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Author Topic: How much jump before pellet hits the grooves?  (Read 3305 times))

Offline Spin

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Re: How much jump before pellet hits the grooves?
« Reply #40 on: November 11, 2021, 11:49:32 PM »
Agreed, I think the drill press will produce a better result.  Or do a hybrid…use the bench grinder/drill approach to remove the bulk of the material.  Then chuck the reamer into a drill press (or hand drill clamped to a surface) and spin it up, then slowly bring in a spinning emery wheel and just kiss the shoulder.  Be patient and continue to just barely let the wheel abrade the shoulder so it takes down only the high spots.  Eventually it will get to the point where it is touching all flutes equally for the full rotation.  Usually can tell by the way it sounds.  If uncertain, color the shoulder with a Sharpie (or blue layout dye) and spin it up again and briefly touch it with the emery wheel and stop to see if it removed the marking from all flutes.
Guys the spindle bearings on drill presses, moto tools, etc aren't meant to handle the side torque you're talking about applying. A Bridgeport or similar knee mill would be a better choice but even there slop from wear and inaccuracies in original machining can foul you up before you even get started. Take a precision ground pin and chuck it up in a Bridgeport collet some time and put a tenth or half thou indicator and rotate the spindle by hand. And grinding requires rigidity or that wheel or grinding drum will start bouncing around like Roy Rodgers on Trigger!
     Now clear things up a bit. Are you trying to put in a short free bored throat A La' Roy Weatherby effectively creating a very short smoothbore before the projectile engages the rifling, also was commonly done in large artillery pieces for quite a time. (sounds kind of like it and that does boost velocity) or are you trying to cut and grind in a shallow long angled throat that will gradually constrict down to meet the inside groove diameter?
     For skirted pellets the initial air blast and breech pressure assures maximum ID bore dia. seal. You might grind in a tiny angled lead in the face of the lands? Simple polishing will go a ways towards accomplishing that. Precision seating seems like it might serve you better and with less "metal wrecking" -( trade slang for Machinist - Metal Wrecker) some Carm magazines and single shot loaders employ internal O-rings that gently center the pellet or slug before final seating. Doesn't FX have internal
O=rings in their breeches that the probe pushes the round and itself through when it seats the projectile.
     It just seems to me you're going to great effort for something that may see minimal reward or go south and cost you for your efforts.
« Last Edit: November 11, 2021, 11:53:47 PM by Spin »
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Re: How much jump before pellet hits the grooves?
« Reply #41 on: November 11, 2021, 11:53:15 PM »
Don,

The length of the ramp into the lands is independent of caliber.  Only the breech cone angle and land depth matter.  Because .177 and 22 barrels tend to have rifling that is half the depth of .357 and .45 barrels, this means their ramp lengths would be about half as long - assuming the same standard reamer angle was used.
« Last Edit: November 12, 2021, 12:42:18 AM by subscriber »
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Offline Spin

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Re: How much jump before pellet hits the grooves?
« Reply #42 on: November 12, 2021, 12:08:05 AM »

Don,

The length of the ramp into the lands is independent of caliber.  Only the angle and land depth matter.  As such, .177 and 22 barrels tend to have rifling that is half the depth of .357 and .45 barrels.  This means the ramp length would be half as long - assuming the same standard reamer angle was used.
OK so if you only want to angle the faces of the lands use an oversize reamer and have it ground to the leading bore diameter minus .0006 to .0012.  It will serve as a guide just stone off their leading edges so they won't catch and dig or scar the bore. The angles front of the cutting flute will be the only cutting edges with back relief. Just grind them to whatever angle you want on the face of the lands. Do the actual cutting inside the barrel by hand, plenty of lube and stop and withdraw the reamer and blow out any chips and metal particulate frequently Layout dye and a good  gooseneck LED light. The centers should already be in both ends of the reamer. If they aren't buy a reamer that does have them. A tool grinder would be great but with the right tooling you could do a real precision job fabing just the kind of hand reamer you need.
« Last Edit: November 12, 2021, 12:12:32 AM by Spin »
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Re: How much jump before pellet hits the grooves?
« Reply #43 on: November 12, 2021, 12:40:31 AM »
Jerry,

The focus of this thread is an optimal chamber shape for a .357 slug.  One that combines easy loading with peak muzzle energy and the tightest possible groups.  Pellet performance was discussed, but is assumed something that might need to be compromised to optimize slug performance.

