Different ways to chamber a rifle barrel?

[BumbleBug]

I’ve been reading/googling about different chambering methods. I’ve never chambered a rifle barrel, but I would like to someday. Please excuse me if I get some of the nomenclature wrong.

It looks like the preferred method is to have a lathe with a big enough headstock to pass the barrel through & align the muzzle with a spider. Then a fixed reamer is passed into the turning barrel.

If the lathe head stock is too small, can the reamer be chucked & aligned & be turning while the fixed barrel is advanced on to the reamer?

Also I’ve seen where short chambered barrels are tightened on to the action & a reamer on a T-handle is hand turned “in-&-out” to gradually get a perfect closer on the go-gage. Can a barrel blank be short chambered with drill bit that only removed metal inside the chamber dimensions & then use this method to finish?

I’ve also read about a reamer that is on a long rod with a T-handle that attaches at the muzzle end & is gradually turned pulling outward until the bolt just closes. I’m not sure but perhaps these are only made for the .223 cartridge, although it seems like it could work for other cartridges.

Are there any other methods? Is the first method the only way to go if you are serious about accuracy? Are the hand reamer methods only good for mediocre hunting rifles. What methods do the big companies like Remington & Winchester use to mass produce their various barrel chambering’s?

TIA - Any info or comments are appreciated…

…bug

 

[Dixie Gunsmithing]

The way it should be done on a lathe, is to use a four jaw chuck, and adjust the barrels bore to the center line of the lathe using the chuck. Then, you use a roughing reamer, first, then the finish reamer. They are mounted to the tail stock with a floating holder, in case the bore is off, and so the reamers nose will follow the bore. However, when it gets down to a few thousandths at the end, I use a finish reamer by hand, and use a go gauge to know when to stop.

 

[HiBC]

I agree with the idea of a floating reamer holder.The old 1941 South Bend just does not have a precise enough tailstock to center the reamer true to the axis of the bore.That is true no matter how precisely I 4-jaw and spider the bore axis true to the spindle axis.

So the tailstock misalignment will deflect the reamer and cause the flutes on one side to cut heavy,resulting in an oversize chamber.

I would not rough the chamber with a drill.It is very important the reamer pilot guides the reamer .The roughing you suggest will cause the reamer body to follow your rough hole,with the pilot hanging in the air.When the pilot does find the bore,any deviation caused by following your drill will be a problem.

A lot of chambers have been cut with only a finish reamer.It takes patience,thats all.

Always keep the reamer turning in the cutting direction,including when you withdraw it.

Realize you must withdraw and clear chips before they pack up in the flutes.

The reamer is tapered,so the entire cutting edge cuts.Your forward progress will be in small fractions of an inch.

I use a coffee can half full of automotive solvent and a small paintbrush to clean the reamer each time I pull it out,then I blow it off and set it on a clean rag.

Then I blow the chips and oil out of the bore,followed by a cleaning rod and a patch .

It is imperative that everything is clean when the reamer goes back in.One little chip stradding a cutting edge is disaster.

Apply a good cutting fluid to the reamer before you go back in.

There is a lot more,but I assume other folks will step up.

Oh,the pull through reamers are for the final cuts on a semi-auto like a Garand or M-1A that does not allow breech access with the barrel in the receiver.No need for one on a bolt gun or AR.

On an AR,best to just buy a chambered barrel with matched bolt.Has to do with gas port,barrel extension,etc.unless you are tooling up to do a lot of AR barrels.

 

[James K]

Many factories use a pull through reamer. The barrel is chambered at the barrel shop to within a few thousandths, installed (and aligned as needed for markings, sights, etc.), then the reamer inserted and the bolt used to push it in as it is turned by the long rod from the muzzle end. When the bolt locks, the job is done, no gauge needed (though they are used.)

Jim

 

[Scorch]

All these cutting techniques are for a rifled barrel that is threaded then chambered. Nowadays, most factory barrels are hammer-forged, including the chamber. Finish reamers are only used for final fitting, if at all.

 

[BumbleBug]

Thanks everyone...

