Tips on Gunsmithing BlackStar AccuMax II Barrels

By BlackStar, with major contributions by Bruce Baer, Dan Green, Dave Kiff, Dave Manson

The birth of any new thing is full of challenges and even opposition. Soon after BlackStar announced our new AccuMax II barrel line, the rumor mill went into high gear.  Rumors abounded that gunsmiths hated the stuff, that it was impossible to machine and that it would destroy reamers and other cutting tools.  Perhaps you have heard some of the stories yourself. As is so often the case, the facts are very different from the rumors. It is true that BlackStar Accumax II Barrels are different from 416 stainless barrel steel.  It is not necessarily more difficult to machine than 416 barrel steel, but it does machine differently.  After hearing all of the same stories you've probably heard, we at BlackStar decided to set the record straight about what it takes to chamber, thread and crown an AccuMax II barrel.  This article is not meant to be definitive, but it is authoritative.

Section A of this article consists of the machining instructions to be used on BlackStar Accumax II (Lothar Walther) barrel steel.  As experienced gunsmiths will immediately see, we assumed nothing in making up these instructions, so even the seemingly self-evident issues are addressed.

Section B of this article includes the perspectives of several reamer makers and gunsmiths on what it takes to thread, chamber and crown a BlackStar barrel.  In some cases, we received written reports from the individual, and in others we had to rely information given to us on the phone. Where appropriate, an individual's direct quote has been used in order to elaborate on a particular point. Despite Editor Dave Brennan's generosity, there obviously was not enough room in this article to include all of the super machining data that we have received.  In addition to those individuals whose comments are featured in this article, BlackStar's Barrel Steel Project benefited greatly from many kind and generous people whose input, assistance and encouragement are reflected in various ways in the text of this article.  In order to cover all the bases, BlackStar solicited, and received, a lot of help from a lot of people. Even some men who are technically our competitors offered help, a fact that says volumes about their love of the sport and the quality of their personalities.

We would like to thank the following people for their various contributions:  Dan Green; Bob White; Jim Borden; Clarence Hammond; Bruce Baer; Dwight Scott; Jim Carmichel; Dick Wright; Greg Tannel; Dave Kiff; Dave Manson; Bob Gamboa; Johnie Franklin; Earl Liebetrau; Pete Pieper; Dan Hackett; Lowell Frei; Jerry Hensler; Glenn Newick; Harley Licht; Dan Dowling; Mark Hendricks, Brownells; Frank and Gerd Walther; Woody Woodall; Ken and Peggy Johnson; Rick Taylor; Dick Barber, Ed Severson and Steve Courtney, Crucible Materials Corporation; Chris Dichter, Pac-Nor Barreling; and the good folks at JGS. You all really made a difference in the success of this project, and we thank you.
 

Part A
TURNING OPERATIONS

The vast majority of people who contributed to the knowledge in this article commented that as far as turning operations are concerned, BlackStar AccumaxII barrels are not all that different from 416 stainless barrel steel. In many cases, the information here is old hat to experienced gunsmiths and machinists, but many of those involved in this project suggested that it would be best to state the obvious rather than assume anything. Crowning.  Tools used in crowning should be very sharp.  Top relief should be a minimum of 10 degrees with HSS tools.  After grinding the tool, all cutting edges should be honed.  Take lighter cuts than you would with 416 stainless barrel steel.

Threading. While almost any quality tool will produce excellent threads on BlackStar barrels, the best option is to use C2 inserts.  These consistently produce the bright, shiny threads that everyone prefers.  HSS tools should be ground with 10 degrees top relief angle with a honed cutting edge.  A medium back gear speed will generally work best.  Take light cuts, particularly after half of the thread has been formed.  0.010" feed is about right.  Look closely at the surface at the top edge of the thread being cut.  If there is a small rolled over edge, this indicates that the tool is not cutting well and is not sharp enough.  If you use a HSS tool and more than one barrel is to be done, we suggest that you re-hone it between threads.

Tool Material and Cutting Oils.  If you are using a HSS tool, cutting RPM will be less than 300.  Do not make the mistake of threading too slow.  If carbide inserts are used, they can be TiN coated and/or multi-coated, but it is not required.  In all cases, a cutting fluid should used.  At slower speeds, Tap Magic for steel is good.  Other thin thread cutting fluids can be used. For threading, sulfurized cutting oil mixed with an amount of thin tapping fluid seems to work best.  Some gunsmiths also use a cutting oil additive called Moly D, both as an additive mixed into their cutting fluid and in its straight and undiluted state.

Cautionary Note.  If the tool is sharp and there appears to be a rhythmic surface to the cut, this indicates that the lathe has some play in its slides or carriage.

CHAMBERING OPERATIONS

There are two very important requirements to successfully chambering a barrel made from BlackStar steel:  a sharp, concentric reamer with interchangeable pilots and the right cutting fluids.

