Gunsmithing Chambering Process by request

wnroscoe

wnroscoe

Gunny Sergeant
Full Member
Minuteman
Jun 12, 2006
3,907
56
NW Louisiana
#1
I chambered a .260 RP a few days ago for a client and thought I'd share the process for those that may have never seen this. My photos start after initial turning down of the tennon and threading. Sorry, I didn’t think about sharing until after that had been done.

I double indicate everything, meaning I indicate at two points on the range rod that you see in the bore. I also check my set up several times during the process. To remove the TIR at the breech end of the rod I make those adjustments at the chuck, to remove the TIR at the oposite end of the range rod I make those adjustments at the spider. All runout is kept at or under .0002".

I dialed in the barrel prior to making these cuts. This photo shows me dialing in the barrel in again after the cuts. Due to the deep hole drilling process the bore is never straight so I re-dial to make sure the chamber is as parallel to the throat as possible.

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This just shows another view of photo #1 and the bolt nose recess after it was cut.

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These are views prior to chambering and showing the floating reamer pusher I made and use.

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These are views during chambering and the floating pusher again. I had just cleaned the excess chips off.

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These views are after chambering is complete, headspace is set and the entire chamber and breech area have been polished out.

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These two views show the intial clean up after the barrel has been cut to length, faced off for dial in, indicating the muzzle for crowning and the final crown itself.

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#5
Re: Chambering Process by request

Thanks for posting this! Great pics!
I am not at your level, but I enjoy doing things for myself and have been fortunate to get lots of good advice.

I had a buddy call me yesterday complaining of a very loose chamber in his first-ever chambering job. He said he had indicated the rod, but he had only indicated at one point. He was using a floating reamer holder, forget which one. My first few chambers came off just fine without even using a floating reamer holder and I credit much of this to indicating at 2 points on the rod. Can't imagine it going well without that.

Question:
Is there an accepted standard for how much barrel to chop from the chamber end of a blank before attempting to indicate?
 
#6
Re: Chambering Process by request

Double indicating is an absolute must if your to get the bore running as straight as possible. If it's not right you'll know it as soon as the reamer starts to cut, it'll start to wobble around.

<span style="font-weight: bold">Question:
Is there an accepted standard for how much barrel to chop from the chamber end of a blank before attempting to indicate?</span> I've cut 1" off some and none on others. To tell you the truth, I can’t tell any difference. I will cut at least 1.250" off the muzzle though. For chambering, I use the tightest fitting bushing I can for 75% of the chamber. For a .300"/.308" bore I'd start with a .2998" bushing and then switch to a .2996" for the last portion of the chamber, about the length of the neck and shoulder.
 
#7
Re: Chambering Process by request

Thanks, William!
I had heard that the ends of a blank can be off because of the nature of the drill/reamers/buttons/etc starting into the blank.
I guess this has alot to do with who is making the barrel?
 
#8
Re: Chambering Process by request

Thanks for sharing and thanks for the time to post this info.

This is something that I have always wanted to learn how to do. Being that I am a cronic tinkerer and what not. Just wish I had the equiptment and or someone to watch and to teach me how to do it. Knowlage of all aspects of your hobby is something I love.

To be able to build your own like some here have done and have it turn out to be a match winner and such would be the ultimate in satisfaction for a lot of us reading these how to posts.



Brian
 
#9
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">Double indicating is an absolute must if your to get the bore running as straight as possible. If it's not right you'll know it as soon as the reamer starts to cut, it'll start to wobble around.

<span style="font-weight: bold">Question:
Is there an accepted standard for how much barrel to chop from the chamber end of a blank before attempting to indicate?</span> I've cut 1" off some and none on others. To tell you the truth, I can’t tell any difference. I will cut at least 1.250" off the muzzle though. For chambering, I use the tightest fitting bushing I can for 75% of the chamber. For a .300"/.308" bore I'd start with a .2998" bushing and then switch to a .2996" for the last portion of the chamber, about the length of the neck and shoulder. </div></div>

Kind of wondering how you indidcate it "..to within .0002"..." with the indicator you use. Also, Krieger barrels and some others are normally a .299" bore. That .2998" pilot won't fit them.
 
#10
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jim Kobe</div><div class="ubbcode-body">Kind of wondering how you indidcate it "..to within .0002"..." with the indicator you use. Also, Krieger barrels and some others are normally a .299" bore. That .2998" pilot won't fit them. </div></div>

After the initial dial in I switch to a .0001" Mitytoyo for the final adjustment. This indicator can be seen in the receiver truing thread.

Your right, a .2998" won’t fit a .299" bore. They do how ever work fine in a .300"/.308” bore, which is what the barrel in the pictures is. For 6mm (.243) there's also have a .236"/.243 bore but I use the .237"/.243" in those. Again, a .2368” bushing wont work in the .236” bore. There are more than one bore and groove diameter barrels being manufactured and available.

I didn’t put this post up to be picked apart. If you’re going to criticize at least be well informed prior to doing so. The bore diameter comment proves you were not.
 
