Reamer design question

[AckleymanII]

I have a question on reamer design.

Not taking into account the dimensions on your Full length sizer, say your new brass is .470 in the web at the .200 mark from the bolt face. What would you want your reamer dimension to be to avoid issues with extraction? Cartridge in consideration would be pushing some pressure, 260 AI

I got into trouble designing a 7 STW reamer with .002 over web dimension at the .200 mark from the bolt face.

 

[Shooter71]

What was the trouble?

 

[Fast14riot]

I would check your sizing die dimensions. My 260AI Redding dies could have been another .001" smaller with a ptg 260AI Match chamber as I started getting clickers after several firings. I have a couple ring dies now if I need them, but so far my new reamer and die seem to be playing well together. I can check my reamer dimensions later tonight.

 

[Edd]

I have a question on reamer design.

Not taking into account the dimensions on your Full length sizer, say your new brass is .470 in the web at the .200 mark from the bolt face. What would you want your reamer dimension to be to avoid issues with extraction? Cartridge in consideration would be pushing some pressure, 260 AI

I got into trouble designing a 7 STW reamer with .002 over web dimension at the .200 mark from the bolt face.

.474"

 

[gunsandgunsmithing]

I have a question on reamer design.

Not taking into account the dimensions on your Full length sizer, say your new brass is .470 in the web at the .200 mark from the bolt face. What would you want your reamer dimension to be to avoid issues with extraction? Cartridge in consideration would be pushing some pressure, 260 AI

I got into trouble designing a 7 STW reamer with .002 over web dimension at the .200 mark from the bolt face.

IMO, your first mistake was/is factoring in much in for virgin brass dimensions. Sure, you can't form 6ppc brass in a WSM chamber, so it matters to some degree, but brass is only virgin once. From that point on, it's not about virgin but the relationship between fired and sized brass dimensions that matter.

Depending on cartridge, you want a sizer to be 2.5-3 thou smaller than the chamber. There is no relationship(within reason) with virgin brass. You can spec a reamer too big and shorten primer pocket life but that's simply not the critical part of spec'ing a reamer.

edit...A die that is roughly .003 smaller than the chamber, after springback from sizing, will yield brass that is approximately 1.5 thou smaller at the shoulder and about .0005-.0006 smaller at the .200 line. That's about what you want!

 

[Alex Wheeler]

There is a relationship with the virgin brass because you dont want to make the die much smaller than that. PM me with specifics and I can help.

 

[gunsandgunsmithing]

There is a relationship with the virgin brass because you dont want to make the die much smaller than that. PM me with specifics and I can help.

That is very true, but does anybody do that? Even if it wasn't stupid, how would you size it down from its virgin state. Makes no so sense. But then, there are those that do that type of thing. Does virgin brass chamber in their gun?

 

[Alex Wheeler]

Exactly, yet its tried all the time. The PRC case is a great example. Knowing the virgin case head is critical when specing the chamber size.

 

[gunsandgunsmithing]

Exactly, yet its tried all the time. The PRC case is a great example. Knowing the virgin case head is critical when specing the chamber size.

Alright, so knowing the virgin dimension matters..how. The brass comes out of the chamber..any chamber..at .xxxx dimension and comes out of the sizing die at .xxxx dimension. So, what else matters unless we are loosening primer pockets on the first full charge firing?

I'll listen but I won't debate this. I, like you, have bought and paid for these lessons. But I'm still interested in what you have to say on this. It's like this, brass is only virgin for the first firing. I think we'll agree on that. So what is to be gained by spec'ing a reamer upon something that will never be seen again? Thanks!

 

[Alex Wheeler]

Its simple. The die can be as small as the virgin case head, smaller and it may crack. The chamber has to be big enough to give enough sizing. I look at the die as fixed, the chamber is variable. This can vary a lot based on the brass we are dealing with. Even the same chambering can vary based on the brass manufacturer.

 

[AckleymanII]

Thank you to all in this project.

Redding body size dia = .468

Virgin brass web dia is .470

Maybe a disaster.....

Fire brass should be .4725-.473, which means the web would be sized .005.

I do not know if this is a feasible project with this brand of brass that I have a lot of.

All input is greatly appreciated.

 

[Alex Wheeler]

On that case head its thin. Your die will be pretty thick, so your ok. Id like to see the chamber around 472 or so. The actual chamber will likely be about .0005 bigger than reamer spec because they will grind it to the big side of spec. But with the specs you have you wont be out of the ball park.