I'm learning a lot from these responses. Thanks especially to HiBC for detailing the process.

• The floating reamer holder makes a lot of sense.
• The pull-through reamer is definitely an interesting idea & I've never seen one!
• I was very surprised that factories hammer-forge the chamber too, but that definitely makes sense if you are making a bunch!

Another question, does the final torquing down of the action effect the headspacing, especially when you are try for the ultimate precision? While the barrel is in the chuck, how tight do you put on the action to test the Go/No-go & then when you are back out in the barrel vice for final install, now tight do you torque the action?

TIA...

..bug

 

[Scorch]

I allow for .002"-.003" of crush.

 

[mwells72774]

I'm looking at doing the same thing for a mauser build.

rented a pull through reamer from reamerrentals.com

 

[F. Guffey]

“Another question, does the final torqueing down of the action effect the head spacing, especially when you are trying for the ultimate precision? While the barrel is in the chuck, how tight do you put on the action to test the Go/No-go & then when you are back out in the barrel vice for final install, now tight do you torque the action?”

Bumblebug, as,. I am sure, you can see there are those that understood your question, or, would you consider I do not understand their answers.When the pull through reamers is used the bolt closes when the chamber is finished, the reamer is not pushed with the bolt, by name ‘it is a pull through reamer’ not a push through reamer , of a push/pull reamer.

Nothing like checking your work, again I am the fan of verifying. I have head space gages, head space gages are nice, I do not use head space gages, head space gages come in three lengths, the three lengths are go, no and beyond, for the 30/06 the go-gage is .005” longer from the shoulder of the gage to the head of the gage than a minimum length case. The no go-gage is .009” longer than the minimum length sized case, and the field reject gage is .014” longer than a minimum length case when the case is measured from the shoulder back to the head of the case.

Point? Why settle for three gages that cover a range of from .000” .014” when you could be using 14 gages, again, I have an exception, I have a M1917 Eddystone that has a chamber that is .016” longer than a minimum length case, I form cases for short chambers, I form cases for long chambers, the easiest way for me to form cases for the Eddystone is use 280 Remington cases, I adjust the die off the shell holder .014”. By using different methods and techniques I find case comparators a nice tool, not necessary, just nice.

Different methods and or techniques: If you are using a pull through reamer the barrel is secured to the receiver and torqued before the chamber is reamed, meaning after the barrel is secured and the chamber is reamed you apply the leaver policy, basically, you leaver along.

Then there is the reamer that aligns with the pilot and turned with a ‘T’ handle, (by hand), again an option is to install the barrel into the receiver and secure/torque. Many gunsmiths of all levels have used this method/technique with a high percentage of failures, BECAUSE? Everyone of them jeep repeating the same instructions, goes something like this, “Check often because no one knows where they are until it is too late”. It is possible to measure the length of the chamber from the shoulder back to the bolt face before starting. It is possible to measure the length of a ‘short’ chamber with a go-gage. It is possible to measure the length of a short chamber with a no go-gage, etc., and it is possible to use a go-gage as a go to infinity gage.

Then there is the ‘cut the chamber first’, then install the barrel, anyone that is a fan of transfers, standards and verifying can master this technique with a dial caliper/height gages and or depth micrometers. I do not have less than 30 Mauser barrels, it is unusual when measuring the chamber length of a Mauser barrel to find one that does not have a case head protrusion of .110 +/- very few.

Again, I used one Belgum Mauser barrel to test fire 4 Chilean Mausers, the difference in the length of the chamber between the receivers, barrel and 4 bolts was .001”.

F. Guffey

 

[Gunplummer]

Best to start with a Mauser until you get a grip on what is going on. You can get into trouble with the extractor cut out (Model 70, Arisaka, ect.) on some barrels. In Guffy's weird rambling way, I think he is trying to warn you about case head support. The less case sticking out of the barrel when the bolt is locked the better. If you look at an average rimless case, the head is solid brass. The wall of the case expands but not the head (Unless there are other major problems). The wall of the case must be supported by chamber.

 

[Bart B.]