The Reamer.   Above all things, the chambering reamer must be very sharp.  If there is even a small nick on one of the shoulder cutting edges, the reamer will feel as if it was dull.  A build-up of material will occur at this point.  In addition to being very sharp, the reamer must be concentric.  An out of round reamer will cut as if it was dull, so check to see that one flute on the neck area is not doing most of the cutting.  This is particularly true of the neck area. Last but not least, the reamer must have interchangeable pilots. Fixed-pilot reamers are not sufficient to machine this steel.  Excessive space (>.0002") between the pilot and the bore will cause a very rough cut and will reduce tool life.

Today's steel chamber reamers are crafted from several different tool steels, depending on the maker. Carbide reamers continue to gain in popularity, and are suitable for chambering BlackStar steel with the right set-up.  They are not, however, required to do a first-class job.  If you have any questions concerning your particular reamer, please contact the reamer maker.  All of the major reamer makers have positive experience with BlackStar steel, and can help you with any minor problems you might have.

Important Note.  If you chamber using a fairly fast speed, you will build up heat on the edge of the reamer and prematurely dull it.  Under these circumstances, the reamer may need a basic dressing every 5-10 chambers to maintain optimum performance.  However, if you maintain a modest speed and feed, keep the barrel and reamer cool and well-lubed, your reamer should not wear significantly faster than it does cutting 416 stainless barrel steel.

Set-Up.  To chamber with high-speed steel reamers, lathe RPM should be 50-90 RPM.  Use whatever speed you are more comfortable within this range.  In some respects, slower is better, so feel free to run around 50-65 RPM if that feels best to you.  If you are using a carbide finishing reamer, you need to be aware that the best surface finishes are achieved at 230-300 RPM, according to Pacific Precision and many of the other reamer makers.  Obviously, if you are using a carbide rougher, you can chamber at a much slower speed and clean up the surface with a HSS finishing reamer.

Regardless of the barrel steel type, chambering at low RPM with carbide reamers will not give you the same super-high-quality chamber surface that you can get with most high-speed steel reamers. Consequently, many of the reamer makers and gunsmiths that have worked with BlackStar barrels have stated that an ideal combination would be to use a carbide roughing reamer and a high-speed steel finishing reamer.

Set-up the barrel as you normally would. The rigidity of your set-up is always very important, but even more so with BlackStar barrels.  Hold the reamer in a rigid manner relatively close to the flutes.  (Make sure that the tail-stock is lined up exactly with the head-stock)  A floating holder can be used.  We encourage the use of a high-pressure muzzle flush system, as it will enhance the chambering of all steels, including 416R and 4140 chrome moly.  However, the use of a muzzle flush system is not required to produce a top-quality job.

Reaming the Chamber.  Apply a very liberal amount of  lubricant to the reamer.  Thinned high-pressure oil is an excellent option favored by many.  Tap Magic for steel also will work or a thinned sulfurized cutting oil.

Several reamer makers and gunsmiths have reported that a mix of Rustlick high pressure mineral oil, thinned with Tap Magic and a little Moly D delivers optimum results with no appreciable wear on high speed steel reamers.  Still other gunsmiths report using pure, undiluted Moly D with absolutely fantastic results.  (Moly D is a high-pressure additive. Cost is about $50.00 per gallon, but really worth it.)  Others have used a water soluble fluids with equally fine results.  Clearly, there are a variety of cutting fluids that work well with BlackStar barrels.

When you begin, feed slowly and feel the reamer cut.  Do not over-feed. If you are not using a muzzle flush system, consider the maximum tool advancement to be 0.100" between cleanings. For best results,  advance only 0.025"-0.050" between cleanings. The degree of the advancement will vary from caliber to caliber.  Above all, do not try to hurry the process.

When the reamer is removed from the chamber being cut, clean it completely.  Make sure that there are no chips remaining on the bottom. Also swab the chamber and about 3" of the barrel in front of the chamber to make sure that there are not any hidden chips remaining.  The last two cuts will be best if less than 0.030" deep.

If you are using a muzzle flush system with a high pressure pump, feed the reamer about 0.050" per minute, then wait 30 seconds for the reamer to cool and re-lube before proceeding with the next 0.050" of feed.

Part B

Dan Green, Forgreen's
Tel:  915-453-2800

I was contacted by BlackStar and asked if I would be interested in evaluating their new stainless barrel steel.  It appeared to be a good opportunity to work with something new, and I accepted.

A few weeks later, I cut my first two test chamber into samples provided by BlackStar.  I produced both reamers from M7-HSS with a slight change in geometry.  I though that this might provide an efficient cut with a smooth finish.  I used heavy sulfur-based cutting oil, both straight and mixed with tapping fluids. The reaming process was a bit frustrating, and the finish on the chamber walls was not acceptable.

