interesting project/experiment

[mdeland]

A shooting bud of mine recently asked me to help him see if we could make a very nice 7-08 match rifle shoot better than the minute gun it now is. Always willing to help out a shooting bud along with being curious of the possibilities to learn something I agreed.
After disassembly I inspecting the action and barrel by bore scoping, plug gauging and chamber casting. All I could find in need of possible help was a bit of bore carbon fouling. He was wanting me to set the barrel back and re-chamber but after comparing the match reamer with the chamber cast and taking some measurements they appear to be identical and the throat has practically zero erosion.
This is a Krieger barrel of four narrow lands and 9" pitch. The bore is clear of jacket fouling. All I could see odd was the wide grooves appear scorched black about half way up barrel but with no erosion evidence as usually noted by cracked surface metal. The plug gauge indicates a level bore so I'm scratching my head on this one.
I concluded that the best course of action was to lap the bore smooth and see what happens from that point. The owner said go ahead and give it a try so I thought some of you might be interested in the project to see if this course of action may produce a favorable result. I'll be taking some pictures and posting them.

[mdeland]

Here is the subject barrel and the lap rod I rebuilt with a ball bearing oak handle for the job.

[mdeland]

Threaded barrel cap and jag end of lap rod for the job.

[beltfed]

Mike,
Here is an alternative to actual lapping.
Get a Bore Snake in the 7mm size.
Get Turtle Wax Chrome polish from local auto or Fleet Farm type store.
Use a bore guide.
Now, draw the bore snake thru the bore, leaving the working end exposed at the breech.
Shake up the Chrome polish and apply about a teaspoon of it to the working end of bore snake
Draw it thru the bore 10 times.
Repeat application of a teaspoon or so of the polish.
Draw thru again.
Do this to 10 x10=100 draw through's
It will Polish the bore really well. Reduce fouling, easier cleaning after that-jacketed or cast .
A guy with forum name of Onondagua, developed this and published it on the Cast Bullet Ass'n forum.
(He has passed away, may hi RIP)
Works for me. I expect this process will get rid of that black fouling in your friend's barrel,
. The Chrome polish has a slightly more aggressive non embedding
abrasive in it than J-B Bore cleaning paste. It will not change dimensions in the barrel.
beltfed/arnie

[mdeland]

Thanks for the tip Arnie, very interesting idea! I like making lead laps because they maintain land and groove profile keeping all edges square and clean along with leveling and working in some choke toward the muzzle.

[mdeland]

Finished with the lap job tonight. I decided to start with 400 grit and gave it 250 cycles up and back for each cycle. I then move up cast a new lap and concluded with 800 grit for another 250 cycles. I usually don't go any higher than 400 for lead bullet guns but as this is a jacket bullet gun I went up to 800 silicone carbide grit. Scoping the bore she looks like new and is very uniform how ever after removing the carbon I discovered that the rifling button had dragged in some debris and I could now see that the very beginning of three of the four lands have quite a gouge in them.
The lapping smoothed but did not remove them and the bore scope at 24 x makes them look bigger than life. If I cut the shank off and re-thread the chamber reamer will cut out the origin of the scratchs but they continue on up bore anyway.
I think I will put the rifle back together and let him try it with just the lap job and if that does not work then we can resort to more drastic measures with a set back and new chamber.
The case has been drilled out to fit the lap rod for a center guide and the string dam has bee attached to the lap rod.
The short lap is 400 grit and long lap is 800 grit.

[mdeland]

800 grit lap

[mdeland]

800 grit lap

[mdeland]

I cast the laps in he muzzle but make them long enough to with draw to the breech, charge from the chamber end and not loose index. This introduces the grit at the back were it cuts most aggressively in the begging so as not to open up the muzzle any more than necessary for some choke.

[mdeland]

I need to get the camera attachments and super light so I can take some bore scope pictures which would make it more interesting than a description.

[mdeland]

Well the project is done in the lapping dept. The gun is re-assembled and test fired. Head space is good and so now we will see if the lap job made any improvement in accuracy. If it improved I'm a genius if it made things worse or stayed the same then an idiot but doing one thing at a time will tell the story better than all together and not knowing which actually caused the result.
The lapping did produce a bit of choke toward the muzzle as determined buy plug gauges.

[mdeland]

I got to thinking last night how Kreiger barrels are rifled and from their on line page discovered that they are actually single point cut rifled and hand lapped after reaming and finished lapped after rifling so my idea that the scratching of the three lands from button debris is incorrect. But as the gouging is at the beginning of three of the four lands something hard enough to mar the steel was dragged in with the cutting head which would be cutting the grooves.
I noticed the scratches with the bore scope from the initial inspection but did not pick up the origin at the beginning of the lands until after lapping out the carbon fouling that appeared as scorching about half way up bore.
I checked my lap rod for scaring because with the initial lap I could hear it contacting the bore. The rod was smooth and straight and as I used a centering guide it could not physically be making contact so I think what I was hearing was the top of the gouging on the three lands making contact with the rod. The lapping took off the high spots from the lands and the contact sound stopped shortly after the lapping began with 400 grit.
This condition must have left the factory this way as I can see no other cause for it's occurrence as modern barrel steel (even stainless) is pretty tough and reasonably hard.
I will be very interested to see what happens now with this barrel and how it shoots or not as it would hold a minute in the previous condition.

[mdeland]

Well, good news to report! I got a call the day after returning from the hunting trip and my friend reported the lap job had reduced the group size from consistently around a minute to half a minute. He then shot a 600 yard match and put most of them in the ten ring with all the rest in the nine ring. He was really happy about the improved accuracy and how the experiment worked out.
I think many of you would be surprised what a good lap job would do for a barrel that quits shooting but the bore and throat still look good!
It will be interesting to see if this 7-08 accuracy holds up or is only a temporary thing. Always something to be learned!

[mdeland]

Remember a well executed lap job will never ruin a barrel. Accuracy will usually improve or remain the same. Lapping only remove metal in the ten thousands range and if the lap is charged from the rear will usually result in some taper which is almost always good for accuracy.
I think many of you PP shooters wind up with bores that are to smooth and then accuracy begins to decline. Many of the old bench muzzle loading shooter used to believe their guns would shoot smooth and need to be abraded to restore accuracy. Peeing down a bore and letting it soak for a bit to rough it up actually was a practice used by some of them ! I'll just have to give this a try some day to see if true !

[mdeland]

I'm currently rebuilding a .270 I originally made some 35 years ago that I took a couple of black bear with on spring hunts. It has a Shaw barrel that is kind of rough and not very uniform of bore diameter as determined with plug gauges that I'm going to lap out before stocking again.
I put a Wisner three position Model 70 style safety and Timney trigger on the ole Girl and fit a Argentine trigger guard and swing floor plate to the rifle. It's scoped with a 2x7 Leopold compact and is shaping up into a nice sheep rifle for some young hunter some where, perhaps one of my grand kids as they grow up a little. I've always felt that the .270 Win. is one of the great all time American cartridges.