ACCURACY TROUBLE SHOOTING
Chambers Misaligned With The Bore Cannot Be Relied On To Give Acceptable Accuracy.
One must do all the basics to include a good trigger to work with, a rattle free fit at the hinge pin, correct headspace for reliably consistent ignition, optics up to the job of shooting accurately, and bedding work on the forend. But when these measures are addressed and the barrel will still not shoot, the cause more often than not is due to the chamber not being aligned with the bore.
It would seem only normal to expect the chamber to be aligned with the bore, but unless the factory or custom 'smith exercises due diligence to make sure it is aligned, it becomes just "luck of the draw." Some chambers will be acceptably aligned with the bore, some will not, and some may be hideously misaligned to the point one wonders how the reamer made it into the barrel in the first place.
Here is a third party report of his own findings with a problem TC factory barrel and how TC dealt with it.
TC factory .375 JDJ Super 14 Contender/G2, blued. SSK Arrestor muzzle brake installed by SSK. TSOB scope base installed by SSK.
Summary of What Was Done Here
I looked through the barrel from the breech end, and to my eye, the chamber throat was not perfectly aligned, but compared to many it looked acceptably aligned.
On the chance the muzzle brake was causing problems with accuracy, I milled flats on the sides of the Arrestor muzzle brake so the owner could unscrew and reinstall the exit end of the brake. It could then be shot with or without the brake's exit pupil in place to see if that was the problem. No change in accuracy was noted.
I missed it here, but the owner found that the base screws were too long, bottomed out, and the base not pulled down tight on the barrel. It was returned to me.
The owner returned the base to SSK, and I installed a Weaver 92A base converted to 6-screw attachment with the screws the right length and not bottomed out in the holes. Back to the owner and back to the range, it still produced only 3 to 4 inch 100 yard groups. At this point, the owner took the initiative to do a chamber cast.
Quadrant 1. Rifling extend all the way back to the end of the chamber neck.
Quadrant 2. Note there is a normal "throat," the absence of rifling,
between the end of the rifling and the end of the chamber neck.
Quadrant 3. Again, the rifling are cut away, as they are supposed to be in a throat.
Quadrant 4. Some faint signs of rifling showing back to the end of the chamber neck.
A throat is an area where the rifling are removed so the bullet can project up into the groove diameter area of the barrel, which is supposed to be the same diameter as the bullet. Some allowance has to be made for variations in both bullet diameter and barrel groove diameter, but the two are supposed to be closely matched.
What you should be seeing is no rifling at all in front of the chamber neck. Again, this is so the full diameter shank of the bullet can enter into the groove diameter of the barrel. The cut made by the throat section of the reamer should be symmetrical all the way around IF it is centered with the bore. There should be NO rifling extending back to the end of the chamber neck. When it cuts off center, it will leave an asymmetrical condition as in the above photos. If the bullet does not get a straight shot into the rifling, it will be distorted, out of balance, and cannot be relied upon to shoot accurately.
The only thing that can be done with a barrel like this is to rechamber it to a longer round, one that permits cutting out the misaligned throat and cutting a new one ahead of it that IS centered with the bore.
IT MEETS THEIR ACCURACY STANDARDS!
THE BARREL WAS RETURNED WITH NO REMEDIAL ACTION TAKEN.
THE CUSTOMER WAS STUCK WITH A BARREL THAT SHOT 3 TO 4 INCH GROUPS!
TC was sent these same photos. The defect was made plain to them, yet they declined to do anything to correct the problem. Unfortunately, this is what you can expect from TC, so you must be aware of this highly probable scenario and be prepared to have remedial work done to correct it.
That, or simply dump the barrel on someone else until it lands in the hands of someone who is either content with it as it is or will spend the necessary money to have it made into a barrel accurate enough to meet the user's needs.
Finally with the prospect of legal action being taken, the issue was resolved, and a new barrel was provided.
But it took the spectre of legal action before TC could be moved to acknowledge this very apparent defect.
If at some time you find yourself in a similar situation, look into filing a small claims court law suit in the county you live in.
A new barrel chambered in .375 Win. with a factory Muzzle Tamer brake has been received by the owner and sent to me for rechambering to .375x.444 Marlin, equivalent to the .375 JDJ.
Follow Up Report On the Replacement Barrel:
The .375 Win. chamber from TC in the replacement barrel is not centered with the bore even as well as in the original barrel. It is definitely off center.
However, the barrel was to be drilled and tapped for the TSOB 6-screw scope base, just like the barrel above that had the TSOB scope base installed by SSK. Instead, this is what he got:
The front two screw holes spaced wrong! From the right, hole number 6 in the barrel is where hole number 5 is supposed to be!
Hole number 5 in the barrel is supposed to be FORWARD of number 6.
(Base pictured is a Weaver base converted to the standard TSOB spacing for untapered Contender barrels.)
Bear in mind three important points:
One, TC sells and installs the TSOB scope bases and knows what the spacing is. Point two, TC had the owner's barrel in hand already drilled for the TSOB base by SSK as a reference.
Point three, "D/T TSOB" is hand engraved on the side of the lug.
The above barrel was replaced ok, but an inch shorter than stipulated! The order was for a barrel 15" including the Muzzle Tamer brake, but the replacement was only 14" including the Muzzle Tamer brake!
This was after I rechambered it. It was not until after the customer got it back that this error was noted since it had been drop shipped directly to me from TC.
FINALLY! Three TC factory barrels and a 2 year ordeal later, with the right hole spacing, right barrel length, and my .375 Bellm rechambering, this comedy of errors resulted in this nice grouping...... like it should have been in the first place if chambered right to begin with!
Group after I rechambered to .375 Bellm with a nicely centered and dimensioned chamber and throat.
Five 260 gr. AccuBond bullets into about a 1/2" 100 yard group. The 260's averaged 2090.8 fps.
But Wait. It gets even better! .011" group!