Alternate method for determining rifling contact

[Pres100]

I just wanted to share how I go about determining the bullet contact with the rifling. This isn't for everyone, but those who are chambering a new barrel may consider as it requires a piece of your actual barrel. I ordered a 31" barrel originally and had it cut down to 28.5" leaving a section that is approximately 2.5". After the barrel was chambered, the remaining section of barrel was put in the lathe, faced and partially chambered to about 3/4 of the way down the shoulder. This allows the bullet to be seated long and inserted into the rifling gauge (for lack of a better term) by hand. If the bullet contacts the rifling it will not allow the case shoulder to come in contact with the shoulder on the "rifling gauge". As the bullet is nudged further into the neck you can feel whether or not you are in contact with the rifling by lightly trying to turn the round. As you progress further, you can feel the the exact location of where it no longer touches. The amount of feedback you can actually feel is amazing as you bump it down 0.001" to 0.0005" as you get close.

With sorted bullets you can use that seating location to move further off the point of contact or in the lands with more precise measurements. When I use my Stoney point gauge and modified case, i always seem to get a measurement that is actually into the lands (jam).

 

[stubbicatt]

Excellent!

 

[gotcha]

Thanks for sharing pres! I've had the same problems w/ the Hornady comparator. My Smith furnishes bbl stubs chambered to the shoulder/ body junction which also makes the stub a bump gauge/comparator when used with a caliper. More accurate, I think, since the case makes contact w/ the entire shoulder. One gauge then serves TWO purposes. 8) BTW my Smith makes the gauge exactly 1 in. long so I can simply subtract 1 in. from the caliper reading. Keep on keepin' on.

 

[Erik Cortina]

Isn't this tool useless once the throat in your chamber moves out after firing a few rounds?

 

[fe1]

This tool is called a Chamber Guage or OAL Guage.
They have been around aleast 10 years that I know of probably longer.Every custom I have has one to accompany every barrel I own.
As far as throat erosion it does over a certain amount of time make a difference I'm sure but that depends upon a lot of variables cal,load,and how much the barrel is fired.
Its a lot quicker and more reliable than a StoneyPoint or Hornady LOL rod guage.
My 30BR guage and barrel still hold true readings after probably 1000 or 1500 rnds fired, from the best I can tell,it still shoots in the .100's.
So I'm a firm believer in them.

 

[Steve Blair]

This tool is called a Chamber Guage or OAL Guage.
They have been around aleast 10 years that I know of probably longer.Every custom I have has one to accompany every barrel I own.
As far as throat erosion it does over a certain amount of time make a difference I'm sure but that depends upon a lot of variables cal,load,and how much the barrel is fired.
Its a lot quicker and more reliable than a StoneyPoint or Hornady LOL rod guage.
My 30BR guage and barrel still hold true readings after probably 1000 or 1500 rnds fired, from the best I can tell,it still shoots in the .100's.
So I'm a firm believer in them.

[br]I've had barrels with .035" throat erosion still shoot well, as long as I kept up with the leade position. So, erosion can be a significant factor. A chamber gauge may work well for intial setup, but as Erik noted, they are useless once the leade starts moving. My Stoney Point/Hornady gauge has proven very reliable and I obtain repeatable readings over several barrel sets chambered with the same reamers. [br]
[SIZE=small]Citing the .30 BR in a discussion of throat erosion is more than specious. Anecdotal results describe 8,000+ round barrel life for the cartridge. My .300 WSM burns twice that much powder with bullets twice as heavy, at very similar velocities. The two are not really comparable. I would think that your .30 BR, at 1,500 rounds, is just nicely broken in. [/SIZE]

 

[Pres100]

Isn't this tool useless once the throat in your chamber moves out after firing a few rounds?

I guess. I suppose I can use cerrosafe to cast the chamber and monitor the difference. Using the Stoney point gauge I get differences as much as .020" into the rifling which seems a little unreliable. I definitely see your point and may have been underestimating the rate of erosion vs the margin of error. I'll try to monitor to see if there is a correlation between the two.

 

[Terry]

I use a Sharpe to color the bullet. Some use a lighter or candle to smoke the bullet. (place a light covering of suit)
The marks or lack of them tell the story.

 

[Pres100]

Terry, how do you reliably measure the marks? Can you get consistent measurements with calipers fom a scratch on the side of the bullet?

