The TC carbine got an upgrade to a Boyd's thumbhole stock. The problem with the factory tupperware stock is that it's designed for iron sights and there's no cheek weld when you are using a scope. I love the pistolgrip stock for benchrest shooting -- you can use the grip to pull the gun snug against your shoulder, and the trigger finger angle is better so that the trigger feels much lighter compared to the tupperware stock.
Rather than going with the Boyd's forend, I made a forend out of a scrap piece of oak (because oak was the only hardwood I had on hand). As you can see, the color of the oak forend does not match the color of the Boyd's stock. Oh well.
My goal with the forend was 1) a wide flat bottom for benchrest shooting and 2) maintain the factory screw spacing. Unfortunately, I misplaced one of the forend screws and didn't have a spare, so for today there was only one screw holding the forend, and it did not hold it securely. More on that later.
I haven't had time to make a mold or a tapered die for this barrel, or even to slug the barrel, so for today I used the Marlin's 180 grain ammo.
Remember how the too-soft chamber reamer galled and gouged the chamber a bit and I hoped it wouldn't create a problem ? Well it did create a problem. Fired cases were sticky. I tried a reduced load -- a 160 gr. PB at 1500 fps -- but cases were still sticky, so I knew it wasn't due to a hot load. Careful measuring suggested that there was a tight spot about 3/8" inside the chamber where the gouges were. The front of the chamber was 0.383" but the tight spot was 0.382", so the front of the fired case couldn't get past the tight spot. It wasn't the gouges themselves, but it seems they had pushed up some metal. I honed the tight spot with fine emery cloth until most of the tight spot was gone. Then I could extract most cases with my fingers, though occasionally one would still be stubborn. I'm sure if I continue honing the tight spot the extraction problem will eventually go away, the problem is that my benchrest chamber is turning into a sloppy Rossi-style chamber.
Here's the initial range results:
Marlin 180 gr. ammo -- 3.6" @ 100 yards, with vertical dispersion. 1800 fps.
160 gr. PB at 1500 fps -- 8" @ 100 yards. I dunno if these were air cooled WW or heat treated, they were just some bullets left over from some previous project.
So velocity was exactly the same as the Marlin, but accuracy was not what I expect from a decent TC barrel. The loose forend may have contributed to the vertical dispersion, so I tried tightening the single screw, but it didn't help much. Maybe the screw is bottoming out, or maybe it just needs the missing 2nd screw.
After the first round of chamber honing and re-tightening the single forend screw:
Marlin 180 gr. ammo -- 1.8" @ 100 yards, velocity had fallen to 1770 fps due to the larger chamber.
By the end of the day, the target had lots of little specs of Rooster HVR lube. I dunno if that means anything, but I don't recall ever seeing that much lube on the target at 100 yards.
The next step was to firelap the barrel. The barrel itself is pretty smooth and did not need lapping, but I wondered if my homemade throating reamer had perhaps left a rough surface that could benefit from lapping ? Anyway, I fired 5 rounds with 150 grit followed by 10 rounds of 280 grit. The firelapping definitely washed the throat out a bit as measured by dropping a bullet into the chamber until it came to rest against the rifling. The 180 gr. Marlin bullet went in an additional 0.023", while the 160 gr. PB went in an additional 0.175". The latter seems extreme and might be due to measurement error, but nonetheless firelapping definitely pushed out the throat. That's OK because it was a short, tight throat to start with.
Retesting the firelapped barrel with the Marlin 180 gr. ammo:
5 shots 8" horizontal @ 100 yards, last 3 in 3/4"
5 shots 3.8" round @ 100 yards, putting my left hand on the scope instead of holding the forend like I usually do.
So firelapping did not improve accuracy and may have made it worse, not surprising since it pushed the throat out. I've never had much luck with firelapping.Lessons learned and stuff to try next time:
-- while I probably can and will resolve the sticky extraction problem by honing out the tight spot, I'm never going to be happy with a sloppy chamber so I'll eventually set the barrel back and rechamber it. No big deal except that'll throw off the barrel bolts location. I'll prolly address that by making another custom forend with custom screw location.
A PITA, but do-able, and I always have the option of starting over with another barrel, bearing in mind that this barrel only cost $15 and I consider it a learning experience. I want to do my learning on cheap barrels before I move on to match quality barrels.
-- Next time I make a TC barrel, I'll test-fire the barrel before cutting the dovetails for the barrel bolts. It would be much, much easier to set the barrel back if I didn't have to deal with the barrel bolt location.
-- I'll keep practicing at making chamber reamers until I get it right. I like to experiment with custom chambers and throats and it's much more affordable if you can make your own reamers.
-- I want to make a mold and a tapered die for this chamber. The 1 degree throat is what benchrest shooters use, but they use it with a matching tapered bullet, seated far out. I'm thinking a 200 grain semi-spitzer.