Crosman Discovery .22 Barrel Chamber-Leade Reamer

[ACZan]

Hello Forum Members,

I am in a situation to need a Lothar-Walther barrel blank custom machined for a Discovery .22 which has a BNM custom breech.  I have a very good local machinist friend with many advanced machining technology resources.  He does very good work, especially when I provide him with drawings for the parts. Unfortunately, he doesn't have any experience with airguns or parts.  However, he has done quite a bit of work with firearms.  I will need to have him turn down a L-W blank.  But, feel it would be best to provide him with a ream to create the chamber and leade.  If I can get dimensions, then I can draw the reamer up for him to make.  But, I really don't want to put a lot of work into this as this will be rework.  I was not happy with a barrel previously machined.  I would prefer to buy a very well made reamer from a professional machinist.

Is there anyone out there who can make a ream for this particular .22 air rifle barrel, which I can purchase and provide to my friend for his work?

Just curious, I installed a Crosman factory barrel onto the BNM breech and loaded a pellet, JSB Exact Jumbo Express Diabolo 14.35 gr, into the barrel.  Below are the photographs of where it is sitting in the chamber and port area.

Does this look like the pellet is in correct position, or should it be a little further forward into the leade?

Thanks.

[rsterne]

If that is where the pellet stopped when seated with the bolt, there is something seriously wrong.... ie a mismatch between the bolt probe length and the position of the barrel transfer port.... The back of the pellet skirt should be just ahead of the FRONT of the barrel port, so that the air blast does not hit the side of the pellet.... This has nothing to do with the leade, really, as pellets collapse so easily it can be chambered anywhere....

Bob

[ACZan]

I too thought there must be some mistake.  Was thinking maybe I didn't insert the the barrel in far enough into the breech block.

So, I took off the block on the main body of the breech for good visibility.  Position of the barrel port and the breech port do match up there.  Problem doesn't seem to be in that area.  Then, I placed a pellet against the tip of the probe and checked its position relative to the port.  What was seen in the barrel is also seen on the block.  The pellet position is almost blocking the port.

The first photo is of the breech with the block attached.  The rest should be self-explanatory.

[ACZan]

Sorry, RSterne.  I didn't intend to be misleading on the connection between the pellet position and main topic to find reamer to form the chamber and leade.

Since, I was referring to that area of the rifle, I thought it would be relevant to bring up what I discovered with the position of the pellet.  I needed to be educated on where the best position should be.  If that back edge of the skirt needs to be at a minimum the front edge of the barrel port, then that is information I need to retain.

I would guess it would be best to bring this up with the manufacturer of this breech to remedy the issue.  I think there is enough room to add some length to the probe to get the pellet into proper position and still clear the magazine when retracting the bolt.

[KnifeMaker]

I pretty much cheated to cure this same issue on my BNM breach. I stole what Travis had done on his fine AG's, in that I milled a slot, inline with the bolt direction, large enough that the bolt handle would go forward into the slot and fully seat the pellet home, Then with downward pressure on the handle, it would retract and continue its downward travel to lock. 

Knife

[Machinist]

I have been wondering why guys don't just bore the chamber, rather than making a reamer?  Indicate the bore, put a 10 degree angle on the boring tool and go. 

I just lapped the leed on a stock Disco barrel.  It seemed to have a 7 or 8 degree leed from the factory. 

Steve

[ACZan]

Hey Knife',

I thought you might have something interesting to say about this discovery.  Okay, so you found the same issue, and it appears to be consistent among all the breeches.  Your workaround will also get the job done, too.  Great outside the box solution.

I retracted the bolt with the pellet still attached and there is enough room to add 5mm to 6mm to get the skirt to the edge of the port.  There would be just enough room left over when retracted to allow the magazine to advance to the next pellet.

Did you contact BNM about it?  If so, what did they say?

[Rob M]

I have been wondering why guys don't just bore the chamber, rather than making a reamer?  Indicate the bore, put a 10 degree angle on the boring tool and go. 

I just lapped the leed on a stock Disco barrel.  It seemed to have a 7 or 8 degree leed from the factory. 

