Barrel Lapping

[DShortt]

There is so much bad information in this thread it makes my head hurt.

Wow.

How about a prerequisite that you need to have actually lapped at least 10 barrels yourself?

That's a good reference to eliminate most of the hearsay.

 

[Straightshooter1]

Fire lapping with Tubb's Final Finish Bore Lapping System worked really well on my non-lapped factory barrels. It's not as good as the lapping done on my Krieger barrels, but it's a significant improvement.

 

[DShortt]

Fire lapping with Tubb's Final Finish Bore Lapping System worked really well on my non-lapped factory barrels. It's not as good and the lapping done on my Krieger barrels, but it's a significant improvement.

Never understood this approach, either. Firing a projectile coated with abrasive down a barrel.

Sounds like accelerated throat erosion at best.

If it shoots better afterwards, what kind of a hot mess was it to begin with?

 

[Muzzlestuffer]

Ok, so based on the responses hear I am reconsidering doing anything to the barrel.

If you want do some polishing to help when you clean you can use some JB bore polish I use it mixed with Kroil on a tight fitting mop.

 

[Straightshooter1]

Never understood this approach, either. Firing a projectile coated with abrasive down a barrel.

Sounds like accelerated throat erosion at best.

If it shoots better afterwards, what kind of a hot mess was it to begin with?

Yes, it'll result in a little accelerated throat erosion, like for me is was .003 when I followed Tubb's directions for firing the 50 rounds (10 rounds of 5 different grits) that came in his fire lapping kit. There's a regiment of cleaning after the use of each grit.

And BTW, besides helping shoot better. . .like regular lapping, it helped a lot in reducing fowling and made for easier cleaning.

 

[DShortt]

Yes, it'll result in a little accelerated throat erosion, like for me is was .002 when I followed Tubb's directions for firing the 50 rounds (10 rounds of 5 different grits) that came in his fire lapping kit. There's a regiment of cleaning after the use of each grit.

And BTW, besides helping shoot better. . .like regular lapping, it helped a lot in reducing fowling and made fore easier cleaning.

What's better? From what MOA to what MOA?

The OP was discussing a new barrel. So I presume we're not addressing corrosion pitted mil-surps.

 

[Straightshooter1]

What's better? From what MOA to what MOA?

The OP was discussing a new barrel. So I presume we're not addressing corrosion pitted mil-surps.

From .6's to sub .5's and occasionally in .2' & .3's . . . 5 shot groups at 100 yds using Varget to push 168 SMK's. through 20" RPR barrel. This was a little over 6 years ago.

 

[DShortt]

From .6's to sub .5's and occasionally in .2' & .3's . . . 5 shot groups at 100 yds using Varget to push 168 SMK's. through 20" RPR barrel. This was a little over 6 years ago.

Interesting. Thank you for your results. I'd not expected that.

 

[ronemus]

Never understood this approach, either. Firing a projectile coated with abrasive down a barrel.

Sounds like accelerated throat erosion at best.

If it shoots better afterwards, what kind of a hot mess was it to begin with?

Just be aware that the coarser grits in Tubb's firelapping sets are very aggressive and will push the throat significantly. I only use them when there is an identifiable problem. In my case there was a bur that turned my bullets into a puff of smoke between 100 and 300 yards. After firelapping the barrel shot well, but its life was reduced significantly.

 

[Machinist John]

I have lapped a few back when I worked with big bore cut rifled barrels, mainly to clean up tooling marks.

The T handle has two ball bearings. Note the grease fitting!

Different size rods and laps to fit the bores. Laps are adjustable to fit the bore, note the socket head on the end of the lap.'

Barrel is clamped in the barrel vise.

Using a cleaning rod does not "cut" it!

 

[Hal]

John thanks for sharing your knowledge.
Great pictures, they explain a lot.
What is your lap made out of ?

