357 Mag Contender Barrel III

[mtngun]

I'm still debating what to do about this barrel that doesn't want to shoot better than 2.5 MOA. That might be fine for plinking or hunting but the goal was a target-grade barrel that would be useful for "serious" testing of cast bullets.

We know it has a "tight spot" about 4 inches ahead of the breach, but we don't know how much that hurts accuracy, if any. Previous firelapping has reduced the tight spot but failed to completely eliminate it. I finally figured out how to add the extension to my "tri-mic" bore micrometer so it could be used to measure or at least feel the tight spot. The tri-mic did indeed confirm the tight spot was still there.


One option is to cut off enough of the barrel to get rid of the tight spot. That would still leave at least 21", enough to meet my goal of a minimum 20" barrel.

Another option is to continue firelapping. I'm wary of firelapping under the best of circumstances because it can wash out the throat, but on the other hand this barrel is worthless to me unless I can improve the accuracy, so what do I have to lose?

So the tentative plan is:
1) try more firelapping and use the tri-mic to determine if and when the tight spot is gone. Retest to see if accuracy improved.
2) if that fails, shorten the barrel to 21". Retest to see if accuracy improves.
3) if that fails, buy another, hopefully better barrel and start over.

It may sound crazy to go through so many chambers and barrels but this is a target rifle, not a hunting rifle, and there is no "proven" cast bullet chamber for the 357 mag that I am aware of, so I am learning the hard way.

[mtngun]

Today I shot 35 more firelapping rounds, all using #280 grit.

The procedure was to shoot 5 rounds, clean the barrel, and then use the tri-mic to measure the "tight spot." Rinse and repeat.

The #280 grit seemed to produce a decent finish so I didn't bother following up with a finer grit like I usually do.

Before and after groove measurements with the tri-mic. The measurements are not 100% repeatable so sometimes it looks like the diameter got smaller after firelapping. I don't think it really got smaller, that's just measurement error.


A bullet pushed all the way through the barrel measured 0.3556" groove & 0.3483" bore.

The original "tight spot" is 4.5" from the breach and it was just as tight after firelapping. Do I have to shoot 1000 firelapping rounds to get rid of the tight spot?

The throat length increased 0.019" - 0.025" after firelapping.

[mtngun]

Testing to see if the latest firelapping session improved accuracy. The usual recipe -- unless otherwise stated, 155 grain spitzer, sized 0.359", oven treated WW, nose sized, lubed with HVR, 16.1 grains Lil Gun. I had been using CCI #500 primers to firelap so I tried a few on paper.

I also experimented with a different hold. Up till now I've been using my left hand to squeeze the rear bag. With that technique, I don't like the way it recoils. Instead of sliding straight back, it bounces around like a rubber ball. That seems to be a common problem with 2-piece stocks. So today I tried using my left hand to grip the forearm. I didn't pull on the forearm, I just gripped it firmly. The hold felt better and the gun recoiled straight back instead of bouncing around like a rubber ball.

155 gr. GC with CCI #500
-- 1.949" COL (0.005" jump to rifling)
-- 10 shots in 3.05" at 100 yards
-- 1998 fps
-- 0.68% standard deviation
-- left hand squeezing bag

Same but with Winchester Magnum primer
-- 10 shots in 1.85" at 100 yards
-- 0.82" mean radius
-- 0.35" radial standard deviation
-- 2048 fps
-- 1.16% standard deviation
-- left hand squeezing bag

155 gr. bevel base with CCI #500, left hand holding forearm instead of squeezing bag
-- 1.950" COL (0.007" jump to rifling)
-- 9 shots in 1.75" at 100 yards, one called flier not counted
-- 0.64" mean radius
-- 0.32" radial standard deviation
-- 1982 fps
-- 1.27% standard deviation

Same but with Winchester Magnum primer, left hand still holding forearm
-- 10 shots in 1.65" at 100 yards
-- mean radius 0.6"
-- radial standard deviation 0.19"
-- 2005 fps
-- 0.49% standard deviation

Average 10-shot group for all of today's loads = 2.08", compared to 2.5" last week. I'm not sure that today's firelapping helped accuracy, but it didn't hurt.

The barrel was clean after shooting the 20 gas check rounds, but after shooting the bevel base there was a little bit of fouling 1" - 3" ahead of the chamber.


Observations & Lessons Learned
-- the Winchester Mag primer is better than the CCI #500 in this load.
-- using my left hand to grip the forearm may be better than using my left hand to squeeze the rear bag.
-- I'm not sure if the slight fouling is related to the tight spot or not? The fouling begins before the tight spot begins, though it ends about where the tight spot ends.
-- it may not be realistic to expect firelapping to completely eliminate tight spots in the barrel. Previous firelapping sessions seemed to reduce the tight spot noticeably, but today's firelapping did not make a dent in the remaining 0.0003" of tightness.

