by Tom Gaylord
Writing as B.B. Pelletier
Crosman’s DPMS SBR full auto BB gun.
This report covers:
- Never run out of bullets
- The feel of the gun when firing
- Here we go!
- Left cartridge first
- Copperheads first
- How does it feel, single-shot?
- Air Venturi Steel BBs
- Hornady Black Diamond
- How many shots?
- Using the BB speedloader
- Full auto
- Test 1
- Test 2
- Test 3
- Test 4
- Test 5
- Test 6
- Discussion
- Test 7
- Shot count
- Feel of full auto
- Trigger pull
- Forgot I had to cock it
- Summary
Never run out of bullets
The first part of this report didn’t receive that many comments, but those who did say something said similar things. The first was you all want this gun to never run out of BBs. You want it to get no less than 150 shots before it’s time to reload.
When I was a kid I wanted the same thing. I wanted all my guns to hold an infinite numbers of bullet, so they would never run out. Then I went into the Army and got to shoot many fully automatic weapons. I quickly learned that the first thing you want in a machine gun is reliability.
I remember that the M85 .50 caliber machine gun that was designed for fitting inside the turrets of armored vehicles was the worst machine gun to exist since the French Chauchat of WWI. It jammed all the time and seldom would fire an entire belt of ammo without stopping. You had to lubricate the cartridges with fireproof hydraulic oil to keep the gun operating.
The M85 .50 caliber machine gun was designed to fit in small spaces. Too bad it didn’t work!
“Oh, but with this gun the tank commander can stay buttoned-up while he shoots!” Yeah? Well then why did the M1 Abrams tank, the tank of the 21st century, get the M2 machine gun that was first issued in 1933 for its commanders? Because the more modern M85 didn’t work! Nice to stay buttoned up. Better to have a gun that works.
Bottom line — reliability in a full auto gun is the most important thing. After that comes the number of rounds it holds. So, guess what I’m going to look for today in the DPMS?
The feel of the gun when firing
Reader Halfstep asked me to comment on the feel of the gun when it fires. He remembered my comment about the Umarex MP40, where I noted that even when you fire one round it feels like it’s shooting full auto. I will look at that today.
Here we go!
I really wanted to put CO2 cartridges in this gun and start shooting it when I wrote Part 1 last week, but I held off until now so I can get an accurate shot count. We agreed that this is probably a party gun, so gas consumption will be high when we use it. I just wanted to give you an accurate account.
Left cartridge first
I remembered to install the left CO2 cartridge first. That seals the valve. If you install the right one first it will just leak out. The sealing was quick and I appreciate the Allen wrench that’s inside the magazine for piercing.
To load the BBs I used the speedloader that Tyler talks about on the video I asked you to watch. It is so easy to use! And I have a problem that most owners will never face. Since I want to test the velocity of several different BBs I can’t just pour a bunch of BBs into the loader and then load the mag. I have to go 10 at a time, so let’s see how that works.
Copperheads first
This is a Crosman gun, so Crosman Copperhead BBs are first to be tested. Copperheads averaged 414 f.p.s. for 9 shots. I will explain why only 9 in a moment. The spread went from a low of 405 to a high of 433 f.p.s. That’s 27 f.p.s.
After the mag was finished the gun continued to fire tor 4 shots. It’s not supposed to do that. When I loaded the next mag I noticed one Copperhead BB was still in the mag. They are copper-colored so you can tell them from silver BBs. That means the number of shots in that first string was 9, not 10. And that last BB was holding the magazine’s follower from coming all the way up, which must be how the gun knows the mag is empty so it can stop the bolt. I will say more about this in a moment.
How does it feel, single-shot?
I was shooting single shot so I can evaluate the feel upon firing. It does shudder a little like the MP40, but the shudder is not as pronounced, nor does it last as long as the MP40’s. However, the blowback does give you a good feeling of firing.
Air Venturi Steel BBs
Next to be tested were Air Venturi Steel BBs. They averaged 410 f.p.s. with a low of 403 and a high of 416 f.p.s. That’s a range of 13 f.p.s., which was the tightest I saw in all the tests.
Only 9 BBs came out this time, as well, but the gun didn’t fire any blank shots after the string. When I removed the magazine I could see the follower had risen as far as it could. Yet when I loaded the next 10 BBs, there was still one of these left in the mag.
