BNM Bolt Probe Problems?

[ACZan]

Imadunatic,

Do you have a photo of what your port hole on the barrel looks like?  Or, is it just the Crosman stock barrel with no modifications?  Do you have the TP sleeve seating inside bore on the barrel port?

[imadunatic]

Imadunatic,

Is that from the very back of the bolt, including the handle to the probe tip?  What is the measurement from the very back of the bolt in front of the handle (I would assume the front of the handle is considered a stop) to the probe tip?  I think you guys with the rear bolts have to measure from the back of the breech where the handle rests up against it to the probe tip.

For my side bolts, the process is a bit different.  In order for me to get my micrometer on the back an tip of the bolt, I had to move the bolt to its halfway point in the travel.

You were posting while I was typing my reply.  That is a great drawing!  What program did you use to create that?

Yeah that is overall bolt length. Which is now 3.735 with the new probe, the front of the handle is .315" from the back of the bolt, which puts the distance from the front of the handle to the tip of the probe at 3.420". I think if your probe is not flush with the rear side of the magazine slot opening, then it's too short. My pellets are now well past the barrel port.

That drawing is actually out of Unigraphics NX, I was a CAD designer for 12 years and I still have access to a (much lighter) license that I still use in my day job. It is definitely nice to be able to draw these!

In fact, I already had a repeater breach drawn in my solid model for the 2400, this is the components I have drawn so far:



Haven't needed to draw the trigger group yet, but everything else is dimensionally correct.

[Mudbugmitch]

Yes, congrats on your success. You up to making anymore transfer ports ?

Mitch

[imadunatic]

Imadunatic,

Do you have a photo of what your port hole on the barrel looks like?  Or, is it just the Crosman stock barrel with no modifications?  Do you have the TP sleeve seating inside bore on the barrel port?

Chris,

Bone stock on the barrel port. The secret sauce to these BNM TP are that they actually register against the shoulder and compress slightly against the exhaust port seal, I suspect I'm not the only one that also had a major air leak at this point. The pellet partially covering the barrel port certainly isn't helping either.

Yes, congrats on your success. You up to making anymore transfer ports ?

Mitch

Mitch,

I only do machining for myself. I do always try to provide drawings in case anyone else "has a buddy". I don't know that this is problem with everyone elses BNM, but the air leak was VERY obvious on mine.

[Mudbugmitch]

Thanks for the reply,. I am good, or hope to be when BNM makes good on my new breech. I was just asking. I'm sure there are others with the same problem as you. A gain of 120 fps. GOOD FOR YOU.

Oh, and thank you for the great drawing.

[Kmaz]

Well I am pleasantly surprised.... Machined up a new Transfer port that is much tighter in every direction:



and also added a needle probe that is .080" longer (it is perfectly flush with the breech when the bolt is completely retracted so I won't have any issues installing or removing mags. The air leak is completely gone and I actually gained 120 FPS... I wasn't completely interested in the furtherance of science I just wanted to get the 2400 back to shooting like I know it can (actually better than it ever has) so I didn't change just one item at a time and test (I thought I was done with this project, the test and tuning days are behind it!)

It's now sending the 10.3gr heavies at ~880fps which is just shy of 18 FPE. The best I had ever done before the BNM was 830 with the heavies.

Unfortunately, I changed three things, not all of which are accessible to the average cat:

• Installed .060" needle probe (stock BNM was .080)
• Machined up new Transfer port that is much tighter
• Extended probe tip .080" (flush with breech when fully retracted)

Ironically, the reason I had dropped the cash on the BNM kit was so it would just work.

sweet! It never dawned on me that their supplied tp should "seat" into the center block and not the barrel. That would make sense.i feel like mine didn't so it when tightening down the Breech it didn't force it into the main tube seal. Good job
Kris

[ACZan]

Imadunatic,

Chris,

Bone stock on the barrel port. The secret sauce to these BNM TP are that they actually register against the shoulder and compress slightly against the exhaust port seal

I agree with you wholeheartedly there.

I believe the intention BNM Custom had was to create enough of a shoulder to seat up against the bottom of the block, the bottom of the counterbore used for the o-ring.

But, I have to wonder what improvements would be made if the TP sleeve is fully seated into the port on the barrel.  I am going to go for that option as oppose to seating it at the bottom of the block.  The problem with seating it onto the barrel is that the barrel port and the sleeve need to be aligned fairly well for a full seating to occur at the barrel port.  It can not be canted one way or another.  The seal at the valve port will allow some compensation if the sleeve is not too tight in the breech port holes.

[imadunatic]

I'm not having any trouble with mine leaking now. Mine is also forward screw so there is no way to assemble when the barrel block is installed, it partially covers the #4 screw. It does seem like this would definitely help though.

I do now believe these BNM setups can be made to perform, but it appears not all are plug and play. After investing a couple more hours I can honestly say I couldn't be happier with mine. Single shooting is for the birds (did actually drop the second starling of the year with this setup tonight).

[ACZan]

I see what you are saying, Imadunatic.  I didn't look that close at it until now.

Based on that observation, that is the reason it is designed to seat on the bottom of the block and not in the barrel.  It would be impossible to insert the barrel if it needs to seat into a countersink in the barrel port.  The stock assembly obviously uses the other assembly order.

