Posted: 5/20/2021 4:57:52 PM EDT
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Hello, fellow firearms enthusiasts. I thought I’d take my CMMG Banshee to the range today since it appears I may soon be unable to show it in public for fear of violating FATF decrees. I’ve probably fired around a cumulative 750 rounds out of this thing since I got it and I had one FTE off the first or second round of a mag once before and that has been the only malfunction. I ordinarily shoot only 115 or 124 grain ammunition and have never shot anything heavier through it until today. Today I tried it out with my Rugged Obsidian 9 and of course I felt this justified using some 147 grain Speer Lawman I had laying around. In 50 rounds shooting suppressed, I had three double feeds where the spent casing was not ejected and the bolt stripped another round off the magazine and jammed with both the empty casing and live round caught between the bolt and chamber. I also shot some 115 and 124 grain ammo suppressed and did not have the same issue. I wish I’d shot some of the 147 unsuppressed to check if I had the same issue as it did shooting suppressed, but It didn’t occur to me and I was trying the suppressor out on a pistol as well. At first I though it could be the flat nose of the projectile but now I think it’s related to the gas pressure. Any ideas what could be causing this? @amphibian |
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Your round count on a cmmg delayed radial 9mm upper is about right for the ejector spring in the bolt to be worn out. The folks I know with these units, an ejector spring lasts no more than 1000rds. Suppressed or heavy grain weight ammo will kill the ejector spring even faster. Its just one of radial design limitations, with some uppers eating ejector spring faster than others, probably due to headspace variations. Replace the ejector spring with a fresh one and your FTEs will probably go away and keep a couple spares onhand. |
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Quoted: I’m supposed to replace the ejector spring every time I shoot 1,000 rounds? That seems crappy. It could be worse, one of my friends guns ate ejector springs a lot faster than that. Some ejector springs/ ammo/suppressor combos were killing ejector spring every 200 to 300 rounds so you couldnt make it through a single range session without a ejector spring swap. At one point he bought the tool to make swapping them easier/faster before finally giving up on the platform after a bunch of back and forth with cmmg and just bought an HK MP5 instead. I beleive amphibian has documented on this issue on his website c3junkie.com that he eventually went to a milled channel bolt and a fixed ejector setup to resolve it. |
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I'm still on the factory ejector with north of 2.5K rounds. That said, my banshee is very picky on ammo and needs to be tuned to a certain load. If I tune it to 147 subs it'll coke on 115s or anything hot. Tuned for the hot stuff? Chokes on sub 147s. I basically keep it tuned to 124 factory FMJ and don't deviate from that and it's been reliable (when tuned). Rather annoying 
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Quoted: Add or subtract weights to the BCG and charge buffer weight. Quoted: Quoted: @sao What do you mean when you say it’s been tuned to a certain load? Did you add weights to the bolt carrier or change out the buffer spring or buffer? Thanks. Add or subtract weights to the BCG and charge buffer weight. How’s yours configured? As I mentioned, I haven’t had any problems with the 115 or 124 really. It’s only the 147. I don’t know if I want to be screwing around with it if it’s going to be a trial and error thing. |
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Quoted: I love shooting mine. So much fun..Double stamp, SBR and can. As I stated I havent had any issues but I still have a 3 pack of the BCM spring kits in my parts drawer in case I do. No real issue here. Have fun shooting it! I love shooting mine as well. It’s one of my favorite guns. I want it functioning well so it can be my bedside gun. Are the BCM springs you mention ejector springs, buffer springs, or extractor springs? |
| Kinda surprises me b/c 9mm is such a mild round. Furthermore, none of those are exotic loads, everybody at some point will shoot 115, 124 and 147grs in their guns. My blowback Colt pattern with a 10oz buffer and a 10.5" barrel is smooooooooth and eats everything. |
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Quoted: Kinda surprises me b/c 9mm is such a mild round. Furthermore, none of those are exotic loads, everybody at some point will shoot 115, 124 and 147grs in their guns. My blowback Colt pattern with a 10oz buffer and a 10.5" barrel is smooooooooth and eats everything. Ironically the fact that 9mm is such a mild round is my personal take why the 9mm uppers are so hard on ejector springs. Mechanically the problem appears to be "bolt jump". When you fire a 9mm Radial upper the angled bolt lugs are actually not in direct contact with the lugs in the barrel extension. This would be similar to a standard AR15 with excessive headspace. So the first bit of rearward travel of the bolt/carrier/buffer is effectively direct blow back. On the radial design the bolt is actually designed/intended to comes back directly for a brief moment (similar to a blowback design) before the angled lugs on the bolt impact the lugs on the barrel extension. When the lugs finally do make contact after firing the bolt head effectively comes to a sudden stop as the bolt head now begins to rotate as the lugs engage each other. As of result of this high speed bolt to barrel extension collision, the ejector plunger in the bolt head is actually still free to go backwards, similar to an unbelted human in a car crash. The ejector plunger continues backwards after the rest of the bolt stops and the plunger crushes the ejector spring with each shot. Over time the ejector spring is killed. If you look at the pictures over at C3 junkie http://www.c3junkie.com/?page_id=221 you can see pics of the now crushed/collapsed ejector springs. Once the ejector spring loses tension on the ejector plunger you get FTEs. Amphibian in an attempt to resolve this issue even had a custom barrel made that adjusted the headspace so that the lugs on the bolt were always in contact with the lugs on the barrel extension. The net result was that without that high speed direct blowback bolt head "jump" to start the bolt rearward 9mm is just too anemic to make the system function reliably. The larger calibers seem to need less free bolt jump and as a result their ejector springs seem to last longer. CMMG has made adjustments to the ejector springs to lengthen their life and it seems that the free bolt jump/headspace seems to vary from gun to gun. 9MM uppers with a larger bolt jump/headspace may be way some guns eat ejectors faster than ones that do not. The hotter the ammo you put in the gun and/or the more back pressure you add with a suppressor the worse the impact between the bolt and barrel extension lugs is, resulting in an ejector plunger with even more rearward velocity and more damage the ejector spring. As mentioned you can help to mitigate this by tuning the gun with weights so that the bolt/carrier/buffer mass helps to temper the direct blowback travel rear bolt velocity before the lugs engage but then the gun can have problems running when you remove the suppressor or drop down to lower power/lighter weight ammo. |
