Author Topic: BNM Bolt Probe Problems? (Read 22409 times))

pecor · « **Reply #120 on:** May 10, 2018, 01:53:23 PM »

Thailand breech, I would be concerned about that Side-lever

That is clearly cast, And not a good looking casting at that. It should be made from solid Billet aluminum. I also don't like the fact they don't show the Bolt Probe

Mudbugmitch · « **Reply #121 on:** May 10, 2018, 02:02:05 PM »

You are probably right about the paint. Just getting itchy, I guess.

Kmaz · « **Reply #122 on:** May 10, 2018, 02:09:19 PM »

Quote from: pecor on May 10, 2018, 01:53:23 PM

Thailand breech, I would be concerned about that Side-lever That is clearly cast, And not a good looking casting at that. It should be made from solid Billet aluminum. I also don't like the fact they don't show the Bolt Probe

I said I'll find out... 6 pages of bashing one brand and you'll bash this now too? Cast doesn't mean it's bad. Give it a rest.

fivestar45 · « **Reply #123 on:** May 10, 2018, 03:04:17 PM »

Quote from: Kmaz on May 10, 2018, 01:48:37 PM

Quote from: fivestar45 on May 10, 2018, 01:05:45 PM
Guy's $160.00 for a breech that will still be as unstable as a OEM Crosman breech? The only thing that I see interesting is the side lever.
Crosman repeater breech Unstable?... Huh? Side lever should be better for heavier springs. Will it be? I'll find out. The money we spend on these is all subject to question. People spend $150 on a valve or an aluminum tube. $130 on a repeater breech is money well spent if it performs well.
Kris

All the 22xx breech's that i know of still depend on the minute 4/48 screw in the loading tray or under the bolt to hold the breech down and compress the T/P. When a rifle barrel is added to it, chances are it will have a problem holding P.O.I. that's why so far the remedy has been to use two barrel bands. The Tai breech doesn't look like it uses any barrel band and the bore centers don't look like they will match O.E.M. So now where will the barrel bands come from to keep everything glued down?

rsterne · « **Reply #124 on:** May 10, 2018, 03:09:25 PM »

No Disco repeater breech I am aware of can use OEM barrel bands, they are all taller to give room for the magazine notch....

Bob

Kmaz · « **Reply #125 on:** May 10, 2018, 03:19:55 PM »

Quote from: fivestar45 on May 10, 2018, 03:04:17 PM

Quote from: Kmaz on May 10, 2018, 01:48:37 PM
Quote from: fivestar45 on May 10, 2018, 01:05:45 PM
Guy's $160.00 for a breech that will still be as unstable as a OEM Crosman breech? The only thing that I see interesting is the side lever.
Crosman repeater breech Unstable?... Huh? Side lever should be better for heavier springs. Will it be? I'll find out. The money we spend on these is all subject to question. People spend $150 on a valve or an aluminum tube. $130 on a repeater breech is money well spent if it performs well.
Kris

All the 22xx breech's that i know of still depend on the minute 4/48 screw in the loading tray or under the bolt to hold the breech down and compress the T/P. When a rifle barrel is added to it, chances are it will have a problem holding P.O.I. that's why so far the remedy has been to use two barrel bands. The Tai breech doesn't look like it uses any barrel band and the bore centers don't look like they will match O.E.M. So now where will the barrel bands come from to keep everything glued down?

You may be correct... I havnt had a problem. 14.5" barrel carbine.
Kris

pecor · « **Reply #126 on:** May 10, 2018, 03:37:55 PM »

I would have went with the UK breech Because they have the Barrel Bands, and Tank hangers, And they have a lot of Knowledge when it comes to airguns, That's Pretty much all you can Own their. http://www.gmaccustomparts.com/epages/BT3197.sf/en_GB/?ObjectPath=/Shops/BT3197/Products/002-0600 http://www.gmaccustomparts.com/epages/BT3197.sf/en_GB/?ObjectPath=/Shops/BT3197/Categories/"MULTI-SHOT%20BREECHES%20AND%20PARTS

Mudbugmitch · « **Reply #127 on:** May 11, 2018, 07:17:54 PM »

Still nothing. .?

imadunatic · « **Reply #128 on:** May 11, 2018, 07:21:25 PM »

Well I may as well join in. I too lost over 50 FPS with the BNM. Overall I'm happy with the fit/function, not happy with the loss in performance. In my case I have an aggressive leak at the transfer port and the pellet of choice also just slightly covers the barrel port. I don't really have room for extending the probe and if I want to machine the channel further for a deeper push I'd have to make a new bolt anyways since it bottoms out on the back of the breech.

All that being said I'm curious to see what the fix is for this. Anyone have any ideas for sealing up the transfer port? It almost blows what's left of my hair back when I touch it off. I see nothing that actually places any preload on the seal in the exhaust port of the valve (the transfer port will slide well up into the transfer port block, I'm assuming the shoulder is supposed to time out on the opening in the transfer port block).

Mudbugmitch · « **Reply #129 on:** May 11, 2018, 08:11:12 PM »

I truly believe the biggest loss of velocity is from the depth of pellet into the barrel. I had heard of someone using tubing for his too short port. I would check the O-ring in there also for blow back.