Next, I produced a reamer in .308 Winchester, using T15 tool steel and my standard tool geometry.  I also ordered a bottle of Moly-Dee, and when it arrived,  I cut my third chamber.  The improvement was very pleasing.  After trying various RPMs and feed rates, I settled on 80-90 RPM, with a gentle feed rate (by hand) and cutting depth of 0.020 to 0.025 inch between cleanings.  (Forcing the reamer too fast creates a feeling of cutting the chamber dry and results in grabbing and tearing of the chamber walls.)  Chambering the BlackStar steel may take as much as 10-15 percent longer, so be patient.

The overall finish and appearance of the third test chamber was generally acceptable.  The majority of the surface area was smooth, with occasional areas of peripheral tearing.  A closer look revealed that these tears were very shallow and mostly cosmetic.  For those who choose the practice, a light polishing would easily remedy this.

No doubt there was room for improvement in my last chamber, but it is important to note that just a simple change in cutting oil provided much better results than the previous two test chambers.  I do not doubt that there is also room for improvement in my chambering methods, and there are processes now in use that would provide these improvements.  For example, a muzzle flush system would allow shorter chambering time, consistently smoother finishes and deeper cuts between reamer removal and inspection. In my opinion, the quality of BlackStar barrel steel merits our continued efforts to learn better and more efficient ways of working with this new steel.

Many gunsmiths are interested in reamer life.  An inspection of my reamer under magnification revealed no evidence of premature wear or dulling of the cutting edges.
 

Bruce Baer, Baer Custom Rifles
Tel:  717-423-6152

I like the new steel used to make the AccuMax II barrels.  As far as I am  concerned, the surface finishes are superior.  As far as turning operations are concerned, I would recommend going as fast as you are comfortable with.  Get as close to 125-150 RPM as possible.  Flood coolant on the barrel at all times.

As far as chambering is concerned, run about 50 RPM with a high-speed steel reamer.  Feed for the rougher is up to 0.050-0.100" per cut.  I use a Henriksen rougher and a Green  finisher, and that combination works great.  A carbide rougher also would be good.  I use the finish reamer for the very last cut, debur it, and then run it in 0.010" to finish depth.

I ran Mobil Omega cutting oil, which is a highly sulfurized oil.  I use about 50 percent more than normal when reaming AccuMax II barrels, but I don't consider that important at all.  The key is to keep the reamer and the barrel cool.  You will get a great chamber and your reamer will last a long time.
 

Dave Manson, Clymer Manufacturing Inc.
Tel:  248-853-5555

I cut a test chamber (22-250 Rem) in a section of a new AccuMax II made from Lothar Walther steel.  Chambering was done in a lathe at 72 RPM, with one of our standard reamers held in a floating holder and fed from the tailstock.  Soluble oil, diluted 20:1 was constantly supplied to the tool, and chips were cleared as required.

This barrel steel cuts like really good chrome moly, through slightly slower.  Chips produced by the reamer were small and flushed easily.  After reaming, I examined both chamber and reamer in detail. Finish of the chamber was excellent and would, in my judgement, require no polishing whatsoever.  The reamer showed some very slight wear on the cutting edge, but it was not excessive.
 

Dave Kiff, Pacific Precision
Tel:  541-826-5808

I began working with BlackStar in the spring to refine the machining procedures for the new BlackStar steel.  Early on, I found that there was little difference between the turning operations on BlackStar (Lothar Walterh) steel and 416R, so I focused on reaming. As far as chambering is concerned, a quality mass lathe is important. Use a floating pilot reamer, and run it at 45-90 RPM.  For best reamer life, use reamers made from M7 or better, and keep the heat down by going slow and using a first-rate cutting fluid. Use an extreme pressure mineral oil-based cutting fluid, thinned with Tap Magic and Moly D. Take cuts of 0.025"- 0.050", withdraw the reamer, clean and re-lube. To do this right, you will end up spending about 15 minutes longer on a chamber job in BlackStar(Lothar Walther) steel than in 416R, but it is well worth it.  This steel is first-rate material.

Summary

In closing, the machining differences between BlackStar Accumax II (Lothar Walther) barrel steel and 416R are completely and easily surmountable by any competent gunsmith with good quality equipment. If you have any questions concerning turning or reaming operations on BlackStar Barrels, please do not hesitate to call BlackStar at 713-849-2090 or send an email to: info@blackstar-barrels.com.

Further machining instructions and tips can be found by calling Lothar Walther at 770-889-9998. Ask for Woody Woodall.

AccuMax is a registered trademark of Delstar.
AccuMax I is a registered trademark of Delstar.
AccuMax II is a trademark of Delstar.
BlackStar is a registered trademark of Delstar.