Chambering a blank barrel

[augercreek]

When I am going to ream a chamber in a barrel blank and no roughing reamer is available can I STEP DRILL VERY CAREFULLY or just use a finish reamer a little at a time?

[Bent Ramrod]

In many cases you can do either. I know people who step drill every chamber in the lathe, then bore out the rough steps before they use the finish reamer.

I would say the step drill (or rougher) is only an absolute necessity when you have a large, mostly cylindrical, abrupt shouldered, necked down cartridge to chamber for, like a blown out Magnum shell, for instance. The more tapered cartridges, like the .25-35 and .30-40, I just use the finish reamer. Haven't done an intermediate bottlenecked shell like the .30-06, but would probably try to drill as much excess out as possible, just to avoid wear on the shoulder part of the reamer.

Without a lathe, I'd just as soon rent a rougher. I wouldn't trust myself to step drill by hand.

[rockrat]

If only doing a few chambers I just use the finish reamer and a good lube

[Jedman]

I agree with Bent Ramrod, If I am reaming a strait walled cartridge I just use the finish reamer.
If I was reaming a large bottleneck I use a drill bit as large as I feel comfortable with to within 1/16" of where the shoulder starts and if needed bore some taper so that the pilot will reach into the bore.

Jedman

[HollowPoint]

Back when I did my very first barrel job I did it the "Step-Drill" way. It worked out OK in the end. I wanted to make sure I hadn't lost my zero after each step so I'd re-index each time just to be sure.

I had my barrel secured pretty darn good but I still got varying amounts of runout after each step. I have since been told and have read that this is to be expected. Even if I were to have removed my indexing-rod after indexing; and then re-inserted it and indexed it again, it still might show some runout. It's hard for me to wrap my head around that so from then on I figured I'd just use the finish reamer rather than step drilling first.

HollowPoint

[augercreek]

Good advice fellows. I'm stubbing a 7mm Rem. Mag. barrel on to a RB shank which I will be chambering to 7X30 Waters. By my estiments I'll have to cut off about 1 3/4" of the chamber to get to a small enough dia. for the 7X30 reamer to clean up the old chamber. Does any of this make sense?

[Ballistics in Scotland]

There is no single and easy answer to this one. You can ream any chamber completely by hand with no tools but a vice, a tap wrench or carpenter's brace and the finishing reamer, if the reamer pilot is a close fit to the land diameter. In a modern quality barrel it ought to be, though I wouldn't count on that with a polygonal bore or other clever ideas. Some with a big step from neck to shoulder will be confoundedly hard work, but I don't see why you would go wrong at it. The shoulder angle shouldn't make a big difference, since a long shoulder just lengthens the cut being made.

Partly drilling the chamber has two functions. It reduces the work required, and it saves wear and tear on the reamer. The latter isn't of much importance to the man who will ream only one or a few chambers. But the drilling must be done concentrically with the bore, and must allow the pilot a considerable amount of engagement in the bore. In my view this totally limits it to the use of the lathe, and with great care taken to centre the bore. Centring the outside of the barrel, even from a quality barrelmaker, isn't good enough, and even a lightly used three-jaw chuck most certainly isn't.

[Jedman]

Are you talking taking the square threaded shank of a rolling block barrel and stubbing onto a 7MM mag barrel that is cut back far enough to clean up with the 7 X 30 Waters ?
If so, Yes that's the way to do it if your not able to duplicate the square threads.
I would turn your barrel shank to about .750 O.D. then get your RB barrel chucked up and indicated running true to the OD of the thread then with a short stiff boring tool bore the old chamber out until you either get it to a snug fit to the shank or use a 3/4" reamer if you have one then before you cut it off I would flux and tin it with silver solder while turning at your slowest spindle speed then cut it off square. Leave the 7 MM barrel shank a little long then flux and tin the shank and solder the stub on. Before screwing the barrel back into the frame coat the threads with a good anti seize lube and tighten it and then back it off several times until you have a dead solid point at which the barrel stops without tightening any farther. Then if you need to index it to line up with the sights on top or any other point you can cut the front shoulder back until you reach the correct index point then cut the excess shank length back until while holding forward pressure on the breech block you can just get the hammer to fall all the way to lock the breech block and strike the firing pin. Once your comfortable with that fit make witness marks on the bottom of your barrel and front of the frame so you know the correct stop point then your ready to rechamber the barrel.

