357 Mag Contender Barrel III

[mtngun]

Made a 1.5 degree nose die. In theory, sizing the nose in a die that matches the throat will result in a "glove fit." I haven't made up my mind whether or not I like the "glove fit" method, but I'm game to give it a fair chance.
Length A = 0.3"
Diameter A = 0.360"
Length B = 0.225" (creates the 1.5 degree per side angle)
Diameter C = 0.348"

[mtngun]

Yesterday I tested several things: 1) Ardito style sizing and loading 2) I wanted to give Lil Gun another chance because Quickload thought it could safely gain 50 fps over WW296 / H110 3) firelapping the Green Mountain barrel and 4) the Mike Bellm bolt spring.

Firelapping consisted of 10 rounds of 280 grit followed by 10 rounds 500 grit. To the naked eye, it left a mirror finish. However, with the bore scope I could still see some roughness. There was also a surprising amount of pitting -- I have no idea what caused the pitting? It's not deep but it's there.

A bullet sized in the nose die, and loaded so that it was 0.012" away from contact.


Quickload thought that Lil Gun could push the 160 grainer to 2025 fps while WW296 / H110 / WC297 could only go 1950 fps. However, Quickload is not always right. In reality both powders maxed out at 2000 fps. At 2050 fps cases would begin to stick so that was the practical limit, and I backed down to 2000 fps to ensure reliable functioning.

The good news is that before firelapping I was running into leading above 1950 fps, after firelapping there was only minor leading at 2000 fps and the leading did not get any worse as more shots were fired. When I say "minor" I mean it looked great to the naked eye and the bore scope revealed only a few spots with tiny specs of lead, mostly in the corners of the grooves.

However, neither the firelapping nor the Ardito-style loading seemed to improve accuracy.

Starting out with Lil Gun
-- 15.3 gr. Lil Gun,
-- 1.866" COL (0.012" away from contact)
-- 1967 fps
-- 1.48% velocity standard deviation (poor)
-- 11 shots in 2.75" at 100 yards

Same as above except increase the charge of Lil Gun
-- 15.5 gr. Lil Gun
-- 1987 fps
-- 1.01 % velocity standard deviation
-- 11 shots in 2.75"

Increase charge of Lil Gun and nose-size bullet deeper and seat out farther
-- 15.7 gr. Lil Gun
-- 1.916" COL (0.012" away from contact)
-- 2007 fps
-- 0.99% velocity standard deviation
-- 11 shots in 1.9"
-- 11 shots in 2.6"

Same as above except switch to WC297
-- 17.0 gr. WC297
-- 2000 fps
-- 1.71 % velocity standard deviation
-- 11 shots in 3 1/4" but 8 shots in 0.9"
-- one of the fliers was the fouling shot, the other two were unusually high velocity (2057 fps and 2051 fps).


Conclusions and Lessons Learned
-- firelapping made the barrel look better and foul less, however there was no improvement in accuracy.
-- firelapping allowed the velocity to be increased from 1950 fps to 2000 fps.
-- no obvious improvement in accuracy with Ardito-style sizing and loading, compared to a 1-diameter bullet.
-- WC297 acted like it wanted to shoot one ragged hole with the Ardito bullet, but lousy velocity variation caused vertical fliers.
-- I'm still puzzled why this barrel shot more accurately with it's original "bad" chamber than with this current chamber which seems to be a very good chamber and throat?
-- there were no pop-opens with the Mike Bellm bolt spring, not even when I unintentionally ran the velocity up to 2200 fps and had to tap the cases out of the chamber with a cleaning rod. It takes two hands to open the action with the Bellm spring -- I can do it with one hand if I try hard enough but it's very difficult.
-- as I am also learning with the Contender 6x45, high velocity cast loads want to engrave the rifling but that just doesn't work in a Contender. For reliable chambering you have to jump to the rifling and that limits accuracy and makes it tough to ignite slow powders, hence the perpetually lousy velocity standard deviation.
-- unless some breakthrough comes along it looks like the best this chamber will do with high velocity cast is 2 MOA (vs. 1.6 - 1.8 MOA with the original "bad" chamber).

