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PostPosted: Sun Jul 21, 2013 3:30 pm 
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Hope fully Bob or Shaun can help me out here please? Or any one who knows?

I have just turned down an LW barrel to fit a BNM breech. I have the Barrel port drilled too. Please can someone advise me on the type and size of reamer I will need to chamber the lead in? I assume it will be just enough to allow the probe in and just up to the barrel port in depth?

For a .177, will a 3/16 tapered pin reamer do the job??

Nathan


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PostPosted: Sun Jul 21, 2013 11:39 pm 
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Never tried that but cant see why not the barrel is sealed by the oring so you may have to cone or end mill the breech opening for that. Your choice. Just remember polishing is your friend.

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PostPosted: Mon Jul 22, 2013 12:25 am 
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Don't you have a small boring bore? Probably fairly straightforward that way.

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PostPosted: Mon Jul 22, 2013 11:23 am 
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Likely need to get one made posted on the Yellow N54 July 22 2013, 12:11 PM

Are you reusing the original barrel? if so then a polish should do the trick.
For cleaning up B50/51 and QB barrels I made a reamer of the appropriate size with a 2 degree leade and pleased with how that works. If you have access to a lathe, drill rod and a torch you can make a decent reamer.

Walter...

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PostPosted: Mon Jul 22, 2013 2:12 pm 
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lanky94 wrote:
I have the Barrel port drilled too.


Have never seen a reamer that would run straight if cutting unevenly...need to chamber, free bore (if desired) and do the leade (transition into rifling) first.

You might wish to practice on a couple Crosman barrels first...cheap cheap....or at least cheaper than LW. :wink:

YMMV

Al


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PostPosted: Mon Jul 22, 2013 4:10 pm 
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I agree, chambering first, before drilling the transfer port....

Making a proper, hardened reamer is the best way.... You can likely do an acceptable job with a small boring bar.... If you don't want to worry about a tapered leade, you could even just drill a chamber to just past the transfer port location and then polish a bit of a leade just to make sure there are no burrs.... When the pellet is loaded, I like to see the head engaged into the rifling, but the skirt just sitting in an accurately sized chamber, just in front of the transfer port.... Cast bullets are a lot fussier....

Bob

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PostPosted: Mon Jul 22, 2013 4:35 pm 
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Thanks for the replys. I think the easiest approach is to do as Bob suggested. looking at the OEM barrel, I can copy the cone shaped lead in, no probs. I will measure the probe diameter on the BNM breech and go a fraction over with the drill size.. I will, of course polish it up nicely.

I did drill the barrel port first though :oops:


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PostPosted: Mon Jul 22, 2013 4:44 pm 
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lanky94 wrote:
Thanks for the replys. I think the easiest approach is to do as Bob suggested. looking at the OEM barrel, I can copy the cone shaped lead in, no probs. I will measure the probe diameter on the BNM breech and go a fraction over with the drill size.. I will, of course polish it up nicely.

I did drill the barrel port first though :oops:



Probably your first time doing this job, eh? The first time I did a powderburner re-chambering job, I put the extractor slot on the wrong side!!! Cost me $150 of my own money to buy the customer a new barrel!

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PostPosted: Mon Jul 22, 2013 4:48 pm 
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Smallish point...that "cone shape" on the breech end of a Crosman barrel is a forcing cone....the leade is the transition into the rifling from (in this case) the chamber.

Making mistakes is how a lot of folks learn...I include myself in that...still buggering things up. :rolleyes: "Stuff" happens and life goes on. :wink:

Al


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PostPosted: Mon Jul 22, 2013 5:39 pm 
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Gippeto wrote:
Smallish point...that "cone shape" on the breech end of a Crosman barrel is a forcing cone....the leade is the transition into the rifling from (in this case) the chamber.

Making mistakes is how a lot of folks learn...I include myself in that...still buggering things up. :rolleyes: "Stuff" happens and life goes on. :wink:

Al



:mrgreen:
Hopefully, I will get this one right!! It certainly pays to do ya homework and I will deffo have a practice on an old barrel. I have just ordered the tooling to do this ( from a chap on the yellow forum)


Cut and paste from yellow forum member


I reduce the breach end diameter for a snug fit in the receiver. I cut slots in the barrel for the receivers set-screws, drill the transfer port hole with a #42 (0.0935") drill and counter bore the hole 0.070" with a 1/4" end mill for the transfer port. Next I bore the barrel for the bolt and probe 0.050" deep with # 8 drill and another 0.050" deeper with a #10 drill and use a #2 taper pin reamer to cut the chamber throat then I finish the throat to size and finish with 1000 grit silicon carbide paper.

The first drill is to open the breach face to the diameter of the bolt.
The second drill is to open the bore for the o-ring on the probe.

The taper pin reamer is to smooth the transitions from the smoothbore area you drilled for the bolt, o-ring and past the transfer port into the rifling. You can use a long cone of carbide paper for all the polishing instead of the taper pin reamer and then the carbide paper cone; it just takes longer to polish the surfaces smooth. All you want is a smooth taper that guides pellets into the rifling without damage and a good seal inside the bore with the o-ring. The probe on the bolt will push pellets into the rifling to the same depth past the transfer port.


