Would you recut chamber or throat?

[theperfessor]

Lets say you have a 9mm with a .357" diameter barrel. You want to shoot .358" bullets in it but the front of the chamber is too small and the cartridge won't go all the way in. It will chamber cartridges with .356" bullets so it would only take .002" to allow this. Would you recut (lap/bore/ream/whatever) the front of the chamber? Assume the chamber will still have adequate taper for extraction.

Same problem only this time the throat is short and at minimum dimensions and the cartridge won't chamber if any of the full-diameter section of the bullet sticks out of the case. Would you recut the throat to .3585" and lengthen it enough to allow using maximum cartridge length with almost any bullet?

I've heard a lot of folks talk about certain rifles, such as the K-31 Swiss, as having a very short throat, limiting OAL of the cartridge when using certain bullets. If there was no reason to keep it in unaltered condition (in other words it has no collector's or sentimental value) and you wanted to make it a cast bullet-only shooter, would you recut the throat?

Please share your experiences and opinions.

[BulletFactory]

I wish. Simply cant afford the cost though. I dont blame the smith, he doesnt have the tool, its about 60 bucks IIRC. My .40 wont work without leading unless I do this. See the Chamber Shearing thread.

[stubshaft]

I would think you would have to open the chamber or seating it in the case might cause the boolit to become undersize.

[felix]

No, I would not cut a throat giving a gun any kind of freebore. I would cut the throat giving a more gentle leade. Freebore will come about naturally the harder you shoot the gun. ... felix

[williamwaco]

Unless you have a strong sentimenal attraction to this gun, or unless you have the tools, and skills to do it yourself.

Trade it for something that will work.

[mroliver77]

Cutting a cast friendly throat would not be a big deal in most guns. Throating reamers can be rented or it is not real expensive to have a custom made.

Opening the chamber I don't know about. Your reasoning is sound and I know it is done. If you could reach in with a boring bar on straight cases it would not be bad. I have read where Paco Kelly used a straight reamer to open up a .357.

In Veral Smiths book he writes that he hates bore riding cast boolits. He cuts a throat to match the boolit he wants to use or visa versa. If you ever get a chance to read his book it has a great section on throats, boolit fit etc.

For me a Swiss rifle would be shot exclusively with cast. Like you say if it was not a collector piece I would have no qualms about rethroating it. When you can use a full diameter boolit in a rifle there is one less area(bore riding nose) that needs to be fitted.
Jay

[Harter66]

Enter my 32 Remington. It shot j's very well no seating issues w/round,flat or spire point. W/cast it was like you described w/o enough leade or throat to get the action closed. Model 14 Remington pass on cutting. I shortened the necks. It shoots great w/a plain based boolit and out runs jackets by a full 100 fps load for load.

I would lap chamber for .002 ,unless its something like 03 colt pocket or a Nazi luger, uncommon good sense to previal.

[MtGun44]

Perfessor,

As to whether you SHOULD, heck a new bbl is probably only about $150 so that is
the extreme upper limit of the cost of a mistake, unless this is Bill Hickock's personal
9mm (RIGHT !) or similar.

From what I have seen you have the skills to make a piloted reamer to take about
.002 or .003 off of the front of the chamber. I expect that a throating reamer
(gentle leade, like Felix said, not a freebore) may be rentable.

With an indexing head it is not too hard to make up a reamer. I have not done it but
watched my friend who is a tool and die maker set up one.

With your machining skills, I'd think you'd take it as a nice challenge.

If you have another 9mm that does what you want, make a chamber cast and use that as a
guide to making a reamer.

OR - you could make a piloted expandable brass lap with clearance where you are sure you did
not want to cut and just lap out the front of the chamber and rear of the barrel a few thousands.


Bill

[theperfessor]

Yeah, I can make the tooling to do what I need to do, I guess I was kind of hoping somebody else may have done something like this already and how things worked for them before and after. Just trying to figure out if its worth doing. Probably do what you suggest and make a simple brass lap.

