Reamer Question

[aandabooks]

I want to change the caliber of a barrel and am not sure what reamer I should be shopping for.  I acquired an extra 9mm barrel for a Tactical Sport and want to change it to .357sig.  I see finishing reamers and roughing reamers.  Do I need to get both or will just the finishing reamer do the job for a one time cut?  

[Powder Finger]

Finish

[jcc7x7]

1 hour ago, aandabooks said:

I want to change the caliber of a barrel and am not sure what reamer I should be shopping for.  I acquired an extra 9mm barrel for a Tactical Sport and want to change it to .357sig.  I see finishing reamers and roughing reamers.  Do I need to get both or will just the finishing reamer do the job for a one time cut?  

The only concern I can foresee is if the pilot will reach into the rifling to keep the reamer straight.

Agreed that all you should need is a finish reamer unless you were going to be doing several bbls.

[ltdmstr]

I dunno.  You're taking off about .043.  Seems like a lot for a finish reamer.  Also, just curious on how you intend to do this.  Cutting it by hand is pretty sketchy.  Much better to do it on a lathe and have everything dialed in to make sure it's straight.

[aandabooks]

42 minutes ago, ltdmstr said:

I dunno.  You're taking off about .043.  Seems like a lot for a finish reamer.  Also, just curious on how you intend to do this.  Cutting it by hand is pretty sketchy.  Much better to do it on a lathe and have everything dialed in to make sure it's straight.

I've always used reamers for the last .002-.003" and that is why I asked.  I have a 9mm finish reamer that I have used on a couple 9mm barrels too make deeper but changing a caliber of a bore is something that I have not done.  It will be done on a lathe with the barrel indicated in. 

[zzt]

You can rent reamers.  So I'd use roughing and finish.

[Yondering]

Seems to me there are a couple things to consider before the finishing/roughing reamer question matters.

 

- Is this 357 Sig going in a 40 S&W slide or a 9mm slide? If it's a 9mm slide, it won't work; the breech face has to accomodate the 40 S&W size case head.

 

- Is that TS barrel nitrided? If it is, a regular HSS reamer is no good; you'll need to locate a carbide reamer.

 

If you've sorted out both of those things - a finish reamer is fine. You won't see any benefit from a roughing reamer in this case, other than to save wear on the finish reamer; for a one-off job it doesn't matter much. 

[aandabooks]

5 hours ago, Yondering said:

Seems to me there are a couple things to consider before the finishing/roughing reamer question matters.

 

- Is this 357 Sig going in a 40 S&W slide or a 9mm slide? If it's a 9mm slide, it won't work; the breech face has to accomodate the 40 S&W size case head.

 

- Is that TS barrel nitrided? If it is, a regular HSS reamer is no good; you'll need to locate a carbide reamer.

 

If you've sorted out both of those things - a finish reamer is fine. You won't see any benefit from a roughing reamer in this case, other than to save wear on the finish reamer; for a one-off job it doesn't matter much. 

Going in a .40 TS slide.  The barrel is not nitrided.  It is a barrel that CZCustom carries and is the OEM equipment.  

 

I let go of my only .357sig a couple months ago and am kind of excited to be setting up a TS as a .357sig Limited gun.  I love the round and been loading for it for several years and have a lot of supplies to load.  I asked around about getting this done and when the extra 9mm barrel fell in my lap I decided it was time to do this.  

[Yondering]

OK good, in that case it's a pretty easy job to run a finish reamer in there. Do make sure to use go/no-go gauges though (don't just use a piece of brass). I rent mine from 4D Reamer Rentals; generally they have an option to rent the gauges along with the reamer although I haven't checked on 357 Sig. 

[MB DOC]

Unless you are reaming a lot of barrels roughing reamer is not needed. Another thing to consider is bore diameter. Nowlin and SV have tight 9mm bores. Most standard reamers wont fit. I've not checked a CZ barrel.

[zzt]

You get a much nicer finish if you finish ream only the last thou or two.

[Yondering]

23 hours ago, zzt said:

You get a much nicer finish if you finish ream only the last thou or two.

 

Are you basing that on experience reaming chambers, or just straight holes with chucking reamers? 

 

[zzt]

1 hour ago, Yondering said:

 

Are you basing that on experience reaming chambers, or just straight holes with chucking reamers? 

