Cmmg Banshee and brass bulges

[Muskrat]

Ran a few hundred rounds through the Banshee with the 8oz buffer. It definitely slows the carrier down, but everything ran fine...even powder-puff loads (165 grains @ 1200 fps).

No idea how it affects brass bulging. I got a lot of bulging with A-USA brass, but none with S&B brass shooting 200 grains @ 1200 fps.

[phaloxx]

Ran a few hundred rounds through the Banshee with the 8oz buffer. It definitely slows the carrier down, but everything ran fine...even powder-puff loads (165 grains @ 1200 fps).

No idea how it affects brass bulging. I got a lot of bulging with A-USA brass, but none with S&B brass shooting 200 grains @ 1200 fps.

I'm telling ya that S&B brass is some stout stuff. Order a 100 round bag or 2 of Jaggemann brass stuff to before corona virus shuts down the country!

[BENTENMM]

I just noticed Sootch did a review, seems like he had to wait for his Sample. Unlike the the other Shills that had them 6 months ago

Sootch Banshee MK10 Review
https://youtu.be/ghmbx7Np5dY

On his pull-down of the carbine, a little more in-depth than others. I've come to realize a little more of how the thing is assembled, operates, and it brings up a few questions.

What is the total BCG's weight? Does the angled weight int he back of the carrier look to be made tungsten or stainless steel? Any chance anyone knows the weight of it?
How light does the spring on the bolt itself feel? Any known dimensions?

I'm just spit balling some ideas and some possible tweaks that could be made to perhaps offer a little more in the way of controlling un-locking of the bolt.. although just now after re-reading past post's with info from CMMG concerning the chamber lead and chamber itself being partially unsupported I'm not sure that it would help in case bulging.

Adding a stronger spring to the bolt itself to delay unlocking couldn't possible hurt anything or even be considered a modification that would void the warranty. Also checking to see if there could be a possible alternative to a carrier weight, maybe heavier.

Now for a crazy Idea that would most certainly void the warranty and possibly have ill effects. Would be to alter the angle and or length of the locking lugs themselves on the bolt. I would most certainly order another bolt for this.. but theoretically changing the angle or length of the angle would change the timing of the unlocking from the lugs of the barrel. However reducing the OAL of the locking lugs would create a gap in the lock up and could result in VERY negative results.   

These are just some random thoughts, I know it all seems crazy, as CMMG has had engineers design the MK10 with 1,000's of hours of work and 10's of thousands of rounds to produce and market what they have deemed most suitable for safety, reliability, and performance.

What are the lengths of the buffers the MK10 uses? Are the standard AR15 Carbine length? since the bolt length itself is essentially the same?

Aside from the random ideas and questions I would like to add that I really am still thoroughly impressed with the design of most all of the system. I wonder if it really does boil down to a chamber lead/chamber dimensions itself.. Perhaps a company down the line or even a custom barrel manufacturer could make one that would offer better support while still utilizing CMMG's radial delayed system.

Best of luck in finding the best brass and optimal loads for these.

[Muskrat]

Ya... I don't think the bolt opening early is the issue. I think the issue is that the Banshee chamber is not fully supported and even if you locked the bolt in place to make it a single-shot, it'll bulge the brass at a certain pressure.

The (my) Banshee only bulges full-house 10mm loads in good brass, or warm loads in very poor brass. So download a 200 grain slug to 1200 fps out of the Banshee rather than 1275~1350 fps, and you can reload the brass. Folks wanting to be able to reload Underwood-level loads just need to pick a different platform. You can still shoot Underwood-level loads, just not reuse the brass. Or bring it down ten or twelve percent from max and the brass is just fine.

I'm pretty happy with that. I just think CMMG should have be up-front and center with that information rather than dolling it out to customers who buy the gun and then think "WTF!?!" when they collect their brass.

Range report...about 1,000 rounds through it, and the only malfunction was a hand-load that somehow ended up really long. I'm not getting any bulging from well used S&B or Starline brass pushing 200 grain bullets to 1210 fps, or 165 grain bullets to 1420 fps. If that isn't enough plinking-power then I'd recommend the .458 Socom chambering...

