Barrel Throat Lap -Thoughts?

[Jeff Peinhardt]

Thought all would enjoy. Made a chamber lap tool to lap the lands of a freshly chambered barrel. Had it pilot on the body of the case within 0.0005' and the neck portion very closely to lap free-bore area and the taper into the lands. Used various diamond solutions,started with 1 micron cut, then 1200) and a final polish agent. Wow! The finish is unreal....looks way superior to a Kreiger barrel!

I started a business in 2000 that refurbished/polished Compact Disc,CD) molds. These molds are made from 420 stainless,very similar to 416)and are the most highly polished surfaces you have ever seen. There are no defects,max 3 pits not exceeding 15 microns) over the entire 120mm diameter. This is the most precise tooling manufactured in the world. Any-who my partners and myself developed the lapping/polishing techniques for these molds.

Does it shoot or more important not foul? You bet. Usually I break-in barrels with the shoot clean for five ordeal. Then shoot 5 and clean and so on. Small amounts of copper is the norm during break-in. I have chambered 6 kreiger barrels - 3 6mm PPC and 3 243 with this procedure with very good results. Chamber the barrel shoot 10 and no copper! Even hot loads in the 243 with new barrels -very little copper.

Throat seems to hold real well.....less wear. Polish must reflect heat and limit the heat affected zone in the throat.

Just wondering if this is a process that is desirable for all out there? Should I make them? Yes, there is a ton special size chambers, throats, leads etc. PTG does it with reamers! Give me your thoughts.

 

[Hal]

PR2

It would be great to see a pic of the before/after affects.

Lead bullet shooters are interested in this area also.

This topic was discussed on the benchrest forum.

One of the top .22 rim fire gunsmiths burnishes the front slopping edge of the rifling. One of the secrets to his success.

How much would a lap tool kit cost?

Hal

 

[Jeff Peinhardt]

Hal

I will try to photograph next chambering job.

The custom lapping tool can be made for about $50. The initial lapping compounds might cost more......but it will be enough for many chambers. I will put pricing together.

Thank you

 

[btrapr]

I'll be watching to see what you come up with...

 

[Louisiana Shooter]

Watching this......sounds interesting.

 

[GerryM]

I think your on to something there'
I'm watching TOO'
The IR 50 /50 guys will Love this. Not to mention the BR guys'

 

[Jeff Peinhardt]

OK guys......did two more barrels here, Krieger LV for my 6mm PPC. Getting ready for the Supershoot. I am trying to get good quality photos using our Snap On digital video bore scope for all to see.

I will try to post ASAP. Wow...the before and after is amazing. I am getting a great finish with the reamer...I use a special one from Clarence Hammond's...they cut unreal...perfect chip on each flute. However, the finish is nothing like a precision lapped and polished throat. I will describe the comparison as best as possible. Sand a piece of 416SS with 200, 400, and 600 and consider that your baseline as cut reamer surface. Now if you have a piece of aluminum polished with 600 paper and lightly polish with Mothers or Flitz metal polish....that's the difference!

I have shoot the other barrel that I lapped the throat in,6mm PPC) 500+ rounds and cleanup is simple. I now shoot 22-26 rounds before cleaning. I only brush every 75 rounds now. After 24 rounds I run 3 patches soaked in Butches Bore Shine, two or three dry patches and one Kroil when done. Presto no copper! My other barrels always take some brush work every 12-15 rounds.

Side note.....Anyone shooting a 6mmPPC should try Mr Hammond's 68gr match bullet for their LV and his 62gr in their HV rig!

will be posting pics soon!

 

[eddyverhoeven]

I'm sitting on the fence

Ed

 

[Jeff Peinhardt]

OK guys......here are the pics. My bore scope did not have the quality I was looking for so I reamed the both ends of a barrel cut-off and milled to reveal the lapped portion. There are two pics of the reamed chamber,could not erase the one).

Anyway, if the pictures don't come out labeled they should be as follows:
1. Reamed throat
2. Reamed throat
3. Reamed and Lapped throat

Notice the the long bur on the as reamed land...I am certain this would disappear quickly....but what damage would it do to the new barrel as it gets ripped through the bore? There is also a very small bur on the lapped one as well.

Please comment

 

[kevinbritvec]

How much metal is being removed? Would the reamer's chamber print have to be altered to accamodate the amount of metal removed? I prefer no turn necks and don't want the dimensions altered more than .0005'. I would be willing to custom order reamers to allow for any dimensional change created. Chamber and throat looks much better after your process.

 

[Jeff Peinhardt]

Kevin,

Chamber reamer does not need altered. What I do is review your chamber print, or your gunsmith's chamber print and custom manufacture a precision lapping tool to accommodate your specific chamber. I have lapped 5 chambers with the 6mm PPC tool and it still works perfect. The primary emphasis is to lap only the throat area. Lapping is very delicate, the process removes very little material.

These photos show a 6mm PPC with a 0.2435 finished throat and a 1 1/2 degree into the lands as called out on the reamer print. I used precise carbide plug gages to look for any change in diameter before and after lapping. Our 0.24350 carbide 'GO' gage is 0.00002,20 millionths) over nominal size. The 0.24350 carbide 'NO GO' gage is 0.00002,20 millionths) under nominal size.

I checked the reamed throat and the 'GO' gage would not easily fit. After lapping id did just slip into the throat. Mind you a 40 millionth's difference in size is very small but the 'feel' of the plug gage going in once lapped is different. Precision lapping is only removing the 'peaks from the reamed surface.

Answering your question- with a good sharp reamer the lapping tool will remove less than a 0.0001' in the diameter of the throat and the neck portion of the surface. The tool is designed to remove more in the lead where the rifling is,this is where the bur forms) in the axial direction. I removed about 0.001' in the 1 1/2 lead in area.

Hope this answers your questions. Sorry for all the words, figured I would post the detail for others as well. These are the same questions I would have if trying this process.

Yes, next we are working on pricing for the lapping compounds and the custom made lapping tool.

I will be at the Super Shoot at Kelby's in May.

Jeff Peinhardt

How much metal is being removed? Would the reamer's chamber print have to be altered to accommodate the amount of metal removed? I prefer no turn necks and don't want the dimensions altered more than .0005'. I would be willing to custom order reamers to allow for any dimensional change created. Chamber and throat looks much better after your process.

 

[bingo1010]

i think any polishing of the main body of the chamber is a bad thing as it will increase bolt thrust, however the polished lead/neck area does look good. how do you keep the lapping tool straight in the neck area,in order not to increase runout)with out rubbing/scoring the body portion of the chmber??

 

[moosemoose]

great post and great idea, I appreciate the effort you took to show us your idea. I'm wondering about your video camera borescope and where you got it?

Thanks for the hard work.