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verifying freebore

Jay Christopherson

Jay Christopherson

Not An Admin
Anyone have a cool trick for verifying the freebore on a newly cut chamber, vs. the freebore from the reamer spec? Like, my reamer says ".170" and I want to verify that that is actually what it is cutting.

What I thought of doing is reaming a small gage with the reamer. According to the print, the freebore is .170" long x .3083" in diameter. My thinking is that I could turn a piece of drill rod or something to .3082", and it should insert into the gage no more than .170" if the freebore is correct. Maybe there's a simpler way.
 
The freebore is dependent on the barrel dia and rifling itself . If the bore is off by .0005 your measure will be off . Best way I know , not having a barrel stub cut off , is to make a cerrosafe cast and measure .
Cutting drill rod or old barre will only get you close .
All of this is before my coffee !
It is applicable only if you want to measure to the lands .
 
Last edited:
Jay

Cut a dummy neck and throat in a piece of barrel, section it and under a little magnification, using calipers, you can measure to within a few thousandths.

Many times you can do that on the reamer itself if there is a definitive line between the cylinder section and the lead angle.
 
When you order a reamer with a specific freebore you do this with the idea of having the base of a certain bullet at a certain spot in the neck of the case. It seems to me that you could use a split case and that bullet to verify that the bullet is in the spot in the neck that you intended. If so then the freebore is what you asked for.
 
DaveTooley said:
Jay

Cut a dummy neck and throat in a piece of barrel, section it and under a little magnification, using calipers, you can measure to within a few thousandths.

Many times you can do that on the reamer itself if there is a definitive line between the cylinder section and the lead angle.
Click to expand...

Yeah, I was able to see the line delineated on the reamer itself under light and the measurement I took looks like the freebore is consistent with the print. I was thinking about your idea to cut a dummy/neck and throat, but I thought I might use Delrin since it would be a little faster to do the work on.
 
Just a precautionary comment. You can't, with high precision, measure the diameter of the neck or free bore by cutting a short piece of barrel. Many many years ago my first new BR barrel was a 22PPC that Ferris Pindell chambered for me. He furnished a neck/throat/shoulder gage. I wanted to run fitted necks which means no sizing required. I used the gage provided to turn my necks for a proper fit. It work for about 4 firings then I had problems. Ferris confirmed that until the reamer is fully supported the reamer will cut slightly oversize. No more fitted necks after that.
 
On a somewhat related topic... is there a good/reliable way to determine the freebore of an arbitrary chamber? Say if you have a firearm that you didn't personally chamber, and the information as to what reamer was actually used is... lacking.
 
@FredBohl interesting stuff, thanks for the link. I forgot to mention I was looking for methods *other* than CerroSafe, mainly because a) I've heard some concerns about the accuracy of it, and b) because I've had a run-in with a ham-fisted local gunsmith who managed to fill the lug recesses in my gun with the stuff :mad: Kinda tends to turn me off of a product..
 
The Reprorubber medium is most accurate within the first hour much like CerroSafe. I should note that this product does not set-up hard so some measurements like diameters need a very gentile technique. You will be surprised by what will show including the fire cracking pattern in the throat and the dreaded carbon ring at the neck-throat junction.
 
Jay Christopherson said:
FredBohl, is there any special setup or prep needed for the stuff (i.e., TL;DR the user manual yet)
Click to expand...

For a chamber cast I clean the camber, free bore and throat till I get a clean dry patch (get any residual oil or cleaning solvent out). I plug the bore just past the full depth rifling using one of those VFG felt cleaning pellets then with the barrel held crown down fill from the breech. I allow about 15 to 20 minutes set time then push out from crown end using a brass rod. The felt pellet will usually stick to the end but can be cut off if needed.

The material dosen't stick to most materials that are not porous. Some solvents and oils seem to interfere with the curing process resulting in poor surface reproduction so a clean surface is best.
 
A down and dirty way of figuring out a freebore length in a chamber...
Make a dummy round at touch, lock a caliper .002" under bullet diameter and spin the bullet against it to mark the ogive. Measure from that mark to the end of the neck. Subtract .020". That should get you close.
 
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