I think the magazine is a little rough on the inside of the BB channel and may need a break-in period. I need to watch it as the test progresses.
Hornady Black Diamond
The final BB I tested was the Hornady Black Diamond that Umarex sells. They averaged 418 f.p.s. with a spread from 411 to 428 f.p.s. That’s a range of 17 f.p.s. All ten BBs fed this time and the gun stopped shooting after the last BB was fired.
How many shots?
To this point I have fired 34 shots. All were fired semiautomatic, which means one at a time. Now it was time to Rock-N-Roll!
Using the BB speedloader
The BB speedloader was easy to use, though the plunger didn’t always want to go down. I found that it helped if I angled the magazine down, so the BBs that had just loaded rolled out of the way. I wouldn’t want to load this magazine any other way than with this speedloader, so I’m happy Crosman provided it with the gun. And, it loaded 10 BBs as easily as it did an unlimited number.
Full auto
I can’t just pour BBs into the speedloader. I have to know how many are in there because I can’t count the shots in the full-auto mode. I know — poor me. Well, it’s a tough job but somebody has to do it.
Then it hit me — of course I had to count when I shot semiauto, but I thought I had to count all the BBs for full auto too until it dawned on me that the magazine only accepts 25 BB max. Duh! Just fill it and shoot it. It has to be 25. It doesn’t get any easier.
Test 1
This was a test of the effect of short bursts on velocity. I shot a burst of 6-8 rounds, and followed it with a single shot semiauto. I shot the Black Diamonds because they had no feeding issues. First burst was followed by a shot at 407 f.p.s. A second burst was followed by a shot at 400 f.p.s. Then I shot off the rest of the BBs and reloaded.
Test 2
Still shooting Black Diamonds. A short burst was followed by a shot at 391 f.p.s. A second short burst was followed by a shot at 386 f.p.s. A third short burst was followed by a shot at 372 f.p.s. I didn’t have to dump the mag because that was the last BB. I reloaded.
Test 3
Black Diamonds again. Long burst of 15-20? shots, followed by a single shot at 351 f.p.s. Shot off remaining BBs and reloaded.
Test 4
Long burst, followed by a single shot at 339 f.p.s. Reloaded.
Test 5
Long burst, followed by a shot at 315. Then fired the rest of the shots.
Test 6
Then I took an hour break for lunch. That was followed by another full mag of Black Diamonds. The first shot from that mag went out at 376 f.p.s. Followed that with a short burst and a shot at 354 f.p.s. Another short burst and a shot at 335 f.p.s. Another short burst and a shot at 317 f.p.s. Fired the remaining shots. Then I reloaded.
Discussion
Notice that the long pause caused the velocity to rise considerably. So there is a cooling effect on this gun. But it does not seem to affect the shooting. It never freezes like some CO2 guns have been known to.
Point two is the two CO2 cartridges now have fired 184 shots since they were new and they are still going strong. If you were shooting at a party you would never notice the drop in velocity. And, since the gun is still going I loaded another 25 Black Diamonds.
Point three is since I started shooting full auto there has not been a single malfunction or failure to feed. The gun now stops at the end of the mag, period! I think this magazine has broken in.
Test 7
I wrote up the previous part of the report, so the gun got to rest for another 10-12 minutes. The first shot after that went out at 313 f.p.s. Okay, she’s now running out of gas. Short burst followed by a shot at 287 f.p.s. A second short burst followed by a shot at 250 f.p.s. Final burst to clear all the BBs out and the gun continued to fire after it was empty. Then the bolt locked up and the gun stopped shooting. I removed both CO2 cartridge (right one first) and they each had a very small amount of gas in them.
Shot count
In today’s testing I got a total of 209 shots from two CO2 cartridges. I have described every shot for you, so you now have a good idea of what you get from the DPMS.
Feel of full auto
The DPMS has a heavy recoil, so shooting full auto is very pleasurable. The cyclic rate is much faster than the MP40, so it’s a different feel, but it’s still a very realistic feel. This is definitely going to be a crowd-pleaser and a party gun!
Trigger pull
The DPMS trigger I’m testing is two-stage and heavy. I measured stage two at 10 lbs. 6 oz. It doesn’t feel that heavy because of the pistol grip, but that’s what it measured.