Hal

 

[Will Henry]

John,
That "lap" appears to be leather washers. Is that correct? Your guide system is much more elegant than the way I do it (an empty case, held in place with my thumb), and probably works commensurately better! WH

 

[Will Henry]

By the way, John, I really appreciate your pictures of your tooling. They encourage me to do better! WH

 

[Machinist John]

Old machinist here by birth. Dad had a machine shop. When I was a newborn, mom threw me and a blanket in a laundry basket and stuffed me under a bench in the shop, she had a full-time day job.

The leather lap is handy: Can be tightened up when it is barely sticking out of the barrel. I can get a barrel warm when lapping.

I enjoy making tooling, just my heritage.

 

[Steadfast]

There are definitely some interesting comments on here. It seems I may have opened Pandora's box!
Comments seem to range from Don't do it! to You don't need to do it, if you don't do it right, you'll bugger it, Lapping will definitely improve your accuracy to lapping will only make it foul less.
I think what I'll do is scope the bore when I get it and give it a good examination. I was told the barrel will be button riffled so I'm not expecting any burrs from cutting the grooves. However, unless the bore was lapped prior the riffling, there is likely to be at least some witness marks on the lands left over from the reaming process. If this is the case then lapping the lands could at least provide some benefit from copper fouling. If I were to do any lapping, I would do it prior to chambering and crowning. Also, I would likely block the muzzle end so as to not bell it from exiting.
I should note that I have been a Machinist for 5 years, tool and die maker for 15 years and Tool and Machine designer for 12 years. I retired from that in 2016 after 32 years in that field. I have made extruding as well as embossing tools and I have designed them too. Button riffling is an extruding process. Even though I have never actually seen it done, I can however visualize in my minds eye, the lands on the button, which form the grooves, forcing the the steel, like plastic, up into the grooves of the button to produce the lands. If the bore diameter is too big, then the lands will be incomplete and if the bore is too small then the button will get very tight and plow material in front. I can't imagine that would be desirable. For obvious reasons, the bore should be the exact size, be very smooth and be very clean. Lots of oil would also be needed. What I don't know is if this is done in a single pass or if it's done progressively like broaching.
Part of me wants to only lap the top of the lands with an impregnated copper pin as that surface and diameter would be a resultant of the original bore size/finish. I won't do anything until I examine the bore because it might just be fantastic, which is what I'm expecting. The barrel is being made by HW Precision in Calgary Alberta. Those folks bought the machines from and were trained by Rob McLennan of Midland Ontario. Rob has been my barrel maker since the 90s.
Thane

 

[Steadfast]

I should note that all of my previous barrel made by Rob were 6mm and were hand lapped by him. Earlier ones were button riffled and the last barrel he did for me was a 4 groove cut riffled. Apparently HW Precision only laps barrels 6mm and up. This would leave my .224 barrel unlapped, for the first time.

 

[Will Henry]

Rob's barrels most definitely did not have any ironed out reamer marks and I doubt that HW's do either. Buttoning is done in one pass. The lubricants used are usually a secret! When Mike Walker came up with the process, he used a copper plating as a lubricating layer. Most early makers continued with this as part of the process (I believe the barrels were plated using copper sulfate). Later on, lubricants which were superior to copper became available and each maker is likely to have a favourite.
Lapping, or more likely, polishing, was used to remove the copper wash which remained in the barrel, and to produce the desired internal finish. Lapping is seldom employed to correct dimensional variations or to create a particular bore profile. If I bought one of HW's barrels (or any other premium barrel), I would not be inclined to do any lapping on it. If there were ironed out reamer marks visible in the bore, I would simply return the barrel.
Very good, buttoned barrels which I have inspected, showed no evidence that there was any clearance between the button and the tops of the lands. I have seen some which definitely DID have clearance on top of the lands. I once got a Shilen 35 cal, in which the button obviously did not touch the lands and there were reamer marks visible. I called and asked if they had started broaching that caliber. The barrel was replaced with one which did not exhibit that flaw.
If the reamed hole is not consistent in diameter, pulling the button through won't fix it.
Occasionally, if there is a hitch in the process, the button may not produce an entirely consistent twist rate. When pushing a long lap through, areas where the twist lags will mimic a tight spot. After a few passes, the lap will deform enough that the "tight spot" goes away. Of course, the flaw still exists, you just can't feel it anymore.
I was once asked, by a custom gunmaker, to remedy a barrel he had installed and which shot poorly. This barrel was from Ferlach and was button rifled. I'm not sure how they accomplished it, but the bore was like an impression of a snake swallowing eggs. It was a 7mm and I lapped it out to nearly .286 in order to remove most of the loose places. I left the biggest loose place, which was right in the middle of the barrel. The rifle, which had previously shot into about 7 inches, would now shoot into an inch and a half, which he considered satisfactory. WH

