The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > The Smithy

Reply
 
Thread Tools
Old August 19, 2008, 10:42 AM   #1
Lt. Dangle
Junior Member
 
Join Date: August 6, 2008
Location: Arizona
Posts: 4
Bore Conditioning Ammo

Hello all,
Just wondering what the general consensus is on the Tubb's final finish bore conditioning ammo is? http://www.davidtubb.com/ff_loaded_ammo.html.

It’s available through Cabalas at: http://www.cabelas.com/cabelas/en/templates/product/standard-item.jsp?_DARGS=/cabelas/en/common/catalog/item-link.jsp_A&_DAV=MainCatcat20712-cat20726-cat20839&id=0044350216321a&navCount=3&podId=0044350&parentId=cat20839&masterpathid=&navAction=push&catalogCode=IJ&rid=&parentType=index&indexId=cat20839&hasJS=true

Thanks and be safe
Lt. Dangle is offline  
Old August 19, 2008, 05:19 PM   #2
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 10,462
It is a bore finishing system. It isn't fire or pressure lapping, though, meaning it isn't designed to correct constrictions or other significant dimensional errors as the better lapping methods do. The only complaint I've heard about it was a fellow complaining it had ruined a Marlin Micro-groove barrel. Micro-groove barrels are not something I would put an abrasive to without have a borescope to keep a constant eye on the throat.

I use the NECO pressure lapping kit. A simpler system that also produces good results is sold by Beartooth Bullets. Avoid the Wheeler kit. It's starting abrasive is too coarse and the instructions illustrate an improperly fire lapped barrel and claim it is properly done. They clearly were trying to get on the firelapping/pressure lapping bandwagon without understanding what they were doing.

Whether you use firelapping or, if your bore is good dimensionally, the Final Finish system, you will find fouling is reduced and the gun is easier to clean. Whether you garner benefits for accuracy or not depends on the condition of bore and throat you start with.
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member
Unclenick is offline  
Old August 30, 2008, 01:05 AM   #3
SST
Member
 
Join Date: January 13, 2008
Location: Missouri
Posts: 37
I'm going to respectfully disagree with Unclenick. Tubb's Final Finish is definitely a firelapping product. The abrasive has already been applied to the bullets provided in the kit. The kit contains 50 bullets with 10 bullets in each of the 5 different grits provided. I used it on one of my Dad's rifles. It was the worst fouling rifle I have ever seen. Final Finish greatly diminished the excessive fouling, but it did move the throat forward quite a bit. Using Final Finish, or any other firelapping product, is a last ditch effort to salvage a barrel that is otherwise destined to become a tomato stake. Overall, it was a positive experience. The rifle no longer fouls badly and actually shoots a little better.
__________________
Regards,
Sam Taylor
SST's Rifle Room
http://angelfire.com/mo2/rifleroom
SST is offline  
Old August 30, 2008, 09:50 PM   #4
Ruger4570
Senior Member
 
Join Date: April 3, 2005
Location: Rochester, New York
Posts: 2,136
Firelapping started out as a thought as to how to improve accuracy in barrels. It was assumed that "Lapping" a barrel would make it MORE accurate. This MAY be possible when done by a barrel maker. As noted someplace, if you have a barrel that will not shoot, regardless of bullets or loads, go ahead and "fire lap" it. I doubt that it would make it much worse. I know, my lifelong friend tried it and simply degraded his .308 from being a poor shooter into being a "Lousy" shooter. He switched barrels and he now shoots sub minute groups all day. Barrels are just like cars, some work better than others and NO amount of STP or anything else is gonna make it better.
Ruger4570 is offline  
Old August 30, 2008, 10:25 PM   #5
fourdogs
Senior Member
 
Join Date: May 1, 2008
Posts: 152
I don't think anyone can unequivocally say fire lapping or lapping is good or bad. There are simply too many variables. The most important part of the equation is the individual who must think through the process. Not only the process of lapping, but the process of understanding different type of steels, rifling techniques, what the gun will be used for, and predicting with a high degree of certainty the final result

I fire lapped my 50 BMG with very good results. It had cut rifling. Many high end button riflings don't need lapping at all.... especially match grade. I like Neco. I've rolled my own fire lapping bullets. On other barrels, I simply use a little JB then 1200 grit Neco and work it back and forth on a patch over a bore mop, and my bores are super easy to clean after shooting. If you condition you're barrel properly before shooting ( and while shooting it) your way ahead of the game.