Grinding the cutting edges off a taper reamer does not have to take a lot of force.  After all, while the reamer is hard, not much metal is removed.  The idea is to remove only a short section of cutting flutes behind the .358" section of the cone. 

To better illustrate what we are on about; I used Solidworks to modify a standard #7 taper pin 3D model I had downloaded from McMaster .  See attached images. 

If a less than rigid and controlled grinder is used then the relieved section may be cut as a reverse taper, rather than the cylinder shown in the first image below.  In that way the reverse taper section is just clearance for tool relief.  Thus the flutes in that relieved section are not sharp, and don't need to be.

I agree that a rigid setup for the grinder would make this easier; and reduce the risk of dulling the reamer flutes that form the cone up to the .358" section.

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Re: How much jump before pellet hits the grooves?
« Reply #45 on: November 12, 2021, 01:08:38 AM »
Jerry,

Are you suggesting modifying a standard diameter reamer by grinding in tapered cutting flutes at the front end?  Modifying a standard taper pin reamer to stop cutting at a given diameter seems easier...

While a pilot can help with alignment and prevent chatter (like Bob's DIY reamers), a badly made pilot will score the land tops.  At low speeds, by hand, even a pilotless modified taper pin reamer works - see makeral5's post links in the above message.
« Last Edit: November 12, 2021, 01:15:11 AM by subscriber »
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Offline nervoustrigger

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Re: How much jump before pellet hits the grooves?
« Reply #46 on: November 12, 2021, 02:11:11 AM »
Guys the spindle bearings on drill presses, moto tools, etc aren't meant to handle the side torque you're talking about applying. A Bridgeport or similar knee mill would be a better choice but even there slop from wear and inaccuracies in original machining can foul you up before you even get started. Take a precision ground pin and chuck it up in a Bridgeport collet some time and put a tenth or half thou indicator and rotate the spindle by hand. And grinding requires rigidity or that wheel or grinding drum will start bouncing around like Roy Rodgers on Trigger!

A mill with near-zero runout would be nice but not at all necessary for the operation we were talking about.  This is just knocking down the flutes at the fat end of the tapered reamer.  The part of the reamer that will be doing the actual cutting of the leade is still preserved in its OEM form.  And on top that, the cleanup pass of "just kiss the shoulder" with a light touch from a spinning emery wheel...that means there is practically zero side load.  Really, a drill press is perfectly acceptable for this operation.
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Re: How much jump before pellet hits the grooves?
« Reply #47 on: November 12, 2021, 03:41:25 AM »
You know, if you made a thimble for the actual "chamber" part - you wouldn't have to modify the reamer. Just push in the reamer until the lands are removed at the very end of the barrel and then attach it to a thimble.
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Re: How much jump before pellet hits the grooves?
« Reply #48 on: November 12, 2021, 04:16:16 AM »
I very much like the thimble approach.  The question is if the Benjamin Bulldog can be adapted with a thimble.  That is for Greg to figure out.

You know, if you made a thimble for the actual "chamber" part - you wouldn't have to modify the reamer. Just push in the reamer until the lands are removed at the very end of the barrel and then attach it to a thimble.
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Offline lennyk

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Re: How much jump before pellet hits the grooves?
« Reply #49 on: November 12, 2021, 08:13:52 AM »
FX uses a brass section which has the transfer port which is then attached to the barrel.
Do they do the ramp transition in that brass piece ?
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Offline rkr

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Re: How much jump before pellet hits the grooves?
« Reply #50 on: November 12, 2021, 08:45:07 AM »
FX uses a brass section which has the transfer port which is then attached to the barrel.
Do they do the ramp transition in that brass piece ?


It's just a straight thimble with a barrel port they use. Leade in starts right at the beginning of the liner.
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #51 on: November 12, 2021, 10:27:01 AM »
One of the reamers arrived yesterday and I started looking at the work ahead...

I want to grind the tip a little to install a brass tube to help center the small end.