#11
Re: Chambering Process by request

Nice photos. I appreciate your comment about the bore never being straight. Many don't believe that but it seems to be true. Some are straighter than others, of course. And some not-so-straight barrels shoot fine.
 
#12
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: g5</div><div class="ubbcode-body">Nice photos. I appreciate your comment about the bore never being straight. Many don't believe that but it seems to be true. Some are straighter than others, of course. And some not-so-straight barrels shoot fine. </div></div>

The total amount of TIR in the bore and what happens there doesnt really bother me. It's what happens at the throat and crown that matters the most.
 
#14
Re: Chambering Process by request

Great post and pictures. G5: you are right about barrels not being straight. Anyone that has looked down more than a few barrels after they have been indicated on both ends as they are being turned will agree.
 
#15
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jim Kobe</div><div class="ubbcode-body">
Also, Krieger barrels and some others are normally a .299" bore. That .2998" pilot won't fit them. </div></div>

Of course it won't fit because .2998 is bigger then .299. Pilots come in sizes that are measured to the forth decimal point and the barrels are only marked to the third.

This is why I will never chamber a barrel with a reamer that doesn’t have a removable pilot.

You don’t indicate both ends of the barrel you will have out of round chambers. I have never seen a perfectly true bore from any barrel maker.
 
#16
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Harold Dale</div><div class="ubbcode-body">Thanks for sharing the photos and info. Great stuff, what brand name on the lathe? First time for me. </div></div>

It's a Grizzly G4003G. It's been nothing short of fantastic.
 
#17
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: HateCA</div><div class="ubbcode-body">You don&#146;t indicate both ends of the barrel you will have out of round chambers. I have never seen a perfectly true bore from any barrel maker.
</div></div>

Randy,

Just a quick question on this: If the bore isn't straight, and you dial in both ends, does the barrel bend slightly to conform? Or are you just saying the bore isn't straight in relation to the exterior of the barrel? I am just a little confused how the chamber could be out of round if you indicate in just the chamber end?

Thanks!

Dave
 
#18
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: HateCA</div><div class="ubbcode-body">You don&#146;t indicate both ends of the barrel you will have out of round chambers. I have never seen a perfectly true bore from any barrel maker.
</div></div>

Randy,

Just a quick question on this: If the bore isn't straight, and you dial in both ends, does the barrel bend slightly to conform? Or are you just saying the bore isn't straight in relation to the exterior of the barrel? I am just a little confused how the chamber could be out of round if you indicate in just the chamber end?

Thanks!

Dave </div></div>

Yes the bore is never true to the outside of the barrel, and no you are not bending the barrel.

I don't care what the outside of the barrel looks like, I'm only worried about the end of the barrel I'm cutting on, and that the bore is as close to perfect for the entire length of the chamber. You want the bullet going in straight and leaving straight, as long as it does that the bullet could make a loop for all I care. If there is run-out and you indicate from the outside of the barrel before doing any cutting on the bore you may have just screwed your barrel.

Where most guys make a mistake is putting the barrel in the lathe and dial indicting both ends at the same time. This can cause issues. There is no control of bore run-out doing it this way. You dial indicated the end you are working on with one rod and two indicators. One indicator close to the barrel face and the other indicator at the end of the rod.

You also need to make certain that the barrel can pivot at the end you are working on. If not then yes you will bend the barrel in the lathe. I use a brass or steal rod wrapped around the barrel at the chuck end. This way I can use sufficient clamping force on the barrel but at the spider end I can still push the barrel in any direction without having the barrel bend.

When you indicate the breach end or the muzzle end to do cutting chances are good the other end (at the spider end) is spinning like a banshee but that doesn't really matter. If you dial out the run-out on one end (the end you are working on) the other end will show the run-out.

If the barrel has run-out I will time the breach shoulder to put that run-out at the muzzle end at TDC or BDC when the action is torqued to the barrel. If you don't do this and the run-out is at lets say 3 or 9 o'clock you will loose windage in your scope adjustment. This is by far the leading cause of not having enough windage in scopes, far greater then scope base holes being off. You want to see a barrel spin like crazy, watch a factory barrel in a lathe.

Here is one more for you. Lets say you true the barrel at 24" and both ends were indicated true when the chamber and crown were cut, and the run-out on the muzzle end was torqued to the action at TDC.

Now lets say you want to cut the barrel back to 20", is the barrel going to torque to TDC again? Maybe, maybe not. It all depends on where the bore wondered at the 20" mark.

When chambering a new barrel I will almost always cut the barrel blank back close to the finished length before I do any other cutting so I can control where the run-out will be in relation to the action.
 
#20
Re: Chambering Process by request

I was not trying to critisize, only trying to inform some of the uninformed as to different bore sizes. Also, you did not indicate in your original post about the tenth indicator. I was wondering about that as maybe others were.
 
