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Page AR-15 » Rimfire and Pistol Calibers
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Maxim Defense RDB review (Page 11 of 11)
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Link Posted: 11/17/2023 2:25:27 PM EST
[#1]
I've been shooting my AR-9 with Maxim RDB for a couple months now.

On the whole, I think I like it. I've had a couple of difficult to explain feeding failures that could have been magazine related (I run the stendos) or short-powder or something. I shoot reloads, weird shit happens. My MPXs are hardly perfection, in comparison.

One thing to note is that I shoot high PF (135) ammo, and it would not shock me if lighter ammo was causing issues with this system.
Link Posted: 11/23/2023 5:25:36 PM EST
[#2]
Finally got to shoot and sight in my Palmetto State AR-V with Maxim buffer system. Has a 9" PSA barrel and Silencer Central Banish suppressor. Ran like a top and the rounds used were a mix of super and subsonic in the same mag. Deffinate difference in sound between them and shot great. Glad it ran with no hiccups and ejected great. This is a replacement for my CMMG RDB that I was tired of fighting ejection issues with. The AR-V takes the CZ Evo mags. I only have PSA mags right now but bought some Magpul mags to try. I need to run this thing through some local matches and see how it does. Way to go PSA and Maxim.
Link Posted: 11/23/2023 9:36:17 PM EST
[#3]
My AR-V hates the Magpul scorpion mag I bought to test. I just bought a bunch of PSA mags after testing it, as they work great, look great, and are cheap to boot.
Link Posted: 11/24/2023 9:25:32 AM EST
[#4]
Well crap. Hope they fixed something or I can offload them on a CZ owner.
Link Posted: 11/27/2023 7:42:53 AM EST
[#5]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By erwos:
I've been shooting my AR-9 with Maxim RDB for a couple months now.

On the whole, I think I like it. I've had a couple of difficult to explain feeding failures that could have been magazine related (I run the stendos) or short-powder or something. I shoot reloads, weird shit happens. My MPXs are hardly perfection, in comparison.

One thing to note is that I shoot high PF (135) ammo, and it would not shock me if lighter ammo was causing issues with this system.
View Quote

@erwos
Most 9mm AR feed failures can be fixed using a barrel with an enhanced feed cone (the funnel-shaped cut that leads into the chamber).  The larger feed cone compensates for many issues including mag height and cartridge presentation angle.

See here: 4-step guide to make (almost) any AR9 run 100%

Won't help with shortstroking, though.  I noticed my Maxim was very sensitive to extra bolt mass and wouldn't lock back on LRBHO.

Hope this helps.
Link Posted: 11/27/2023 8:37:14 AM EST
[#6]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Droppoint:

@erwos
Most 9mm AR feed failures can be fixed using a barrel with an enhanced feed cone (the funnel-shaped cut that leads into the chamber).  The larger feed cone compensates for many issues including mag height and cartridge presentation angle.

See here: 4-step guide to make (almost) any AR9 run 100%

Won't help with shortstroking, though.  I noticed my Maxim was very sensitive to extra bolt mass and wouldn't lock back on LRBHO.

Hope this helps.
View Quote

I'm using a JP Supermatch 9mm barrel that, in theory, has pretty good feeding. I may be swapping over to a shorter barrel to make this thing a suppressor host, though.

No problems with short-stroking, but my ammo is 135 PF.
Link Posted: 11/27/2023 9:34:24 AM EST
[#7]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Joedirt199:
Finally got to shoot and sight in my Palmetto State AR-V with Maxim buffer system. Has a 9" PSA barrel and Silencer Central Banish suppressor. Ran like a top and the rounds used were a mix of super and subsonic in the same mag. Deffinate difference in sound between them and shot great. Glad it ran with no hiccups and ejected great. This is a replacement for my CMMG RDB that I was tired of fighting ejection issues with. The AR-V takes the CZ Evo mags. I only have PSA mags right now but bought some Magpul mags to try. I need to run this thing through some local matches and see how it does. Way to go PSA and Maxim.
View Quote


@Joedirt199

Did you have to modify your AR-V in any way to get the Maxim to work?  I'm tempted to get a Maxim for my AR-V but haven't read too many experiences with the combo.  Thanks for posting your's!
Link Posted: 11/27/2023 12:26:49 PM EST
[Last Edit: Joedirt199] [#8]
Just have to pull the weight out of the bolt. Forgot to do that and thought, "Man this thing is impossible to charge." I butted the carbine extension right up against the bolt so there is no free space between the bolt and buffer system. I also pulled the buffer back some before installing and greased up the balls in the buffer. Not sure if it makes it easier to charge but figured it couldn't hurt. May help keep ware and tear down.
Link Posted: 12/7/2023 12:41:03 PM EST
[#9]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Joedirt199: I also pulled the buffer back some before installing and greased up the balls in the buffer. Not sure if it makes it easier to charge but figured it couldn't hurt. May help keep ware and tear down.
View Quote


