BNM Multi-Shot breech and shroud on Benjamin Maximus

[ACZan]

Well, I am going to have to rely on you guys' advice when I get started on the BNM breech project.

BTW I thought that my current erratic POI on my barrel replacement was due to scope.  It is a Vism 1.1-4X 24mm Evolution Series Scope which I believe were designed to be used more for AR 15s.  So, those should be able to take a bit of a beating.  However, it might be best to take the rifle back out to range and throw my Steiner MBS-AA Laser Boresight on it between shots and rule that out as the cause of erratic POIs. 

[KnifeMaker]

Bill, you hit the nail on the head! Crosman would be well advised to add a multi shot Disco/Maximus to their line up. They are getting passed in the emerging "Low End" PCP World. 

Exciting times we live in!

Knife

[ACZan]

Do any of you guys know how much clearance I need from the groove of the 11mm dovetail on the BMDSH3002 breech and above it to avoid any scope interference?  I have low mount scope rings.  Does the pellet clip engage and disengage sideways from the breech?

On a side note, my rifle took a hard fall onto concrete yesterday. Thought that was the end of it, at least for the scope.  Took it out to range.  Thumped it hard between shots in different directions, still held zero.  Still believe my erratic POIs have something to do with the barrel not being optimally machined.  My NcStar scope has certain lived up to its name, claim and definitely worth the money.

Thanks,
ACZan

[ACZan]

Guess no one knows on this.  So, I contacted BNM Custom.  The said that the clip extends 0.395" from the 11mm dovetail groove to the top of the clip.  Measuring from the groove to the bottom of the scope tube, I have around 5/8 or 0.625.  That's just enough to clear my BLK low mount scope rings and my NcStar scope.

KnifeMaker,

I am preparing for a mod on my Discovery .22.  I have to have a repeater on rifle and a better barrel (too many bad Crosman barrels).  In the next week or two, I will be ordering the BMDSH3002 breech from BNM Custom.

Also, I am working with Roy at Mountain Air Custom to have him turn/machine a new Lothar Walther barrel to fit the BNM breech and accept my TKO VMod suppressor.

The last thing I need to work out is determine what needs to be done to maintain the 920 fps.  Did you figure out everything that needed to be done to recover the velocity with the new breech?

Did your BNM breech come with the port sleeve and connecting hardware?

Thanks.

[KnifeMaker]

Chris;

Yes it did come with all hardware. Including the longer transfer port tube machined from alu. Didn't have to do anything but add a hammer spring adjuster.

Playing with a HUMA Reg now. A bit down on power. New spring came in yesterday, but terrible weather here in central Tx.
Biggest reason the power is down, is that I got a wild hair and shortened the barrel by 4.5".  I got tired of banging the LDC into everything I got close to in the woods. LOL!!!

Put the larger dia. Rocker1 Carbon Fiber LDC on it as well. Man it's good looking now.   

More testing when the weather improves.

 

[ACZan]

Oops, meant port tube.  Hate when I don't call things by their proper name.  But, you knew what I meant.

So, There is nothing that will need to be done to the BNM breech, port tube or the barrel to recover the velocity?  Anything that needs to be done to those parts, I have to have Roy do at Mountain Air Custom while he has it.  Want to make sure things are done right first time around as opposed to the tuner who did work on it previously.  I found out after I got the rifle back from him there were problems, when he should have told me while it was disassembled.

At what velocity did it start shooting after the new BNM breech was installed?  Based on the graph report the tuner sent back with my rifle still with the factory configuration, it was down in the lower 800s.  I am fairly sure now that the tuner did some bad work on the gun.  So, the mid to higher 800s will be a good start if anything at all.

Do you think you can get it back to the 920 fps factory spec?  Oh, wait a minute, you have the Maximus.  Those are rated at a lower velocity, right?  Do you think those Discovery .22 rifles actually shoot at that velocity shortly out of the box following their break-in period?

Yep, know that all too well.  Think my TKO VMod is 6.5" long.  I have knocked it a little on several occasions thinking that I moved the barrel out of alignment again.  With the BNM breech, I can have new barrel band style I came up with made for the new configuration.  Should stiffen and align the air tube and barrel assembly quite a bit.  Haven't decided what diameter L/W barrel I want to get, thinking little thicker than factory stock.  Do you have any suggestions?

[ACZan]

Yes, I see all that really bad weather down there on my desktop radar map widgets.  My older Brother told me some stories about the weather in Lubbock, TX.

I know about the hammer spring adjuster.  I can just put in a different spring with out having the adjuster screw, right?  Looks like there are a variety of springs which can be installed.

What is the MUMA Reg?  Not completely familiar with the abbreviations on the part names.

[KnifeMaker]

   LOL!!! Misstyped.It is the HUMA brand Reg. LOL!!!

Lost 60 fps when shortening bbl. Before it was 890's with JSB 18's, and was the same with the BNM.

