Newton24b,
TXGunNut likely hit the cause. Fouling that is heavier near the muzzle is unusual. If you slug the bore, I expect you will discover they cut a dovetail too fast or forced a dull cutter to do it (or both) and it indented the bore. This is annoyingly common with lever action rifles where you often have a sight dovetail and a magazine hanger dovetail cut.
Before you slug the bore, first get it clean. The foaming cleaners (there are at least two I recall trying) work very well. I have, however, settled on Boretech Eliminator myself. Read the reviews on Midway from others who, like myself, have tried about everything else ever made for bore cleaning. In addition to attacking copper faster than anything else I've tried (you can't use brass jags or rods with it because they turn the patches blue before they get through even a clean bore), it is non-toxic, virtually odorless, water-based so even corrosive priming residue is removed by it, and if left in the bore, is a rust inhibitor. They also make a copper-only product called Cu++, that I've heard is impressive.
The only thing I know of that will remove more copper weight per patch is KG-12, but it has a little ammonia in it (not odorless) and doesn't turn the copper green or blue, so you have no color indicator to tell you when you are done.
If you want to get fancier, you can get or borrow an Outer's Foul Out. This tool cleans the bore electrolytically by plating the copper from the bore onto a stainless center rod. It's not actually faster than the Boretech stuff, but for diagnostic purposes, you will see exactly where the copper was most heavily deposited in the bore by where most of it is on the rod (withdraw it slowly so you don't disturb it; the structure is weak almost like wet dust). As mentioned earlier, it is normally seen nearer the throat because that's where the bullet is when the chamber pressure peaks. Peak chamber pressure upsets the bullet most strongly, including lateral swelling pressure, so friction with the bore is highest at that point in a straight bore. As a result, the most copper rubs off there. Indeed, in a rifle load the pressure is so high there that if you cut a rifle barrel down so it is just a couple inches longer than the chamber, the muzzle blast actually deforms the bullet base as it exits. An illustration is on page 25 (pdf page 36) of
this study.
So, once you have the gun clean, you may slug it. This consists of pushing a pure or very nearly pure lead slug (cast bullet alloy is too hard) slowly down the lightly oiled bore with a cleaning rod. The pure lead is very plastic but inelastic, so when it passes through a tight spot you feel the extra drag of deforming it, but then it feels loose beyond the constriction.
I used to use cast separate pure lead bullets for slugging, just tapping them in at the muzzle with a short piece of wood dowel and a brass hammer (in case I missed). Today I'm too lazy to run separate lead melts and usually use a Hornady round ball that is oversize. I roll it between two flat pieces of steel until it is just a couple or three thousandths over the expected groove diameter, then tap the resulting little pill in to start it. Then you just push it slowly, feeling for hesitations.
Do put an oily patch through the bore before starting the slug. Some even like to put STP on the slug itself. Try until you find what you like. The main thing is learning the feel. If you don't want to case your own or use lead balls, Beartooth Bullets sells slugging supplies. NECO also has pure lead slugs.
So, if you find a constriction, what next? Well you can measure the slug to see how far out of round it is, if you are curious. One of the uses of slugs in a straight bore is to measure it for actual groove diameter for choosing case bullet sizes. You can send the gun back to the factory. The postage isn't cheap, but you don't need an FFL to send guns for repair or for the factory to return them to your address. Getting some personal attention for your gun is often a good idea, and the factory guys should have seen the largest number of them with this same problem. If you don't think you qualify for warranty work (check with the factory first) then you can either hand lap the bore, as they would, or you can firelap the bore, which is easier. Again, there are kits available and there should be past posts describing the process.
The only poor firelapping kit I've seen is the Wheeler kit sold by Midway. It's a rip-off of NECO's patented multi-grade format, but doesn't use the same high quality abrasives and has instructions that show an incorrectly lapped bore and claim it is correct. In addition to NECO's method, Beartooth Bullets has a kit that works with a single abrasive grade, and Veral Smith (LBT) sells a single abrasive version and instructions in his book, as well. For those who can't bring themselves to use a mild abrasive bore cleaner, this will cause heart attacks, but boy does it ever put an end to fouling problems.
I personally use three types, as they all have they're place, 1. G96,2. Shooters Coice, bore cleaner and copper remover, 3. Smith and Wesson Copper and Lead remover GEL. Good luck and happy shootin!!