I would like to enlarge the front of my HiPower's chamber by about 0.0015" and enlarge the throat to 0.3585" and extend it enough to allow a 0.358" bullet to line up properly. The current chamber is just a snidge tight with some brass and 0.358" bullets, and won't allow anything over 0.3565" to stick out of the case.

I don't ever intend to shoot anything other than cast bullets in it and even so i don't see how it would hurt anything to do what I propose.

[MBTcustom]

I built a rifle over the summer. I cut the chamber to the shoulder with a boring bar, but I cut the neck and throat parts with piloted reamers that I "modified". I bought chucking reamers off of e-bay for low money (like $10-$15) and modified them on a cylindrical grinder to do what I needed them to do. One of those is a .358 reamer that I cut to run a pilot. I ground down the first half inch of flute to .345 and gently tapered it to the .358 diameter and resharpened it by hand with a diamond stone. I have found so many uses for that reamer since but something like that would work for your throating problem.
http://i1120.photobucket.com/albums/l481/goodsteel/IMG_0800.jpg
You can use e-bay to find reamers in almost any size you can dream up, and if you have use of a cylindrical grinder, the rest is down hill.

[leftiye]

Nice stuff Goodsteel! I'm not 100% sure the pilot is needed though. The reamer should cut concentrically for the short length needed for a 9mm neck (something on the order of 1/4").

Perfessor, my answer ( the other knowledgeable gentlemen have given good answers too already, and I don' slight them at all) would be to do both operations, and get the chamber/leade proper. Though the leade will lengthen with wear, some freebore (as tight as will allow chambering of the .358 boolit and long enough to allow the desired boolit design to chamber), as little as possible, will allow you to load the pistol to its potential. Both accuracy, and performance wise. Of course a different boolit design could solve the freebore/leade problem, though not as satisfactorily.

[Houndog]

I would just buy a chamber reamer and have it made to the demensions I wanted. If you are like me you tend to stick with one calibre for a long time and use it in several different guns. You have the option by owning your own reamer to make them all the same. In your case if you want a slightly larger chamber, a .020 frebore setup for a .358 diameter boolet and say a 1.5 degree leade for cast bullets, all you do is use your reamer and it's done. Best of all it's repeatable without much fuss.

[W.R.Buchanan]

Perff: a tapered reamer like used for dowel pin holes would do what you want and not cost too much.

You would just turn the thing down so the max dia is less than the dia of the chamber so it doesn't screw that up. All you need to do is taper the lands in front of the chamber until they are the same size as the grooves or maybe .001-3 larger.

It is just like cutting a forcing cone except you are not going to go but .001-3 deeper than the grooves.

In fact you ARE making it a forcing cone, which would allow the boolit to funnel into the bore which it is not doing right now.

I see no harm in doing this whatsoever, and it would accomidate your slightly bigger boolits in the process, as now, they are hanging up on the sharp edge of the rifling when being jammed into the chamber. That condition also causes a spike in pressure that you might not want in a 9MM running at 35K + psi

I got a tapered reamer at my local hardware store. It was the "Irwin Brand" and has a removable tee handle so it could be ran in a lathe tailstock chuck. It is tapered from 1/8-1/2" and it would have to have about 1.25" of flutes ground off of it to get the max OD down to .380 ish. Also this would be no big loss as this tool was about $5.00!

I think you probably have access to a surface grinder so all you would need to do is put the reamer into a whirlygig or spindex rotary fixture and grind the OD of the reamer down until it would go into the chamber without touching it. Somewhere around .380? (all I have to measure is a spent 9MM case)

The actual taper rate of the reamer is pretty much immaterial as your new forcing cone is only going to be probably .040-.060 long, and all you'll be removing is the lands of the rifling which are .004 ish deep on a side, plus maybe .001-3 extra just to chamfer the front edge of the chamber. You could easily do this much by hand with about 5-10 turns of the reamer, but putting it in a lathe will insure concentricity.

You obviously need to leave a step at the front of the chamber to headspace the round so don't get too froggy with the chamfer after the cone is cut. There is only about .010-.012 on a side there.

