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Author Topic: Bore Lapping... A lost Art  (Read 381 times)

Offline Dutch-Hunter

  • TH Staff - Contest Team
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Bore Lapping... A lost Art
« on: March 06, 2013, 05:54:26 PM »
Rifle Bore Lapping/Polishing A Lost Art and First Step Stage in Accurizing your Rifle.

For those interested in the best possible accuracy and precision, whether for competition our just their own satisfaction, custom or semi-custom rifles begin with the best custom barrels. Those barrels, whether button rifled (from: Broughton, Hart, Lilja & Shilen) or cut rifled (from: Badger or Krieger) all share a common and critical processing step – hand lapping! Factory barrels are made the same way just normally not lapped unless you pay extra for it.

The purposes for lapping the bore are:
1.   remove tooling marks left from the rifling process
2.   ensure a dimensionally uniform bore, end to end
3.   provide a uniform, clean, polished interior finish that follows the direction of the rifling groove spiral
The benefits of lapping the bore are:
1.   more consistency in velocity and accuracy
2.   eliminates much of the break-in process
3.   less copper and powder fouling
4.   the barrel will clean much easier (less solvent, patches and effort)

FACTORY BARRELS
Currently there are three principal levels of factory made rifles and associated barrel processing:
1.   Semi-custom – with lapped barrels and polished chamber-throat-crown
2.   Semi-custom – with lapped barrels but no polishing
3.   Commercial – no lapping or polishing

Other than the information offered by the manufacture or dealer there is little that the buyer can do to ascertain the bore conditions prior to the sale. After taking delivery of a rifle and before firing it, do one or both of the following:
1.   Clean the bore using one solvent moistened patch followed by two dry patches using a properly sized jag and solid rod taking note of the effort required – a slip/stick irregular stroke indicates rough finish while an even easy stroke indicates a lapped bore.
2.   If accessible, have an experienced user check the bore with an illuminated borescope including the chamber, throat and crown. Note, for used rifles (irrespective of manufacturer or seller), the above initial cleaning and inspection of the bore is probably more important.

Custom and Semi-Custom Barrels
In practice a barrel manufacturer makes a lead lap which is cast inside each barrel creating a lap that is formed perfectly for that particular barrel. Next, the lap is pushed out of the bore and deburred. Then a lapping compound, which is an abrasive suspended in a lubricating medium (that eases the cutting action and carries away the residue created), is liberally applied to the lap. The lap is guided back into the barrel and the pushed and pulled through the barrel until the barrel maker feels an even resistance. The actual process can take hundreds of strokes, usually three laps and require about an hour on each barrel by an experienced practitioner. This process is done to a barrel blank after boring, rifling, contouring and straightening, but before chambering and muzzle crowning. Blanks are made long so that the muzzle end can be cut off and crowned to remove any damage caused by the lap effects on the bore edge. The gunsmith will turn and thread the breach end, ream the chamber, trim the barrel to finished length and crown the muzzle. Depending upon the services offered and ordered the chamber, throat and crown may also be polished.

OWNER/USER OPTIONS
Conventional Break-in (Factory Barrels);  various sequences of shoot and clean using conventional ammunition to burnish the irregularities in the bore and throat surface finish – for example (commercial new barrels):
1.   Clean rifle prior to first shot (ignore accuracy and just shoot).
2.   Clean after every shot for the first 10 shots.
3.   Clean after every other shot from 11 to 20 shots. *
4.   Clean after every 5 shots from 21 to 50 shots. *
5.   After 50 shots, completely clean and you should be ready.
* WARNING: Do not over heat the barrel 1 shot per 5 minute timing at minimum depending on ambient temperature.
Break-in For Custom or Semi-Custom lapped barrels: may not be necessary.