 

 

I'm basing that on years of tool & die making experience.

[Yondering]

So no chamber reaming experience then. 

 

Here's the thing with reaming a chamber for a bottneck cartridge - as it gets close to final size, you go in small steps and clean and measure between steps. That final step is just removing a thousandth or two. When it's done right the finish turns out great, regardless whether a roughing or finish reamer was used to get there. 

 

I get it, I have years of machining experience too. However, that machining experience doesn't necessarily translate to gunsmithing experience; often it helps and sometimes it overlaps, but lots of times it doesn't. 

[zzt]

2 hours ago, Yondering said:

So no chamber reaming experience then. 

 

Here's the thing with reaming a chamber for a bottneck cartridge - as it gets close to final size, you go in small steps and clean and measure between steps. That final step is just removing a thousandth or two. When it's done right the finish turns out great, regardless whether a roughing or finish reamer was used to get there. 

 

I get it, I have years of machining experience too. However, that machining experience doesn't necessarily translate to gunsmithing experience; often it helps and sometimes it overlaps, but lots of times it doesn't. 

 

There is absolutely no difference between chambering for a straight walled (or tapered) pistol cartridge and reaming a set of holes with a two diameter reamer (or three for that matter).  In fact, that is exactly what a pistol cartridge is, a two diameter (or three) reamer.  If you want the best finish, rough and then finish ream. 

 

a doesn't want to deepen a short chamber.  He wants to enlarge a large portion of a 9mm chamber to 40.  I think your definition of a good finish differs from mine.

[MemphisMechanic]

Having reamed at least fifty barrels for guys, I will say that you have the ideal gun for a large amount of material removal.

 

SP-01 shadow and TS barrels cut like butter. As easy as they come.

 

Shadow 2s? Well, there’s a reason I have a carbide reamer. Too many guns feature hardened barrels and polygonal rifling nowadays.

That said, @zzt has a point. What you need to do is to open up a substantial portion of the rear of the chamber itself from a hole sized for 9mm brass to one for .40 brass, right? Gotta make room for that fat bottom of the case.

 

It *seems* to me that you need a 357SIG roughing and finish reamer for this task. Most of what you need to do has nothing to do with the rifled portion of the barrel.

 

Edited November 7, 2019 by MemphisMechanic

[aandabooks]

1 hour ago, MemphisMechanic said:

Having reamed at least fifty barrels for guys, I will say that you have the ideal gun for a large amount of material removal.

 

SP-01 shadow and TS barrels cut like butter. As easy as they come.

 

Shadow 2s? Well, there’s a reason I have a carbide reamer. Too many guns feature hardened barrels and polygonal rifling nowadays.

That said, @zzt has a point. What you need to do is to open up a substantial portion of the rear of the chamber itself from a hole sized for 9mm brass to one for .40 brass, right? Gotta make room for that fat bottom of the case.

 

It *seems* to me that you need a 357SIG roughing and finish reamer for this task. Most of what you need to do has nothing to do with the rifled portion of the barrel.

 

 

I went ahead and rented both a roughing and finishing reamer.  Still cheaper than buying one.  I figure this is a one time project that I won't need to actually own the reamer forever.  I did buy a 9mm reamer a couple years ago because I own a lot of 9mm handguns.  I've loaned it out to friends a few time too.

 

 

 

[zzt]

16 hours ago, aandabooks said:

I went ahead and rented both a roughing and finishing reamer.

 

Good move.  You'll have smoother chamber walls that way.

[Yondering]

1 hour ago, zzt said:

 

Good move.  You'll have smoother chamber walls that way.

 

If you say so. I've reamed a bunch of chambers for bottleneck cartridges, including what the OP is doing with 357 Sig, and have done it both ways. For his job, it won't make a lick of difference. It won't hurt, but I wouldn't have bothered. 

[aandabooks]

Finally got this project done.  Rechambered the 9mm barrel yesterday and went out today and ran 50 rounds of previously built loads.  Barrel cut like butter with some good cutting oil and 50 RPM in the lathe.  I have to look up the load data but I know they are made using 135gr S&S Casting bullets.  

 

Going to take some tuning of the recoil spring weight as there was a bit more snap to the .357sig rounds vs. .40.  I finally have a .357sig back in the stable.  I like the round and have a ton of reloading supplies for it.  I'll likely shoot it a bit in Limited in the future.