RIck,
do you know what the buffer weight is? I shoot an AR-45 / 8.5" with 200gr's and 5.7 of W231 they crono @ 990+.
I believe my setup is a KVP 7.5 oz buffer and a std AR-10 spring, brass clears horizontal at 3:00. Mine is a blowback not GI.
sounds like to much sripng and not enough buffer weight. Any peening on the buffer face?
When I get home this afternoon I will check my setup. I worked with the guys at New Frontier Armory in Vegas they do a lot of PCC stuff and are pretty helpful.

 

RIck,
do you know what the buffer weight is? I shoot an AR-45 / 8.5" with 200gr's and 5.7 of W231 they crono @ 990+.
I believe my setup is a KVP 7.5 oz buffer and a std AR-10 spring, brass clears horizontal at 3:00. Mine is a blowback not GI.
sounds like to much sripng and not enough buffer weight. Any peening on the buffer face?
When I get home this afternoon I will check my setup. I worked with the guys at New Frontier Armory in Vegas they do a lot of PCC stuff and are pretty helpful.

H3 buffer, 5.5 ounces.
The buffer was included with the gun when returned from service, and appears to be used, with scratches on the face. The buffer that was in the gun when I returned it was unmarked, but was the heavier of the two buffers supplied.

The instructions indicate that loads between 190-220 power factor, which would be a 200gr @ 950-1100, should use the heavier of the two buffers, and "sustained use" of loads hotter than that require a heavier buffer.
I'm near the top of the range for the supplied buffer, which seems to indicate a heavier buffer is in order.
An 8oz buffer will be delivered today, I was going to try that with the load I've been using, but now I'm wondering if I should just stay with the H3 and try some hotter loads.
That goes against my intuition, but maybe the weak ejection is what I should be paying attention to.
I'm accustomed to my Delta Elite throwing brass 15-20 feet, even with mid-range loads.

 

How about a ladder test evaluating the ejection through the ladder?

 

Yes, I was going to chrono them through my Delta Elite, so I'd have apples/apples comparison with previous data, but might put them through the AR, instead.
My goal is a 220gr load that makes 1200fps from the 8" barrel, using a slow powder to take advantage of the long barrel; may as well jump right in.

 

Really need to video the rounds ejecting from the port, then we can see what may be too fast or too slow on spitting out the case.
As-is, is the case just flipping 180° and hitting the port? A video would help.

 

If your gun is blowback the 5.5 oz buffer is probably too light. Blowback ARs (even 9mms) use heavier buffers and they still have more felt recoil than a 5.56 AR. I've been wanting to try a CMMG radial locking bolt/barrel in my 9mm. My current buffer is 7.7 oz with a blowback bolt.

 

I agree with this. My BCG and buffer weigh about 21 ounces, more than a pound of metal and it functions flawlessly.

I say look up other people's builds and see what their weights are.

 

It's a CMMG, so I feel a bit on my own.
I really liked the idea of radial delay reducing reciprocating weight by ounces, but I certainly don't see downloading 10mm to .40 power levels to be a proper fix, nor is adding a lot of weight to the buffer.
I've seen some advocacy for a stronger extractor spring, or adding the o-ring.
A longer buffer, so the bolt can't cycle back far enough for the brass to contact the rear of the port, is another suggestion.
I'm not the only person having this problem with their Banshee, and it's not confined to 10mm.
Customer service has been receptive to discussing the issue, but "increase buffer weight first, then reduce load" seems to be the extent of suggested fixes.

 

I‘m happy i found your post. I was going to buy the Banshee 10mm today, 1,489,00. Started to find all of these types of post. I read one post that said CMMG said the gouges were normal wear and tear and did nothing. Another guy had continuous jams. After much conversation with CMMG they told him they couldn’t fix it. Seems you either get a great one or a bad one. Shouldn’t have to tune the gun or worry about the ammo you are using. A quality firearm normally rips right out of the box and eats just about everything you feed it. More importantly, it shouldn’t gouge the port. It appears their customer service people are nice and friendly but don‘t stand by their lifetime warranty. A 1,500.00 dollar gun should perform flawlessly. I am not buying one of these thanks to the people who let us know of all the issues with these guns. Guess i’ll just stick with my Razorback and Delta Elite. Thanks

 

 

I'll keep my mouth shut as I've got a Dpms

 

Probably won't help but my Kel Tec SUB2000 is a blowback in .40 and it has a huge solid steel buffer/weight so I can easily see how you would need a heavy buffer to slow the bolt down for cleaner ejection. I also wonder if yours has a problem with the ejector.

