how do you smooth out/polish the leade-in/chamber on your barrel?

[quickster47 †]

Any of you guys familiar with a Conical cutter, some call them a tapered end mill? They come in any degree taper. I suspect a nice leade can be achieved with one of these once the correct angle is established with a little math. Why doesn't someone do some measuring of the length and max diameter, figure the angle and machine it with a conical cutter in the lathe. Or, turn the compound on the lathe to the proper angle and use a small boring bar?

I am familiar with the conical cutter but have never used one.  I also just happened to visit a web site yesterday that was discussing conical cutters.

Going to need to do some digging and research on the best way to do the leade for Cormans and then see about cutting a new one.  At least I have a couple of barrels to play around with and can screw up if need be.

Thanks 007...

Carl

[Brent]

The pics looked fine/ good Carl. I could make out the machining marks.

What struck me, is that neither looked that great. It seems that close enough works for most pellets OK. Can't imagine what mine is going to look like when I finally get it out of the 2300s. Hell or high water... mine does not like small wad cutters (like Daisy) when loading them. They always catch bottom front... and I have to use a plastic pick to bring the skirt back down straight and help them in. Even adding a drop of pelletgunoil there... helps very little.

Thanks again... that was educational to see/ know!

[mr007s]

I gathered up a few Conical cutters today and snapped a pic for posting here. This will clarify what I am referring to. In the photo from the left are a 5, 10, 15, 20, 30, and 45 degree cutter. We have them in 1, 3, 7, 12, 25 degree but they must be stashed in one of the guys tool box so they are not pictured.






I had a spare .22 cal barrel in my stash and did some measuring to determine a starting point as to what Crosman had cut it. My limited math skill came up with 19.58 degrees for this barrel. I have not determined if a .177 will be the same for the lead but I suspect it will be near that.
After chucking the barrel up close in the lathe and placing the 20 degree cutter in the tail stock  I gently touched off on the barrel end. I had painted the end with Dykem to help me see when things made contact. Since I only wanted to smooth the factory finish I turned the chuck by hand only, after freeing up the brake. It cleaned up nice and I only did a final finish with a piece of Scotchbrite.
Took it all home and fitted the barrel in a spare breech with a stock probe. Using a CPHP I used the probe to set the pellet. I then pulled the barrel out and could see half the pellet blocking the TP opening.I then mounted an extended probe and repeated the previous steps. The pellet and complete skirt were well past the TP. I took the probe from the breech and eased it into the pellet by hand to get a feel for how much contact was being applied to the probe O-Ring. It felt very snug and I imagine no air would blow back by it.

So, I conclude a 20 degree taper works for a .22 cal barrel with the large end of the leade to measure in the .275-.280" range. This allows the lead to be app. .08" long. If you were to use the 15 degree with a .275 opening at the rear the length of the leade would increase to .118 or 3 mm. I believe that would be acceptable also but I will need to round up another barrel an repeat this test to say for sure.
Hope this helps clear some of the mystery as to the barrel machining. I really wish CM would revel his operation on this subject.

Below is a photo of today's finished experiment.

[Brent]

Wow!!
Very Cool!!!

Thanks so much for doing all that! Really good information to know! Nice

[quickster47 †]

Mr007 where would be the best place to get a 15 and 20 degree conical cutter?

I have several barrels that I would like to play around with and see if I can improve them.

Thanks,

arl

[Pumpmeister]

Would a Bullet shaped Rotary File,work here?

Mario

[quickster47 †]

Would a Bullet shaped Rotary File,work here?

Mario

Don't think it would because you would end up taking off way more than you intended because of the shape of the tool.

Carl

[Pumpmeister]

I see.......Hmmmm. Okay Do Most Harware stores or Machinists supply shops have tha 20 deg. Tool?

Mario

[mr007s]

With some careful grinding and sharpening, a 3/8 split point drill bit could be reshaped to 20 degrees and used in place of a 20 degree Con.. We have to make our own tools in this fashion occasionally for odd cuts and such. This approach would not leave as nice a finish as the Con  simple because the Con is multi fluted.

Carl I will look tomorrow for our supplier, it is either McMaster Carr or MSC

edit to change MSG to MSC

[mr007s]

I see.......Hmmmm. Okay Do Most Hardware stores or Machinists supply shops have the 20 deg. Tool?

Mario

Doubtful they can be found at any hardware. The two businesses posted above carry them. Even though they are called Conical cutters do your search using "tapered end mill"

[1377x]

very nice
there is a thread on airgunhome that covers chamber making but your method is much easier unless you have to make the tool
maybe gippeto will chime in since he makes his own leade-in/chamber

[JEBert]

Thank you Ray,
I want to try resharpening a drill to the correct angle but didn't know what angle.  I cut a leade in a .22 caliber barrel with a tapered reamer and am using it on a gun but the angle is too shallow.  I stopped when the o-ring is still sealing and then drilled for the transfer port using the steel breech to figure that location.  The extended probe pushes the pellet past the transfer port but the pellet is a little loose in the barrel.  I'll cut the barrel off just ahead of the transfer port, loosing 1/2" of length, and try again now that I know the angle.  I'm pretty good at sharpening drill bits but it will be fun trying to sharpen one at that angle as I've never done that before.
I'm not a trained machinist, so just to be clear, it's 20 degrees from the centerline of the bit, not 20 degrees included angle, correct?
Cheers,

[Gippeto]

maybe gippeto will chime in since he makes his own leade-in/chamber

I use a small HSS boring bar @ 11 degrees for forcing cones and the bolts. Polish to 1000 grit with cutting oil. Have had excellent results in .22...I don't play with Crosmans in .177 much at all.

My .25" barrels do not have any forcing cone as IMO they don't need one...the pellet rides in the trough of the receiver and gets pushed through the o-ring. The edge between the chamber and the o-ring is relieved and polished to eliminate any hang ups there.

Have used 11 degrees for the forcing cones on a couple 1077's and a Night Stalker as well...big improvement in feeding.

11 degrees is the "standard" (IIRC) for the forcing cone on pb revolvers.

Al

[mr007s]

Thank you Ray,
I want to try resharpening a drill to the correct angle but didn't know what angle.  I cut a leade in a .22 caliber barrel with a tapered reamer and am using it on a gun but the angle is too shallow.  I stopped when the o-ring is still sealing and then drilled for the transfer port using the steel breech to figure that location.  The extended probe pushes the pellet past the transfer port but the pellet is a little loose in the barrel.  I'll cut the barrel off just ahead of the transfer port, loosing 1/2" of length, and try again now that I know the angle.  I'm pretty good at sharpening drill bits but it will be fun trying to sharpen one at that angle as I've never done that before.
I'm not a trained machinist, so just to be clear, it's 20 degrees from the centerline of the bit, not 20 degrees included angle, correct?
Cheers,

Bert, if you look at the photo on reply 47 the 20 degree cutter is 4th from the left. That will give you an idea as to how sharp the angle should be.
After I had measured and did the math yesterday I took a stick of dental wax, heated it and stuck it in the barrel. After it cooled I removed it and took it to the comparator to double check my figures. The total angle was right at 40 degrees so the 20 degree is per side.
Looked today at prices and mcMaster Carr has one that should do a good job for app. 25 and change.
MSC was considerable more. I have not checked on Amazon or E-Bay which may be an option.

[JEBert]

Thanks Ray,
I am considering recycling all of the front of the barrels I have cut off.  I have about four pieces long enough to make more barrels out of.
Cheers,