#21
Re: Chambering Process by request

Great post thanks.
I am taking a slightly different tact but based on a similar philosophy. I first indicate in using a range rod, then remove the range rod and focus on the lands where the bullet will first contact and try to center up at this point 100% My reasoning for this is that I am going to drill and taper bore as close to this point as possible as the reamer design will allow. Everything that was crooked behind the point where the lands are indicated in will be removed, so I do not care if it is crooked. Does this make sense?
I do not see a reason to indicate the muzzle in when chambering and physically cannot do it with my current setup as my headstock is too long. I use tight fitting bushings on the barrel that fit the spindle bore almost perfectly. The only concern I have when chambering is making absolutely sure that everything lines up with where the bullet will contact the lands.
I probably over emphasize trying to get everything concentric with the bullet/lands convergence. I have seen some rifles that were way out that still shot. I figure that if it is within my power to do it I may as well bite the bullet and take the extra time.
 
#22
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Harold Dale</div><div class="ubbcode-body">Thanks for sharing the photos and info. Great stuff, what brand name on the lathe? First time for me. </div></div>

It's a Grizzly G4003G. It's been nothing short of fantastic. </div></div>

For $3k I'd say you got your moneys worth


Looks great btw
 
#23
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: eddybo</div><div class="ubbcode-body">I figure that if it is within my power to do it I may as well bite the bullet and take the extra time. </div></div>

We only get one shot to get it right or it's a trip to the chop saw. I like to measure three times and cut once.
 
#24
Re: Chambering Process by request

How did you hold the reamer to the tailstock? Some pictures would be helpful, is it just on a center then you use a wrench to hold it from spinning. I guess how do you know your reamer is cutting on center even if your tailstock is dailed in it would seem to me like it wouldn't be good enough. great info
 
#25
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 6.81star</div><div class="ubbcode-body">How did you hold the reamer to the tailstock? Some pictures would be helpful, is it just on a center then you use a wrench to hold it from spinning. <span style="font-weight: bold">I guess how do you know your reamer is cutting on center even if your tailstock is dailed in it would seem to me like it wouldn't be good enough.</span> great info </div></div>

Oh, it's better than "good enough" Tailstocks may be lined up horozontally but, are seldom lined up verticly. The floating reamer holders and pushers make this a non-issue.

Look closer at the pictures. The reamer is being pushed by a cup I made that is held in the drill chuck. It's a Floating Reamer Pusher. There is a small tap handle on the reamer shank that the pusher is pushing against.I simply hold the tap handle to keep it from spinning. In the pusher cup there is clearance around the reamer shank and underneath. When I made this set up I turned down a small piece of material and attached the tap handle to it. I then faced off the tap handle so it would be square and perpendicular to the pusher and reamer shank. This is a proven method.
 
#26
Re: Chambering Process by request

Awesome on both of these posts William, thanks for sharing. Are these things taught in gunsmithing school, or are these things learned as a machnist. I know these items are not part of the cirriculum at the Police Academy
 
#27
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jackinfl</div><div class="ubbcode-body">Are these things taught in gunsmithing school, or are these things learned as a machnist.</div></div>

In gunsmithing school there's probably a class as an introduction to machine shop where they would give you the basic run down on lathes, mills, grinders, band saws, tooling etc. Not to be a smart ass but, what your seeing in these post's are what’s considered gunsmithing as far as rifle building and would be taught in the class.

The police academy was a different kind of fun
wink.gif
 
#29
Re: Chambering Process by request

If I may ask...

Do you try to maintain equal resistance on both ends of the tap wrench(or whatever you use to hold the reamer still), or does it not matter....and you only hold one side?

In my very limited experience, I used an open-end wrench so I was holding it only from one side. I was always curious if I was costing myself some accuracy.
 
#30
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rafael</div><div class="ubbcode-body">If I may ask...

Do you try to maintain equal resistance on both ends of the tap wrench(or whatever you use to hold the reamer still), or does it not matter....and you only hold one side?

In my very limited experience, I used an open-end wrench so I was holding it only from one side. I was always curious if I was costing myself some accuracy. </div></div>

Rafael,

I hold the reamer in my left hand, between my index and middle finger using my thumb and fingers to keep the reamer from spinning. I try not to influence the reamer and let it follow the bore while the tail stock is pushing it forward. Check your next chamber with a .0001" dial indicator, that'll tell you if you did good.
 
#34
Re: Chambering Process by request

looking at this again, do you ream the entire chamber? i have been drilling and then boring the majority of it out. i'm curious what your thoughts are on that.
 
#36
Re: Chambering Process by request

Rifling requires some very special hardware and is rarely done by gunsmiths, if at all. There are a few barrel manufacturers who frequent the board, but they are likely the only ones with rifling machines. This thread is based on using a barrel blank that is already rifled.
 
#37
Re: Chambering Process by request

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rafael</div><div class="ubbcode-body">Rifling requires some very special hardware and is rarely done by gunsmiths, if at all. <span style="font-weight: bold">There are a few barrel manufacturers who frequent the board, but they are likely the only ones with rifling machines.</span> This thread is based on using a barrel blank that is already rifled. </div></div>

Well said and very true.
 
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