Mitch

Kmaz · « **Reply #130 on:** May 11, 2018, 09:14:45 PM »

Quote from: imadunatic on May 11, 2018, 07:21:25 PM

Well I may as well join in. I too lost over 50 FPS with the BNM. Overall I'm happy with the fit/function, not happy with the loss in performance. In my case I have an aggressive leak at the transfer port and the pellet of choice also just slightly covers the barrel port. I don't really have room for extending the probe and if I want to machine the channel further for a deeper push I'd have to make a new bolt anyways since it bottoms out on the back of the breech.

All that being said I'm curious to see what the fix is for this. Anyone have any ideas for sealing up the transfer port? It almost blows what's left of my hair back when I touch it off. I see nothing that actually places any preload on the seal in the exhaust port of the valve (the transfer port will slide well up into the transfer port block, I'm assuming the shoulder is supposed to time out on the opening in the transfer port block).

I'm confident if you replaced the aluminum tp that bnm supplies you would surely make up that 50fps. In my limited experience messing with it, if you can feel air leakage it should deff equal at least 50 fps. I believe I used 1/4" polypropylene tubing. Same tubing used for refrigerators or r/o systems.
Kris

ACZan · « **Reply #131 on:** May 11, 2018, 09:50:30 PM »

Imadunatic,

Is that a rear bolt. Can you measure the length of the bolt and post it on a reply?

Mitch, did you provide a measurement of your bolt? Also, I haven't received anything from BNM Custom, either.

Below is a photograph of the bolt opening leading into the barrel. There is a o-ring in there. The non-shroud version of my breeches felt a little loose. Thought one or two people mentioned their o-rings were missing.

For any of you new visitors to this topic, please view the diagram cross section of the transfer port assembly. The TP sleeve of the BNM does not touch (seat into the counter bore of) the barrel. The TP sleeve in Crosman stock assembly does.

Mudbugmitch · « **Reply #132 on:** May 11, 2018, 10:19:33 PM »

Mine is a 3 5/8" Rear bolt.

ACZan · « **Reply #133 on:** May 12, 2018, 12:38:32 AM »

How much of the port in the barrel was covered by the pellet?

Mudbugmitch · « **Reply #134 on:** May 12, 2018, 01:31:44 AM »

Roughly 40 %

imadunatic · « **Reply #135 on:** May 12, 2018, 08:15:18 AM »

Quote from: ACZan on May 11, 2018, 09:50:30 PM

Imadunatic,

Is that a rear bolt. Can you measure the length of the bolt and post it on a reply?

Mitch, did you provide a measurement of your bolt? Also, I haven't received anything from BNM Custom, either.

Below is a photograph of the bolt opening leading into the barrel. There is a o-ring in there. The non-shroud version of my breeches felt a little loose. Thought one or two people mentioned their o-rings were missing.

For any of you new visitors to this topic, please view the diagram cross section of the transfer port assembly. The TP sleeve of the BNM does not touch (seat into the counter bore of) the barrel. The TP sleeve in Crosman stock assembly does.

Mine is a rear cocker, bolt length is 3.665". I'm going to lob the end off and install a needle probe that is ~.085" longer (that is as long as I can go and still be able to remove the magazine).

What holds the aluminum transfers port against the exhaust port seal? The easy fix in my mind to spin up a new TP that has a larger (currently od is .240", I think I can make it ~.265" without modifying the breech hole) shoulder so the main body of it can't slip up into the transfer block (mine will slide up into the barrel if you so desired, it's very loose up and down and nothing actually holds it ).

I run tubing on several guns which is an easy mod; the part I can't figure out with this is how do you assemble it with a BNM? I have to slide the barrel in after the breech is attached since the #4 screw is partially covered by the transfer port block. I have both #4 holes tapped in pressure tube, maybe I can add the rearward screw to the breech and be able to access it with the transfer block installed....

ACZan · « **Reply #136 on:** May 12, 2018, 06:10:53 PM »

That's supposed to be a 4:1 scale drawing when I created that diagram in MS Word.

The shoulder of my TP sleeve stops up against the bottom of TP block where it is counterbored for the o-ring. It does not touch the barrel at all. There is a bit of play there, which is represented in the diagram.

This is not how the Crosman stock TP assembly works. If my perception of the Crosman design works, is that the tapered end of the stock TP sleeve fits up against the countersink of the TP hole in the barrel. The length of the TP sleeve allows for it to be pressed against the barrel port and into the seal just sitting inside the counterbore of the TP on the valve of the air tube.

Like I said before, If my barrel was a little larger in diameter at that point and the breech designed for the larger diameter, I would machine the TP sleeve and barrel to allow for the sleeve to be screwed into the barrel after barrel is inserted into the block. I think I could be done with fine machine thread. But, I would definitely had to do a prototype or two to be sure it can be done with the way it is. There just simply might not be enough material to put that off the way it is now without a lot of rework.

What I suspect is that BNM Custom is not consistent on the output of the machined parts. They will differ from one piece to another.

imadunatic · « **Reply #137 on:** May 12, 2018, 07:52:33 PM »

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.

ACZan · « **Reply #138 on:** May 12, 2018, 08:04:23 PM »

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?

Machinist · « **Reply #139 on:** May 12, 2018, 08:13:24 PM »

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

I laughed when I read that. Actually, I almost bought one thinking the same thing!

Glad you were able to recover the missing fps. A good feeling when something finally works.

Steve

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BNM Bolt Probe Problems?

Author Topic: BNM Bolt Probe Problems? (Read 22409 times))