=6 I made a custom bumper down to drop the cyclic rate some. Bear in mind that they don't support using it in FA or with an FRT / SS though. |
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My personal limited experience was the Maxim Roller Delay Buffer wasn't great. That said I don't specifically recall any bolt bounce issues being present either. My experience with the Maxim was that by the time you tuned the buffer to have enough delay to actually slow the cyclic rate down to something reasonable you had to be gorilla strong to pull the charging handle back. If you set it up where the charging handle was reasonable to pull back (still much harder than normal but at least doable) than the cyclic rate was through the roof. The other similar product (Scheel) where there are holes cut in the buffer tube worked better than the Maxim but suffered the same issue where if you set it up for meaningful amount of delay it became a bear to charge and if you set it up where it was easy enough to charge it didn't provide enough meaningful delay and the cyclic rate and recoil impulse was bad. Personally I found the best direct blowback (non-integrally ported suppressed barrel) option was just the Kynshot Hydraulic with and extra kynshot weight or two. Its does slow down the rate of fire and tame the recoil impulse but all that extra reciprocating mass makes the gun feel choppy on auto, kind of like an Uzi. If you go with a MP5SD style ported barrel with an SD suppressor and a standard Kynshot hydraulic its pretty nice. The ported barrel seems to implement it down delay on the action. The CMMG radial with the now fixed ejector (the old spring loaded ejector was garbage) and which uses a more standard carrier and buffer tube is the best AR9 platform I have shot so far. (although I have never shot a JP5 unit which I suspect is also really nice but challenged to run in auto due to the design and is super $$$) Out of curiosity does you gun run with say a regular H2 or H3 style buffer (usually in 9mm it will be a steel body buffer with sliding tungsten weights) If it doesn't run with a traditional reciprocating weight style buffer its probably firing pin bounce with the 9mm guns also suffer from and you will need to replace the firing pin spring with a new and/or stronger spring. |
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Originally Posted By jbntex: My personal limited experience was the Maxim Roller Delay Buffer wasn't great. That said I don't specifically recall any bolt bounce issues being present either. My experience with the Maxim was that by the time you tuned the buffer to have enough delay to actually slow the cyclic rate down to something reasonable you had to be gorilla strong to pull the charging handle back. If you set it up where the charging handle was reasonable to pull back (still much harder than normal but at least doable) than the cyclic rate was through the roof. Originally Posted By jbntex: My personal limited experience was the Maxim Roller Delay Buffer wasn't great. That said I don't specifically recall any bolt bounce issues being present either. My experience with the Maxim was that by the time you tuned the buffer to have enough delay to actually slow the cyclic rate down to something reasonable you had to be gorilla strong to pull the charging handle back. If you set it up where the charging handle was reasonable to pull back (still much harder than normal but at least doable) than the cyclic rate was through the roof. The other similar product (Scheel) where there are holes cut in the buffer tube worked better than the Maxim but suffered the same issue where if you set it up for meaningful amount of delay it became a bear to charge and if you set it up where it was easy enough to charge it didn't provide enough meaningful delay and the cyclic rate and recoil impulse was bad. Personally I found the best direct blowback (non-integrally ported suppressed barrel) option was just the Kynshot Hydraulic with and extra kynshot weight or two. Its does slow down the rate of fire and tame the recoil impulse but all that extra reciprocating mass makes the gun feel choppy on auto, kind of like an Uzi. If you go with a MP5SD style ported barrel with an SD suppressor and a standard Kynshot hydraulic its pretty nice. The ported barrel seems to implement it down delay on the action. The CMMG radial with the now fixed ejector (the old spring loaded ejector was garbage) and which uses a more standard carrier and buffer tube is the best AR9 platform I have shot so far. However I posted this recently and very impressed with the results: https://www.ar15.com/forums/AR-15/Interesting-results-with-magnetic-buffer/15-792274/   (although I have never shot a JP5 unit which I suspect is also really nice but challenged to run in auto due to the design and is super $$$) Out of curiosity does you gun run with say a regular H2 or H3 style buffer (usually in 9mm it will be a steel body buffer with sliding tungsten weights) If it doesn't run with a traditional reciprocating weight style buffer its probably firing pin bounce with the 9mm guns also suffer from and you will need to replace the firing pin spring with a new and/or stronger spring. Being delayed blowback, it also is just about impossible to have an OOBD since the bolt must rotate inside the extension for the proper FP protrusion. The one weak link is the the FP design is crap and breaks. I've been through so many already....but fortunately an easy fix: I need to put a tutorial up on my site but I've found some bushings off Amazon that are drop in so you don't need a lathe to make them.  |