New spring arrived and will install probably today. I really enjoy the hammer spring adjuster. Just dial it in in a second or two. Ordered it from Joseph here on the GTA. His business in Discos-R-US

Knife

[ACZan]

Okay, found it, now.  It is a Huma-Air Pressure Regulator (pictured below).  I was not familiar with that component and it appears to be one that is inside the air tube.  Looks to be very well made.   May have to consider upgrading the air tube components in the next reseal maintenance.  Seems like there are a lot of nice high quality after market parts for this rifle.

I can live with it shooting in the 890s range.  Did find out that the L/W Barrels are only available at 23.75" in length.  Being one quarter inch short shouldn't be a problem.  The BNM breech is a bit higher which will allow a little more of the barrel and its components to clear the air tube.

Would really love to replace the plastic trigger housing with a metal one of the same shape parts.  Have a lead on something I found on the Internet.  May have to pay a pretty penny for that and will if I have to.

Did the machined arch on the bottom of the BNM breech match up well with the curvature of the air tube?  That would be key to the air tube, breech and barrel aligning very nicely with each other.

[KnifeMaker]

Breach fits perfectly.

For an outstanding trigger, most go to the Gen 1 Marauder trigger with the spacer.

Again, Discos-R-Us has them, and at the best price I have found.

The MRod trigger is a clone of the world renowned Rapid airgun triggers, and what is very similar to the trigger group found on the very nice, high end RAW AirGuns.

Knife   

[ACZan]

Does anyone know what the overall length of the BMDSH3002 Breech is without the shroud?

Correct me if I am wrong, but I believe it has to be roughly the same as the Crosman stock breech.  I was worried that the BNM breech might have differences in the X dimensions that might cause the barrel to be shifted.  However, the BNM breech needs to match up with the port and mounting screws which means it is nearly the same in size if not exactly the same.

[ACZan]

Never mind looking that up, guys.

BNM Custom got back with me this weekend and confirmed the breech is the exact same length as the Crosman stock breech, 6 inches.

[ACZan]

KnifeMaker,

Finally received the BNM BMDSH3002 breech.  Strangely, they sent me the wrong one, for barrel shroud, instead the non-shroud one.  Did specifically mention the non-shroud model number, but still sent the wrong one.  On a good note, they got the right one out to me in a short time.

That aluminum transfer port tube has two different ends.  Do you know how it is orientated?  I assume the one o-ring seal fits on one of the ends of the tube.

[KnifeMaker]

LOL, I ordered for shroud,l and got non shroud breah. GRRRRR!!!

Not sure on the tp tube. I ended up using the old standby ice maker tubing. almost seems to be a standard among tuners and owners who are searching for power.  Crush to seal.

Knife

[ACZan]

Looks like we had the opposite problem.  I was wondering about going to a press to seal, much like some HVAC and plumbing connections.

I had a airgun tuner give me a big list of reasons why Crosman and BNM repeater breeches diminish shot accuracy compared to the stock setup.  I sent you a private message with the full text of it.  I'm really interested to hear your comments on it.  The tuner was making it sound like I made a very bad decision.

[ACZan]

KnifeMaker,

I received the L-W custom barrel from Mountain Air Custom.  The barrel looks great except for one thing, the port on the barrel.  Looking at the photo with the Crosman factory barrel next to it for comparison with the transfer port tube next to it.

On the custom barrel, there isn't a prominent seat on which the tube sits.  It looks a little tapered but not much.  Is this how yours looks?  The way it was machined doesn't look like the BNM Custom transfer port tube which came with the breech will work with the way the barrel port was machined.

[ACZan]

A closer look at the port shows the taper machined into the barrel appears to be off center from the hole.  Also, it almost looks as if the port was opened up too much.

How do I deal with this, or do I need to have another barrel made?

[ACZan]

Okay, had to take apart a spare BNM breech to see how the transfer port assembly is set up.  It is obvious the TP tube stops at the bottom of the counter bore beyond the o-ring in the block.  Is there a name to refer to this block attached to the main body of the breech?

The first photo is the block turned over to the left side to expose the TP to the barrel.  The second photo is the block rotated 90 degrees to show the bore and o-ring for the barrel.

So, there three o-rings.  One for the bolt, one for the barrel and one for the TP tube.

Anyone know what end of the TP tube goes where?  Don't recall those instructions being packed with the breech.

[Blue]

Anyone know what end of the TP tube goes where?  Don't recall those instructions being packed with the breech.

I don't remember either but I do remember watching their assembly videos online a couple times when I originally got mine.  If their videos are still available there might be something in them that helps.

Blue

[ACZan]

Okay, found the info on which way the TP Tube is supposed to be oriented.  I attached a photo with text.

Also, I took some time to measure out the elements of the BNM transfer port assembly.  Don't have my CAD software installed yet.  But, this is the best I can do with Microsoft Word.  Placements and dimensions will be a little off.  However, it is a good representation of the assembly.  Obviously the yellow object is the BNM TP Tube.  See some slight issues which could lead to air leaking.

Can anyone tell me what the largest size hole can be machined into a .22 cal barrel for the transfer port?  I can see too large of a hole causing problems with loading the pellet into the leade.