Then there is a lot of stuff that may need to come off the big end to get it to slip inside the chamber. Need to pull an o ring and do some measuring. I may wait to do the grinding until the chamber cast material arrives and I can really see (and measure) what I need. While I do have a junk barrel, I still want to be successful with the first and second try.

I have a straight flute on the way, and a spiral flute in hand. Bought the spiral after the first reamer was shipped as the wrong part, still waiting for a replacement and hedged my bets and bought the spiral flute.

Both of these are HSS, would a carbide end mill cut these well enough that they would work after the cutting? I may set them up on my little mill with rotary table and tail stock to be more precise. Need to check my mills but I think I have a couple of solid carbide that should be able to cut this tool steel. Grinding without a proper grinding machine will be haphazard at best, no matter the amount of care given. Since I couldn't find any small (and decent) cup wheel stone or diamond tools to put in my little mill, a carbide might be best. I'll fall back on a bench grinder and taking a bunch of time, but not my first choice.
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Offline sb327

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Re: How much jump before pellet hits the grooves?
« Reply #52 on: November 12, 2021, 10:42:22 AM »
Your not going to be cutting hss with carbide tooling.

Can you make up a makeshift toolpost grinder from a dremel? (Can’t remember if you have a lathe)

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Offline JuryRigger

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Re: How much jump before pellet hits the grooves?
« Reply #53 on: November 12, 2021, 11:18:18 AM »
Agreed, I think the drill press will produce a better result.  Or do a hybrid…use the bench grinder/drill approach to remove the bulk of the material.  Then chuck the reamer into a drill press (or hand drill clamped to a surface) and spin it up, then slowly bring in a spinning emery wheel and just kiss the shoulder.  Be patient and continue to just barely let the wheel abrade the shoulder so it takes down only the high spots.  Eventually it will get to the point where it is touching all flutes equally for the full rotation.  Usually can tell by the way it sounds.  If uncertain, color the shoulder with a Sharpie (or blue layout dye) and spin it up again and briefly touch it with the emery wheel and stop to see if it removed the marking from all flutes.
Guys the spindle bearings on drill presses, moto tools, etc aren't meant to handle the side torque you're talking about applying. A Bridgeport or similar knee mill would be a better choice but even there slop from wear and inaccuracies in original machining can foul you up before you even get started. Take a precision ground pin and chuck it up in a Bridgeport collet some time and put a tenth or half thou indicator and rotate the spindle by hand. And grinding requires rigidity or that wheel or grinding drum will start bouncing around like Roy Rodgers on Trigger!
     Now clear things up a bit. Are you trying to put in a short free bored throat A La' Roy Weatherby effectively creating a very short smoothbore before the projectile engages the rifling, also was commonly done in large artillery pieces for quite a time. (sounds kind of like it and that does boost velocity) or are you trying to cut and grind in a shallow long angled throat that will gradually constrict down to meet the inside groove diameter?
     For skirted pellets the initial air blast and breech pressure assures maximum ID bore dia. seal. You might grind in a tiny angled lead in the face of the lands? Simple polishing will go a ways towards accomplishing that. Precision seating seems like it might serve you better and with less "metal wrecking" -( trade slang for Machinist - Metal Wrecker) some Carm magazines and single shot loaders employ internal O-rings that gently center the pellet or slug before final seating. Doesn't FX have internal
O=rings in their breeches that the probe pushes the round and itself through when it seats the projectile.
     It just seems to me you're going to great effort for something that may see minimal reward or go south and cost you for your efforts.
While you're absolutely right concerning side loading on drill press spindles; I can tell you from experience that a passable (IE not exactly precision; but workable and certainly better that could be achieved by hand) result can be had... the key is in going SLOOOOOOOOOOOOOOWWWWW... It's all about the concept of sparkout; and the highest points of rotation... After all; we're only after getting some material out of the way; and keep the 'top end' of the taper to cut the throat at least fairly concentric/perpendicular...
I've done some grinding in a Bridgeport with a 1/4" die grinder in the vise BTW  ;)
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #54 on: November 12, 2021, 03:25:13 PM »
I don't have a lathe, but I might be able to rig something on my mill. Put the reamer in a collet and a rotary tool on the table. I'll have to look at that as an option since it would be far more accurate than a bench grinder. Height is my biggest issue here, only have a little desktop micro mill, but I've never let it stop me from doing projects bigger than it can handle.
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Re: How much jump before pellet hits the grooves?
« Reply #55 on: November 12, 2021, 04:01:08 PM »
Greg,

I have removed a broken HSS steel tap from a threaded hole by drilling it out with a tungsten carbide endmill.  If you do this, the carbide endmill should be considered consumable - an overhead cost.