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PostPosted: Tue Jul 23, 2013 4:17 pm 
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lanky94 wrote:
Cut and paste from yellow forum member


I reduce the breach end diameter for a snug fit in the receiver. I cut slots in the barrel for the receivers set-screws, drill the transfer port hole with a #42 (0.0935") drill and counter bore the hole 0.070" with a 1/4" end mill for the transfer port. Next I bore the barrel for the bolt and probe 0.050" deep with # 8 drill and another 0.050" deeper with a #10 drill and use a #2 taper pin reamer to cut the chamber throat then I finish the throat to size and finish with 1000 grit silicon carbide paper.

The first drill is to open the breach face to the diameter of the bolt.
The second drill is to open the bore for the o-ring on the probe.

The taper pin reamer is to smooth the transitions from the smoothbore area you drilled for the bolt, o-ring and past the transfer port into the rifling. You can use a long cone of carbide paper for all the polishing instead of the taper pin reamer and then the carbide paper cone; it just takes longer to polish the surfaces smooth. All you want is a smooth taper that guides pellets into the rifling without damage and a good seal inside the bore with the o-ring. The probe on the bolt will push pellets into the rifling to the same depth past the transfer port.


Wow that is a really complicated procedure for a relatively simple operation.

The easiest way to accomplish this is to make a "D" drill. You can research the in's and out's of making them on the net. But essentially all your doing is turning a piece of drill rod to the same shape as the one your trying to produce.

Set your compound to 1.5 to 2deg taper
Turn a piece of drill rod to the OD of the pellet skirt back to 1 1/2" from the end of the work.
From the end of the work turn the diameter of the land ID back 5/16" (this will be the pilot)
Move the carriage back from the tip 1/8" and reduce the remaining 3/16" of pilot by ish 0.010"
Without moving the carriage use the compound to cut the 2deg taper back until the tool clears the stock
Cut off your piece leaving an additional 2" of material. Polish and your done

Chuck the work vertical in the drill press and spin it slowly.
Heat the tool to blue/purple and dip it in powdered borax or brazing/welding flux
Continue to heat evenly until the turned area is bright cherry red. Then quench it by swirling in a can of hot oil.
Remove it and clean off any flux in hot water then give it a quick polish on the lathe.

Finally using your bench grinder, grind exactly half the round away from just behind the pilot back to the section that is the full OD of the skirt. (you can stop anywhere within 0.010" of centerline)

With a little practice you can whip up a D drill in 15 minutes. If your going to use it once don't bother tempering it. If you plan on multiple uses then temper it in a 470 deg oven for 30 min
In use ream in to a depth that places the transition to full OD of the skirt just flush with the forward edge of the TP hole.

If you master this you can make up any odd shaped or sized drill/ream in a jiffy

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PostPosted: Thu Aug 01, 2013 12:26 pm 
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Location: England.
With transfer port going in to the barrel and sealing on pellet probe o ring on a taper, ala Walther LG200/300 and latest 400, they are a right pain but getting it to a fine art now.
No doubt the manufacturer has a special tool and knows the depth to go to.
Duplicating is another story, cant measure it just have a guide of proposed angle going in.

Since o ring has to seal on inside cut taper and also provide the lock up, its a sanding job by trial and error.
Have seen one done professionally who made a tool, rough as ars..oles bearing no attention to the lock up, barrel way forward leaving a gap for pellet to push over.
Bare in mind these match barrels cost three times a full Crossman in blank form.

Done it both ways a few times, taper reamer think was 3/16" but had to open out the start for the bolt and o ring taper.
Last one bored in, cant see what your doing and highly scrappable. Still needs sanding to shape after.
I mark the bolt with blue or a felt pen and look for rub marks either side of o ring, remove metal accordingly. Get a better feed in with less tendency for pellets to flip over or rotate.

The bolt should push the skirt just past the transfer port. The taper may aid damaging the pellet and not fond of that idea.


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PostPosted: Thu Aug 01, 2013 6:04 pm 
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Good news...........The barrel chamber on my LW barrel turned out great. The gun (discovery) shoots very well indeed. Initial tests indicate its the most accurate gun I own.

I use a tapered pin # 2 reamer. I drilled the TP out first, which helped me out as I could see how far to cut the reamer back on grinder. I ground it back so the tip of the reamer was the perfect diameter to allow the rifling to start at the end of the TP. The rest was polished with a cone of emery.
The barrel was held in the lathe and the reamer in the tailstock.

With all the info on here from you. I now have the confidence to do my .22 choked BSA barrel for my QB78 build :mrgreen: Of course, it will use different size reamer


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PostPosted: Thu Aug 01, 2013 6:09 pm 
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Location: Rocky Mtn Hse Alberta
Way to go man!!!!!

Good job on the barrel.

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