Forgot I had to cock it
If there was one thing I kept doing wrong throughout the test it was forgetting to cock the gun after it had stopped firing. That is very realistic and not at all like a video game, so bravo for Crosman!
Summary
I don’t need to wait to say this. The DPMS is a best buy! If you want full auto that’s affordable, this is the way to go. I’m still going to test the accuracy, of course.
BB,
Does your chronograph not record full auto shots?
Edw,
My chronograph can sometimes record full auto shots but with the movement of the gun it can get confused.
No chronograph I am aware of can record each any every shot when shot full auto, so I prefer my system for recording the shots.
B.B.
I don’t have anything full auto to test… But with mine it will record shots faster than I can see if exposed to florescent lights. So I’d guess the Hardware is up to it as long as projectiles aren’t doubling up in the screens.
Could you pop off a couple strings next test and see what happens?
Edw,
I have done that. What I get is one velocity for one of the burst of shots.
B.B.
B.B.,
Very nice. Looks like a ton of fun. Yes, reliable feed is key, even in a M-rod type mag.. Good price too.
Me being me and knowing that air guns are not made with the best quality of metals,…. this thing is putting some pretty severe abuse on some internal parts. How long can this survive would my key question?
I am sure? that Crosman asked the same and hopefully incorporated high quality steel in (just the right) areas. Some high quality lube in those areas would also be key.
Perhaps we will see customer/user reports in the future that say,.. “mine croaked at 5,000”, or 500? Or,… “I have put 30,000 through mine and nary a problem”. Time will tell.
Good day to one and all,…… Chris
Yes it would be nice to take advantage of the fact that it does not freeze up with a very large capacity mag.
What do you suppose is preventing it from freezing up? The shear mass of metal involved with the mag dissipating the cold or the small amount of passage way space between the CO2 cartridge and valve? Heck it could even be warmer air being pushed on it from the bolt cycling or a combination of them all.
The good thing about that trigger pull is you only have to pull it once if you want to!
I guess this is a good as place as any to mention to those who never read my earlier blog entries on the DPMS that the fat flash hider/compensator on the end of the barrel unscrews ‘Counter Clockwise’ and leaves14mm Airsoft threads exposed that will accept all sorts of outer barrel extensions, flash hiders, compensators and imitation sound suppressors. The inner barrel will not fall out.
I installed that custom pistol grip and it really helps control the rifle with all its weight, not to mention it is totally comfortable to hold.
If I remember right I had to drill out the small hole in it that contains the safety selector detent spring. It was not deep enough and put too much tension on the lever to operate easily.
If you remove the stock grip watch out for that small spring and plunger pin on the right side just under the selector shaft pin to prevent it from flying out and getting lost. Same as a real AR15.
I added a removed HellBoy barrel to the front of mine with some Airsoft outer barrel extensions and a small fake silencer to retain it and it increased the FPS to over 500. A bit long but worth it. I may get another and keep it short.
If you type ” Something else ” in the search block it will take you to another July 17, 2018 blog that has another picture with just an outer barrel extension, grip, railed scope, bipod and compensator added, no extra barrel.
Scroll further down that blog and you will come across two pics of my custom Marauder PCPs that you might enjoy if you are into this DPMS. They gave me a nomination for “King Of Tac-T-Cool. 😉
Bob M
Click on pics to expand them. Took me a long time to figure that out. Must be getting old!
CORRECTION to above !
OK its after 2:20 AM and I’m tired … the correct search entry for additional pics is ” Always Something ” ,
NO T” Something Else “
Bob,
If I was to ever get one,…. I would make a force fed tube mag.. Or,… I would end up with a pile of scrap (at least the mag. parts) anyways. I would not be happy until that thing could dump 150 bb’s on a single trigger pull. I will steer clear for now.
You do nice work and I highly admire your modding instincts/talents.
Chris
Bob M,
With my MP40, I think that all the mass of the mag is what retards freeze up. By having the co2 and valve in the magazine proper, owning multiple mags will allow you to change to a warm mag while the previous mag recovers, reducing the chance of freeze up even further.
I have done some tests with the MP40 that show that you can get a higher, more consistent average velocity by shooting in full auto than you get in slow fire single shot mode. You do get fewer shots on full auto but it’s not that many fewer and it’s worth the higher velocity, IMO. I think the cold doesn’t get to sink in until the mag has been emptied of BBs because of the fast rate of fire. In slow fire each shot makes the next shot a little slower.
