Chamber Reamers

[The_Shadow]

Chamber Reamers a good article on types, do's and don't's etc.

http://rifleshooter.com/2015/04/chamber-reamers/

[sqlbullet]

Good info!  Thanks for posting.

I have used pistol caliber finish reamers as well as a freebore or leade reamer.  I free hand them with a T handle, or in the case of the free bore reamer I used a drill.  Not the most precise work but I was not building a 1/4 MOA at 500 yards gun.  For my needs it worked.

[oldman10mm]

One of my upcoming winter projects is converting a 4053 from 40S&W to 10mm. I've got the gun,chamber reamer,4053 barrel from Numrich. A magazine has already been modded,gotta build a recoil spring tester(currently in design stage),with the Numrich 4053 barrel I'll be able to leave the 40S&W barrel intact. I already reload 10mm down to 40S&W levels(for use in my 1006) so I'll be able to play with recoil spring strengths.

[The_Shadow]

A simple spring tester can be made using a small steel plate with a hole to accommodate an eye bolt (longer than the springs in test).  Placing the spring on the eye bolt (you can also slide a drinking straw over the eyebolt to reduce frictional contact) and use a washer and nut to capture the spring between the plate and the nut and washer.

Clamp the plate in a vice, pull the eye of the bolt with a digital fish scale for readings...
   nut - springspring plate V eyebolt
  =[]|(=)(=)(=)(=)(=)(=)||=O
__________________Vice /\    hook scale to eye to pull for measurements

[oldman10mm]

^^^ that's what I was planning on doing !

[The_Shadow]

I will say that measuring the inside the firearm shows what is required to unlock slide and measure the actual weight right where lock open would occur.

I used thick card stock to protect my slide and clamped a small "C" clamp near the rear to pull with the digital scale for real measures at those points...

[TonyRumore]

You can also get extended pilots on reamers for rechambering work.
Here is a 40 Super reamer with an extended pilot for rechambering 40SW or 10mm barrels to 40 Super.  This puts the pilot in the bore when chambering begins, rather than letting the reamer start unsuported with the pilot bouncing around in the old chamber.

Tony

[sqlbullet]

Tony,

Here is a question for you.

I recently built an AR-10 in 358 Winchester.  There is a thread about it around here.  The gun runs great with 200 grain factory ammo.

My goal with the build was to use big heavy cast bullets, and I have a NOE mold that drops a nice RFN at 310 grains, or a RFNHP at 280 grains.

But, the free bore was so tight that my 225 grain JSP handloads would not chamber.  Let alone the 280/310 grain thumpers.

I bought a leade reamer and extended the lead a bit and the 225 grain JSP's run just fine now.  But, I would have a good ways to go to get the 280/310's to chamber.  My concern is effect on accuracy.  I don't need a tac driver.  But I would like to stay around 2MOA or better.

Thoughts?  Keep reaming the leade or just give up on the super heavies in this gun?

[TonyRumore]

I'm certainly not an expert in that area, but on all the Tromix chamber reamer prints, the "Lead" is called out as the free bore portion directly in front of the case neck, where all the rifling is removed.  In front of that is the "Throat" which is the tapered portion where the bullet transitions from free bore and gradually engages the rifling.

With that in mind, if you keep pushing the Lead forward, you're eating into the Throat, so your bullet is going from a free bore area and slamming directly into the ass end of the rifling because  the tapered Lead is gone or at least diminished.  So, if you extend the Lead, you need to extend the throat......or maybe the Lead reamer does that.  I don't know, since I don't have any prints on hand for Lead reamers.

Tony

[oldman10mm]

^^^"slamming directly into the ass end of the rifling because the tapered Lead is gone"

that occurring could also cause a pressure spike.

[sqlbullet]

The reamer recuts the throat as it extends the freebore.  The concern I have is the longer the jump for other bullet profiles, the more time for the bullet to enter the rifling out of true.

Thanks for the feedback.  I think I will stew on it a bit more.  Perhaps I will just wait until the gun has a couple thousand rounds thru it and the throat is getting eroded and then clean it up.

[DM1906]

Have you considered fire lapping? It works.

[sqlbullet]

I have.  Fire lapping would accelerate wear on the entire bore, not just the freebore and throat where I am seeing the issues.  Thanks for the idea though!

[DM1906]

True, but many times they make the mistake of trying to correct bore issues, and completely wash out the freebore. I've seen chambers destroyed with 20 firings (not my doing), never appreciably affecting the bore. 3-5 firings will cause zero accelerated wear on a bore, while that's usually all that's needed to open the leade and throat. More or less, of course, depending on the method and media used. You don't likely need an aggressive process. Fire lapping only accelerates normal erosion wear from firing, so as long as you don't overdo it, you will be there eventually, anyway. You have a unique condition, one I wouldn't consider tooling, yet. Your lead bullets are your own, so you aren't settling for store-bought variations. Is the freebore too tight for the bullet diameter, or is the ogive actually engaging the throat? Or both? Fire lapping is free to try (almost, but you were shooting anyway), with reduced pressure loads seated deep enough to minimize initial interference, progressed with each firing. It usually happens very quickly. Tooling the chamber is a one-shot solution, with no (reasonable) progression. Effective reaming would require a custom cut reamer, designed on your unique cartridge profile, not an off the shelf or custom-guess tool. Ideally, a cast of your current chamber would settle remaining questions. Have you done a profile impression? Do you know, as fact, the chamber neck isn't the only issue? You are dealing with a variation from industry standard, which requires a solution that also varies from the industry standard. Accommodating your longer/fatter bullets may make the chamber unacceptable for use with industry standard bullets, while you need a solution that will place you between the ideal conditions, which may not exist. Any more than a bare minimum accommodation will be too much. Even a bare minimum may be too much, such as a serious competitive .223 shooter would find a 5.56 chamber profile utterly unacceptable. You may ultimately find you can't get there from here, and will have to choose which direction you want to go, or must go.

[sqlbullet]

I havent cast the chamber. I have forced a "dummy" round in to get an idea of how much additonal freebore is needed:



This was before the first and second reaming pass. I need to do a new test like this and see where I am.