If I understood your intentions the cut off 7 MM Mag chamber should allow you to get the reamer pilot in the bore you should be good to ream with a finish reamer at that point.

Good Luck with this project and post pics when you get it underway.

Jedman

[Ballistics in Scotland]

Yes, it sounds like the existing 7mm. chamber would serve as a perfectly centred step drilled hole. Even suppose you shorten it by an inch, get a chamber with a lumpy shoulder and have to shorten it till the chamber is normal, it will have saved you a bit of work and maintained concentricity.

I lot of people will tell you that square threads are hard to cut in the lathe, but I didn't find them so. They aren't actually stronger than any other thread of the same pitch (which have much more longitudinal strength than you need, but they can provide a close fit if either the top or the bottom of that square is accurate, rather than the more difficult feat of producing tightness on the flank of a 60 degree thread. The old pitfall of tight crests and loose flanks is impossible. I think they were used because for a given amount of turning effort, less goes into friction and more into drawing the barrel shoulder up tight. That is why it is particularly advantageous in a takedown rifle. Just try pushing and turning a 120 degree cone in a 120 degree hole, then a cylinder in a cylindrical hole. A V-thread is just a continuous slice of cone, like the language teacher's old friend, the Tower of Babel.

https://en.wikipedia.org/wiki/Tower_of_Babel

All you have to do to cut a square thread is grind a high speed steel toolbit to a square tongue, skewed and slightly relieved so that the bottom doesn't rub on the slot the top cuts. I don't believe you can buy them ready made, since what works for my 1.125x10in. Enfield thread wouldn't be right for anything different.

[Cap'n Morgan]

Even in a lathe with a perfectly centered bore, one should still use a boring bar to drill size for the first 1/2" or so before pre-drilling the chamber to prevent the drill from wandering. As good as a rough reamer (and faster) is a step drill ground with a cylindrical pilot, but not many has the machinery for making such a thingy. I prefer the pilot large enough that it actually burnish the top of the lands ever so slightly - it makes reamer chatter far less likely.

[augercreek]

I've been a machinist all my life and understand you all well, it's just that I've not done any chamber work before. I've rebarreled a few ss before but, just stubbed barrels on them. I've got a 219 Savage and I bought a 220 shot gun barrel and am stubbing a 7.62x39 barrel to the breech end of it. I bought a blank 30 cal barrel so that'll need to be chambered also. I understand pressure for 7.62 is quite high with factory loads but I intend on just using mouse fart loads in it anyway. I'd think the 219 Savage action to be quite strong though?

[screamingjohnny]

I've done many chambering jobs with just a finish reamer. A rougher is good if you are doing a lot of jobs. Take it slow and you will be fine. Say .050 a time.

[KenH]

I just found this thread (been away from forum over Christmas Holidays) and would like a question to confirm what I "think" I'm reading. Ya'll are saying take square threaded shank of a rolling block barrel and stubbing onto a barrel by cutting off the threaded portion of an existing Roller barrel, boring the threaded portion to 3/4" to make a "collar". Then machine down the end of new barrel to slide inside that collar and silver solder in place. This allows the new barrel to screw into roller action without having to cut new square thread - am I correct?

If so, I measure the ID of the action about .910", boring out the barrel stub to .750" leaves only about .080" thick metal for collar - just barely enough metal to hold threads in place. Since square threads are not that hard to cut, I'm assuming this method is used to help with hand grinding the barrel cutout for the breechblock?

Does this method provide enough strength for the full trapdoor loads of 33k psi?

Thank ya'll for any info and guidance,

Ken H>

[fast ronnie]

Seems to me not to be that difficult to cut square threads. I don't do them often. and while true it's a little different than cutting a "v" thread, if you watch your back clearance angles closely and you take small cuts it can be done without too much difficulty. I'm a die maker by profession and am somewhat familiar with lathe work. Recently had the pleasure of re-barreling because the guy who built this piece had no idea of how to line up a tailstock. At the belt face "a belted magnum" it had been wallowed out by about .010. Ruined the brass every single shot. Finishing reamer worked fine, but both ends of that reamer need to be straight with the BORE of the barrel, not the outside. Use a spider chuck or use a chuck on both sides of the headstock. A range rod is needed to get the chamber dead straight with the bore. Setup will take longer than cutting the chamber. Go slow, use plenty of cutting fluid and clean the chips out often. Drilling first is done by many but leaves a lot of room for that reamer not to track straight. The results would be much like cross threading a bolt. Take your time but don't take shortcuts. It will still shoot, but I have a saying that gun control is being able to hit your target. As Flip Wilson used to say "the challenge made me do it!" Well, almost!

