BNM Bolt Probe Problems?

[rsterne]

A thread started recently in the Machine Shop Gate about the position of a pellet when loaded into a stock Disco barrel when fitted into a BNM Repeater breech.... Let me state right off that I have never had one, but I have seen a few oddball questions raised over the years, including low velocity problems when the BNM is fitted, when no other changes were made.... Some guys lost up to 90 fps.... Anyways, perhaps, after all these years, someone finally shone a light on a potential problem.... Look at the third photo in the first post of this thread....

https://www.gatewaytoairguns.org/GTA/index.php?topic=142789.0

Notice that the pellet is not far enough forward, and is obscuring about 3/4 of the barrel port.... Obviously this could lead to low velocity, and possibly even accuracy issues from the blast of HPA hitting the side of the skirt and bending it, or twisting the pellet crooked in the bore.... If you scroll down to Reply #2, you will see where the pellet, hanging on the probe, is located relative to the transfer port.... obviously not an ideal situation.... Now have a look at this thread from 2013....

https://www.gatewaytoairguns.org/GTA/index.php?topic=52276.0

If you compare the photo of a stock BNM probe to the one in the thread in the Machine Shop Gate, it looks to me like the probe in the MS Gate thread is smaller in diameter.... and appears to have file marks, or at least is not as smooth as the stock BNM bolt shown in the thread from 2013.... I suspect that the bolt probe in the MS Gate thread has been slimmed, which means it sits deeper in the skirt of the pellet, and so doesn't push it as far in to the barrel.... However, the stock BNM probe, as shown in the 2013 thread, obscures a large portion of the port because the shoulder is too far forward, and the probe very large in diameter.... My GUESS is that the large OD is to push the pellet further forward so that it doesn't obscure the port as badly.... Again, I have never had a BNM, so if I am guessing wrong, my apologies....

Anyways, my brain suggests, that based on the above evidence.... that the large velocity loss reported by some when installing a BNM breech on a Disco with no other changes.... may be due to the bolt probe, and/or the way the pellet loads in the Disco barrel.... and some pellets may be much worse than others.... Certainly, the stock BNM bolt probe is (was? ) huge and short, with the shoulder far forward (as in the photos from 2013).... although possibly those things have been corrected now, I have no idea.... Slimming the probe would ease the airflow around it, but unless it is made longer at the same time, then the pellet will not load as far into the barrel, and could obstruct the barrel port more.... Curing one problem may be creating another....

All I can tell you is that if I had a BNM breech, and experienced a loss in velocity compared to what I had before installing it.... I would immediately look at this as the source of that power loss.... Certainly, in 2013, the BNM bolt nose and probe was restricting airflow.... Is that still the case, I have no idea.... Perhaps somebody will take the time to do some photos of the current parts, and where they load various pellets.... All I can tell you is that if I had one, I would be looking at a longer, smaller diameter bolt probe.... as it could provide significant airflow (and hence power) improvement.... The limiting factor is likely how long you can make the probe and still have it retract far enough to remove the MRod magazine....

Bob

[Rob M]

seems to me its just a flawed design. they don't include an extended probe, and if they did you could not load the mag.. I actually made a breech that took a bulldog mag and had to make 2 channels for the bolt travel , because the bolt needed to travel past the hammer pin in order to clear the magazine.. I don't feel like taking a pic so I hope you can imagine this.

[ACZan]

Bob,

Sorry.  Thanks for starting a new one.  Probably should have two topics in the first place.

I think is clear the pellet is not in the optimal position.  Checking clearances, I see no problem with making the bolt longer.  I would say pellet position is a good contributor to negative reports.  But, I would also like to see the TP tube fit a little more snugly.  It doesn't have enough shoulder to seat well in the breech, kind of wobbles.  That tells me there won't be a good seal at all.  The tube doesn't even touch the barrel.  See my recent photos on this topic.

https://www.gatewaytoairguns.org/GTA/index.php?topic=130078.40
Bottom of page 3

Here is a photo of the pellet still attached to the tip of the probe in its fully retracted position.  There looks to be plenty of room to turn a longer bolt.  I'll add the other photos for convenience of keeping it in this topic.