Half
Half
Makes sense, The mag empties before it has time to cool everything down and get frosty.
In contrast Airsoft mags can be had with hundreds of rounds to fire, so electric motors probably work out better for them on machine guns.
CO2 still remains functional and practical for sniper rifles and pistols with relatively low capacity mags.
So my desire for a higher capacity mag for a full auto CO2 rifle may be impractical…. unless of course they design a mag that will not frost over or is designed to work with high pressure air, like a refillable bottle that would fit inside or look like an under barrel M203 grenade launcher ! …. or everything is contained in a box mag like an M249 SAW.
Boy, talk about a hip fired fun gun that would be. But something like that may be better off remaining in the realm of Airsoft. It could turn out to be devastating were someone to get carried away with it.
Thanks for the info,
Bob M
BB,
The reality of it is this gun will be very expensive to own. Do you think anyone who buys this will not soon have to buy extra magazines? I had the pleasure of playing with a friend’s M712 a while back. He had three magazines for it. It took about as long to change a magazine as it did to empty one. I spent the vast majority of my time with it reloading the magazines.
Then there are the CO2 cartridges and bbs. Of course you can offset that cost a bit because soon you will be able to go into the scrap metal business.
I am awaiting my invitation to the party.
Speaking of mass quantities of BBs when I was younger and in school I had a soft cardboard target box set up with some old clothes inside to stop and capture the BBs shot from my Spitten Image 1894 spring powered rifle and I reused them over and over with out any problems. Was I alone in doing that ?
Bob,
As kids, pellet guns were our weapons of choice for outdoor use. In the winter we would shoot BB guns indoors.
The back-stop for our indoor shooting range was a blanket draped over a 2×4 so that it didn’t touch the floor. The blanket was light enough to move easily when the BB hit it but had a weave tight enough that the BB wouldn’t penetrate.
The base of the frame that supported the blanket was lined with a sheet of heavy plastic sized such that it made a trough so that gathering up the BBs was easy.
We used to hang bottle-caps on string as targets. One of my friends made motorized targets with paddles that were fun to shoot at.
Something to do over the long Canadian winter 🙂
Hank
Hank
In your case it was the laws of mother nature that kept you shooting indoors. In my case it was the laws of man, all year round! You did get pretty creative.
In hind sight it was much more practical to capture and contain the BBs when shooting inside a house and any slight damage that a BB may have received had no real effect on accuracy when reusing it at such close range and plinkers were, well kind of disposable or not really affected much by a slightly damaged barrel if it happened at all.
Bob,
We checked over the “previously-used” BBs and even the ones that had been shot dozens of times didn’t show any (noticeable) signs of damage and worked was well as fresh ones.
The trick, we found (way back then) was to use a soft, light blanket (think they are made of a cloth called “flannelette”) to “catch” the BB and suck the energy out of it. Then it just drops straight down into the trough.
I use the same principle of trap for my slingshot back-stop that is made from a wooden shipping crate. Because I am dealing with a lot more energy I use towels on coat hangers hung at 45 degrees to line of flight – works quite well.
Hank
“I quickly learned that the first thing you want in a machine gun is reliability.”
Amen, B.B.!
I would even extend that to any gun, but especially battle and self defense guns.
Thanks for the info about the M85 and the Abrams tank; I was not up on that, and that’s another thing I like about your reports – the history lessons!
Due to our current laws limiting firearm submachine gun ownership to the pre-1986 pieces, this looks like a great alternative for those wanting to have a full-auto fun gun.*
(I’ve’ shot an actual Sten and an UZI…and yes, it was fun! =>)
Thanks again, B.B., for another interesting report,
take care & God bless,
dave
BB
Nice with the reliability once you did some shooting time with it.
And what I noticed about how many shots you got out of the two cartridges equals out to about what one cartridge equals out to on some Co2 guns that only hold 1 Co2 cartridge. What I’m getting at is 100 shots per Co2 cartridge. So even though the gun is using 2 Co2 cartridges tour still getting good shot count.
And it sounds like it will be a party pleaser. But remembering what Bob M’s gun did accuracy wise. It will need to be a bit better. But then again when your in full auto your just pointing and adjusting your aim.