TWO METHODS OF BORE LAPPING/POLISHING:
Fire-Lapping; has gain popularity simply because of the ease. The results are better than not lapping at all. I prefer the “hands on” feel of hand lapping. Fire-lapping is the utilization of cartridges made with bullets coated with fine abrasives that are fired in strings of 5 rounds beginning with the coarse grit followed by cleaning the bore and then repeating the firing and cleaning with each successively finer grit. For used badly eroded barrels all grits are appropriate. New commercial barrels need only the three finest grits. For Custom or Semi-Custom lapped barrels with unpolished throats, only the two finest grits are appropriate. And for Custom or Semi-Custom lapped barrels with polished throats do not use these at all. Hand loaders may purchase kits of bullets pre-coated with fine abrasives of several fine grits. Tubb’s Final Finish (five grits) is offered in a limited range of calibers. NECO offers a kit for coating almost any caliber bullet (four grits), some pre-coated bullets, and even limited calibers of pre-coated bullets loaded as ammunition.

Hand Lapping; this is a process using generally available materials, cleaning tools and “sweat – equity” to partially replicate the results and benefits of the barrel makers lapping process. For detailed explanation of the process and required tools and materials see “Detail – Barrel Lapping/Polishing Process” starting on page 3.
This process has been very successful when used on new commercial barrels as well as neglected and/or eroded used barrels. However, it requires care and attention to the details. Therefore it is suggested that for the first attempt  seek out someone experienced in and equipped for doing the process to do that rifle and watch, listen and learn.

Detailed Hand Lapping Process (Dutch Style)
Tools & Material List: (suggestions only use similar products available to you)
1.   Cleaning Rod, 40” or 44”, carbon fiber – correct caliber
2.   Cleaning Brush, Nylon Bristle – correct caliber
3.   Cleaning Jag, brass – correct caliber
4.   Cleaning Patches, 50 minimum suggested – correct caliber
5.   Cleaning Brush, Nylon Bristle – next smaller caliber
6.   Cleaning Patches, 10 pieces – oversized (wrapped on 5 for a snug barrel fit)
7.   J-B Non-Embedding Bore Cleaning Compound (blue label)
8.   J-B Bore Bright (red label)
9.   Iosso Bore Cleaner (white tube)
10.   Hoppe’s Elite Gun Cleaner or Bore Gel (or equivalent)
11.   Wipe-Out Brushless Bore Cleaner, Foam Type (or equivalent)
12.   Wipe-Out Accelerator, Optional (used before 11 to speed action)
13.   Bore Guide, to protect action if still attached to barrel (*Critical, get one or do not go any further)
14.   Cleaning Rod Stop, Optional (use to prevent lap from damaging crown)
15.   Cleaning Rag, Optional (post process cleanup)
16.   Gun Vise – must be sturdy (clamp to work surface if possible)

Work Area Preparation:
Prepare a well-lighted and ventilated work area with protection from cleaning chemicals (will stain porous surfaces and clothing). Place rifle in cleaning position on gun vise (item 16) and clamp both in place (force on cleaning rod both ways will be required).

The Process of Lapping
I prefer to do my lapping on a barrel that has been taken off of the action. Number one you can look right into the chamber and number two the action will not get damaged. It can however be done if you are careful and protect the action with the bore guide.
 