Steve

did you mean you feed into barrel with the compound ?? must be a small small boring bar.. either way I agree.. *(&^ , I just get a reamer for the size I want the lead in , then smooth the transition from the reamer section back to the rifling.. makes life simple ,looks factory, no issues , good mating surface for the oring on the probe , etc.

[ACZan]

RSterne,

Do still stand by your comment below you made on this forum topic?

How Is The Leade In And Barrel Port Made?
https://www.gatewaytoairguns.org/GTA/index.php?topic=37755.0

"The proper way to make a chamber and leade is with a custom reamer...."

[ACZan]

Rob M,

What if your o-ring is in the breach opening like the BNM breech instead of on the probe?

[rsterne]

Here is what chambers "should" look like for pellets and bullets.... The position of the leade for pellets is not critical, it can be as shown below, or the chamber can be smooth all the way to the front of the barrel port, with the leade ahead of that.... The leade angle can be quite steep, factory ones are often 30-45 deg. and some are nearly square corners (likely 61 deg., done with a drill bit)....



For bullets, the parallel chamber should extend forward of the barrel port, and the leade, which should be very shallow (1-2 deg.) should engage the nose or front driving band of the bullet to some degree.... A bullet chamber can work with pellets, if carefully made to the correct length.... Pellet chambers will usually make bullets VERY hard to load, particularly if they are short and/or have steep angles....

Bob

[Rob M]

Rob M,

What if your o-ring is in the breach opening like the BNM breech instead of on the probe?

you mean before the barrel , or in the barrel like the marauder?? I might have missed something because I don't have a BNM

[ACZan]

Rob M,

It is in the breech before the barrel.  The BNMs are a bit different.  Added a photo of the opening.  The .22 cal version of the BNM breech which is designed for the Discovery .22 rifles is also design to use the factory Discovery barrels.

[ACZan]

RSterne,

Those are great graphics, thanks.  Where is the ideal location for a pellet to sit ready to shoot?  I may only be able to get the skirt just about a 1mm in front of the port.  If you saw KnifeMaker's and my posts about the BNM bolt not pushing the pellets far enough into the barrel, you'll what I am asking.  Under those conditions, would it be best to modify the chamber and leade to compensate for the design limitations?

[Machinist]

No Rob...

I'm not suggesting that the leed be generated with a boring tool,  but that could be done pretty easily and quickly with a CNC lathe. I don't happen to have one though.

Using an engine lathe I would grind a 10 degree angle on the boring tool and form the leed.  Should be able to get away with it.  Crosman barrels seem pretty soft.

I just bored a .157" hole .500" deep a few minutes ago.  I bored holes .070" diameter years ago.

Steve

[Machinist]

Back to the problem here, it looks like the bolt needs to be longer. 

Steve

[rsterne]

If the BNM receiver has the O-ring in it, behind the barrel, and is designed to use a stock Crosman barrel, then the port in the receiver must be further forward, relative to the O-ring, to allow room for the material in the receiver (shown in that photo) between the O-ring and the back of the barrel.... Since the transfer port location in the tube is fixed, that means the magazine slot is further back, and also the bolt.... This would require a longer bolt probe to push the pellet past the barrel port, as the distance from the magazine slot to the barrel port has increased.... From the photos of the pellet location, it would appear that is not the case....

I wonder if the reports we see of reduced velocity when using BNM repeater conversions are because the pellet is obscuring the barrel port?.... I've never had one, but it would explain those reports.... Regarding pellet position, you are correct, the back of the skirt should be a fraction forward of the front of the barrel port, so that the blast of HPA entering doesn't hit the side of the skirt.... Some skirts are so soft, that could damage them, and you could also get blow-by of course....

Bob

[rsterne]

New thread on this subject....

https://www.gatewaytoairguns.org/GTA/index.php?topic=142819.0

Bob

[KnifeMaker]

Bob, I wish I culd see your pic. Sadly, Photo Puckett doesn't play well with me, so nothing but a tiny blue square at the top of what was supposed to be a pic. GRRRR!

Knife

[ACZan]

Knife',

There was a photo?  Should I be able to see it, because I can't find it.

Oh, wait a minute,... I can see it.  Do you have something blocking it?

Hey Guys,

I stumbled accross this while I was half asleep with the flu early in the morning.

Dave Manson Precision Reamers
https://mansonreamers.com/