And that makes me wish it held at least 30 rounds or more once you start getting on the target in full auto your out and you got to refill.
If Crosman would make a bigger capacity mag to me it would be more fun. Especially since it’s been determined reliable so far.
Gunfun1,
Maybe Crosman engineers should be given a little more credit. Maybe they limited it to 25 shots knowing that if filled to 30 shots you would experience problems with the CO2 cooling the mechanism too much and decreasing reliability.
Siraniko
Siraniko
Probably true on most Co2 guns. But also it don’t affect some as much.
And another thing when your plinking at a can and spraying full auto your always adjusting your aim point when the cans moving around. So for the most part you don’t notice the gun slowing up that much unless the cartridge is getting low.
And then there’s always the posabilty to convert it to a tethered regulated HPA bottle. Then you for sure would want the extra capacity of ammo.
Surprised I never really heard of the M85 although I do remember seeing that distinctive flash hider sticking out of some vehicles in movies. Looks like it was also set up for use in an aircraft wing pod.
I found some pics of what looks like a serviceman’s service and inspection booklet for it. Very entertaining and simple to understand. They used drawings of scantily clad dancing girls acting as narrators in a very cartoonish way to obviously keep a soldiers attention going. Times have certainly changed.
Bob,
That’s Connie Rodd! She was the star of the maintenance comic books that the Army circulated for a great many years. Many people thought her first name was short for Constance — as in Constance Maintenance. She was joined in the late Vietnam era by a black woman whose name escapes me.
I knew the real Connie Rodd (Susan Bottoms) who worked at Blue Grass Army Depot in Kentucky. When I worked at Ft. Knox as a maintenance instruction she wrote the PS magazine I refer to. It was published from 1951 through today.
B.B.
BB
Very interesting subject there and fascinating bit of military history to read about. Did some research on Sgt. Connie Rodd and Joe Dope and PS: The Preventative Maintenance Monthly. Evidently the publication never entered the field of Aviation, or the Navy?, for I surely would have remembered reading it.
Tom you certainly are a well spring of knowledge and not just an Airgun Reviewer. But, you are very good at that part of our education when you get into it.
Bob M
BB
I thought about posting a picture of ” Connie Rodd: Buxom Star Of The US Military Guide To Keeping ‘Weapons’ In Shape ” but I think I’ll let you make the call on that one. 🙂
Bob,
I would settle for a link,….. (purely for historical reference and education purposes),.. mind you,… 😉
First I have ever heard of this educational, attention keeping method of teaching. Quite clever. I remember having an Algebra teacher that was quite the “dish” from a Freshman’s perspective. A bit foggy now,…. but I do remember what she looked like,.. and coincidentally,… not so much on Algebra. Just sayin’. 😉
Maybe not best educational method after all? Especially for things that you may need to learn to save your life. I can imagine though that the instructor has/had methods of “re-focusing” the class in cases of the class “running amuck”.
Chris
Chris
I afraid you may have to look that one up on your own. At that time in life it was perfectly acceptable and it’s in no way pornographic, just a little racy but by todays standards it may be looked at as exploitive by some and not to relevant to Airguns.
Bob,
Just did a search based on your reference(s) above. Yea,…. me thinks (not) appropriate. 🙂
Chris
A few specific questions please:
1. So what would be your #1 bulk BB brand/model choice to buy for this?
2. So you can put an OEM AR grip on like a normal AR lower (with a little drill mod for the spring – or spring snipping would work)?
3. Would you invest in more mags, or is the 1 included good enough?
4. So it comes with the speed loader or you need to buy seperate?
5. So what would be your #1 bulk Co2 cartridge brand/model choice to buy for this?
6. When you change a co2 must you change both every time?
TY! I’m new to this world but love the idea for my yard.
BlackRifle,
Welcome to the blog.
Until I do the accuracy test I want to hold off on naming a best bulk BB for the DPMS. I think I know what it will be (Hornady Black Diamonds), but let’s wait and see.
As for the CO2, buy the cheapest cartridges you can find. Though there are several different brands, they are not all made by those companies. A CO2 cartridge filling line is very expensive to set up and operate, so only a few manufacturers make all the cartridges. So one is pretty much as good as another.
Buy them by the bulk box. Here are 500:
/product/crosman-12-gram-co2-500-copperhead-powerlet-cartridges?a=76
B.B.