Things to Try Next Time and Down the Road
-- shoot more groups with the forearm grip technique
-- the load seems optimal so I'll leave it alone.
-- I may eventually want to do still more firelapping to try to reduce the tight spot, but if so I'll probably follow up by setting back the barrel and rechambering because all this firelapping is making the throat longer than I would prefer.

[mtngun]

Today's agenda was 1) retest the 155 bevel base with the forearm hold and 2) test a bevel base gas check bullet.

The check shank was cut with a slight bevel, and the gas check was re-swaged with a custom punch & die to give the gas check a slight bevel. The amount of bevel was limited by the lathe-boring process and it probably wasn't enough of a bevel to make a difference. Also the check wanted to teeter totter on the shank, apparently due to an imperfect match between the shank and the check.


I began shooting around mid-day and mirage was definitely a problem. The orange target-dots were just a blur, plus they were dancing around in the mirage so it seemed like I was shooting at a moving target.

Bevel Base Gas Check
-- 1.959" COL (0.007" jump to rifling)
-- 16.1 gr. Lil Gun
-- Winchester magnum primer
-- 1962 fps
-- 0.55% velocity standard deviation
-- 2.65", 3.25" 10-shot groups @ 100 yards

Bevel Base
-- 1.950" COL (0.007" jump to rifling)
-- 16.1 gr. Lil Gun
-- Winchester magnum primer
-- 1979 fps
-- 1.05% velocity standard deviation
-- 2.9", 2.45" 10-shot groups @ 100 yards

Bevel Base with more powder
-- 16.2 gr. Lil Gun
-- otherwise same as above
-- 1993 fps
-- 1.05% velocity standard deviation
-- 2.5" 9-shot group @ 100 yards (one cartridge was a dud)
-- at the end of the session there was light fouling 1" - 3" beyond the chamber.

Note that velocities were about 25 fps slower than last week. I don't know why. I had no confidence in my ability to shoot at blurry dancing targets so I gave up and tried again after supper. The powder charge was increased to bring velocity back up to 2000 fps.

Bevel Base Gas Check, after supper without mirage
-- 16.3 gr. Lil Gun
-- otherwise same as previous gas check load
-- 1993 fps
-- 0.79% velocity standard deviation
-- 4.25", 2.6" 10-shot groups @ 100 yards

Bevel Base
-- 16.3 gr. Lil Gun
-- otherwise same as previous bevel base load
-- 2021 fps
-- 0.76% velocity standard deviation
-- 2.55", 8.85" 10-shot groups @ 100 yards
-- 2nd group started throwing wild shots, found scope eyepiece lockring loose. Tightened lockring and shots settled down.
-- at the end of the session there was significant fouling 1" - 3" beyond the chamber. It took a lot of scrubbing to get the barrel clean.

Today's target. Even though shots felt much better in the evening than in the mid-day mirage, groups were no better in the evening.


Conclusions, Observations, and Lessons Learned
-- I don't know why velocities were lower today than last week
-- I wasn't able to repeat last week's accuracy, even in the evening when range conditions were excellent.
-- There was no accuracy advantage to the bevel base GC. I suspect the concept has merit, but the execution was flawed.
-- the plain bevel base wants to shoot but fouling is definitely a problem. The fouling may be related to the "tight spot" in the barrel. That point in the barrel also coincides with peak pressure.
-- the scope eyepiece has rattled loose several times before, so this time I gave the lock ring a drop of threadlocker and a couple of wraps of electrical tape.

Things to Try Next Time and Down the Road
-- I want to try dacron under the bevel base. There is enough room.
-- I'm leaning toward setting the barrel back enough to get rid of the "tight spot."
-- If setting the barrel back does not improve accuracy then I'll be inclined to to get a new, better barrel and start over, perhaps in a bolt gun rather than the Contender, though that won't happen this year because I'm out of time and money.

[mtngun]

This time we tested dacron filler under the 155 gr. bevel base. We were hoping the dacron might reduce fouling, reduce velocity variation, and of course improve accuracy.
.
The usual load:
155 gr. bevel base
sized 0.359"
oven treated
nose sized to match throat taper
HVR lube
16.1 gr. Lil Gun
1/2" cube of dacron
Win mag primers
1.948" COL (0.010" away from contact)

Results:
1730 fps (vs. 1979 without dacron last time)
2.53% velocity standard deviation (vs. 1.05% without dacron)
2.76" MOA (2.69", 2.82" 10-shot groups @ 100 yards)
0.90" mean radius
Only a tiny bit of fouling in the "tight spot." The dacron definitely reduced fouling.

I used the to analyze the target. This was the first time I used Taran, but I just followed the instructions and it was quick and easy.