165 grain Blue Bullet over 9.7 grains of Power Pistol clocks in at 1421 fps and is FREAKISHLY accurate from my gun...20 rounds into a quarter-sized hole at 30 yards, without really trying very hard to keep them tight.

This isn't the gun for everyone, but if you want one and are worried that it's a brass-eater, it's not, or at least it doesn't have to be...you just need to choose how you feed it.

[Pablo]

I actually want to order one. Bummer is all our ranges are closed due to C-19. Ugg....

So any more teething issues? What are they selling for at retail? TIA

[terdog]

I don't think that your going to find "a deal" on 1, especially right now. When I bought mine about a yr ago, I think all my searching netted me $150 or so off retail.
I enjoy mine.

S&B is pretty much all that I run because its the best combo of affordable and better than 40 while still be "10mm" level.

[Pablo]

I don't think that your going to find "a deal" on 1, especially right now. When I bought mine about a yr ago, I think all my searching netted me $150 or so off retail.
I enjoy mine.

S&B is pretty much all that I run because its the best combo of affordable and better than 40 while still be "10mm" level.

Thanks. Not looking for some killer deal, let me talk to my FFL's in my area - just didn't want to find out they are asking some stupid above retail price.

[PointBlank82]

I'm buying a used 10mm Banshee 300 tomorrow and intend to try some loads with AA#9 and the new AA#11FS to keep the pressures down. Will let you all know what I see.

Will try 180 gr pulled FMJs and some 220 gr Plated RN. Maybe some 200 XTPs one I dial things in.

I think they key for this gun is to avoid the peak pressures you get with the medium speed powders and use better brass. I scored 3k 10mm mixed brass for $265 shipped so will sort out all the A brass and stick with S&B for these trials. I have a shitload of virgin Starline too.

[PointBlank82]

So I've run a bunch of reloads thru my Banshee, 300 180 gr FMJ over 8.5 gr LS w/ CCI #300 and #350 primers. Brass has a minor bulge, but nothing my standard dillon dies cant iron out.

The 9.5 gr LS loads wreck the brass for sure and send them into Canada. I have an 8oz buffer on order from CMMG that might help with full power loads. Recoil difference is negligible as the compensator likes the extra gas.

[Muskrat]

 The 8oz buffer might help you collect some brass, but I don't think it does anything for the bulge. Near as I can tell the bulge happens with the bolt full-closed, and early opening isn't the issue. I think there's just that much unsupported area around the case head with the bolt closed.

The heavy buffer probably does help reduce case separation with full power loads, as the brass has a chance to constrict a bit before the carrier starts moving. I've read about hot loads separating in the Banshee, but I've never experienced it...despite running Underwood and full-house Federal loads through the gun.

I'm pretty happy with the set up, all in all. The Banshee is basically a toy, so 80% loads are fine for shits n' grins, and you can reload them all day long. If you want to shoot full-power or nuclear loads, you just have to discard the brass. In exchange for that you get a platform that will run any-n-all 10mm loads with the monotonous regularity of an atomic clock. So far as I've heard, it's the only 10mm pistol-carbine that even comes close to achieving that.

I still want to score fifty 10mm Magnum brass to cut down for the Banshee. Might work better...might not.

Great toy though...the fact that it runs every cartridge, day-in and day-out, is what I love about it. I just won't tolerate a finicky repeating firearm, and especially not a automatic. If I can't just grab a box of any ammo in my trunk, then load the magazine and shoot, the gun is worthless to me. The Banshee makes the cut.

[SteveinNC]

Well fellas I had a chance to run some reloads through my Banshee and record velocity, case bulge diameter, and accuracy to start a little database of info here to see if we can find that sweet spot for each bullet weight to where the case bulging just gets to be a bit much in our guns.
I tested Longshot, 800x, Blue Dot, and BE-86.  Started with starting level loads and stepped up to .3 increase from starting to see where we stood before going any higher.  Also fired some factory rounds for accuracy and testing case bulge.  Here is a quick rundown of my range testing:

Pistol: CMMG Banshee Mk10 300
Sights: Midwest Industries base mount and Trijicon MRO 2MOA RD sight
Range:  All accuary tests below were shot at 25yds except for the last 2 factory loads were shot at 100yds for POI testing.