 

[L.Sherm]

Will from what I've seen the snake eating the egg thing you describe is coming from the barrel drill and its bad enough its not getting taken out by the bore reamer.
Kinda like reamer chatter in chambering, not correct feed and speed.

 

[wright brothers]

Lapping is above my pay scale.
I have a factory barrel that has a tight spot near the crown. At least it feels so when pulling a brush or patch through.
After reading this I will have my guy look at it in the future.
This rifle never shot as tight as others of the same make. I just "blamed" it on the thinner barrel of the Mountain model, hmm.

 

[Steadfast]

Rob's barrels most definitely did not have any ironed out reamer marks and I doubt that HW's do either. Buttoning is done in one pass. The lubricants used are usually a secret! When Mike Walker came up with the process, he used a copper plating as a lubricating layer. Most early makers continued with this as part of the process (I believe the barrels were plated using copper sulfate). Later on, lubricants which were superior to copper became available and each maker is likely to have a favourite.
Lapping, or more likely, polishing, was used to remove the copper wash which remained in the barrel, and to produce the desired internal finish. Lapping is seldom employed to correct dimensional variations or to create a particular bore profile. If I bought one of HW's barrels (or any other premium barrel), I would not be inclined to do any lapping on it. If there were ironed out reamer marks visible in the bore, I would simply return the barrel.
Very good, buttoned barrels which I have inspected, showed no evidence that there was any clearance between the button and the tops of the lands. I have seen some which definitely DID have clearance on top of the lands. I once got a Shilen 35 cal, in which the button obviously did not touch the lands and there were reamer marks visible. I called and asked if they had started broaching that caliber. The barrel was replaced with one which did not exhibit that flaw.
If the reamed hole is not consistent in diameter, pulling the button through won't fix it.
Occasionally, if there is a hitch in the process, the button may not produce an entirely consistent twist rate. When pushing a long lap through, areas where the twist lags will mimic a tight spot. After a few passes, the lap will deform enough that the "tight spot" goes away. Of course, the flaw still exists, you just can't feel it anymore.
I was once asked, by a custom gunmaker, to remedy a barrel he had installed and which shot poorly. This barrel was from Ferlach and was button rifled. I'm not sure how they accomplished it, but the bore was like an impression of a snake swallowing eggs. It was a 7mm and I lapped it out to nearly .286 in order to remove most of the loose places. I left the biggest loose place, which was right in the middle of the barrel. The rifle, which had previously shot into about 7 inches, would now shoot into an inch and a half, which he considered satisfactory. WH

Thank you for that Will. I guess my question would be then... why does anyone lap barrels if it does nothing to improve it? That would make lapping an extra unnecessary step. Why does HW lap larger barrels but not .224. I know that 6mm is very common for Bench rest where they are trying to produce tiny 0.10" groups and it's true that that's not my intention with the .224 barrel that I ordered. Having said that, all of the barrels I bought from Rob shot very well and cleaned up easily. On a side note, you mentioned copper sulfate. In many tool steels, sulfur is added to the steel to make it more machinable and not work harden. The sulfur in steel is a lubricant.
Thane