 

I know that, I was just effin' with ya. I have a .300BLK AR that I still haven't gotten dialed in yet, and probably never will now that I'm not even allowed to buy AR parts here anymore. Playing with buffer weights and springs seems to be equal parts voodoo, science, and By Golly.

 

I have a 10+ Oz buffer in my suppressed 4" ar-9 and it runs perfect even with weak subsonic ammo. I wouldn't run a 10mm without a 10oz. You can't go too heavy.

 

So the way it was explained to me was:

The buffer controls action speed (extraction and ejection) just like the 1911, the shell trajectory is for the most part extractor / ejector geometry (to an extent), but the bolt speed can interfere with this.

The spring controls the return to battery (RTB), both speed and lockup in RTB. (If the setup is in balance) This is the part that caused a lot of grappling discussions, some heated... it seems everyone has their own "favorite terminology" and gets tedious trying to figure out what does that really mean.



The bottom line is controlling the bolt speed in both directions and how this gets accomplished is the "BALANCE".

Buffer weight translates to moment of inertia in transition, (the smoother). At rest (in battery) it slows the bolt rotation and release (snapping the bolt dogs open is bad) almost as bad as slamming them closed in battery. The combined weight of the buffer/BCG and the gas force that is need to put it into full recoil but not slam the stops and bounce back towards battery is the first balance. Spring weight is the second; when properly loaded the spring should start slowing everything from the get go in recoil, the goal being the buffer and BCG lightly hit the stop point together (no gap between the buffer face and BCG) at this point the energy in the compressed spring takes over and we start closing into battery. When in balance the whole process is sinusoidal and smooth. When something gets out of balance we loose rhythm and stuff starts banging. Unfortunately the banging comes in many forms and can be almost imperceptible in most cases, until something breaks.



Now if the buffer is to heavy the bolt will be to slow to open and not have enough energy to cleanly eject the empty (this will load dependent and usually end with a stove pipe or FTF). With light loads you may not get good lockup either.

If the spring is to light or weak achieving RTB will be the issue, again more so with lighter loads.

If the buffer is to light the action will most likely be very quick (snappy) and have a sharp recoil but operate correctly to a point. This condition is very load dependent as well and will be exacerbated by a heavy spring on the RTB. I would suspect that this is most likely your problem.

If your felt recoil is sharp and the action has that high ping sound you are hammering the stops and the bolt is bouncing back towards battery way to fast and pushing the eject forward clipping the empty on the front of the port. I wouldn’t run anything hotter through it. I’m running a KV 10.0 oz and heavy spring in my AR-45. In a10mm I’d go find a 12-14 oz’er or more. Just my 2 cents.

 

So the way it was explained to me was:

The buffer controls action speed (extraction and ejection) just like the 1911, the shell trajectory is for the most part extractor / ejector geometry (to an extent), but the bolt speed can interfere with this.

The spring controls the return to battery (RTB), both speed and lockup in RTB. (If the setup is in balance) This is the part that caused a lot of grappling discussions, some heated... it seems everyone has their own "favorite terminology" and gets tedious trying to figure out what does that really mean.

I'd say that's close, but not 100%
If the spring were massless then the buffer mass is all of it on the acceleration parts. Also related is static and kinetic friction related to the mass.

Short barrels might find it interesting to dabble with progressive rate springs.

 

Buffer.

How to Choose the Right Buffer for Your AR-15 Pistol

An AR-15 pistol is a handgun with a shorter barrel less than 410 mm that you can use with a hand. You can either purchase a mediocre or a high-quality AR 15 pistol or plan to build one from the scratch. However, before assembling parts and building an AR-15, you must get comprehensive knowledge...

mcsgearup.com

 

RickB says he has a CMMG with the radial delayed blowback feature. That's a totally different animal from a standard pistol caliber AR. There is no lockup of bolt to barrel, but there is an interface between the two that differs significantly from either a straight blowback or a conventional gas operated AR.

 

You are right about that. Just read his post on his make of gun. Does CMMG use the same kind of blow back system as H&K?
RickB maybe head over to these:

AR15 Forums

A forum community dedicated to AR15 firearm owners and enthusiasts. Come join the discussion about optics, hunting, gunsmithing, styles, reviews, accessories, classifieds, and more!

www.ar15forums.com

ar15.com - Your Firearm Resource. (AR-15, AR-10, M4, M16, AK-47, and More!)