Cases: FC  (All cases were from an original batch of "FBI" loads from years ago)
Primer: Win WLP
Bullet: 180gr CMJ Hollowpoint
COAL: 1.252"

Factory: 180gr SIG Performance Elite for initial sight in and shot a 3 shot group.  These were the first rounds from a completely cold weapon on a hot NC day.  90F and probably 70% humidity.

Velocity: Avg=1241fps  1156,1259,1271,1262, & 1259
Accuracy: 1/2 to 5/8" 3 shot group.
Case Bulge Diameter: didn't record it but visual inspection when picking up brass didn't give any excessive alarms.


BE-86:
==========
Wgt: 7.7gr
Velocity: Avg=1265  1277,1273,1275,1270,1229
Accuracy: .688" for all 5 shots
Case Bulge Diameter: .4305"

Wgt: 8.0gr
Velocity: Avg=1271  1268,1257,1270,1273,1287
Accuracy: 1.120" for all 5 shots
Case Bulge Diameter: .4315"

LongShot:
==========
Wgt: 8.5gr
Velocity: Avg=1176   1181,1169,1197,1162,1172
Accuracy: 1.430" for all 5 shots
Case Bulge Diameter: .430"

Wgt: 8.8gr
Velocity: Avg=1241  1217,1244,1246,1237,1263
Accuracy: 1.170" for all 5 shots
Case Bulge Diameter: .431"

800X:
==========
Wgt: 8.5gr
Velocity: Avg=1267  1252,1266,1331,1268,1218
Accuracy: 1.250" for all 5 shots
Case Bulge Diameter: .430"

Wgt: 8.8gr
Velocity: Avg=1326  1319,1338,1337,1315,1321
Accuracy: 1.040" for all 5 shots  (1 loose shot, 4 shots =.700"
Case Bulge Diameter: .432"

Blue Dot:
==========
Wgt: 9.8gr
Velocity: Avg=1134  1163,1132,1136,1106,1131
Accuracy: 1.530" for all 5 shots
Case Bulge Diameter: .4305"

Wgt: 10.2gr
Velocity: Avg=1175  1173,1197,1162,1180,1164
Accuracy: 1.750" for all 5 shots
Case Bulge Diameter: .431"

Hornady Custom 180gr XTP Factory
100yd POI testing
4" high at 100yds from 25yd zero of SIG 180gr Elite ammo.  So this is hotter than the SIG stuff
Accuracy:  3 3/8" 5 shots
Case Bulge Diameter:  .440 to .454"!!!!!   these cases were scary to pickup and look at

SIG Performance Elite 180gr FMJ Factory
100yd POI testing
Dead on at 100yds from 25yd zero of this ammo.
Accuracy: 9 1/4" 5 shots (9 1/4" wide and 2 1/4" tall)
Case Bulge Diameter: .435"

These rounds were fired in this order and the gun wasn't cooled off or nothing between groups.  So by the time I got to the 100yd impact testing the weapon was very hot to the touch.  I wonder if the Hornady 180gr XTP factory loads would bulge that much if fired in a completely cold weapon?  Future experiment there.  I didn't have velocity numbers for the 100yd testing because I had to swing over for the 100yd burm and didn't move my chrono over and set it back up.

Hope this helps.  Will post more data as I shoot this thing more.  BE-86 right now is giving we very good raw accuracy.  But the heavier 800X charge just might be telling me something.  Blue Dot isn't even in the ballpark.  Plus I don't know the characteristics of this gun yet to know if it starts walking when hot, how this RD MRO sight is for repeatability etc.  I might transfer the 1.25-4x Leupold scope from my AR over to this platform for some better accuracy testing.

Steve

[Muskrat]

Good stuff Steve!

At this point I don't even consider brass bulged unless I can see the bulge before I pick it up. As long as they'll fit through the resizer without stripping off a ring of material, I consider them good to reload.

In my experience Blue Dot gets more accurate towards the top end, not really coming into its own until about 10.4~10.6 grains with a 180 grain bullet. Blue Dot has provided some of the most accurate loads I've ever worked up in 10mm.