Not sure but maybe enough of a groove can be machined into the bottom corner of the block, above the screw hole to allow the change in assembly for seating the sleeve on the barrel.  I can do a test on the spare breech I have.  Thinking of switching the screw to a hex cap head.  Then can use a ball hex allen key to get at it from an angle.

Actually, there isn't enough depth to keep it clear of the magazine.  So, using a different fastener will not work.

Anyone know what the max torque needs to be on that #4 screw?

[ACZan]

Here is a good close-up view of the BNM Custom TP sleeve and where it sits on the inside of the block.  The view is through the bore where the barrel is inserted.  You can see off to the left a little bit of the TP sleeve on the outside.

[Kmaz]

I'm surprised you can't screw yours to the tube with your center block in place. Mine is together as a unit with the barrel installed before I mount it to the tube.
Kris

[ACZan]

So, Kmaz.

You are putting the breech body, TP block, TP sleeve and barrel all together before mounting the whole assembly to the air-tube.  So, what did you do special to accomplish that?  Would love to see a photograph(s) detailing what you have accomplished.

I should follow your lead on this as that is what I'll try to do.

I have more things to add here but my sleep medication has different ideas at the moment. I'll post them tomorrow.

I need to add that when the o-ring which holds and seals the barrel at the front side of the TP block is removed, there is quite a bit of play between the barrel an the block.  It looks a bit rough in there and would prefer to clean that up some how for a much tighter fit.  Another area to rework and improve.  Sounds just like what Pecor was warning us about.

[Kmaz]

So, Kmaz.

You are putting the breech body, TP block, TP sleeve and barrel all together before mounting the whole assembly to the air-tube.  So, what did you do special to accomplish that?  Would love to see a photograph(s) detailing what you have accomplished.

I should follow your lead on this as that is what I'll try to do.

I have more things to add here but my sleep medication has different ideas at the moment. I'll post them tomorrow.

I presumed that is what everyone was doing until the other gentleman said he couldn't screw his onto the tube because the tp block hindered screwing it down. Keep in mind I'm using tubing for tp so I have to because the tubing is locked into the chamfer in the barrel through the tp port block. once the unit is all together I insert tubing from underside. Once tubing is installed the barrel cannot be removed from the breech without removing tp. Install on tube trimming tp to fit. I don't know how to post pics... should learn. But can text or email.
Kris

[ACZan]

Kmaz,

That is good to hear.  If you can do the factory stock assembled way, then I should be able to do it, as well.  Initially, I thought there was enough access to get to the screw head.  Will the screw go into the hole with the block installed?  Or, did you have to take the block off just to insert the screw, prepping for the assembly?

[ACZan]

Did some additional measuring for anyone who could use the info.

Probe retraction 5/16 behind magazine slot.

Pellet bad position 0.3400 - Measurement from end barrel to the inside waist of the skirt

Ideal pellet position change 3/16" to clear port, rough measurement

Pellet good position 0.4710 (0 .131") difference  - Measurement from end barrel to the inside waist of the skirt, pellet skirt clears the front edge of the barrel port.

From what my math is telling me, I need to add 3/16 of an inch to the area behind the probe (between cocking pin and probe).  Moving the pellet 0.1875" putting it well clear of barrel port and should be good for all pellets.  That leaves me with a retraction of 1/8 inch beyond the magazine slot.  I don't want to push that pellet too far forward.

I haven't gotten around to doing this with the stock assembly to see what Crosman's assembly leave the pellet on lock.

[Kmaz]

Kmaz,

That is good to hear.  If you can do the factory stock assembled way, then I should be able to do it, as well.  Initially, I thought there was enough access to get to the screw head.  Will the screw go into the hole with the block installed?  Or, did you have to take the block off just to insert the screw, prepping for the assembly?

I'm able to completely insert or remove the screw at will with it completely assembled. Is that 5/16" behind magazine slot measurement taken while mounted and actually cocking the hammer? Because mounted and unmounted yields different measurements.(bolt cocks farther without hammer)
Kris

[ACZan]

I'll let the photo do most of the talking.  It is mostly likely a few hundreds short of 5/16 of an inch.  Bolt is all the way back.  Remember my breeches are side bolts.  That is with it not be mounted.

That is a good point.  Unfortunately, it is assumed the bolt will travel all the way to the back.  However, I can see the possibility of the hammer travel cutting that short.  I don't have an air tube to check it against.  Unfortunately, the rifle is still on duty to take care of pest while I try to hammer out this BNM breech mess.

Hey Mitch, have you heard anything yet from BNM Custom?

[ACZan]

Well, if the hammer travel is going to shorten that travel, then I am most likely in the same boat as Imadunatic.  He added enough to just stop short of the edge, magazine slot.

This is the reason I was considering building out an air tube, too.  It would allow me to check part fitting and placement.  Rifle is busy and can't have it down for long.

[Mudbugmitch]

Still no email today, nothing...
Tomorrow is another day.
Well fiddle Dee Dee.

[rsterne]

The hammer travel will likely limit the rearward bolt travel, you MUST check it with the gun assembled....

Bob