[Willbird]

I would not be the least bit afraid to cut the square threads, if your nervous just thread some bar stock a few times . Honestly should be simpler than a Vee thread. I have done a lot of Acme over the years, and a few Square. One thing you will want to do probably is keep some "drag" on the carriage handwheel to ensure that any backlash in the half nuts does not cause issues, I do this on a lot of smaller lathes...on both my South Bend 9" and my Grizzley.

I have done quite a few barrels and never used a roughing reamer once. The step drill deal if you think about it has you running the reamer into a drilled hole without the pilot touching anything until it is rudely poked into the rifling once it gets deep enough .

I have heard of folks rough drilling then BORING with the compound set to the body taper of the case....so the reamer is entering a precision bored tapered hole. Drilling is honestly a roughing operation, sometimes a drilled hole is plenty good enough for some things, but not when we are going for .0001"

When we are playing around doing a chamber and we are not "on the clock" we do not have to get in a big hurry, we can take our time.

I feed it in about 1/8" at a time to begin with (.1 on my Grizzly because it has .1" graduations on the tailstock quill).
Holding reamer back against center back off a little.
Stop spindle
Withdraw reamer.
Clean chamber and reamer (I use compressed air)
Brush oil on reamer (I use Brownells Do Drill,,,which is a high sulfur cutting oil)
Put reamer back in by hand then back it away a little....reamer is held against center
When it is time...then go to 1/16" increments(.05 on the Grizzley, again...those are the graduations)

When you get within .1" of depth, I set up a test indicator so the front face of the tailstock quill engages it, then I can move the reamer in to the .001" of where I want it.

Again no hurry, take your time . Measure twice, even three times, cut once. There is an old school theory that if you need to remove 1" you take off .500, then of the ,500 you remove .250, then of the .250 remove .125 ....something to be said for that .

I have a Mauser barrel around here I traded into that the previous owner somehow ran a 300 win mag reamer in 1/2" too deep.....NO IDEA how he did that...it started out as a short chambered barrel I think.


Bill

[fast ronnie]

A half inch too deep ??????

[Willbird]

A half inch too deep ??????

Ask and ya shall receive hehe. I got this from a guy who got it from a guy...it is an Adams and Bennett barrel I think.





The guy I got it from, told me the guy HE got it from just said "I screwed up, don't want to talk about it anymore than that". I have exactly zero $$ in it and told him I would take it, hoping there was enough straight portion to cut it off, re thread, and chamber to something or other, or maybe use for some other project entirely .

But it really is a fine example of....."DUH" hehe.

Bill

[augercreek]

I think this is getting off track. The reason for stubbing is the new barrel is much smaller in diameter than the RB barrel shank so that is why I use it not fear of cutting square threads!

[Willbird]

I think this is getting off track. The reason for stubbing is the new barrel is much smaller in diameter than the RB barrel shank so that is why I use it not fear of cutting square threads!

That is a good topic too, In have pondered that situation myself .

[augercreek]

Well the job is done, only took half an hour, looks good. Sending the reamer back today. An odd thing in this job is that I had gotten some empty FC brass from a fellow, so I run the brass threw the LEE dies I bought and loaded some up in anticipation test firing the new barrel. Guess what ! They won't chamber! Lack about a 1/4" of going in all the way! UNBELIEVEABLE!!!!! So I compare the reamer to the brass I've got and they are not nearly the same! The brass looks more like it's been Ackley improved! So I hop in the truck and go to town and buy a box of Federal ctgs. and they fit perfectly! These new Feds are nickel plated they look real pretty. Now I'm wondering are the dies wrong? Next I take some 30-30 brass and just neck size them and they fit okay, they'll fire form. What gives????