Don't forget to measure the exact bore diameter of the barrel's chamber end then get both a roughing and finish reamer with a floating pilot whose diameter is an exact fit. That'll well center the chamber on the bore.

 

[F. Guffey]

“I think he is trying to warn you about case head support”

Case head protrusion is unsupported case head, back to “Who measures?” Again, the case head thickness of WW11 surplus 30/06 is .200” (for the most part), Remington (R-P) commercial 30/06 is .260”, back to “Who measures?”. The standard response when discussing surplus brass, on the Internet, is “It is heavier”, heavier is only half correct, the case head is thinner by .060” thinner, deductive reason should suggest the extra weight is in the case body, meaning the case head is heavier meaning the case body is thicker.

A thinner case head lengthens the powder column, a thicker case body decreases the diameter of the powder column.

And out of curiosity, who measures the diameter of the case head, turns the case around and places the case in the chamber when determining case head support. Back to case head thickness, there is an advantage when using R-P brass over surplus brass.

F. Guffey

Unsupported case head on the 03 and M1917, from the bottom of the extractor cut to the case head is .090” meaning both the 03 and M1917 have more case head support than the Mauser, On the Internet, there are claims .175” unsupported case head is acceptable? Back to “Who keeps up with this stuff?” With .175” unsupported case head when using a LC 30/06 case there is only .025” of the case head that is supported.

Then there is the .7854 factor, a heavy load created by what ever mistake will crush the case head, when the case head is crushed the amount of unsupported case head will increase.

 

[Gunplummer]

Good enough. Don't forget max chamber specs added to min brass specs added to max allowable headspace. There are a lot of variables. Who checks unsupported head protrusion? I do!

 

[BumbleBug]

Some great info - Thanks...

...Then there is the ‘cut the chamber first’, then install the barrel, anyone that is a fan of transfers, standards and verifying can master this technique with a dial caliper/height gages and or depth micrometers....

F.Guffy, thanks for the good info, as best I could understand with my limited experience. I like the way you think, which is understanding the dimensions & relationships & simple arithmetic (i.e. transfers, standards and verifying) & then using measuring tools to get the desired results. Being able to consistently measure properly & accurately is a skill in itself (at least to me & I need more practice).

...I think he is trying to warn you about case head support...

To tell you the truth, I didn't consider case head support. On thinking about it, it is obvious that you may have cut a perfectly dimensioned chamber, but due to a number of factors, it is possible that the case wall just above the case web may be unsupported. Bad, bad deal!

Also, if you need BR sort of accuracy, you are not cutting a chamber that needs to be perfect to spec's, but just perfect. By handloading you will be matching your cases exactly to that chamber anyway. The example of making .30-06 cases from .280's illustrates that point. As long as a factory cartridge (if there is one) is safe in the chamber, it's good.

I allow for .002"-.003" of crush.

My question stems from something I saw on a YouTube with a 'smithy installing a Stiller action on to a fresh cut target barrel. He "hand" tightened the action onto the barrel while still on the lathe. Then he used his go-gauge to verify that the bolt closed, but with some effort. The amount of "effort" is probably something you learn by experience(?) At this point, he removed barrel from the lathe, put it into a vice then screwed on the action but used a torque wrench to tighten to 100 ft/lb. He then repeated the go, no-go & sized case test & commented that the bolt would now close with the slightest but firm pressure. Scorch, I'm assuming that this is the "crush" fit you are referring to. How do you determine that .002" to .003" measurement before disturbing your lathe set-up? Adding to this, I'd most likely be barreling a Rem 700 with a separate recoil lug (which acts like a giant washer) & would that effect the "crush"?

Thanks again for your help in explaining the minutia.

...bug

 

[Gunplummer]

I do not get that scenario you described. If I am reading that correctly, the guy hand tightened the receiver on the barrel, inserted the go (Snugly) and then torqued the barrel on. This is backwards. Are you sure he did not insert the NO GO ? When you crank the barrel on, the face of the barrel (or shoulder) area is compressed. This shortens the head space area. The area between the chamber shoulder and the bolt face is now closer together by whatever amount the steel compressed to. I often cut barrels in the bench block by hand. If you get the GO too tight on a hand fit, it will never work after you hammer the barrel on. You can see there are many ways to do this. Just find the one for you.