BlackRifle
With a moniker like that I can certainly tell where your interest in guns is. When I first started blogging mine was ‘Max Firepower’ but it turned out to be too long for me and it fit my image better when talking about real firearms.
I would not guarantee that all AR pistol grips are exactly the same or that the spring on this air rifle is Mil Spec in size.
Some aftermarket airgun pistol grips are gun specific and not interchangeable. The ones that are made for a real AR’s have the spring retaining hole and mount hardware that fit this one. Some Airgun aftermarket grips have neither.
Airgun receivers are not made to be interchangeable with real firearms so their may be slight differences that caused the spring fit problem I had.The grip I chose is a custom design anyway and may have added to the problem or it was just not properly drilled in the first place, who knows. The drill may have only widened the bottom of the hole to match the opening?
My advice, If there it a spring installation problem I would make the pistol grip fit the receivers operation as I did . You can always fill a hole later but you can’t make a spring grow, and function the same.
You will spend the same amount of time filling a second mag but if you want to continue firing after the mag runs out get another. Switching them also gives them time to warm up again and perform a little better.
One point, It is not advisable to leave a CO2 cartridge in the mag for any length of time after your done shooting. Not good for the seals, so plan ahead to shoot them out till they are empty, or just dump the CO2 and remove them.
It comes with the speed loader.
Not sure on the mag replacement question. I believe there is a transfer valve of some sort in the mag. The left one should operate first. If you remove the left one it will dump the pressure in the right one. You should be able to leave the left one in empty and only use the right one and replace it when empty.
Be sure to read all the info and reviews on the Pyramyd AIR site.
Am new here, love the blog. Bought one of these today, and OMG what fun! I am a novice with just a few co2 pistols and a break barrel pellet gun, but i love shooting them and this one takes the cake. Thanks for having me here
T Bone,
Welcome to the blog.
B.B.
as a second post on this rifle, my magazine started leaking c02 within 500 rounds of using it,after looking through the blog archives i found BB’s article about the leaking c02 subject in general not about this gun, I tried using automatic transmission stop leak instead of pellgun oil…….worked like a champ! I have bought 2 other mags for this rifle and have only used the trans stop leak on the original, 2 months later no leaks whatsoever and i have left c02 carts in it for weeks at a time with no leaks and no ill effects. thought i would throw that one out there.
Thanks BB!
T Bone
T Bone,
Isn’t that stuff fantastic?
B.B.
more than fantastic, i am strictly using the auto trans stop leak on this mag, using it on one c02 pistol i have also. bought some cheap 1 oz plastic bottles with tips on them to dispense it. am strongly starting to lean towards using it all the time on all my guns…………what are your thoughts?
t bone
T Bone,
I can’t think of a reason not to.
B.B.
Nouser
I am replying to a comment that was evidently made over a year after this blog came out. It was emailed to me but I do not see it here for a direct reply.
In short Nouser questioned my decision to put an extended barrel and a $200. scope on a smoothbore BB rifle as they are not known for being very accurate or known to shoot very far in the first place. (See my picture entered earlier in this blog) Is it practical? Probably not. it’s just tinkering around.
First off that is a Bug Buster scope, cost under $100, and is intended for short range shooting, down to 3 yds. It also helps to see the intended target and where the BB is hitting. When you are over 70 years old and have trifocal glasses. It really helps. I have over 25 scopes and it’s not enough for the amount of airguns I have so I only keep a scope on the ones I shoot most of the time. I just picked that one off the shelf for use that day only.
Doesn’t take long to sight in once installed. I probably would not get that particular scope for this rifle if it was to stay with the rifle. I wanted to check for accuracy. A low cost Dot sight would be just fine for plinking.
I was not impressed with the FPS this rifle had and extending the barrel was an easy solution and it did increase it to over 500 FPS. I used parts I already had that were not being used at the time, airsoft stuff, easy to install and remove. It was just a fun project.
Get a better airgun if I wanted more power and accuracy? I already have some of the best and more than one of every type including other SBR’s. Even a full-auto Evanix PCP.
I just enjoy doing some modifications to see what can be done and what the results are.
I am fortunate and cost is not a problem I need to consider when tinkering with airguns and it may seem to be impractical to many who do. I am a collector and like all kinds of airguns for all kinds of shooting and reasons.
Bob M