I was getting pretty concerned with brass bulge...Underwood loads and Federal Trophy Bonded bulge like crazy...but I've yet to have one come apart. I think the heavy buffer is a reasonable safety precaution when shooting those loads. I haven't heard of any rupturing in the Banshee, but I have heard of them tearing in half and leaving part of the case in the chamber.

I've not seen any big discrepancy in accuracy between a cold and hot barrel, but every gun is different.

[Kenk]

I second the BD accuracy, at least in a pistol format

[SteveinNC]

Good stuff Steve!

At this point I don't even consider brass bulged unless I can see the bulge before I pick it up. As long as they'll fit through the resizer without stripping off a ring of material, I consider them good to reload.

In my experience Blue Dot gets more accurate towards the top end, not really coming into its own until about 10.4~10.6 grains with a 180 grain bullet. Blue Dot has provided some of the most accurate loads I've ever worked up in 10mm.

I was getting pretty concerned with brass bulge...Underwood loads and Federal Trophy Bonded bulge like crazy...but I've yet to have one come apart. I think the heavy buffer is a reasonable safety precaution when shooting those loads. I haven't heard of any rupturing in the Banshee, but I have heard of them tearing in half and leaving part of the case in the chamber.

I've not seen any big discrepancy in accuracy between a cold and hot barrel, but every gun is different.

I'm building a 1911 10mm using an original Colt Delta Elite slide fitted to an oversized Les Baer frame.  Did all the filing and fitting myself.  The gun is functional right now but still have more mechanical work to do and a lot of small cosmetic work.  Then I'll get some reloads run through that and will concentrate on heavier BD loads as suggested.

I think I am going to transfer my Leupold scope over for some repeatable accuracy testing for now.  And also do some heat tests to see how much influence heat my have on chamber pressure and bulging and also affecting accuracy.  If I find it does walk, I'll tear it down and go through it and see what if anything can be done to improve this.

Hopefully we can get a good database of info built up here by comparing notes using several guns.

Steve

[SteveinNC]

Got some more data fellas.  I read earlier in this thread (possibly a different thread) about CMMG recommending Hornady brass to help with case bulge.  So I have to know so I sectioned 6 different case today with the data collected below.  See the included image also of 5 or those 6 cases for you own visual reference to go by.

In the attached pic the cases by brand from left to right are: 
FC(Heavy), Starline, S&B, Hornady, SIG.


The reason for the FC heavy is that of the FC cases I have which are from the late 80's "FBI" load vintage.  There is 2 distinct lots in this brass.  One headstamp where the FC is smaller and embossed much deeper in the brass weighs a lot lighter.  The more shallow and larger sized FC weight much more.  I will get one of the FC light cases sectioned and compare to the heavy lot# and post back.  Will also get pics of the CBC sectioned case.

Case Brands                           
SIG       CBC        S&B           Speer  Starline  Hornady  FC (light) FC(Heavy)  LAX
75.1      76.6        72.3           68.0    71.6        69.9         71.6          78.3            75.6           = Avg wgt of 10 cases (gr)
0.0100   0.0100   0.0095                   0.0090    0.0100                      0.0100                         = Neck wall thickness
0.0330   0.0330   0.0275                   0.0270    0.0265                      0.0320                         = Wall Thickness at .300" above case head/bolt face
0.5520   0.5460   0.4810                   0.5360    0.5100                      0.6580                         = Distance from case head to end of taper
0.1590   0.1770   0.1690                   0.1650    0.1660                      0.1920                         = Thickness of case head webbing
                           
Speer 200gr Gold Dots = .435" case bulge


Will post more data when I get it.  But judging by these raw dimensions, the Hornady bass doesn't appear to be only stout sort of speaking.  Granted these measurements don't prove anything about the metallurgy of the brass itself.  But its still interesting none the less.   My experience with Hornady brass with 2 different bottleneck rifles cartridges is that it is really hard and too brittle.   Have gotten splits up the side of the body and necks on 30-06 and 243 brass on more than 1 occasion sometimes on the first reload (obviously 2nd firing after factory).

Hope this helps,
Steve

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