Things To Try Next Time and Down The Road
-- a few more firelapping shots. The bore scope reveals that there is still a little roughness and fouling in the corners of the grooves.
-- I could try tweaking the jump-to-rifling on the WC297 load, though my previous experience suggests that I'll never get rid of the velocity variation.
-- do a side by side comparison of 1-diameter vs. Ardito style.
-- down the road I may recut the leade to 1 degree instead of 1.5 degree, but I'm cautious after the failure with the 1/2 degree throat. In theory there is nothing wrong with a 1.5 degree leade.
-- down the road I may try some minor tweaks to the 160 grain spitzer, like changing the GtoB to 0.8 and making the nose longer or shorter.

[mtngun]

Today's experiments: 1) more firelapping 2) fine tune seating depth and 3) compare the Ardito-style bullet to a 1-diameter bullet.

I shot ten #280 grit firelapping bullets followed by three #500 grit bullets. To the naked eye, the resulting barrel was smooth as glass and shiny as a mirror. Through the borescope I could still see some pitting and some darkness in the corners of the grooves, but not as much as before.

The jam fit distance for the Ardito-sized bullet increased 0.002" - 0.020" after today's firelapping (the variation is due to measuring the fit with several different bullets). Firelapping always washes out the throat to some extent, one reason I am leery of firelapping.

Yesterday's WC297 load with the Ardito-style bullet and more jump to the rifling
-- 17 gr. WC297
-- 1.911" COL (0.019" away from contact)
-- 1883 fps (compared to 2000 fps yesterday !!! )
-- 1.92% velocity standard deviation
-- 10 shots in 3.3"

Same as above except closer to rifling
-- 1.925" COL (0.005" away from contact)
-- 1928 fps
-- 1.95% velocity standard deviation
-- 10 shots in 3.0"

Increase charge of WC297
-- 17.7 gr. WC297
-- 1.911 COL (0.019" away from contact)
-- 2000 fps
-- 1.5% velocity standard deviation
-- 10 shots in 2.4"

Switch to Lil Gun, still with the Ardito-style bullet
-- 16.1 Lil Gun
-- 1.911 COL (0.019" away from contact)
-- 2011 fps
-- 1.13% velocity standard deviation
-- 10 shots in 2.3"

Same except seat closer to rifling
-- 16.1 Lil Gun
-- 1.916" COL (0.014" away from contact
-- 1993 fps
-- 1.26% velocity standard deviation
-- 10 shots in 2.75"

Now compare to 1-diameter bullet at same velocity
-- 15.2 Lil Gun
-- 1.754" COL (0.014" away from contact)
-- 2012 fps
-- 0.83% velocity standard deviation
-- 10 shots in 11.75", 9 in 3.4", the flyer was the first shot
-- 10 shots in 6"


Today's target:


Conclusions, Observations, and Lessons Learned
-- Ardito-style sizing and loading is definitely superior to 1-diameter sizing, at least for this load in this barrel
-- it lost 100 fps due to today's firelapping!
-- today's firelapping was probably a mistake. Yes, the barrel looks slightly prettier now, but there was no improvement in accuracy and it bothers me that it lost 100 fps.
-- Today I measured the COL of every round to check for consistency. I discovered that COL was very consistent as long as the primer was fully seated. But occasionally a primer would be proud of the case and that would increase the COL. The longer COL can cause difficult chambering and increased velocity variation.
-- 0.019" away from contact seems to be close to optimal for the Contender with the Ardito bullet.
-- my new standard load will be the LiL Gun Ardito load seated 0.019" away from contact.
-- if the best this chamber can do with its pet load is 2.0 - 2.5 MOA then something is wrong, I just haven't figured out what.

Things to Try Next Time
-- tweak the GtoB and the nose length on the 160 gr. spitzer

Things to Try Longer Term
-- I increasingly suspect that either the chamber or the throat is not concentric to the bore. Why do I say that? Because this chamber is not shooting as well as it should and I've ruled everything else out. Also, this chamber has always fouled just ahead of the throat at 1:30. Not all the way around, just at the 1:30 position. Firelapping did not change that. Using the bore scope, I can't detect any flaws in the throat or barrel at that spot.