Knife' and I have been discussing the BNM breech mod for the Disco for a while and he mentioned the drop in velocity.  His comments and suggestions prompted me to take the BMDSHSH3001 (shrouded version) BNM Custom sent to me in error apart to check dimensions and part relationships.  BNM Custom didn't want the breech back for some reason.  Guess BNM didn't want to pay for the return shipping.  So, I put it to good use doing research.

I'll contact those guys at BNM Custom to see what they say, considering that I purchased the breech not to long ago.

[ACZan]

What the heck, I'll throw the TP tube drawing in here, too.

This is the cross section view of the port assembly looking along the length of the gun.

Addendum: I do want to point out that I did this drawing in Microsoft Word.  It will get most of the job done in representing the parts.  However, it will not be as accurate as a CAD program.  Can't wait to get my TurboCAD software installed.

[rsterne]

Chris, I take it you did not modify the bolt by thinning the probe then?.... no mods at all?.... If that is the case, it would seem BNM need to supply a bolt with a longer probe, especially since there seems to be lots of length for it.... Please keep us advised as to BNM's response....

Bob

[ACZan]

Yes, that is absolutely correct.  No modifications, the breech is as it was received from BNM Custom.

I did send an email to Sergio with my photographs.  Hope to hear from him.  I understand he can get very busy at times, but I did put high priority on the email along with a subject they couldn't ignore.

The best I can tell is that a 6mm longer probe, not changing anything else should put the back edge of that skirt 1mm beyond the front edge of the port.  I'll have to take some time with my micrometer to be sure of that distance.

Looking at the TP tube hole diameter, I don't think the barrel port needs to be much larger than the tube hole.  Correct me if I am wrong, it would be best to minimize the volume of space between the valve and the pellet.  I have to grab my notes to see what the diameter of the TP tube hole is.

[Blue]

I remember when I first got my BNM breech a few years ago having trouble getting the barrel to seat fully into the breech during assembly.

Not a result of design/manufacturing, just a tight fit.  I had to REALLY push it into place, I remember feeling it slide that last bit (1/8 inch?).  The last time I swapped it into a new build, I made sure to really push the barrel in to seat it but it hasn't given me as much of problem as it did on that initial build.

I'll try to load a pellet later and see if it looks similar to how yours sits in the breech.

Mine's on a .22 disco hybrid with a 18" barrel (so the shroud can end even with the air tube and still accommodate some baffles) and shoots AA 16 grain domes at around 700 FPS with a stock disco valve.

Blue

[Kmaz]

Edit... mine is perfectly fine. Pellet is pushed to outermost edge of tp. Using lw barrel on a hpa 2240. Erased original post because I didn't want to cause confusion.
Kris

[Kmaz]

no post

[ACZan]

I made sure the barrel was fully seated by turning over the breech and looking at the alignment of the TP holes.  Below is a photograph of assembly when looking at it through the TP hole from the bottom side of breech.  You can see a little of the probe tip.  In this photo I didn't load a pellet.  I was mostly inspecting the interpart relationship of the TP assembly.

Despite the test, my fundamental education in engineering and physics dictates the position is bad.  I can see how easyly the HPA flow can collapse or damage the skirt.

[Kmaz]

I made sure the barrel was fully seated by turning over the breech and looking at the alignment of the TP holes.  Below is a photograph of assembly when looking at it through the TP hole from the bottom side of breech.  You can see a little of the probe tip.  In this photo I didn't load a pellet.  I was mostly inspecting the interpart relationship of the TP assembly.

Despite the test, my fundamental education in engineering and physics dictates the position is bad.  I can see how easyly the HPA flow can collapse or damage the skirt.