Interesting note here, as I bought 2 RDB systems at different times.  The first one was in pristine, shiny-new condition, and the bearings were WELL greased.  The second one had some rust webbing around the laser engraved serial # on the outside and had less grease on the bearings.  The first one was very low serial number.  The second was much higher serial #.

We know Maxim received far more interest in this than they originally expected, and they sold out their first batches quickly (the carbine version first, from what I saw in availability).  I suspect some later batches were hurried, and while of quality manufacture, some may have had less attention paid to finishing details like amount of grease on bearings, or proper moisture & temperature control before/while/immediately after laser cutting serial #s (explaining the rust).  Thus, I'd expect those systems that were rushed to have a higher probability of benefitting from some extra lovin' like ensuring proper grease amounts in the bearings.

That said, any change to the bearings alters the resistance to cycling as well as charging, so it better not make charging too easy.  
Link Posted: 12/7/2023 3:55:42 PM EST
[#10]
I have a spring loaded bow weight scale I could put on the charging handle and see how much weight it needs to pull loose. I still have to lock the stock into the shoulder and give the charging handle a sharp tug to get it to cycle.
Link Posted: 2/9/2024 11:09:27 AM EST
[#11]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Kiranslee:



Haha this is what I have coming this Wednesday. Was able to snag it for under $100 with a promo so I will be testing this with my build this week.

I'm also at about 500 rounds now and I notice its much easier to charge or maybe my technique just got better.....(I'm not a gorilla).

View Quote

@Kiranslee how did the DDC Hard Charger work with your RDB setup?

I'm really considering one of the RDBs for a PSA AR-V project, but I am hesitant to deal with the difficult charging aspect.
Link Posted: 2/9/2024 1:51:29 PM EST
[#12]
Get large handles on your charging handle. I have a PRI gasbuster with large ambi handles and it is not hard to charge. I can get more fingers on the handles. Leave the stock in the shoulder and give it a sharp tug.
Link Posted: 2/10/2024 9:43:34 PM EST
[#13]
Ok, so I want to make a spacer that will limit the length of travel since my 9mm build doesn't need all that extra space. Anyone have any ideas of a rubber bumper that would fit over the the rear of the buffer system to keep it from moving about a half inch less?
Link Posted: 2/11/2024 12:27:45 AM EST
[#14]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Joedirt199: Ok, so I want to make a spacer that will limit the length of travel since my 9mm build doesn't need all that extra space. Anyone have any ideas of a rubber bumper that would fit over the the rear of the buffer system to keep it from moving about a half inch less?
View Quote


Quarters.
Link Posted: 2/11/2024 9:48:28 AM EST
[#15]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By backbencher:Quarters.
View Quote


Really bad idea. That will make the system non-functional.
Link Posted: 2/11/2024 9:56:15 AM EST
[Last Edit: November5] [#16]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Joedirt199:
Ok, so I want to make a spacer that will limit the length of travel since my 9mm build doesn't need all that extra space. Anyone have any ideas of a rubber bumper that would fit over the the rear of the buffer system to keep it from moving about a half inch less?
View Quote
JP makes spacers for their SCS that would likely work or could be modified pretty easily.  The tall bumper in the SCS maintenance kit would probably be about perfect.
Link Posted: 2/11/2024 10:47:34 AM EST
[#17]
I saw that and I think that is for using the carbine system in a rifle length buffer tube. I saw a reddit post where a guy made a spacer out of delrin and added some orings on the ends for bumpers. May be an option if I can get access to a lathe. With the extra buffer travel, I have had some brass get stuck behind the bolt lock when they failed to eject.
Link Posted: 2/11/2024 10:52:02 AM EST
[#18]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Joedirt199:
I saw that and I think that is for using the carbine system in a rifle length buffer tube. I saw a reddit post where a guy made a spacer out of delrin and added some orings on the ends for bumpers. May be an option if I can get access to a lathe. With the extra buffer travel, I have had some brass get stuck behind the bolt lock when they failed to eject.
View Quote
The bumper in the maintenance kit should work as is.  The spacers are designed to use it in a longer tube, but I'm sure they could be made to work with minimal work.