There is no visible lack of concentricity. It looks concentric to the naked eye, and the throat impression looked concentric, so if something is off, it's not off by much. But suppose the chamber is off by 0.0005". You wouldn't be able to see that, yet it would push the bullet to one side of the throat (the chamber is too snug to allow the cartridge to self-align in the throat). Maybe that is what is causing the fouling at 1:30 and the substandard accuracy?

-- so long term I may recut the chamber yet again. One option would be to punch it out to 357 Maxi. If that didn't work, then set it back and start over.

-- The barrel is currently 25" and I want to have at least 20" when all is said and done, so I have room to set the barrel back. I just want to rule everything else out first, and I think I have ruled everything else out.

[mtngun]

I have been thinking more about this chamber because it really bugs me. Let's review the facts:
-- the original, "bad" chamber was averaging < 2 MOA and it almost never fouled the barrel, despite numerous flaws with the chamber.
-- the current chamber struggles to shoot 2 MOA and has always fouled more than the original chamber, particularly at the 1:30 position in the throat, even though the chamber has perfect dimensions.
-- same barrel, same bullet, only the chamber has changed.
-- the load has been tweaked extensively yet it still doesn't shoot as well as the "bad" chamber.
-- I have no way to measure the concentricity of the chamber relative to the bore.
-- Two things make me wonder if the chamber is not concentric 1) the persistent fouling at 1:30 and 2) everything else has been ruled out.

Options:
-- try to devise a way to measure the concentricity of the chamber.
-- recut to 357 Maxi. However, the reamer would want to follow the existing chamber, so if the existing chamber is off-center then the Maxi chamber would end up off center, too.
-- recut the chamber to a wildcat based on the 30-30 case, similar to a 357 Herrett except shorter.
-- set the barrel back and start over. That would work, except it takes time and I'd lose 2" of barrel.

Update:
-- I ordered a test indicator with a 1.5" long probe. When it gets here I'll dial in the barrel in the lathe and then test the chamber for concentricity with the bore.
-- I verified that the reamers used to cut this chamber had snug pilots, 0.3467" on the throating reamer and 0.3468" on the chamber reamer. At the time, the biggest pilot that would slide into the barrel was 0.347" (that was before I firelapped the barrel). It's hard to believe the reamers could have cut off-center more than 0.0003".
-- a 0.3469" pin gage would slide into the breach end about 6 inches and then stop (using finger pressure, obviously I'm not going to beat on it with a hammer).
-- the 0.3469" pin gage would slide into the muzzle end and keep going until it hit the same tight spot 6 inches from the breach.
-- to rule out fouling causing the tight spot, I gave the barrel an extra good cleaning with JB Bore Cleaner on an extra tight fitting patching. I could never feel a tight spot with the tight fitting patch.
-- after cleaning, the 0.3469" pin gage still met resistance at the tight spot, but could be pushed through with moderate finger pressure. I'm guessing the bore in the tight spot must be 0.3469" - 0.3470".
-- the current bore measurement (this is after the recent firelapping) is 0.3477" just ahead of the throat, and 0.3471" at the muzzle, as measured with an expanding ball gage and rotating the ball gage as I measure.
-- so even after firelapping the barrel still has a 0.0007" constriction about 6" from the breach. That's interesting, but I don't think it is the cause of the lackluster accuracy because presumably that constriction was there from day one, and yet the barrel shot better with the original "bad" chamber.
-- I don't want to firelap the existing chamber any more because I don't want to wash out the throat, but if I ever decide to rechamber this barrel then I'll first do more firelapping to try to eliminate the tight spot.

[mtngun]

Today we compared two new 160 gr. plain base bullets, long ogive vs. short ogive. The barrel still has the 0.0007" tight spot, more on that later. For the record we're having a heat wave, in the 90's, and it must have been over 100 inside the shooting shack.

Same basic load as last time except with the new bullets. Unless otherwise stated, all of today's loads were nose-sized and loaded Ardito-style, 0.015" jump to the rifling, 16.1 grains Lil Gun, Winchester magnum primer, sized 0.359", oven treated, and lubed with Rooster HVR.