Initial Cleaning:
Used Rifles (barrels)
1.   Inspect bore, if copper residue or burnt powder fowling is present (assume it is if you can’t inspect).
2.   Insert Bore Guide (item 13)
3.   Start by cleaning using foam type cleaner (items 11&12) as specified on product container.
4.   Clean the bore normally: run a patch (item 4) wetted lightly with cleaner (item 10) on jag (Item 3) mounted on rod (item 1) thru the bore; repeat with dry patches 3 times.
New Rifles (barrels)
1.   Insert Bore Guide (item 13)
2.   Clean the bore normally: run a patch (item 4) wetted lightly with cleaner (item 10) on jag (Item 3) mounted on rod (item 1) thru the bore; repeat with dry patches 3 times.
Lapping 1st Stage
1.   Assemble lap: put rod stop (item14 if desired)on rod (item1); put undersized brush (item 5) on rod (item1); wrap oversized patch (item 6) on the brush so as to be a snug fit in the bore; adjust rod stop (if used) or mark the rod so that the patch can be restrained from crossing the crown excessively.
2.   Insert Bore Guide (item 13)
3.   Apply coarse abrasive compound (item 7) to the lap patch to coat the surface and lightly work it into fabric surface.
4.   Alternately push and pull the lap through the bore for a total of 20 strokes in each direction taking care not to push the lap past the crown or pull it out of the throat until the last pull stroke.
Clean Bore 1
1.   Insert Bore Guide (item 13)
2.   Clean the bore normally: run a patch (item 4) wetted lightly with cleaner (item 10) on jag (Item 3) mounted on rod (item 1) thru the bore; repeat with dry patches 3 times.
Lapping 2nd Stage
1.   Assemble lap: put rod stop (item14)on rod (item1); put undersized brush (item 5) on rod (item1); wrap oversized patch (item 6) on the brush so as to be a snug fit in the bore; adjust rod stop (if used) or mark the rod so that the patch can be re strained from crossing the crown excessively.
2.   Insert Bore Guide (item 13)
3.   Apply fine abrasive compound (item 8) to the lap patch to coat the surface and lightly work it into fabric surface.
4.   Alternately push and pull the lap through the bore for a total of 20 strokes in each direction taking care not to push the lap past the crown or pull it out of the throat until the last pull stroke.
Clean Bore 2
1. Insert Bore Guide (item 13)
2. Clean the bore normally: run a patch (item 4) wetted lightly with cleaner (item 10) on jag (Item 3) mounted on rod (item 1) thru the bore; repeat with dry patches 3 times.
Lapping 3rd Stage
1. Assemble lap: put rod stop (item14)on rod (item1); put undersized brush (item 5) on rod (item1); wrap oversized patch (item 6) on the brush so as to be a snug fit in the bore; adjust rod stop (if used) or mark the rod so that the patch can be re strained from crossing the crown excessively.
2. Insert Bore Guide (item 13)
3. Apply bore polishing paste (item 9) to the lap patch to coat the surface and lightly work it into fabric surface.
4. Alternately push and pull the lap through the bore for a total of 20 strokes in each direction taking care not to push the lap past the crown or pull it out of the throat until the last pull stroke.
Final Cleaning
1. Insert Bore Guide (item 13)
2. Clean the bore normally: run a patch (item 4) wetted lightly with cleaner (item 10) on jag (Item 3) mounted on rod (item 1) thru the bore; repeat with wetted patches 2 more times; repeat with dry patches 5 times.

The rifle barrel is now ready for use! Happy shooting!

Additions from Bo:

Dutch - I like this article very much...little long even for a loquacious person like me....Glad you listed a parts list for what you need. Well laid out...and agree that it is a lost art form. Just one more step that the serious shoot doesn't mind taking because they know it will pay off down range.
Hand or fire Lapping can be down any time you want to. If you have used it for season or two hunting, you still can see the benefits of lapping. I have this Kimber 8400 Patrol rifle due in after Christmas (I was hoping to get it in before Christmas, but doesn't look like it, but when it does come in, I will do my usual tearing it down/apart to see what makes it tick. This normal for me.
Too often when people get a rifle in they quickly mount a scope on it and maybe head for the range. Not me.....when I get this Kimber in, I will take it down and pull out my Hawkeye bore scope and inspect the barrel. With a Kimber, they might have did a semi-lapping process at the factory, but I will clean for sure, do this for every rifle I have when I first get it. Then inspect the barrel using the Hawkeye, this will determine whether I need to lap or not. It takes me a week or so before I am ready to mount the scope and when I do, it takes me another week to finish mounting the scope....
But if I do need to do a complete lap job on the barrel I will strip it down and place it in my padded vise and start the lapping process, then I will rotate the barrel 90 degrees and continue and then rotate it another 90 until I have completely rotated the barrel 360 degrees. This way I can ensure that the compound, my pressure and the wet patches are evenly distributed around the barrel. 
I even do a hand lapping on my Coopers. My Shilen DGA is amazing. It cleans up in about 5 patches! but that is quality. You might want to mention the cost associated with hand lapping that is generally built into the price of the rifle. Some barrel manufacturers list the price of the lapping as a option. I always take that option and then will do some myself after I get it home. But you pay for quality...

Gun Geek! Proud of it!
Old enough to know better!
TO old to care!

 

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