 

[MarkS]

Pres100,

I have used about everything, even a rifling guage. The Stoney point type can lie to you. been there and done that. I do use them to get close. The ONLY thing I trust is chamber a dummy round, with the bullet steel wooled, and see the rifling marks on the bullet. I start with the bullet marked with square marks by the riflings, that is about 0.020" into the lands, depending on the barrel. You can check this, by seeing when the marks are gone from the bullet. I use a SP guage for measuring AOL. I keep this round for reference, for check wear. I like to be into the lands or out. just touching can bite you.

Mark Schronce

 

[johara1]

What you made is what we call a stub, and is used to measure case shoulder set back. Can be used to see what you have with the bullet but,running them in the barreled action is the most precise. I do as Mark said but i find zero and i move from there. The more stuff introduced the more inaccurate it is, most is junk...... A stub is needed for precise shoulder set back and the exact length of your chamber,that's all you need except for quality mics. and vernier....... jim

 

[jonbearman]

If there is difference's in the ogive from bullet to bullet can that be why the stoney point seems inaccurate.I always read about ugys measuring the ogive starting point with height gages and sorting them into groups. Can or will this induce the reading errors of the stoney point?

 

[gotcha]

I think you're right Jon. Sorted or higher quality (uniformity) bullets would seem to lend to more accurate readings and consequently, groups. So, how do you determine if measuring inconsistencies in bullets come from irregularities in ogive or base? ??? Are we chasing our tails?......... Some folks use two bullet comparator bodies on their calipers. Will this improve consistency of readings? I've always suspected that an ogive measurement w/ comparator is a very ticklish thing. Seems the tiniest bit of variance of force applied to the caliper will skew readings due to taper of ogive. Not trying to hi-jack. Just ques. I have had re; this general subject.

 

[Pres100]

I do all of my bullet sorting prior to even checking with the Stoney point OAL gauge. I get inconsistent readings even using the same bullet. The stub gives me the precise measurement to the lands, but obviously becomes inaccurate once the throat wears. I'm going to try what Mark and Jim are suggesting and see how it works out. I am also going to cast the chamber to measure the variance from the original and check the wear based on round count and also compare the delta to what the dummy round indicates.
Dmoran also has some interesting info to check out as well.

Thanks for the input - I hope that it is helping others as well.

 

[Nomad47]

I don't know if it is the 5R rifling in my new barrel or what but when I take readings with my usual designated "Stoney Point" bullet, those reading are all over the place. But if I grab a new bullet out of the box I'm currently loading from, my readings settle down and 5 readings will be within +/_.001". But I can use the designated bullet in my Criterion barrels and readings are consistent.

 

[gotcha]

Thanks PRES, You've definitely helped me The idea of gently attempting to twist a loaded cartridge in the chamber worked very well for me this morning. It took two cartridges to establish exact seating depth. But, I'm very confident of the reading for the 1st time ever! BTW I used a fully fire formed case, neck sized only. No slip fit of bullet, just small increments of downward seating depth change w/ .001" neck tension. The 2nd cartridge yielded an almost invisible striation from lands. Close enough for me!

 

[Pres100]

Its pretty amazing how much you can feel when you just barely touch the lands and know fo absolutely sure you are RIGHT there. Once you are just barely touching with this method there is no way it will leave striations on the bullet because it isn't going into the lands to leave them- it's just barely touching them. Definitely a feeling of confidence far beyond any other method. The trick is finding a method that is just as reliable with throat erosion (and not removing the barrel to chamber check!)

 

[butchlambert]

Below is with one of my gizzies.

Do not pay any attention to the measurements in the photo. Pics were to illustrate what your gizzie will do. Since there are difference in size, rifling, and so I have a gizzie for each chambering job. Yes, I have a lot of them. If you are able to set your barrel back about .035" every 250 rounds or so you will not have to worry about throat erosion.

 

[gotcha]

[quote author= The trick is finding a method that is just as reliable with throat erosion (and not removing the barrel to chamber check!)
Agreed. Maybe 3/8th drive thin walled socket w/ extension pushed through action. Socket provides enough "bite" on rim to gently turn cartridge? Or, drill & tap primer pocket? Lots of inventive guys here that might offer their suggestions. BTW Nice pic Butch!

 

[Erik Cortina]

You guys are making this much more complicated than it needs to be.

Remove firing pin from bolt, seat bullet long, apply die wax to bullet, insert into chamber and close bolt, bullet gets pushed in by the rifling, snap bolt open, extract and measure, done. No gadgets needed, no need to remove barrel from action, no need to have a gizzie, a modified case, or a special tool, or the same bullet saved for reference, or any of that. The best gauge is your barrel, anything else you do is stacking tolerances. Oh, and you can't "feel" .001"!