Relation of reamer dimension to actual chamber dimension ?

[big5ifty]

If I measure the diameter at the point on a reamer, how much extra is actually cut at that point in the chamber ? I'm measuring it .485 at the case mouth on the reamer.

Can I add one thou ?

I've got a 458x1.5 reamer.

I found that cutting down 458 Win Mag or 7mm Rem Mag brass to 1.5" does not work on it's own, the walls are too thick.

The case walls at the 1.5" mark are +- 20 thou. If I seat a .459 bullet in there, the round can't chamber because the .459 + 40 thou exceeds the chamber dimension at the case mouth.

When i size the brass in a .375 H&H die, the diameter at the case mouth comes out at .469.

I'm tryng to work out what size case reamer I can use to run into the sized cases to bring the case wall thickness down at the mouth, and by how much.

Has anyone done this before for the 458x1.5 ?

 

[David Christian]

???

Maybe try breaking down you question a bit more? Add a reamer print? Simplify and specify your question?

 

[SKWERLZ]

If I measure the diameter at the point on a reamer, how much extra is actually cut at that point in the chamber ? I'm measuring it .485 at the case mouth on the reamer.

Can I add one thou ?

I've got a 458x1.5 reamer.

I found that cutting down 458 Win Mag or 7mm Rem Mag brass to 1.5" does not work on it's own, the walls are too thick.

The case walls at the 1.5" mark are +- 20 thou. If I seat a .459 bullet in there, the round can't chamber because the .459 + 40 thou exceeds the chamber dimension at the case mouth.

When i size the brass in a .375 H&H die, the diameter at the case mouth comes out at .469.

I'm tryng to work out what size case reamer I can use to run into the sized cases to bring the case wall thickness down at the mouth, and by how much.

Has anyone done this before for the 458x1.5 ?

You need to ream and probably anneal the bullet seating area.
Common practice on all the shortened wildcats.

 

[big5ifty]

???

Maybe try breaking down you question a bit more? Add a reamer print? Simplify and specify your question?

What is the size of the hole a reamer makes compared to it's actual size ?

The finishing reamer print says 0.483 at the case mouth. The actual reamer is measuring 0.485.

 

[Walt Krafft]

Your machining practices will have a lot to do with what size and how repeatable a reamer will cut.

 

[big5ifty]

So there is no rule of thumb to say a finished hole is half or one thou bigger than the reamer ?

I't probably not a material dimension for my purpose, I know the reamer is 0.485 at the case mouth, I should just work on that minus 3 thou for the maximum loaded case mouth diameter.

 

[Dave M.]

What is the size of the hole a reamer makes compared to it's actual size ?

The finishing reamer print says 0.483 at the case mouth. The actual reamer is measuring 0.485.

How are you measuring this? If you are using calipers they aren’t nearly accurate enough to hang your hat on. The reamer is only going to be as accurate as the guy that set up the grind process for it felt it needed to be. And in this case, I’d say he thought .002” was close enough. Who made the reamer? What is the listed print tolerance on the dimension in question? How many times has the reamer been used? All of these factors will drive how close any given reamer is to matching its print. Tolerances exist on any machined part. There is no such thing as the perfectly machined part.
Dave

 

[divingin]

I'm tryng to work out what size case reamer I can use to run into the sized cases to bring the case wall thickness down at the mouth, and by how much.

I think you need to research neck turning. Easier than trying to shave the inside of the case neck.

Unless I'm misunderstanding.

 

[DaveTooley]

It's been my experience and confirmed by Ferris Pindell years ago that when a reamer is run in full length/depth, with a properly setup barrel, the diameters are very close to reamer dimensions. Close enough that we don't have the capability to measure the difference. Run a reamer in to make a shoulder bump gage and the neck and FB will be slightly over size.

 

[Dusty Stevens]

It wont cut smaller but you can make it cut bigger

 

[RegionRat]

Too many variables to make a general statement but in the right setup with a skilled operator the finish hole/chamber can be within a hundred microinches of the reamer, but then in a sloppy setup in the wrong hands you may find ten times that much.

 

[DShortt]

If the chamber has been cut correctly the reamer will fit so tightly you won't be able to detect any movement. Back the reamer out a couple of thousands and it'll still be difficult but not impossible to detect movement.

If your set-up and methods are wonky then there's no telling what sort of mess you'll wind up with.

So as mentioned above, if done correctly you won't be able to measure the difference from the reamer dimensions. If you've got the reamer running non-concentric then you could wind up with just about anything.

Also - just because you have a reamer print that doesn't automatically mean the reamer was ground to match it perfectly. But I'd want to be damn sure I knew what I was doing measuring it before I started complaining.