Short Ogive:
-- 2013 fps for 22 shots
-- 0.65% velocity standard deviation
-- 2.88" average 10 shot groups at 100 yards (2.45", 3.3")
-- 0.91" average mean radius
-- 0.83" average radial standard deviation
-- minor fouling at the "tight spot," otherwise clean

Long Ogive:
-- 2025 fps for 21 shots
-- 0.8% velocity standard deviation
-- 2.5" average 10 shot group at 100 yards (3", 2" excluding one flyer that was prolly due to seasoning)
-- 0.90 average mean radius
-- 0.62 average radial standard deviation
-- minor fouling at the "tight spot," otherwise clean.

The group on the bottom right was shot after scrubbing the barrel. The first shot is marked "fouler," this barrel usually throws the first seasoning shot from a cold or clean barrel. The 2nd shot is marked "shot #2" and it was a bit of a flier, too. I ignored those two seasoning shots and only counted the remaining 9.


Conclusions, Observations, and Lessons Learned:
-- I expected the short ogive, with its longer bearing length, to be more accurate than the long ogive, but in fact there seems to be no measurable difference.
-- standard deviation was better than usual today. All I can guess is the 100 degree heat made the powder burn better ???
-- the short ogive had better standard deviation, probably because it seated deeper (more neck tension) and had more engraving resistance.
-- no pop-open problems since the Mike Belm bolt spring was installed.
-- it's hard to prove anything with only 2 groups so I'll probably repeat this experiment.
-- this chamber struggles to do better than 2 MOA no matter what I feed it. It's not as accurate as the "bad" chamber.

Things to Try Next Time and Down the Road:
-- repeat the ogive shoot-out.
-- at some point I will attempt to firelap the tight spot. I dunno if the tight spot is hurting accuracy, but at a minimum it is causing some minor fouling. Firelapping may wash out the throat, so even if if getting rid of the tight spot helps accuracy, washing out the throat may hurt accuracy. There's a possibility that I may have to rechamber to repair a washed-out throat, we'll see.
-- otherwise I am out of ideas at the moment.

[mtngun]

OK, I did more firelapping, hoping to eliminate the tight spot in the barrel

-- 5 rounds #280 grit
-- clean barrel
-- 5 rounds #280 grit
-- clean barrel
-- 5 rounds #500 grit
-- clean barrel
-- 5 rounds #500 grit
-- clean & JB barrel

Then I re-measured the jam fit with 3 different bullet designs:

-- gained 0.023" on the original 160 PB spitzer
-- gained 0.004" on the 164 PB long ogive
-- gained 0.003" - 0.005" on the 163 PB short ogive.

I can live with that, it didn't wash out the throat as much as I feared.

Is the tight spot gone? Well, the same 0.3469" pin gage now slides all the way through the barrel with no resistance. The next size larger pin gage, 0.3477" - 0.3479", won't even enter the bore from the breach end. So all I can say is that it is better than it was before. Now let's see if shoots any better.

[mtngun]

Today we were trying to 1) determine if firelapping out the tight spot improved accuracy 2) continue last week's ogive shoot-out and 3) test a new bevel base bullet.

The new bevel base bullet. It weighs 155 grains and has the same "long" ogive as the other "long" ogive bullet. The bevel is not particularly large, but nonetheless it should prove whatever there is to prove about bevel base bullets.


It was hot today, in the 90's, and the shooting shack was even hotter. I mention that because the temperature may affect the powder ignition and velocity. Unless otherwise stated, all of today's loads used Winchester magnum primers, oven treated wheelweight, sized 0.359", nose-sized, and lubed with Rooster HVR.

