Home Forums Hunting & Shooting Gunsmithing Safely turn down stepped barrel to straight taper?

Never blew one up and learned to draw file on many...

I did exactly one, a military 7x57 barrel. It turned out ok, a nice lightweight profile. Just one fly in the ointment: it would start walking its shots vertically as the the barrel heated up. First two would be nearly touching then the 3rd would be around two inches higher, the fourth that much higher yet, and the fifth would end up creating a vertical group about 8-10" long. I deemed it ok to hunt with and did so for a couple years. I've always assumed I released hidden stresses in that barrel when we turned it.

A buddy turned down a couple Swedish Mauser barrels a few years ago, from the first step forward of the chamber on out to the muzzle. He then milled that back section from the chamber to the first step into an octagon. The barrels were pretty cool looking but I was a little leery about them being weakened by cutting the octagons - they were rather slender looking over the chamber area - but they held up fine and I assume they're still being used.

I have two ex-Military M98s in 8x57 with the original barrels turned down to a sporter contour. One is quite accurate; the other, I haven't shot very much.

I have done it many times. In fact I have an 8X57 with a 19 inch barrel cut from a 29 inch original length that I turned the steps out of and it's one of the most accurate rifles I own.
The trick is to never let the barrel get very hot. Take light cuts. You need to be able to touch the barrel about 1 inch from the tool at any time and not feel heat that would make you wan to pull away.

I use 2 loads in this rifle.

One with Speer and Nosler 200 grain bullets , shown here. This is the less accurate load.

PC070001 by Steve Zihn, on [bleep]


PC070002 by Steve Zihn, on [bleep]

And my other load I only shoot deer and antelope with because the bullet is too "soft" to do good work with elk. I did kill one 5X5 bull with an SST but was unimpressed as to the depth of penetration's and the fact that the bullets (2 of them) came apart and didn't do as well as I like for elk rounds. That load is 46.0 gr of IMR4895 and a 170 GR Hornady 170 gr SSTs These bullet shoot groups about 1/2 the size of the ones I get with the 200 grain bullets shown here, but the 200 Gr Partitions kill elk very well. I use the Speer 200 gr as practice bullets but have not killed anything with one of them so I have no reports on their performance. They may be good, but I don't really know.

Anyway, as you can see, the old turned down military barrel is just fine. If you are going to shorten one, do that first. A shorter barrel is stiffer, so when you turn the steps out it's a bit more forgiving if the barrel is cut and crowned first.

Do you want to turn it for weight or looks (or both).

I had a guy turn ringlets on two barrels right at the steps. They look like round to octagon type ringlets

I have seen many that were turned down carefully and slowly by a highly respected gunsmith. None of them shot as good as they did before turning them down. Most shot OK, but none shot nearly as tight a group as they did before turning them down. I haven't seen anyone turn one down in at least 25 years. There are too many quality, affordable aftermarket barrels available.

I think maybe the key is in accurately indexing the bore in the lathe.

This has been my experience...even just reducing or blending the radii of the steps changes the harmonics would be my guess.
Although, I just love the look of the barrel Richj posted above...I might need to try that. Ye olde gunsmithys of colonial tymes referred to those as wedding rings...presumably wedding octagon to round? Although engineers tell us shapes like that tend to concentrate stress..some things are just too cool to let engineers dictate.

I had the wedding rings done on 2 barrels. I got them from RSI many years ago in 7x57mm. One is on a Chilean 1912 Steyr Mauser and one , believe it or not , is on a Yugo 24/47. 100yds - IMR3031 - light loads. at about 2400fps

Sweet...nothing wrong with results like that, I'ma a gonna grind me some tools this afternoon...practice on a junk barrel first though, lol.

Questions for Steve Szihn. Help out an amateur here...do you turn the barrel between centers with a dog, or do you chuck the drive end? Do you run a steady or follower rest pretty close to the tool?

Flintlocke, I first cut and crown the barrel if I want it shorter. Next I chuck the muzzle end of the barrel first and put a live center in the chamber and then turn a few thousandths to make sure the OD is concentric with the chamber/bore. 3rd, I reverse the barrel and chuck on the now concentric area and place the live center in the newly crowned muzzle.
After those steps are done I set my taper attachment at what ever taper I choose and starting at the muzzle end, start with cuts about 4" long. By tapering the muzzle first you can back up another 4" on the 2nd cut and it tapers down the barrel, but when it gets over your first cut the tool is not diving deeper and deeper because the taper and the cut are turning the same amount of stock off the outside of the barrel. Keep backing the tool up after each cut toward the breach end until all the barrel is tapered.
I run only about 300 RMP and I only cut about .015" at each pass. As I said above, I never let the barrel get hot. Take the time to turn it cool (300 RPM and a slow feed) and if the barrel was accurate before you started it will be just as accurate when you are done. In fact in most cases if you shortened it, it come out more accurate, because you have a stiffer barrel when it's sorter. 19 times in 20, men rush it far too much, and as was said by others above , the accuracy can suffer. The heat generated is only concentrated where the pressure is. (the tool) So by not heating the steel up and putting pressure only on the hot spot the stresses and warpage is not a problem. When I turn them my chips don't come off blue, and I never move more than about .015" at a pass.

