custom throat lapping ?

[mike in co]

does this make sense ? or is throat wear too quick for this to benefit ?

for a br chamber, seat your bullet firmly and a little long in a thin lubed case which has been threaded thru the primer hole for a handle of some sort. fine lapping compound applied to the bullet and then with lite pressure lap the throat to match your bullet .

yes no ??????
how about doing the same to to an non-br gun ?

inquiring minds want to know....

mike in co

 

[Don]

does this make sense ? or is throat wear too quick for this to benefit ?

for a br chamber, seat your bullet firmly and a little long in a thin lubed case which has been threaded thru the primer hole for a handle of some sort. fine lapping compound applied to the bullet and then with lite pressure lap the throat to match your bullet .

yes no ??????
how about doing the same to to an non-br gun ?

inquiring minds want to know....

mike in co

Ive added this to my chambering protocol, although using a different method which includes a close tolerance boreguide and lapping rod setup fitted with Cratex rubberized abrasive tips, lapping the throat area longitudenly 10-20 strokes in order to smooth 80 percent of throat reamer cyclindrical texture cut and replace it with longitudenal lap texture comparable with the remaining of barrel lapping texture.

Benefits are;

1. Reduced throat erosion changes for first 50 rounds.

2. Reduced copper fouling changes for first 50 rounds.

50 rounds of live fire break-in seems to accomplish the same results as the throat lapping, but with more throat erosion variation and more copper cleaning needed, so this method buys one a little bit more barrel consistency.

I can begin my load developement from the very first shot without any break-in work or accelerated seating changes...............Don

 

[mturner]

Throat lapping

This is something I also do. Didn't think anybody else was. My method may not be quiet as good as lapping in the same direction as the rifling, but here is how I do it. I chuck the reamer in the lathe and indicate the throat angle to get the compound set to the same angle. I then turn a brass lap to that throat angle. I roll charge the lap with a fine compound. Then I lap the throat using a guide bushing.

Michael

 

[Dennis Sorensen]

It isn't something I would consider doing... the throat is cut by a precision reamer to exactly what I want... why alter it?

In a modern center fire I would think after 20 shots your throat is well lapped...

 

[Don]

It isn't something I would consider doing... the throat is cut by a precision reamer to exactly what I want... why alter it?
...

Same reason that a barrel mfg. laps after precision reaming/rifling a bore.........Don

 

[Dennis Sorensen]

Same reason that a barrel mfg. laps after precision reaming/rifling a bore.........Don

That makes sense but after a barrel is lapped you cut off an inch or so at the muzzle to get rid of irregularities and the chamber gets rid of them at the other end... I would think it would be very hard not to create an irregularity trying to lap the tapered lands and bore. (most throats are a few ten thou larger than bore)

My experience with custom barrels "breaking in" quickly and with little fouling is that it is not a problem worth considering trying to lap the throat. I don't have the experience or skill to do that... so it is still something I wouldn't attempt...


.

 

[mturner]

Dennis

The reason you have to cut an inch off the end of a barrel is because the nature of lapping a barrel causes bell mouthing at the ends. This happens when the lap reverses direction at each end. A reamer leaves cylindrical marks in the throat. These are the same as in a barrel caused by the same operation (reaming). Lapping a throat the way I do still does not get rid of cylindrical marks, but I lap the throat in a way that I get a much smoother finish in the throat, and much more precision. This method of lapping would be similar to lapping a bullet die, better finish, more precision. You shouldn't simply smear lapping compound on a bullet or brass lap. This is not precision lapping. You must charge the lap, and then wipe away any excessive compound. In my experiance this does keep copper from sticking in the throat during the first 50-100 shots. Keep in mind that if copper fouling is reduced by lapping the barrel, it would be reduced in the same way by lapping the throat. The throat has to engrave the bullet, so the lands don't see near the pressure against copper as the throat. With all this said, I agree that this should only be done by someone who knows exactly how to do it. A throat could easily be hurt rather than helped by someone with no experiance. In this case you are correct, unless you develope this skill for yourself. Throat lapping was one of my deep kept secrets. Mike in Colorado definetly has a mind for details that can improve accuracy, and so does Don.

Michael