I have cut HSS and tungsten carbide with diamond coated disc, cylinders, burrs, files and laps.  You are not cutting cemented tungsten carbide, but if you did, you should avoid breathing the dust.  The cobalt binder is very bad for your lungs.  High cobalt HSS might carry a similar risk. 

Diamond coated burrs, discs and files are not expensive:
https://www.mcmaster.com/4490A66/
www.amazon.com/Diamond-Cutting-Coated-Mandrel-Dremel/dp/B07D9L8MNN
www.amazon.com/gp/product/B01DFO18BC
www.amazon.com/gp/product/B002RL83DQ/


I made a "toolpost grinder" out of wood that I gripped in my mill vice, to hold a Proxon grinder (fancy Dremel).  The HSS part was in the mill spindle collet, while the Proxon provided the speed for the diamond grit to work. 

The images below show a taper reamer being relief ground.  The first image has the Proxon axis perpendicular to the mill spindle as an initial setup.  The next two images show the Proxon set to provide the desired relief angle.

« Last Edit: November 12, 2021, 04:05:56 PM by subscriber »
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #56 on: November 12, 2021, 05:45:05 PM »
I was looking at my 123 blocks and figuring out how to clamp the rotary tool hand piece to them, very similar to what you did. Going to stick some round stock through the holes, drill and tap for a clamping screw, and go for broke. Just need to measure the hand piece when I get home to make sure I can do everything I want. An angle plate would be nice, but don't have one.

I do have some cheap HarborFreight diamond tools, they might work with light pressure. I think I need to take around 0.070 inch off the big end which might be a lot of travel.
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Re: How much jump before pellet hits the grooves?
« Reply #57 on: November 12, 2021, 06:15:08 PM »
Greg,

What you describe is going to be easier than you imagine.  Even if it takes most of an hour to set it up carefully. 

All you need is a clearance angle.  You can eyeball it.  A goal of the same taper angle as the reamer, but tilted the other way is achievable by eye.

Grinding relief into the reamer is going to take 10 minutes, tops. The hardest part is figuring out where to stop in order to preserve the cutting flutes at the desired diameter.
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Offline Greg_E

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Re: How much jump before pellet hits the grooves?
« Reply #58 on: November 12, 2021, 09:56:43 PM »
I just need to knock the flutes down, the tip is around .320 and the big end .4xx so I don't need to worry at all about angles. If I didn't want to try and put some kind of pilot on the small end, I'd only need to reduce the big end to fit.
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Re: How much jump before pellet hits the grooves?
« Reply #59 on: November 12, 2021, 11:28:37 PM »
Grinding a pilot onto the reamer nose is not trivial.  You should know the land diameter of the barrel to make the pilot very slightly smaller.  The pilot needs to be very smooth and very round, else it may do more harm than good.

What the pilot does is reduce the propensity for the reamer to chatter against the lands; even when the chambering job is run in a lathe.  It also help the reamer "cut to true size" when used in a lathe.   

An unpiloted chambering reamer must only be turned by hand or it is guaranteed to chatter.  Using a left hand spiral flute reamer in a righthand twist barrel will make the job much easier.  The same direction of flute spiral as the rifling, at the same "twist", with the same number of flutes as rifling grooves is the worst for catching on every land...

I know I posted a bunch of threads earlier.  The one by makeral5 shows what a modified unpiloted reamer can do.  Note that the finish obtained with that reamer is before any kind of polishing, after chambering.

Bob Sterne makes piloted chamber reamers and they well work for him.  I suspect he offer many pointers on making them and the pros and cons.  It may be that a D-section reamer must have a pilot to support the cutting loads; while a multi-flute reamer can support its cutting loads between flutes; even without a pilot.
« Last Edit: November 12, 2021, 11:31:24 PM by subscriber »
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