Probably a good idea to go in with a Cratex polishing point on a Dremel or Foredom tool to deburr the thing afterwards.

This is a cheap way to fix your problem. or a brass lapp would work too, it would just take longer to accomplish.

Hope this helps.

Randyhttp://castboolits.gunloads.com/imagehosting/thum_182084f13247b22a58.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=3461)

[W.R.Buchanan]

Perff: a tapered reamer like used for dowel pin holes would do what you want and not cost too much.

You would just turn the thing down so the max dia is less than the dia of the chamber so it doesn't screw that up. All you need to do is taper the lands in front of the chamber until they are the same size as the grooves or maybe .001-3 larger.

It is just like cutting a forcing cone except you are not going to go but .001-3 deeper than the grooves.

In fact you ARE making it a forcing cone, which would allow the boolit to funnel into the bore which it is not doing right now.

I see no harm in doing this whatsoever.

I got a tapered reamer at my local hardware store. It was the "Irwin Brand" and has a removable tee handle so it could be ran in a lathe tailstock chuck. It is tapered from 1/8-1/2" and it would have to have about 1.25" of flutes ground off of it to get the max OD down to .380 ish. Also this would be no big loss as this tool was about $5.00!

I think you probably have access to a surface grinder so all you would need to do is put the reamer into a whirlygig or spindex rotary fixture and grind the OD of the reamer down until it would go into the chamber without touching it. Somewhere around .380? (all I have to measure is a spent 9MM case)

The actual taper rate of the reamer is pretty much immaterial as your new forcing cone is only going to be probably .020-.030 long, and all you'll be removing is the lands of the rifling which are .004 ish deep on a side, plus maybe .001-3 just to chamfer the front of the chamber. You could easily do this much by hand with about 5-10 turns of the reamer, but putting it in a lathe will insure concentricity.

This is a cheap way to fix you problem.

Hope this helps.

Randyhttp://castboolits.gunloads.com/imagehosting/thum_182084f13247b22a58.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=3461)

[theperfessor]

Wow, this has gotten some great responses and really good suggestions on how to accomplish this project. Here's the backstory:

A few years ago I ought a Lee two cavity 358-125 RF mold. Sized to 0.3575 - 0.3580", and seated with the crimp groove flush with the case mouth, it worked fine in my 9mm HiPower. The only problem was that some brands of brass wouldn't quite chamber with bullets this size. OK, pull those out of the mixed brass pile and use the rest, no problem.

I liked the mold enough I bought a six cavity version. That's when the fun started. Jams and failure to go into battery, turns out the two cavity mold dropped bullets with the nose section above the crimp groove at about 0.002" under the body diameter, which was barely being kissed round as it got sized in a 0.358" die. The six cavity mold dropped a bullet that was large enough that it was 0.358" above the crimp groove after sizing and would not feed into the throat.

I gave the two cavity away before I discovered this. Oops! Well, I really don't like Lee's two cavity molds as much as I like their six cavity molds, and I've done this before - try the two and if it works for me I buy a six and use the two for trading or to give a new caster.

I thought about making a simple sizing die to size the exposed portion of the bullet down enough to chamber, but this adds another step every time I'd load for this gun. I'd rather take the time (once) to set it up for cast. I've got a couple other bullets I'd like to use in this gun but they really need to be seated out a little more than I can seat them right now.

Thanks again for all the responses and suggestions. I appreciate you sharing your experiences.

[EDG]

>>I would like to enlarge the front of my HiPower's chamber by about 0.0015"<<<

You could rub that much out using JB compound on expanded cases.
As far as the throat goes take a case with a bullet in it and turn it against the throat with a little JB on it until you see how easy it cuts. The figure out if you want to use a more aggressive lapping compound.

[HeavyMetal]

I'd taper the leade`/throat /rifling / whatever you want to call the area in front of the chamber until my boolit of choice chambered 100% of the time.

A little "freebore" wouldn't hurt either as that will reduce pressure, generally, and has been a"trick" used bymany a rifle smith with wildcat cartridge conversions.

In most 9mm's I've found the limiting factor to OAl is the mag not the chamber!