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Yeah.... another problem with the CMMG Radial. Now that they have fixed the ejector the firing pin quality is bad as well. Have you tried a standard M16 firing pin with no spring? As you mentioned you really can't have a out of battery with the rotating bolt and I wouldn't think that a rotating bolt would have enough energy by the time it closed that the firing pin could inertia set off the primer. Worst case maybe just a standard 5.56 firing pin with a 9mm blowback carrier firing pin spring (as the CMMG spring it too wide/big for a standard 5.56 firing pin) Worst case making that little collar on a lathe to put on a standard 5.56 firing pin is like 15 minutes worth of work at best. |
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Originally Posted By jbntex: Yeah.... another problem with the CMMG Radial. Now that they have fixed the ejector the firing pin quality is bad as well. Have you tried a standard M16 firing pin with no spring? As you mentioned you really can't have a out of battery with the rotating bolt and I wouldn't think that a rotating bolt would have enough energy by the time it closed that the firing pin could inertia set off the primer. Worst case maybe just a standard 5.56 firing pin with a 9mm blowback carrier firing pin spring (as the CMMG spring it too wide/big for a standard 5.56 firing pin) Worst case making that little collar on a lathe to put on a standard 5.56 firing pin is like 15 minutes worth of work at best. |
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Fair point about the extra safety margin. If when my pin breaks, I may do some testing just to see how it goes, either add a standard blowback 9 firing pin spring and/or you mention for ~$30 I can get a TI firing pin and machine the collar on my lathe and call it a day knowing that solves it. Looking at my bolt carrier I wonder if the radial bolt carrier firing pin spring is forcing the firing pin to stick out to far back out of the carrier and is also inducing the firing pin failures as the hammer has got to be hitting the head of the firing pin a bit off axis given how far it sticks out the back via the spring. Doesn't explain the busted pin tips but maybe helps explain the broken off heads. To answer your other questions above. The Scheel system is a bit better than the maxim as you can better tune the delay as you have all those internal spring options inside the buffer as well as the amount of preload on the buffer via how deep you seat the buffer tube into the receiver (i.e. basically bolt gap equivalent in HK land) The maxim all you can adjust is the preload/bolt gap and the spring pressure is all based off the internal recoil spring. For the the ported AR9 yes its traditional blowback. I have had a ported LRM made AR9 SD upper for probably 20 years that is really soft shooting compared to any standard AR9. Its also set up for a RLL that removed a decent amount of mass on the underside of the carrier as you have to mill a channel in the carrier. I use the same Kynshot hydraulic 5007 as well. I have seen online influencers recently "rediscovery" how soft shooting a blowback 9 can be with SD barrels and those Broad River uppers. The downside like all SDs is they run really dirty, which is why we have been chasing a non-ported and/or non-suppressed AR9 solution for years. Some friends and myself have played with many of these different AR9 options over the years and the only one we really have not messed with was the JP due to cost and the same reasons you mentioned that it isn't really sear compatible. That said I am pretty sure I could get an RLL around the pivoting HK style ejector but with the advent of the CMMG Radial with the Fixed Ejector cured any desire for a JP unit. The CMMG Radial with the FE, when paired with a kynshot buffer, flatwire spring, and the carrier losing a bunch of mass after being milled to SP1 spec so its RLL compatible is I think my final solution as long as it doesn't continuously break parts. Its so close to MP5 ROF and Recoil impulse that any additional improvement is going to be pretty small/incremental. |
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Originally Posted By jbntex: Looking at my bolt carrier I wonder if the radial bolt carrier firing pin spring is forcing the firing pin to stick out to far back out of the carrier and is also inducing the firing pin failures as the hammer has got to be hitting the head of the firing pin a bit off axis given how far it sticks out the back via the spring. Doesn't explain the busted pin tips but maybe helps explain the broken off heads. Originally Posted By jbntex: Looking at my bolt carrier I wonder if the radial bolt carrier firing pin spring is forcing the firing pin to stick out to far back out of the carrier and is also inducing the firing pin failures as the hammer has got to be hitting the head of the firing pin a bit off axis given how far it sticks out the back via the spring. Doesn't explain the busted pin tips but maybe helps explain the broken off heads. To answer your other questions above. The Scheel system is a bit better than the maxim as you can better tune the delay as you have all those internal spring options inside the buffer as well as the amount of preload on the buffer via how deep you seat the buffer tube into the receiver (i.e. basically bolt gap equivalent in HK land) The maxim all you can adjust is the preload/bolt gap and the spring pressure is