https://www.jprifles.com/buy.php?item=JPSCS2-MAINT-K15
Link Posted: 2/11/2024 11:09:43 AM EST
[#19]
They did have an aluminum spacer for the short stroke kit. I wonder if puting the aluminum spacer at the end of the rod, then mounting the bumper next to the spacer would be enough. They add 2 aluminum spacers next to the weights on their captured buffer short stroke kits. I sent an email to Maxim to see if this is an idea they have thought of. Will send an email to JP asking about the specific parts and their take on it.
Link Posted: 2/11/2024 11:43:11 AM EST
[Last Edit: hdcharlie] [#20]
Don't make this difficult. Fashion a 1/2" spacer(thick washer, has to have a hole in it to clear the spring) out of aluminum, Delrin, or whatever, and place it under the original bumper. Done!
Link Posted: 2/11/2024 12:21:19 PM EST
[#21]
That's what I was I thinking. Now to source some aluminum tubing.
Link Posted: 2/11/2024 12:54:01 PM EST
[Last Edit: hdcharlie] [#22]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Joedirt199:
That's what I was I thinking. Now to source some aluminum tubing.
View Quote


See below.
Link Posted: 2/11/2024 7:15:49 PM EST
[#23]
I looked closely at my RDS and now I'm not sure you'll be able to modify one the way you want. It appears as though the bottom steel piece has an extension that goes into the nylon bumper. If that is the case, you won't be able to put a spacer under the bumper and be able to keep the bumper centered on the rod. The only way I can envision something working would be to make an entirely new bumper the length you want to replace the old one entirely. That wouldn't be hard if you had a lathe and some material, but, otherwise...
Link Posted: 2/11/2024 9:46:34 PM EST
[#24]
Hopefully JP and Maxim have some ideas and I hear back from them.
Link Posted: 2/12/2024 10:54:42 AM EST
[#25]
So you are trying to do what I did on page 6 of this thread but longer not shorter right?
https://www.ar15.com/forums/AR-15/Maxim-Defense-RDB-review/15-780933/?page=6


Link Posted: 2/12/2024 12:20:11 PM EST
[#26]
Yeah needs to be about 1/2" longer bumper to reduce the length of travel of the buffer. I have a PSA AR-V using Evo style mags and the bolt travels way past the bolt lock allowing brass that fails to eject to get stuck behind the bolt locked back nub.
Link Posted: 2/12/2024 9:53:15 PM EST
[#27]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Joedirt199:
Hopefully JP and Maxim have some ideas and I hear back from them.
View Quote


No need to wait. Go to post #21 and look at the pic Amphibian shows of the bumper. You can see how the steel piece below the nylon bumper is inserted into the bumper. This allowed them to have a steel seat for the spring. So, all you would have to do is make a new bumper the length you want by cutting one from a piece of Delrin rod and them machining/drilling a through hole the same size as the one in the original bumper. Push the steel collar into the new bumper and you're done. I can't see why you'd even have to taper the new piece to match the old bumper. That taper seems to be purely cosmetic.
Link Posted: 2/12/2024 10:54:14 PM EST
[#28]
I just use these from Home Depot

Nylon Spacer
Link Posted: 2/15/2024 11:50:01 AM EST
[#29]
Got a foot of delrin tube coming so I will be able to make several short stroke spacers if anyone is interested. Should be here tomorrow and I can start figuring out the length needed this weekend.
Link Posted: 2/19/2024 8:56:32 PM EST
[Last Edit: Joedirt199] [#30]
Got my delrin short stroke bumper done. Man I wish I had a mill and a lathe. Modding parts on a poor man's lathe, aka electic hand drill with part held on a bolt, sucks. Got it turned down under an inch on the outside and inside is just under half an inch. I went with 3/4" long as you have a little over an inch of space between the bolt face and the bolt hold open nub. The bolt release is much better now that the small nub on the bolt stop is gone. I can seat a mag and drop the bolt much easier with the bolt release button. Now to run a few rounds through it tomorrow.
Link Posted: Today 3:48:41 PM EST
[#31]
Got to test it out. I think I will grab a JP SCS spring kit and try to tune the Maxim just a little firmer. Throws brass pretty far and still has a decent port pop so hoping a stiffer spring will hold the bolt closed just a little bit longer. Short stroke worked great and only problem I had was a couple of fail to feeds where the round looked like it missed the ramp and went straight up. Happened on a PSA mag and a Magpul Mag, both the very last round.
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Maxim Defense RDB review (Page 11 of 11)
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