Firearm Discussion and Resources from AR-15, AK-47, Handguns and more! Buy, Sell, and Trade your Firearms and Gear.

www.ar15.com

 

Cool tutorial, thank you.

2 takeaways form that.

In the AR platform design once the spring / buffer S/B) is installed the spring applies a constant pressure on the buffer/bolt even in battery so there is really no equilibrium for applied spring travel. As the blowback pressure level is in constant decay after the bolt opens and the spring force is in constant increase during compression It is always at some level of positive pressure. In the blowback design the maximum acceleration and moment of inertia (acceleration) will be at the start of recoil and the end of RTB. If the spring and buffer weights are in balance with respect to the blowback pressure level the cycling of the action should sinusoidal and at an amplitude sufficient to complete the extraction/ejection and feed process without causing unintended deviations in the cycling process (physical impedances or impacts).

If the S/B is to heavy there won’t be enough velocity to cycle the action, it with either FTE, FTF or FTRB.

If the S/B is to light or out of balance with respect to S vs B there are a myriad of symptoms that can occur, none of them are pretty.

Progressive springing would be and interesting approach. Wish I still by parts…

 

In the AR platform design once the spring / buffer S/B) is installed the spring applies a constant pressure on the buffer/bolt even in battery

Should be.

 

How about contacting CMMG? From what I've read they're nice guys to deal with. Maybe send them these pics and ask for their opinion on what setup you should be running.

 

I have a multi-page email chain going with their customer service, including pics, chrono data, etc.
It took almost three weeks for their initial reply to my inquiry, but since then, they have been very responsive, replying to emails same day.

They had the gun for a week, and they sent me a video of their tech firing 30 rounds through it; it functions fine. I'm shooting 1.5" groups at 50 yards.
I'm trying to come up with something better, in the interest of the gun not damaging itself, than their suggestion of first, heavier buffer, and then, reduced loads.
The instruction manual says the installed buffer is good for loads with power factor of 190-220, I'm at 207, so, why would I need a heavier buffer or reduced loads?

Looking around the World Wide Wasteland, I see it's not just me, and not just 10mm chamberings of the Banshee.
It's already a really, really expensive gun, so I don't want to just throw money at parts.

 

If the AR is made to proper specs the spring still exerts pressure while in battery. El Cheapo components often result in a gap, with the buffer resting against the stop pin (which in turn will eventually shear off).

 

Any vid of the action?

 

Action? Me stomping around, cursing?

 

Watched a video on the CMMG bolt carrier with the delay blowback and I still think our theory is somewhat correct.

From what the CMMG video said, these set ups can be tuned to handle different loads. My guess is that the OP's is out of tune or something is defective.

 

As stated in this thread several times start with a heavier buffer. I think they are classified as H3.

 

It has an H3 in it, now; it came from the factory that way.
I bought an even heavier buffer, eight ounces to the H3's five-and-a-half, but I'm concerned that the former is about an inch longer than any of the three buffers supplied to me by CMMG.
In stock configuration, the bolt face disappears into the upper in recoil, which leaves the rear of the ejection port exposed, so a longer buffer, which stops just forward of the rear of the port, would/should prevent cases from impacting the port? When the H3 already has three tungsten slugs in it, a buffer heavier than that would just about have to be longer; how else would additional weight be possible?
The gun runs, feeds/fires/extracts/ejects, and CMMG probably isn't going to replace it or "fix" it due to scratches that don't affect function.

I've seen vids of 10mm Banshees with the spent cases rocketing out of the port (Double Tap with claimed ballistics of 220grs at over 1250fps), when my ejected cases are dropping 2-3 feet away, so, I'm again having to ask, is my ammo too hot, or too weak; I don't understand the dynamics of the pistol caliber AR, or the radial delay system, to know?
Customer service recommends heavy buffer/reduced loads, which says, "loads too hot, slow it down", while the weak ejection and bullet weight/velocity says not hot at all, and slowing it down means .40 S&W ballistics.

I watched a somewhat mesmerizing slow-motion video of a 9mm, with the extracted cases spinning in the ejection port, kicked out, or not, by the bolt face as it returns to battery; the ejector appears to be doing nothing but separating the case from the bolt, and nothing to kick the case out of the port.

That doesn't appear to be exactly what's happening to me, in the sense that the case's rearward travel in the video stops within the length of the port, while my cases are still moving rearward and striking the rear edge, but I may be relying on the returning bolt, to some extent, for ejection. I've had no failures to eject.