all based off the internal recoil spring. I also like being able to swap uppers for 556 with the same lower which is another reason I passed on the Scheel For the the ported AR9 yes its traditional blowback. I have had a ported LRM made AR9 SD upper for probably 20 years that is really soft shooting compared to any standard AR9. It's also set up for a RLL that removed a decent amount of mass on the underside of the carrier as you have to mill a channel in the carrier. I use the same Kynshot hydraulic 5007 as well. I have seen online influencers recently "rediscovery" how soft shooting a blowback 9 can be with SD barrels and those Broad River uppers. The downside like all SDs is they run really dirty, which is why we have been chasing a non-ported and/or non-suppressed AR9 solution for years. Some friends and myself have played with many of these different AR9 options over the years and the only one we really have not messed with was the JP due to cost and the same reasons you mentioned that it isn't really sear compatible. That said I am pretty sure I could get an RLL around the pivoting HK style ejector but with the advent of the CMMG Radial with the Fixed Ejector cured any desire for a JP unit. The CMMG Radial with the FE, when paired with a kynshot buffer, flatwire spring, and the carrier losing a bunch of mass after being milled to SP1 spec so its RLL compatible is I think my final solution as long as it doesn't continuously break parts. It's so close to MP5 ROF and Recoil impulse that any additional improvement is going to be pretty small/incremental. like this  C3Junkie custom 9mm Banshee 12-2025 |
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Originally Posted By amphibian: I also like being able to swap uppers for 556 with the same lower which is another reason I passed on the ScheelI too have an LRM integral. I re-cored mine and made a stainless ported RDB barrel for it. Interesting, does the radial converted LRM unit work well? I would have through that with the porting and reduced recoil impulse that the radial delay may not function properly. I think I read (maybe from you) that the CMMG Radial Fixed Ejector unit used the more aggressive delay dissent bufferless system locking angle and when that system was transitioned to the Banshee traditional buffered system with the higher carrier weight+buffer struggled to cycle lighter loaded 115gr ammo. It would be pretty straight forward to just buy another fixed ejector radial "kit" (upper, barrel, and carrier group) plus the Colt pattern mag "kit" and profile the barrel on my lathe and port it on the mill to match the existing LRM barrel. |
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Originally Posted By jbntex: Interesting, does the radial converted LRM unit work well? Originally Posted By jbntex: Interesting, does the radial converted LRM unit work well? I just did it because I had it laying around. I will say that it is smooth though.  I would have through that with the porting and reduced recoil impulse that the radial delay may not function properly. I think I read (maybe from you) that the CMMG Radial Fixed Ejector unit used the more aggressive delay dissent bufferless system locking angle and when that system was transitioned to the Banshee traditional buffered system with the higher carrier weight+buffer struggled to cycle lighter loaded 115gr ammo.  It would be pretty straight forward to just buy another fixed ejector radial "kit" (upper, barrel, and carrier group) plus the Colt pattern mag "kit" and profile the barrel on my lathe and port it on the mill to match the existing LRM barrel. There barrels are definitely hit or miss which is why I had a run of 416R barrels made. |
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Thanks for the reply. I think my use case is probably a bit different than yours. All of these are just range toys for me so the downrange difference in energy for me between a 115gr to 124gr vs. 140 to 150gr projos both at ~1000fps on a paper target or recreational steel target "for fun" doesn't make any real difference to me. I can also buy commercial 115/124gr 9mm significantly cheaper than commercial subsonic 9mm and the availability of true round nose profile ball subsonic is also kinda limited as it seems like most of it is truncated cone that doesn't run well in many of my subguns. That said I want something that is a decent shooter from a reliability (function and parts breakage), recoil, and rate of fire perspective (which I prefer closer to 800 vs. 600) The AR9 has always been a bit elusive in that regard. We have only built up and tested only one of the new fixed ejector CMMG radial upper as a POC and it seems to run just fine with Colt mags and nothing has broke yet. I have all the parts on my bench to build up a second ground up fixed ejector radial unit in the next month or so when I find the time. If I could eventually update my LRM and keep it cleaner and actually make it a slightly better shooter I may eventually do that as well. |
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Thanks for the thorough responses to my question. It sounds like I’ll want go back to the previous blowback buffer system. This SBR runs just fine in FRT mode with a tungsten weight plus an H3 buffer. I will set the Roller Delayed Buffer aside for semi-auto only use. The CMMG RDB system is my primary 9mm PCC platform, and it works fine with all the FRTs I’ve tried. Thanks for sharing your experiences with this system also. |
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