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Quoted: I wanted one of these to use P320 mags but so far the reviews have been mixed on them. Now I find out you have to replace an ejector every 1,000 rounds?  No thanks.Yeah, I’d pass if I were you. I paid $1,200-1,300 for this thing and for it to have these kinds of problems is absolutely unacceptable. It’s a shame because I absolutely love shooting this thing and if it wasn’t for this issue I’d be a satisfied customer. Now I have to find another PCC to use as a host for my suppressor because this one obviously isn’t up to the task. |
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Guitargod1985, As I answered in the CMMG forum, I had the same problem with mine after about 1000-2000 rounds. Last couple hundred suppressed 147's. I had read the posts about early ones having this issue and CMMG replacing the ejector springs with heavier ones. CMMg sent me a couple of them and my issues got worse after installing one. (Pain in the ass without the tool but doable for sure) A shooting buddy found a You Tube video showing a guy with EXTRACTOR issues that were the same as what I experienced. He corrected his with the BCM Extractor upgrade. I had some of the o-rings at hand and tried one. Voila'! No more fte's. I've ran a few hundred rounds now with no issues. Ordered the BCM kit too. A shame if this is how they are as I hope to run mine weekly, some suppressed. I've marked this thread and will check in with results from time to time. |
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@docslester Thanks for the information. Did you use the o-ring with the new extractor spring or no? Are you still running the factory ejector spring with the new extractor spring or are you running upgraded springs for both? I’ve been in touch with CMMG via email this morning. We’ll see what happens. I’ve bookmarked the BCM extractor kit you linked to in the CMMG industry thread. |
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@Guitargod1985, I left the original extractor spring in at first and used just the o-ring and it ran flawlessly. After I received the BCM kit I went ahead and installed it; still runs flawlessly. I had installed the new ejector spring from CMMG first and it made it worse. I left it in because they are a bit of a pita to install if you don't have the tool. (Hint; a c-clamp and an empty 9mm case along with the right size punch and a third hand are your friends.) So I am now running new springs in both along with the o-ring. The tuning kit (which I wasn't aware of till now.) is looking like an interesting option. |
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Quoted: Is there an aftermarket "heavy duty" ejector spring that will last longer than the CMMG ones? Based on the numerous threads I’ve read over the past 24 hours, the one people appear to be using to replace the factory 9mm Banshee ejector spring is CMMG’s own 10mm Banshee ejector spring. This one. |
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Quoted: @Guitargod1985, I left the original extractor spring in at first and used just the o-ring and it ran flawlessly. After I received the BCM kit I went ahead and installed it; still runs flawlessly. I had installed the new ejector spring from CMMG first and it made it worse. I left it in because they are a bit of a pita to install if you don't have the tool. (Hint; a c-clamp and an empty 9mm case along with the right size punch and a third hand are your friends.) So I am now running new springs in both along with the o-ring. The tuning kit (which I wasn't aware of till now.) is looking like an interesting option. @docslester Thanks for all the info with regard to this issue. It looks like I’ll order the 10mm ejector spring, the BCM extractor kit, and the tuning kit, and screw around until it’s tuned reliably and to my liking. I’ll update the thread in a few weeks to a couple months when I’ve tried everything. |
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@Guitargod1985 Is this the tuning kit? Tuning Kit I could only find two, this one and a "short" one. I plan on following your lead on some experimenting. I really like this platform and would like to switch between suppressed and un-suppressed without a big hassle. Just wish they had come out with their Colt/Uzi pattern mag one first as I have a pile of them from my other 9mm AR's. Oh well in ARFCOM fashion perhaps I'll get both! |
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Short update; Tuning kit arrived, installed the middle weight and it's roll-pin. (Took a bit of work to get the pin in. Grease and a heavy hand with a hammer and brass punch.) Ran about 50 124's, half or so suppressed. Ran 50 +/- each of very lightly loaded 147 and 150 grain suppressed with no problems whatsoever. Was a bit surprised as neither will run in a couple of pistols. Next step is to load some 150's towards a normal load that will run in everything and see if they will run without the weird Banshee case bulge that plagued my first suppressor trials. @Guitargod1985 Any update on your issues? |
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My upper arrived in January and the extractor broke in half on the 3rd mag. CMMG sent me a replacement. Finally picked up my MkGs lower earlier this week so when I replaced the extractor and stuck an O-Ring in. I also added the middle weight of the action tuning kit. (Yeah, this took some force). Using my Omega 9K and Fiocchi 158gr fmj ammo. one box worked just fine. Tried some Winchester 147gr fmj and it worked fine also. Haven't had time to try my heavier ammo but so far everything is working. I ordered a BCM extractor kit to keep as a spare in case this extractor breaks. |
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Ran the Banshee in a Steel Challenge Saturday. (Only center fire carbine on our squad. All .22's. &$#@ ammo drought.) Little under 200 rounds of 124's. No issues at all. Managed to place fourth overall. Hoping to run some suppressed heavies this Thursday but family medical issues may sideline us for a while. |