Fire lapping can be used with excellent results, but you better know what you are doing......no guessing......no experimenting. You simply must be able to predict with certainty what the end result will be....or don't do it.
fourdogs is offline  
Old August 30, 2008, 10:38 PM   #6
Ruger4570
Senior Member
 
Join Date: April 3, 2005
Location: Rochester, New York
Posts: 2,136
I have nothing against fire lapping, it sure is your choice. But,, If I had a barrel that was so bad as to "think" fire lapping was my answer, I would also be thinking,,, new barrel..
Ruger4570 is offline  
Old August 30, 2008, 10:51 PM   #7
fourdogs
Senior Member
 
Join Date: May 1, 2008
Posts: 152
You're right. I would never fire lap a barrel as a last chance effort. I think fire lapping should be restricted to new barrels with specific reasons and goals in mind. Fire lapping is very tricky. I only used the finest grit when I fire lapped. My bore was good, and I made it better.

If I could offer a bit more advice. If you are not very well versed with weapons, loading, and ballistics.....stay away from fire lapping. Use a lapping compound on a patch over a bore mop. 1200 grit works great and will remove very little metal. Carefully hand lap your barrel, frequently stopping to clean and inspect your work. You can't go too wrong hand lapping ( don't hit the bore with your rod ) and your barrel will shoot better and clean easier as a result.
fourdogs is offline  
Old September 2, 2008, 02:37 PM   #8
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 10,462
Lapping vs. Polishing

This subject probably needs a bit of detailing to get everyone on the same page.

Where I distinguish lapping from polishing is the former affects barrel geometry while the latter abrades and works the whole surface down. Firelapping, like hand lapping, is to remove identified constrictions or irregularities in the bore as well as tool marks to improve cleaning qualities. Such constrictions affect fouling in both cast and jacketed bullets. They generally affect the accuracy of cast bullets greatly and of jacketed bullets only a little. Polishing is strictly for smoothing the bore surface to reduce fouling or to clear up the alligator skin heat stress cracking in a throat. It does not remove constrictions significantly.

Whether your barrel needs lapping or not is determined by slugging the bore. Obviously a hand-lapped custom barrel has already been done. Other than lightly polishing the toolmarks in the throat, further lapping will be of no benefit. Determining whether a commercial grade barrel needs it or not requires slugging it with a pure lead bullet, ball, or fishing sinker. The bore is cleaned and a lightly oiled patch is pushed through. The lead object of choice is tapped into the rifling at the muzzle or at the breech with a dowel rod and mallet, then slowly pushed through the bore by hand, using a brass rod or a wood dowel. Pure lead is nearly perfectly plastic, so when it passes through a constriction it will keep the OD of the constriction and be loose in other parts of the barrel. You can feel the difference in how hard you are having to push it. Hard cast bullet alloy is not perfectly plastic and will spring back out after passing through a constriction, revealing no change in the feel of how hard the rod is to push. Indeed, I have run hard cast bullets through a bore then aligned the rifling back up in its original orientation and pushed it through again and found it just as uniformly resistant on both passes. .22 rim fire lead bullets are about as hard as you can get and still feel the bore properly. In my experience it is much easier to feel a constriction entering it from a looser spot in the bore than it is to feel a loose spot after exiting a constriction. For this reason I always slug a bore from both ends before I believe for certain that I have identified any tight spots.

Tight spots commonly occur on commercial grade barrels owing to there having been little or no stress reliving done to the barrel blank before it is contoured. When contouring is done, the places where the barrel is thinnest offer the least resistance to any residual stress, and so they expand the most. Constrictions also commonly appear where sight dovetails are cut into a barrel by a machining operation done with a dull cutter or a cutter with too high a feed speed. The other really common place to see constrictions are in revolver barrels where the tight threads screw into the frame.