The earlier photos sure look bad... this one not so much. For full clarification can you do one like this with a pellet?
Kris

[ACZan]

Yes, give me some time.  Suffering from the flu the past several days.  Have tremendous aches and pains with this one that meds are just not alleviating.

To tell you the truth, it won't be much different than the barrel with the pellet in it.  The only difference is the barrel was removed from the breech.  Trying to photograph close-ups of stuff like that can be difficult to focus using autofocus only cameras.  I have to perform some photography tricks to override auto-focus.  So, without all the breech parts, it is easier to focus.

What are you particularly looking for with the whole assembly together?

[toku58]

I had my share of PITA with the BNM kit I got for my Discovery. BNM Customer service really not worthy!
Long story short I'd never do business with them again.
Sad because if the did good work and stood behind their products? It would actually be a good option.
But as it stands, it doesn't seem like they really care.
All I got every time was excuses why they forgot to send parts or made things that wasn't quite correct. (Really not worth my time to deal with that &^^&!)
Too bad!

You'd be 100% better off at the end of the day and just buy a gun that you can just go out and shoot, rather than dealing with these half @@@, part time so called gunsmiths.
Excuse my French!

Good luck! With getting this taken cared of. In the end I just gave up and sold the gun.

[ACZan]

Here is the photo.  Very difficult to get the focus at the very bottom in barrel port area.  Barrel port is aligned with the breech TP hole.  The photo without the breech is much better in representing the problem.

Toku58,

What other issues did you have, or was it just this one?  You mean to say that this issue was brought up to BNM Custom and they completely ignored it and continued to manufacture the items incorrectly?  That is pathetic.  How can anyone stay in business conducting themselves like that?

I sent them photographs and did get a read receipt on the email message.  Let's see if they will even respond at all.

Maybe that explains why they didn't want the wrong breech they sent to me back.  Assuming, they know it is not quality product and didn't want to waste the money to ship it back to them.  Hmmm?

[mann]

Never had a problem with either of my bnm breeches one  was a 25 Cal and a 22 Cal have now I ordered baffles for there shroud that  I have it took for ever to get those to me though

[Kmaz]

That sure doesn't seem right. I can only go by mine and you had me concerned so I removed the breech to view it from the bottom like your photo and it turned out perfect. Just for full disclosure mine is a rear bolt, not a side bolt. Mine is also on a 22xx. I did replace the transfer port. It wasn't quite long enough. It's too bad because I'll probably order one more. Fingers crossed.
Kris

[ACZan]

Thinking about this more.  My guess is that someone might not paying attention to parts upon assembly.  They might just be simply interchanging parts.  This most likely is specific to the side bolt version of that breech.  Without a comparison of parts' dimensions, the clear picture of the defect or issue in not known.

[Kmaz]

Thinking about this more.  My guess is that someone might not paying attention to parts upon assembly.  They might just be simply interchanging parts.  This most likely is specific to the side bolt version of that breech.  Without a comparison of parts' dimensions, the clear picture of the defect or issue in not known.

Here's a shot in the dark... keep in mind I don't have the side bolt model to check. Check the bolt,  Is it possible that the cocking handle and the threaded Allen bolt ( the one that cocks the pin on the hammer) are the same thread and maybe they inadvertently were switched? (Assuming one may be slightly ahead of the other)
Kris

[ACZan]

That was a good thought, but it wouldn't work at all with the handle and cocking pin switched (see photo).  Hypothetically, if you could swap them, the cocking pin is further forward and switching the two would make it worse.

[toku58]

I had multiple issues including mishandled orders.
You'll probably get a semi apologetic email, in a few days he won't offer any resolution. just sort of low on his list of concerns because he already has your money.
I got the impression he didn't give a &^^&! The people who give good reviews are those who never had to resolve issue with his products.

I did hear that when he started he did care about the business. But I guess he's just over it and selling things without giving a &^^& how good they are.
Not a way to run a company. I would never do business  with him again.
Not worth the potential issues.

Hope your experience is better than mine!
Good Luck!