I'm considering an extractor upgrade kit, which includes a spring, a post that sits inside the spring, and an O-ring that surrounds the spring, to see if the extractor isn't holding the cases securely enough for the ejector to do its job . . . but, if it's as simple as that, you'd think it would come from the factory with the best configuration.

 

RickB, contact this guy: Slash's Heavy Buffers | Home and see what his opinion is. I use their buffers in all my AR15 and AR10/LR308's. Hope this helps

 

Not to get too far afield from the topic I've established, but I was discussing my issue with a buddy who has a straight blow-back 9mm PCC.
He was getting bulged brass, decided his gun was extracting early, when chamber pressures were high, and that was causing his issue.
He started increasing buffer weight from the factory 3oz., to hold the bolt closed longer, until he'd reached eleven ounces, and was still getting bulged brass (the gun was still functioning correctly).
Deciding he'd misdiagnosed the problem, reinstalled the 3oz. buffer and started separating his ammo by headstamp.
Low and behold, certain brands of brass were bulging, while others weren't.
He'd spent money on parts, on ammo, following an incorrect path.

I'm trying to avoid doing that.
When someone suggested, "Try some spicier loads, it's a 10mm . . .", I thought, that's crazy, the problem seems to be ammo that, while not hot, appears too hot for the gun?
But maybe he's exactly right, intuition be damned.
Get those 200 grain bullets up to 1100-1200fps, and 180s up to 1200-1300, and see what happens? Does a FASTER moving bolt fix it?
That's contrary to what the manufacturer indicates, but I'm not trying to exceed normal 10mm loads, just get them to run in the gun without beating-up the ejection port.
Doesn't cost a thing, but a few grains of powder.

 

Another range trip, another scarred ejection port.
I shot loads pushing 180gr bullets at close to 1200fps, 200s @ 1000fps, a handload progression launching 220 grain bullets at 970-1050fps, tried an 8oz. buffer, then switched back to the 5.5oz (the heavy buffer sounded and felt very clunky).
The only change I could see was the cases hitting a different area of the port; heavy buffer caused cases to impact the lower half, while the lighter buffer showed impacts mostly in the top half.

I googled "banshee ejection port", and this problem is not limited to 10mm, and certainly not limited to me.
I haven't made any demand of CMMG, such as replacing my defective gun, as others, further along in their customer service experience with them, are getting form-letter style responses, like, "We have a lifetime warranty, so if the gun breaks or doesn't work . . .", and, "Rocks chip the paint of Ferraris just as they do Hondas".

I think I'm on my own, as long as the gun feeds, fires, and ejects.
I've ordered an extractor upgrade kit, and will try swapping springs, and adding the o-ring; the Banshee has a short, three-coil spring, and no o-ring, so there's something to experiment with.

It does seem to really prefer 180 grain bullets, groups shrinking dramatically as bullets get lighter.

 

Haven't got one but looking for the fix. Good posting.

 

Does the firearm have a fixed ejector? I don't recall if it is fixed or in the bolt head. If it is a fixed ejector, would "adjusting" it be a possibility? Such as on the 1911, direction can be changed by the angle on the face of the ejector. Could changing the length of the ejector be a possible option? longer to get it moving out earlier (as long as it allows a loaded round to be cycled out of the action), or shorter to delay it moving so it will not contact the ejection port?

Just thoughts I was having.

Good luck.

 

The ejector is a spring-loaded plunger in the bolt face. Some youtubers have made changes to the ejector spring, as they have with the extractor spring, but I'm still left to wonder if it's as simple as a spring change, why doesn't the gun ship with the correct spring(s)?
The gun is on its way back to CMMG, again, they've offered to refinish the upper, but I'm not interested in a fresh Cerakote finish over the jagged metal; fix it so that it's not damaging itself, then refinish it.

CMMG has not told me it's normal, they have not pushed back in any way, they've twice paid to ship my gun back to them for service, so at this point I'm hopeful they'll have a fix, but it is not going to be loads or buffers that fixes it, as I've already pursued that.

 

why doesn't the gun ship with the correct spring(s)?

Maybe the spring they used is a faulty batch, or, perhaps just a generic that works ok for some COTS ammo?

How could CMMG test the item w/o having your "problem" ammo?

 

All of this is precisely why I have not gone the pistol caliber route....yet.

I hope you get this rectified and right quick!!

 

I fired it off to the manufacturer just before leaving on a ten-day vacation, so there will hopefully be a resolution shortly after I return home; they turned it around in six days, last time.
I'd been working on a mechanical fix, but I may have to pursue adding material to the case deflector, so the extracted cases never reach the rear of the ejection port.