Short Ogive 163 gr. Plain Base
-- 1.915" COL, 0.014" into rifling (I screwed up the math and jammed it into the rifling instead of 0.014" away from the rifling )
-- 16.2 gr. Lil Gun (I increased the powder charge from 16.1 to 16.2 based on the assumption that the firelapping & longer throat would reduce velocity. That proved untrue.)
-- 2040 fps
-- 0.64% velocity standard deviation
-- 10 shots in 2.5" at 100 yards

Same but backed off the powder charge
-- 16.1 gr. Lil Gun
-- 2015 fps
-- 1.04% velocity standard deviation
-- 10 shots in 2.9" at 100 yards

Long Ogive 155 gr. Bevel Base
-- 1.926" COL, 0.015" into the rifling (an unintentional screw-up)
-- 16.1 gr. Lil Gun
-- 2041 fps
-- 0.65% velocity standard deviation
-- 10 shots in 2.3" at 100 yards, strung vertically
-- 0.76" mean radius
-- 0.38" radial standard deviation

Same but corrected the COL
-- 1.901" COL (0.010" away from contact)
-- 2037 fps
-- 0.57% velocity standard deviation
-- 10 shots in 1.85" at 100 yards
-- 0.64" mean radius
-- 0.28" radial standard deviation

Long Ogive 164 gr. Plain Base
-- 1.964" COL (0.010" away from contact)
-- 16.1 gr. Lil Gun
-- 2025 fps
-- 0.77% velocity standard deviation
-- 10 shots in 2.0", 2.9" at 100 yards
-- 0.7", 0.89" mean radius
-- 0.52", 0.81" radial standard deviation

The bevel base was definitely the most promising of the 3 bullets.


Conclusions, Observations, & Lessons Learned
-- there were no pop-opens, not even with the unintentional jam-fit loads
-- there was slight fouling in the throat at 1:30, and slight fouling just past the throat. The rest of the barrel was clean. The fouling was not enough to complain about and never got any worse as more shots were fired.
-- the fouling at the "tight spot" seems to be gone.
-- combining today's 2 groups for the long ogive plus last week's 2 groups it averages 2.48" ES, 0.85" mean radius, and 0.64" radial standard deviation.
-- I'll have to retest the short ogive since I screwed up the COL today.
-- the bevel base bullet showed some potential
-- after today's firelapping, the barrel looks awesome, the tight spot seems to be gone or at least greatly reduced, and the fouling at the tight spot seems to be gone -- but there was no change in accuracy.

Things to Try Next Time
-- retest the short ogive
-- retest the bevel base
-- possibly try some minor tweaks with the bevel base, like a different brand primer, or slightly different seating depth.

[mtngun]

Today we continued testing the 155 gr. bevel base and the 163 gr. short ogive. Unless otherwise noted all loads used 16.1 gr. Lil Gun, Winchester magnum primer, oven treated WW, sized 0.359", nose-sized & loaded Ardito-style.

Once again the temperature was in the 90's. Mirage was a problem, it made the target blurry and it danced in the boiling mirage, so it was like shooting at a moving target. This seems to be a common problem on my range during hot weather but I figure it's part of the game and I just have to learn to shoot through it.

155 gr. bevel base, same load as yesterday
-- 1.901" COL, 0.010" jump to rifling
-- 2024 fps
-- 0.81% velocity standard deviation
-- 10 shots in 3.0" at 100 yards
-- 1.07" mean radius
-- 1.22" radial standard deviation

Same as above except with CCI #550 primer
-- 2011 fps
-- 0.54% velocity standard deviation
-- 10 shots in 1.45" at 100 yards
-- 0.59" mean radius
-- 0.23" radial standard deviation

155 gr. bevel base, nose sized deeper and loaded longer
-- 1.947" COL, 0.010" jump to rifling
-- 2024 fps
-- 1.03% velocity standard deviation
-- 10 shots in 2.75" at 100 yards

163 gr. short ogive plain base
-- 1.899" COL, 0.010" jump to rifling
-- 2019 fps
-- 0.64% velocity standard deviation
-- 10 shots in 5.5", 3.45"
-- previous groups were 2.45", 3.3" so it averages 3.7"

At the end of today's session, there was some light fouling visible just ahead of the throat, and a tight fitting patch did show a few specs of lead.

Today's target.


Conclusions, Observations, & Lessons Learned
-- the long ogive was more accurate than the short ogive. 2.5" average vs. 3.7".
-- the bevel base teases me with an occasional good group, but can't do it every time.
-- the CCI primer was more accurate and had lower standard deviation than the Winchester. No surprise, I've never cared for Winchester primers, but during the primer shortage one had to take what one could get.
-- nose-sizing depth does not seem to matter that much.