Military Mauser barrels are not very heavy so getting them to cut with no tool-rings and with a slick finish is difficult, but you need not be bothered because if you strike (draw file) the barrel when your turning is done, and then polish the barrel on a wheel, or even with grit paper on a block, the amount of time needed to make a very nice looking barrel is not really all that long.

"...and place the live center in the newly crowned muzzle...."

This sounds like a recipe for disaster, do you have any idea how that live center would destroy the crown? I would hope you would re-crown it after doing the taper.

Turning down a stepped military barrel to a straight taper with a lathe is fairly simple. You figure how long you want the finished barrel to be, add 1/2", cut and face the barrel. Put the barrel shank in the tail stock and the muzzle on a live center. Put a straight edge on the barrel to determine the tail stock off-set to remove the top of the steps back to the first step. Cut the barrel its length, the military barrels are CM so cut fairly smooth. You can spin the barrel doing a barrel spinner or a belt sander with a 220 metal belt. Reface the muzzle and cut a new crown...re-finish as desired.

I reshaped twelve M-96s barrels in one day to 23" after I removed the rear sights and filled the rear sight screw hole.

do you have any idea how that live center would destroy the crown?

Yup, been doing it for almost 60 years now.

That rifle I shot those groups above was done that way -----------------------along with many dozens of others.
Many of them shoot very very well when I was done and I have had dozens and dozens of very happy customers.
Anytime facts and theory disagree,,,,,, try to guess which one is wrong.

Well then, I suppose its possible the first half dozen rounds out the barrel probably cleared out that burr you generated!

If one is offsetting the tailstock to cut a taper, the crown will most definitely be burred. If one is able to leave the tailstock on center and use a taper attachment, a live center will do not harm to the crown; providing there is a 60 degree taper for the center to ride on. Taper attachments and/or copiers are a great improvement to tapering a barrel. Off setting the tailstock is easy enough but can also promote chatter. GD

^^^I like this. As long as you are here, would you comment on max depth of cut with HSS on chrome moly and the use of steady rests?

The depth of cut is dependent on the tool, the machine, the speed, and the rate of feed. Assuming a typical 13x40 gunsmith's lathe (a little on the light side), I'll run at around 280 RPM for a full blank and bump that up to 400 or so once I'm down to .7 at the muzzle or so. The depth of cut will be between 25 and 35 thou and the the feed rate .006" per revolution. The tool is a knife edged, modified chip breaker with a groove behind the cutting edge of about 1/16 radius. The tool is set .015 above center and ground for clearance at this setting. The use of a steady rest is a crutch for when the tool isn't cutting right and you can't get it to stop chattering. I'm always a little bummed if I have to resort to the steady! A travelling steady can be used, provided it is made so that it can back off to accommodate the taper. A hydraulic damper works and a hinged steady, weighted with lead shot, works well too. One trick I have used a couple of times was to fill the bore with lead shot as a damper. It worked.
When the tool is cutting right, it should produce a coil about three inches long then the chip should break. A longer coil is alright from a turning standpoint, but can be unsafe. A chip that breaks constantly as it comes off will tend to set up vibration.
Barrel material can make a real difference in how the turning operation goes. A modern 4140 barrel is tough but turns fairly well. 416 stainless machines very nicely except the chip doesn't break well. The old mauser barrels mostly machine very nicely.
With a heavier machine (14x40 or 16xwhatever) you can usually push a little harder but I generally don't cut more than .050 deep and keep the feed rate at around .006.
I have tapered barrels using a taper attachment or copier, and by offsetting the tailstock and using an attachment is far better. In offsetting the tailstock, the barrel must be set up on centers with a faceplate driving a dog. The dog wiggles as the barrel turns and the centers squirm in the ends. Both of these actions can generate a vibration pattern and induce or worsen chatter. I think it's best to run between centers with a taper attachment as well but you can hold in the chuck if you want. That's about all I've got. GD