Once you have tight spots, you have two options. You can hand lap or firelap the barrel to remove them. The principle is to embed abrasive in a lead lap and pass it through the bore. The constrictions will be abraded most, while the loose spots will be abraded least because the lap will not spring back out to bear against them after passing through a constriction. With a hand lap, you often just cast some pure lead directly in the bore and onto the end of a rod. After tapping it out of the bore you cut grooves in it to hold abrasive compound. You then load it up with the compound, usually about 320 grit, and work it back and forth. When it stops rubbing even the constrictions, you run the lap to the breech end of the rifling and use a dowel and mallet to bump it back up in diameter and repeat the stroking. You keep repeating this, adding abrasive if needed, until the barrel is uniform and free of constrictions.

Firelapping is easier that all that casting and cutting and the skill of constantly feeling for rubbing. It has its own problems, however. For one thing, you can't use those hard springy alloy bullets or you will find the cutting pressure is about equal in the constrictions and in the wide spots. That will polish but it won't remove constrictions. On the other hand, you can't use pure lead bullets either. Pure lead gets bumped up by the firing pressure after passing through a constriction. This doesn't happen in hand lapping and the result is the pure lead under pressure will polish in much the same way a hard bullet does. As a result, it is necessary to use a compromise: A bullet that is soft enough not to spring back much, but is still hard enough to resist obturating pressure at the lapping load level. Several different combinations of load pressure and bullet hardness have been proposed, but, generally speaking, a consensus has developed that you need a bullet that has a hardness of about BHN 11, fired with a peak pressure of about 10-15,000 PSI. BHN 11 does not spring back nearly as much as a BHN 16 bullet and will abrade harder, therefore on the constrictions than on the wide spots.

You can also firelap with jacketed bullets if you choose them carefully. I have done this with bullets pulled from M2 ball. These bullets come out with a crimp indentation in the center of the bearing surface so they only touch the rifling in two rings at the front and back of the bearing surface. Those narrow bands engrave completely in the bullet even with modest pressure, like 10,000 PSI.

I have also tried long bearing surface bullets like the Tubb Final Finsh system uses, thinking they would make the job go faster. But they did not fill into the corners of the rifling well at low pressure. Instead, as Tubb's instructions state, they have to be propelled by starting loads at the bottom of the normal load pressure range. Pehaps 40,000 PSI for most rifles. That is much higher pressure than is normally used in firelapping and is enough to bump these long bullets up to fill out the bore properly. Unfortunately that bump-up also means the bullet works the whole surface pretty evenly, same as an overly soft one would, removing the bore's wide spots as fast as the constrictions. That is why I say the Tubb system polishes rather than laps the bore.

Unlike hand lapping, because firelapping, in effect, strokes the lap in just one direction and because obturating pressure drops with the bullets travel down the bore, it will apply more lapping force near the breech than at the muzzle. Thus firelapping tends to taper the bore slightly narrower at the muzzle, where hand lapping tends to just make it straight. This is considered favorable for shooting lead bullets. With jacketed bullets, because they are under highrt pressure, obturate enough to not care much one way or the other. Indeed, some European shooters like guns with bores a thousandth or two over bullet diameter and use them very successfully with jacketed bullets. Hand lapping has the limitation that it does nothing to remove toolmarks from the throat of the barrel.

One of the keys to successfully firelapping a barrel is to constantly monitor progress. I run a new slug every 5 firelapping rounds, per NECO's instructions, which I find to be pretty good. Once constrictions are cleared, only polishing rounds are used. Firelapping M1 Garand barrels to clear their constriction under the thick part of their contour below the lower band purchase, I found about 20 of the pulled M2 bullets were needed when embedded with NECO's lab grade 240 grit abrasive. At that point the slugs no longer felt the constriction, and I switched to their finer polishing grades. At the end of the process it took 1/6 the number of patches and strokes with JB to get the barrel completely clean than it had taken before firelapping. The throat wear gage said the throat had been moved forward 0.001”. Not enough to matter.