 

[gunsandgunsmithing]

Its simple. The die can be as small as the virgin case head, smaller and it may crack. The chamber has to be big enough to give enough sizing. I look at the die as fixed, the chamber is variable. This can vary a lot based on the brass we are dealing with. Even the same chambering can vary based on the brass manufacturer.

If brass can vary, why do you chamber to that brass? Also, the chamber expands under pressure, so how can a perfectly fitted pieced of fired brass fit inside of a chamber cut for virgin brass? Sure, dies can be made to anything, but why? I don't follow the logic of making a chamber reamer that will only fit virgin brass for one firing and I don't see how that can change with the cartridge it's chambered for.
We can simply agree to disagree and I'll be fine with that. I don't see this going anywhere good except for a select few of this forum, if at all.

 

[Alex Wheeler]

Your not following me/not making myself clear, but yes lets agree to disagree on this.

 

[mikecr]

Different thinking here: your chamber is your best die
This question goes to chamber dimensions that YOU can set, which is what your brass will form to, and then you plan desired sizing from there (even if with custom sizing, or no sizing).

I do not subscribe to sloppy clearances at the .200 datum as a solution to anything.
A big clearance there, and poor breech support, leads to big webline growth, loosening pockets, and eventual popping extraction. This is because of all the brass yielding, and brass always wants to go where it's been.
In contrast, with proper breech support for the cartridge, and no more than 1thou clearance(total) at the .200 datum, from NEW case dimension, you will not be left with interference fitting cases at SAAMI max pressure.
With this, the brass barely yields to begin with.

I'm around ~85 reloads on WSSM cases in chambers 'fitted' to new brass. I run right at SAAMI max loads per QuickLoad/chrono. The case bodies have never been sized, and I have never had growth beyond initial fire forming. No extraction issue -ever. This is a BAT coned breech magnum action.
I've done the same in brown box 6BR and 223REM. Have not had to replace any cases.

When I was a teenager, every hot rod engine builder believed that they were throwing rods/breaking crankshafts/valve train timing, because they ran out of clearances. But the TRUTH was that they were breaking everything because their clearances were already too high. Then, as they kept increasing clearances, it just made it worse. This is also why we were left to feel lucky to get 100K miles between rebuilds. Factory clearances were too high.
Smokey Yunick proved all this, successfully countered, and the rest is history.
We don't have to rebuild our engines every 100K miles since.

You don't have to replace brass. You can actually make it last forever.

 

[Alex Wheeler]

My fired brass wont fit back into the chamber. Pressures are too high. Fl sizing is needed. No matter what the chamber is, once the case is formed to it theres minimal clearance. Everything is fine until you run high pressures. You can get over 100 reloads fl sizing a case. They just dont wear out if your doing it right.

 

[Ggmac]

Just my opinion, before coffee, the chamber is plastic like ( meaning chamber can be one size but changes under pressure, the die isnt under pressure so the size is more or less a constant. 50,000 psi does expand the chamber BUT I think my point is off track ,I better wake up more and think about it .
Good morning guys and be safe .

 

[Papa Charlie]

@Alex Wheeler Trying to follow this. Would it be more logical to design the chamber (reamer) to fired and sized brass rather than virgin brass as the size of the case from the factory may be smaller or larger depending on the particular sizing die caused? Further wouldn't this be more important if you were to design a custom chamber reamer?

 

[Fast14riot]

According to my reamer print for my 260AI, it is .4696 at the .200 line, tolerance is +.0004". Other than using a mic, I dont have an accurate way to physically measure my reamer and I don't want to damage it trying. This reamer seams to be playing nice with my die/brass this time around compared to my old barrel (different reamer). Just food for thought.

 

[DaveTooley]

I have reamers made for Winchester brass from 30 years ago. We though we could extend the life of the primer pocket by having minimal clearance on the case head. We went down to .468". That's about .001"+ clearance. Nothing but problems. The term clickers was invented about that time. Primer pockets went away as soon as we exceeded the yield strength of the brass. Tight or loose chamber it didn't matter. Exceed the yield point and primer pockets go away.
For the system to work, brass, chamber and FL die there has to be room for expansion with spring back for extraction and enough sizing with spring back to allow chambering. You can't size brass down smaller than it was new so there has to be enough room for the expansion and sizing for it to work.
In a perfect world. Perfect being the finish reamer and resize matched perfectly together you need at a bare minimum .003" over virgin brass. This works but just barely. If I ordered the reamer sets today I would go +.005" over virgin brass.
YMMV