Here is the Taran summary. I like that it overlayed the 2 groups onto one target. The main reason to use Taran is to determine if load "A" is better than load "B", and I only shot the one load today, but I think Taran is going to work out well for my experiments. It's faster and easier than the way I was doing it before.


Conclusions and Lessons Learned:
-- dacron reduced the velocity 249 fps.
-- maybe dacron is soaking up energy by melting? If so, that would explain the lower velocity.
-- if the dacron is soaking up energy by melting, that would explain the reduced fouling. However, you might be able to accomplish the same thing without dacron by reducing the powder charge ????
-- dacron did not improve accuracy

Things to Try Next Time:
-- this was my last experiment with this chamber. I have tried every trick I can think of yet this chamber struggles to shoot under 2 MOA. As near as I can determine the chamber is very good and the only known defect is the "tight spot" in the barrel about 4" from the breach. I find it hard to believe the "tight spot" would hurt accuracy that much yet I don't have any better ideas.
-- So I have decided to set the barrel back enough to clean up the tight spot.

[mtngun]

The barrel has been set back enough to clean up the "tight spot." It's now 21 1/2" long.

Before re-chambering, I measured the groove diameter at both ends with a tri-mic. 0.3559" at the breach end and 0.3556" at the muzzle end (the factory spec was 0.355" x 0.347" and that's about what it was before I firelapped it). There's no logical reason to shoot oversize bullets in this tight barrel so I decided to aim for a throat that would be a good fit with a 0.3570" - 0.3575" bullet. I used the same homemade reamers as last time, with a 1.5 degree per side throat, but this time I did not run the throating reamer in as far. The entrance to the throat should be 0.3575" - 0.3580" if I did my homework right. There's no freebore, the leade begins immediately after the chamber.

The homemade reamers cut fine, the dimensions were spot on, and inspection with a bore scope showed a smooth chamber and a concentric throat. I feel like I have done all I can do and the rest is up to the barrel.

[mtngun]

OK, here we go with the 21.5" barrel and the usual 155 gr. bevel base load. Here's how the bullet looked when sized to fit this throat:

155 gr. bevel base
16.2 gr. Lil Gun
Win mag primers
1.913" COL (0.009" jump to rifling)

The first group was shot with bullets that were several weeks old, meaning they were prolly about 30 BHN. The .359 bullets were resized in a .357" push-thru die but because they were hard they sprang back to 0.3575". There was some moderate mirage when I shot the first group so I decided to wait until evening to shoot more groups.

The 2nd and 3rd groups were shot with bullets that were heat treated this morning, meaning they were prolly only about 20 BHN because they haven't had time to reach peak hardness. They were sized before hardening so they actually measured 0.357". There was only a tiny bit of mirage during group #2. By the time I got to group #3 the mirage was gone.

As you can see, group #1 was respectable, group #2 opened up, and group #3 opened up even more. Also the vertical point of impact kept moving up as more shots were fired.
Group #1, mean radius = 0.50", velocity = 1982 fps, standard deviation = 0.8%
Group #2, mean radius = 0.78", velocity = 1986 fps, standard deviation = 1.13%
Group #3, mean radius = 0.93", velocity = 1984 fps, standard deviation = 1.22%

After group #1, there was slight fouling about 4" ahead of the breach (the 25" barrel had also fouled about 4" ahead of the breach). The fouled spot was only about an inch long. The rest of the barrel was squeaky clean. I did not clean the barrel between groups.

After group #3, the fouled spot was slightly more fouled. It was not severe fouling, most people would not worry about it, but nonetheless it was there, and a tight patch showed significant specs of lead.

Observations, Questions, and Conclusions
-- was the first group merely luck, or was it because of the clean barrel and/or harder bullets ?
-- did groups #2 and #3 open up because the bullets were softer, or because of fouling ?
-- getting rid of the "tight spot" did not eliminate fouling. It so happened that the tight spot was about where the fouling occurred, 4" past the breach, but that is also near where peak pressure occurs. Apparently the fouling at that spot is due to peak pressure?
-- Are 30 BHN bullets more accurate than 20 BHN bullets ?
-- I don't know if this 21.5" barrel is an improvement over the 25" barrel because there are too many variables. I need to retest with 30 BHN bullets to eliminate the hardness variable.
-- could it be Lil Gun that it causing the fouling? Recall that I have alternated between WW296 (or 297 or H110, same thing) and Lil Gun. Both are capable of similar velocities, but ..... what if Lil Gun burns hotter than WW296 and causes more cast bullet fouling? You might not notice it right away, it might take 20 or 30 shots before fouling built up enough to cause a problem.
-- what caused the point of impact to drift? Fouling? Barrel heating up?