 

[Ray123]

A properly cutting reamer cuts to size to maybe plus 1 ten thousanths of an inch oversize on diameters used in normal gun work.. It has to be sharp with good machining practices, cutting fluid, with enough material left in the hole to have the flutes actually cut...not rub on oversize hole.
I cut cases down all the time, .020" thickness on brass neck or straight wall is too thick.
So I cut a .338 case down to 1.5" and a .458 bullet falls in with lots of clearance. Like .466" dia hole...but that doesn't matter here. The relationship between the die and the chamber is what is needed.
So your sizing die is a real .458 X1.5" die then without an expander ball, just FL size a case measure the inside diameter at the case mouth...with thick brass it should be much smaller than say .456" dia for a .458" bullet as seating expands the case past where the diameter interfears with chambering.
I bore the ID in a lathe collet and also turn ODs with a taper blend out on the tool...if a lot of metal has to be removed...if you ream or just bore the ID the depth must go past the length of the deepest seating bullet you intend to use. And you could try seating a .452 pistol bullet with your set up to see if it chambers freely...that will give you an idea where to start...or if your dimensions are correct cut the wall thickness of the brass down to .012" thick over the bullet seating depth. Then run through the die seat the bullet, should chamber.

 

[cmysix]

all depends greatly on how you control "CHATTER"

 

[Ray123]

If I measure the diameter at the point on a reamer, how much extra is actually cut at that point in the chamber ? I'm measuring it .485 at the case mouth on the reamer.

Can I add one thou ?

I've got a 458x1.5 reamer.

I found that cutting down 458 Win Mag or 7mm Rem Mag brass to 1.5" does not work on it's own, the walls are too thick.

The case walls at the 1.5" mark are +- 20 thou. If I seat a .459 bullet in there, the round can't chamber because the .459 + 40 thou exceeds the chamber dimension at the case mouth.

When i size the brass in a .375 H&H die, the diameter at the case mouth comes out at .469.

I'm tryng to work out what size case reamer I can use to run into the sized cases to bring the case wall thickness down at the mouth, and by how much.

Has anyone done this before for the 458x1.5 ?

So I just went out and made a .458X1.5" and seated a bullet a .458 cast bullet the diameter over the bullet and brass was .484 - .485" and would load in the chamber.
What I did was "turn" in a lathe the .338 mag trimmed to 1.5" down to a brass wall thickness of .012" blend out past where the bullet seats. Then run through sizing die, and seat the .458 350 gr cast bullet...measure dia .484-.485" So if you can get .456" reamer to run true and your case on center and use a sized case from your die come up with .012" wall thickness..it might work well, for shorter bullets or longer bullets sticking out of the case...but boring and turning in a lathe, together, make for an accurate, consistent, .012" wall ...as the case will also taper thicker internally and externally faster as you're close to the solid head...especially on deep seated .458" 500 gr bullets, that take up alot of case length. Not hard to do, just make a few that fits, fire it, compare, with another one you made. Then go make a few hundred, cases if ya like the outcome, or adjust. I Do it with a variety of calibers, mill them down, form die them, turn & bore in a lathe, even recut extractor grooves. 308 to 6mm ARC or 8.6 Blackout from 30-06,270, 25-06, or 308 brass. All chamber nicely.

 

[big5ifty]

So I just went out and made a .458X1.5" and seated a bullet a .458 cast bullet the diameter over the bullet and brass was .484 - .485" and would load in the chamber.
What I did was "turn" in a lathe ...

I made the dummy rounds that way, by turning on a mini lathe I had. Those rounds were used to check the headspace, etc. by the gunsmith when the rifle was built.

I since sold the mini lathe, because I had it for years, used it only once or twice, and I needed the space. They say junk is the stuff you get rid of after not using it for years, then need it a week later.

In any case, I can't use a lathe well enough to get consistency of case wall thickness, that brass I turned originally was a hack job.

I do have a drill press. I was thinking to get a chucking reamer, and ream the sized brass that way. That could give me 10 or 11 thou wall thickness, consistently.

Any ideas on how to set it up ?

I do have a 375 H&H sizing die cut down to 1.5", I could hold the brass in that while reaming.

 

[Ray123]

I made the dummy rounds that way, by turning on a mini lathe I had. Those rounds were used to check the headspace, etc. by the gunsmith when the rifle was built.

I since sold the mini lathe, because I had it for years, used it only once or twice, and I needed the space. They say junk is the stuff you get rid of after not using it for years, then need it a week later.

In any case, I can't use a lathe well enough to get consistency of case wall thickness, that brass I turned originally was a hack job.

I do have a drill press. I was thinking to get a chucking reamer, and ream the sized brass that way. That could give me 10 or 11 thou wall thickness, consistently.

Any ideas on how to set it up ?

I do have a 375 H&H sizing die cut down to 1.5", I could hold the brass in that while reaming.

Not having any precision tools, makes it more difficult. The 1.5" sizing die could be utilized to hold the case. I make my case holders, but Wilson makes case holders to for triming brass. Tap in tap out ..they also make inside neck reamers. Forester does too...but not a variety of diameters, like .458 ". These are hand tools and hand power, but a drill motor attachments are available.
An inexpensive drll press spindle and chuck have too much runout ..so a homemade floating reamer holder to let it run out at the chuck and a hardened drill bushing guide pressed in a fixture about .0005" larger hole than the reamer selected, will keep it centered and true. A V block in a vise or vertical groove milled in vise jaws to hold the captured case with its holder perpendicular in the exact same place. But the adding drill motor power to the above hand tools from Wilson or Forester, or others, would be an easier option for one who has few power tools. Just check out inside neck turning tools from them online, see if something is workable in the .458" dia.