Handloading for a chamber is backwards also. Take a couple different brand cases and fire them. Re-size the cases. Now make the reamer to the case dimensions, which is also your die specs. I have been able to do that and get no more than .001 stretch from cases after making up a reamer like that. Or, you could just make a die to match a chamber, but it is a lot harder to do. Neck sizing is not what it is built up to be. Everything else has to work with it.

 

[BumbleBug]

Per usual, I confused myself!

It's a bit confusing, so I watch it again to understand.

With the barrel still in the lathe chuck, he hand tightened the receiver to the barrel. He then tested the go-gage & got a "snug" fit. Then he test a no-gage & got a no close as expected. Then he tried a sized case & it closed just fine & normal. In essence, he used the case as the go gage. Then with all gages & cases removed, he removed barrel & action from the lathe. Hand tightened barrel to action & put the barrel in a vice & applied 100lb of torque to tighten. This is what I missed. The go-gage was even tighter & almost a no close. But the sized case was only a slightly tight close.

http://www.youtube.com/watch?v=xZoP7-nr2-o

watch at 2:10 into video

I guess this method lets you more closely match your sizing die without making a custom die or modifing a reamer(?)

Thanks...

...bug

 

[4V50 Gary]

I did a barrel as described by DixieGunsmith.

The fellow in the lathe behind me used a drill bit and then a finishing reamer.

 

[Scorch]

Scorch, I'm assuming that this is the "crush" fit you are referring to. How do you determine that .002" to .003" measurement before disturbing your lathe set-up? Adding to this, I'd most likely be barreling a Rem 700 with a separate recoil lug (which acts like a giant washer) & would that effect the "crush"?

The crush I was referring to is the difference between a barrel snugged up hand tight to the same barrel tightened in a barrel vise. If you have cut your threads tight and worked the action over the threads to smooth out any roughness in the threads (some of us even lap the threads), the difference between hand tight and tight-tight in a barrel vise is about .002"-.003". When the action closes on a go gauge, with just enough drag to allow the handle to drop slowly under its own weight, you will have a tight chamber when you tighten the barrel, just enough to have to push the handle down on a go gauge. And yes, it is a "feel thing". After you feel a few dozen, you know when it's right.

 

[Bart B.]

Gunplummers remarks:

Handloading for a chamber is backwards also. Take a couple different brand cases and fire them. Re-size the cases. Now make the reamer to the case dimensions, which is also your die specs. I have been able to do that and get no more than .001 stretch from cases after making up a reamer like that. Or, you could just make a die to match a chamber, but it is a lot harder to do.

I don't think this'll work. Unless I've completely misunderstood your idea.

The chamber neck will not have zero clearance to the loaded round's neck; it'll be an interference fit because the seated bullet makes the loaded round's neck larger than what it was coming out of the sizing die.

Sized cases' dimensions are larger than the sizing die they came out of; sizing dies have to be smaller than the desired end result of the sized case dimensions.

Even the most accurate benchrest rifles do not have their loaded rounds a "perfect fit" matching the barrel's chamber dimensions.

 

[Gunplummer]

You have misunderstood the idea. It does not matter if the case springs larger than it was in the die. You are measuring the case not the die. You give yourself enough on the neck dimension (SAMMI). The little bit the neck expands really won't show up. I made a bolt for a rifle with excess headspace once. The chamber was oversize. I got rid of the excess headspace, and a fired case hardly grew in length, but when re-sized the OAL grew about .015 . The case walls expanded outward. That is an extreme example of what an oversize chamber dimension will do. Using ammo that was manufactured on the low in chambers cut on the high will give you the same effect. If mixed ammo is all resized and fired in a chamber matched to it, the OAL increase when re-sized again is almost non-existent. With the new CNC grinders that tool shops use now, I don't see why the idea is not more popular.