Things To Try Next Time and Down the Road
-- heat treat at higher temperature. I have been using the kitchen oven at 435 degrees, but have not verified the accuracy of the oven thermostat. I use 435 because from experience that's a safe temperature even allowing for the inaccuracy common to kitchen ovens. But .... my heat treat oven has a PID controller so it ought to be able to safely heat treat at 450 or so. I just need to make a pan that fits in the heat treat oven.
-- let the heat treated bullets age at least 2 weeks. That should bring them up to 30 BHN or so.
-- comparison test between Lil Gun and WW296 with a focus on fouling.
-- possibly revisit coatings to eliminate fouling.
-- possibly go back to a gas check bullet to eliminate fouling. I've been using the bevel base because it seems to have a slight edge in accuracy, but the catch is that accuracy seems to deteriorate as more shots are fired and fouling builds up.

It's going to take some time to refine my heat treating process and to let the bullets age-harden several weeks, so this barrel may be put on hold for a month or so.

In the meantime I feel comfortable that the hardware is good -- no more "tight spots" or "bad chambers" to worry about, so I can focus on the load rather than the gun. That's the way it should be.

[mtngun]

Some thoughts on this 357 project, because I better write them down before I forget them.

-- this barrel started out being remarkably friendly to plain base bullets. Leading was rare. Yet currently it has a leading problem about 4" from the breach, presumably corresponding to peak pressure. What changed?
-- We started out with WW296 but later switched to Lil Gun. Does Lil Gun cause more leading than WW296?
-- this barrel began its career in cool weather. The leading problem reared its head in hot weather. Could the warmer temperatures affect lube performance?
-- we started out with 1-diameter bullets but are now using tapered Ardito-style bullets. The Ardito fit seems to improve accuracy but could it increase leading because there are fewer full diameter bands to form a gas seal?
-- bullet hardness varies with age, and sometimes due to time constraints I shoot bullets that haven't aged very long.

Things to Try:
-- test to see if WW296 leads less than Lil Gun
-- test to see if 1-diameter bullets lead less than Ardito'd bullets.
-- test to see if 30+BHN bullets lead less than 20+ BHN bullets.

[mtngun]

Wow, it's been 6 weeks since the last time I shot. I have been busy on non-shooting projects.

I was rushed for time today so didn't do my usual throrough and careful job and can only provide a brief summary of the results.

Today's target. Groups are numbered in the order in which they were fired. I got off to a rough start because I had forgotten how to shoot and had to relearn the Contender's fussy benchrest technique.

All of today's loads used the 155 gr. bevel base spitzer, reclaimed shot treated to 40 BHN. Sized 0.3575", the noses were sized either "full Ardito" or "partial Ardito," and seated 0.009" away from contact. Velocity approximately 2000 fps.


#1)
-- "partially Ardito'd"
-- 16.1 Lil Gun
-- 2060 fps
-- 1.08% standard deviation
-- 5 MOA
-- very light fouling 2" beyond chamber

#2)
-- reduce powder to 15.9 Lil Gun otherwise same as above
-- 2026 fps
-- 0.82% standard deviation
-- 3.3 MOA
-- very light fouling 2" beyond chamber

#3)
-- "full Ardito" nose-sized instead of "partial Ardito"
-- increase powder 16.2 Lil Gun to compensate for longer COL
-- 2011 fps
-- 1.73% standard deviation
-- 4.6 MOA
-- light fouling 2" beyond chamber

#4)
-- back to "partial Ardito" nose
-- 17 gr. WC297
-- 1991 fps
-- 1.09% standard deviation
-- 2.88 MOA
-- light fouling 2" beyond chamber, perfectly clean after pushing 1 dry patch through, no specs of lead on patch.

#5)
-- increase powder to 17.2 gr. WC297, otherwise same as above
-- > insert missing velocity data <
-- 2.44 MOA
-- 1 dry patch removed 80% of fouling. 1 wetted patch removed remainder of fouling.

Conclusions:
-- less fouling today than last time though still not perfectly clean
-- "partial Ardito" seems good compromise between having a good gas seal and good alignment in throat.
-- I had previously abandoned WC297 because of vertical stringing but today no worse than Lil Gun
-- not sure what gets credit for reduced fouling because several things were changed at once

Plan for next time:
-- continue "partial Ardito"
-- continue tweaking charge of WC297 with eye for getting rid of vertical stringing
-- continue trying to isolate reduction in leading

[mtngun]

Here's a photo of a 25 BHN bevel base shot into my water tank at 2000 fps. This bullet was "full Ardito" sized not "partial Ardito."

What is the weird stuff going on at the bevel? It looks like the corner of the bevel melted? Gas cutting, or simply exposure to the hot gases? Or did it erode due to cavitation when it entered the water?

Otherwise there is no sign of skidding, twisting, or yawing. The only possible problem I can detect is the melted bevel.


If the bevel is melting at peak pressure, could that explain the fouling problem?