Firelapping always makes a gun easier to clean. It does not always affect accuracy. Once in a long while it can even make a gun worse, though I would like to be able to study those cases because I suspect the process was done incorrectly using overly coarse abrasives, such as provided in the Wheeler kit, or because there was another problem such as crown irregularities that were exacerbated by the lapping process, or because excessive propellant was used. It is also logical to assume a gun would need its accuracy loads worked back up once the removal of constrictions and reduction in throat friction had occurred. These could easily affect barrel time and take the gun off a sweet spot.

A quick note on NECO's lab grade abrasives. These are not cheap but have two advantages. If you look at standard grade abrasives the particle distribution is pretty wide. The coarsest particle allowed is about twice the diameter of the average particle. The lab grade stuff has a much narrower distribution. This accomplishes two things: One is the chance a large particle will gouge a scratch deeper than average is reduced. The other is that fewer fine particles pack around the average size ones, so these abrasives cut faster. Amateur telescope makers report the cut glass about twice as fast as standard grades. NECO's coarsest abrasive is 240 grit lab grade, which means its largest particle size is about the same as a standard grade 280 grit particle would have. The Wheeler kit I caution againsts uses 220 grit standard grade. Its largest particle will be about the size of the height of a rifling land. That is too big. Precision shooting had a report by a fellow who used that kit on a .22 LR. It opened the bore half a thousandth, about 5 times more than the NECO kit opens a muzzle. That .22 shot more poorly after lapping. I'm not surprised, given that much material removal.

Nick
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member
Unclenick is offline  
Old September 2, 2008, 03:17 PM   #9
SST
Member
 
Join Date: January 13, 2008
Location: Missouri
Posts: 37
Unclenick,
Thank you for the clarification.
__________________
Regards,
Sam Taylor
SST's Rifle Room
http://angelfire.com/mo2/rifleroom
SST is offline  
Old September 2, 2008, 03:59 PM   #10
Harry Bonar
Senior Member
 
Join Date: December 5, 2004
Location: In the Vincent, Ohio general area.
Posts: 1,804
bore

Sir;
I don't "condition" my bores' with anything but a bronze bristle brush, Hoppes and maybe J.B. Bore paste and a good cleaning rod and a good patch.
The cut rifled bore as explained can use some light lapping but only to correct tight places in the old cut rifled barrels - you always remove some steel as you do everytime you fire your rifle.
Buttoned or hammer forged bores TODAY are so smooth and uniform it (in my opinion) lapping or treating isn't needed.
Lapping a barrel does not remove any lengthwise striations in the bore because the lap is cast in the barrel to be lapped!
If a bore needs lapped or shot with ammo loaded with even the finest abrasive should be returned to the maker. Douglas does not ever need treating any way except cleaning as I've described. If you barrel doesn't shoot, change your load, check your bedding etc.
In my 60 years I've NEVER lapped a barrel. And, I'll tell you a danger we have today. Some old boy will buy a surpluss rifle with a horribly rusted bore and try to shoot out the rust! DO NOT DO THAT - you just may have a blown up rifle!
Harry B.
Harry Bonar is offline  
Old September 2, 2008, 08:58 PM   #11
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 10,462
Harry,

Good warning on the rust. A patch with a little oil will detect it.

Agree on Douglas. Douglas properly stress relieves their barrel blanks at 1100°F, so they don't develop constrictions with contouring.

Nick
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member
Unclenick is offline  
Old September 3, 2008, 04:42 PM   #12
Harry Bonar
Senior Member
 
Join Date: December 5, 2004
Location: In the Vincent, Ohio general area.
Posts: 1,804
bore

Sir;
Hey, Nick! Good to hear from you.
Douglas has a real process:
They buy their 4140 already heat treated.
They drill it.
They ream it and air guage it.
They button rifle it and air guage it.
They then stress relieve it, and, how much fun is this - the final "stress relief" give the bore the final dimension!!
Then it is checked by eye for straghtness, and given the final air guage.

When Fred told me about stress relief giving the bore the final dimension I thought "H---- Sh---!
They have the most sophisticated process I've ever seen! Mr. Depoy has retired but a very capable man has replaced him.
How do they make their buttons? They make them in a special area of the shop - a precision grinding area. G.R. Douglas designed this all himself - the rifling hydraulic presses are the same ones he designed and built!
Harry B.
Harry Bonar is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 05:59 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.10291 seconds with 9 queries