Things to Try Next Time
-- retest the CCI 550 primer
-- tweak the distance-to-rifling
-- try a GC bullet with no gas check

[mtngun]

Today's mission was 1) more tests with the 155 bevel base & CCI 550 primers and 2) a 155 gas check bullet.

Unless otherwise stated, all of today's loads used oven treated WW, sized 0.359", lubed with HVR, and nose sized. Range conditions were good today, no mirage.

Bevel base with 0.003" jump to rifling
-- 1.935" COL
-- CCI 550 primers
-- 2000 fps
-- 0.82% velocity standard deviation
-- 2.6" for 10 shots @ 100 yards
-- 0.95" mean radius
-- 1.07" radial standard deviation

Same but 0.010" jump to rifling
-- 1.928" COL
-- 2004 fps
-- 0.44% velocity standard deviation
-- 2.85" for 10 shots @ 100 yards
-- 0.76" mean radius
-- 0.29" radial standard deviation

Same but 0.015" jump to rifling
-- 1.923" COL
-- 1994 fps
-- 0.99% velocity standard deviation
-- 3.75" for 10 shots at 100 yards
-- 0.96" mean radius
-- 0.94" radial standard deviation

Same but 0.020" jump to rifling
-- 1.918" COL
-- 2017 fps
-- 0.91% velocity standard deviation
-- 4.85" for 10 shots at 100 yards
-- 1.22" mean radius
-- 1.82" radial standard deviation

Conclusions & Observations for 155 Bevel Base
-- At the end of this session there was some fouling at the "tight spot". It seems like there were more flyers as more shots were fired, and groups got larger as more shots were fired. Apparently the tight spot is still there.
-- on the whole accuracy is about the same for the bevel base vs. the plain base.
-- on the whole accuracy is about the same for CCI 550 vs. Winchester magnums.
-- the CCI 550 primers were slower than the Winchester magnums.
-- 0.010" jump to rifling seems about optimal.

[mtngun]

The 155 grain gas check. Same "long" ogive as the other 155 grain bullets.


With Gas Check installed, three 10-shot groups:
-- 1.924" COL, 0.010" jump to rifling
-- 16.1 gr. Lil Gun
-- Winchester mag primers
-- 2106, 2063, and 2070 fps. 2080 average.
-- 0.77%, 0.79%, and 0.82% velocity standard deviation. 0.79% average.
-- 1.85", 3.3", and 2.5" 10-shot groups @ 100 yards. 2.55 average.
-- 0.5", 0.91", and 0.82" mean radius. 0.74" average.
-- 0.27", 0.65", and 0.33" radial standard deviation. 0.42" average.
-- very little fouling if any

Without Gas Check installed, otherwise same:
-- 2091 fps
-- 2.6" 10 shot group @ 100 yards
-- 0.9" mean radius
-- 0.76" radial standard deviation
-- definitely fouling at the "tight" spot. The remainder of the barrel was clean.

Today's target:


Conclusions and Observationst:
-- if you go by group size, no difference in gas check vs. no gas check, or plain base vs. bevel base. All average 2.5" on a good day, with lots of variation from one group to the next.
-- if you go by radial standard deviation, the gas check is better than no gas check, 0.42" vs. 0.76"
-- in general this chamber seems to average 2.5 MOA with its pet loads, vs. the "bad" chamber averaged about 1.8 MOA.
-- the only obvious thing wrong with this chamber is the "tight spot" in the barrel. I don't know if the tight spot was delivered from the factory, or if I created the tight spot while handling the barrel, perhaps from over tightening in a barrel clamp? If the latter, that might explain why the original "bad" chamber was more accurate and fouled less than subsequent chambers.

Things to Try Next Time
-- keep firelapping until the fouling at the tight spot disappears. Worse case, the fire lapping may wash out the throat and require setting back the barrel, but the alternative is to buy a new barrel and start over, so I might as well try firelapping.
-- I'm out of ideas for load tweaks.