357 Mag Contender Barrel III

[mtngun]

Today we continued tweaking WC297 load.

All of today's loads used the "partially Ardito'd" 40 BHN bevel base, sized 0.3575", and seated 0.009" away from contact. This is what I mean by "partially Ardito'd" -- it was intended to be a compromise between the good alignment of a tapered Ardito style bullet and the good gas sealing of a 1-diameter bullet.


Today's target. The numbers refer to the order in which they were shot.


#5 yesterday)
-- 17.2 gr WC297
-- 2006 fps
-- 0.87% standard deviation
-- 2.63 MOA
-- 0.77" mean radius

#1 today
-- increase powder to 17.4 gr. WC297
-- 1977 fps (slower than yesterday perhaps due to cooler temperatures)
-- 1.05% standard deviation
-- 2.15 MOA
-- 0.62" mean radius

#2)
-- increase powder to 17.7 gr. WC297
-- 1982 fps
-- 0.87% standard deviation
-- 3.2 MOA
-- 0.98" mean radius

#3)
-- return to 17.4 gr. WC 297 because that seemed to be the sweet spot
-- 1975 fps
-- 1.07% standard deviation
-- 2.19 MOA
-- 0.63" mean radius

#4)
-- same as above
-- 1997 fps
-- 1.06% standard deviation
-- 3.46 MOA
-- 0.97" mean radius

Conclusions and Observations:
-- these WC297 groups taken together averaged 2.73 MOA and 0.79" mean radius. Nothing to brag about, basically the same as the old Lil Gun load.
-- all of today's loads fouled slightly for 2" past the chamber. Most of the time a single dry patch would clean it up. A couple of times the dry patch had to be followed up by one wet patch. I never had to use the brush or any other "scrub-a-dub-dub" stuff. On the whole this load fouls about 50% less than the old "full Ardito" bullet with Lil Gun. Nonetheless I consider any significant fouling to be unacceptable because it may cause fliers.
-- I had abandoned WC297 a while back because it seemed prone to vertical stringing, but it appears that most of the vertical stringing can be eliminated by tweaking the powder charge.
-- Yet the fact remains that this "good" chamber is not as accurate or as clean as the original bad chamber, and I don't know why.
-- At the end of the day I fired the 17.4 gr. load into the water trap, and the bullet definitely yawed. It definitely was enough to cause a flier.


Things To Try Next Time
-- try the WC297 load with 25 BHN bullets rather than 40 BHN.
-- possibly try an "Intermediate Ardito" to improve alignment and reduce yawing.
-- check cases for wall runout that might cause the bullet to be off-center
-- possibly return to 0.359" diameter to ensure the bullet is centered in the chamber. I haven't noticed a difference in performance between 0.3575" and 0.359", though.
-- possibly try a card stock wad under the bullet.
-- shoot more bullets into the water trap to check for yaw, gas cutting, bevel melting, etc..

[mtngun]

More Musings on why the current "good" chamber does not shoot as well as the original "bad" chamber:

-- I'm beginning to suspect that the Ardito throat & sizing system, while proven beyond doubt for long 30 caliber bullets in bolt guns, may not be optimal for aligning short stubby bullets in a Contender.

-- an alternative alignment system would be to have a snug-fitting freebore guiding a 1-diameter bullet into the rifling. One advantage would be that a jam fit would not be required for good alignment, merely a snug slip fit. Contenders don't like jam fits.

-- if we decide to go with a freebore system, the next question is how long should the freebore be? I think that depends on how deep we want to seat the bullet. Let's assume we want to keep 0.150" of the bullet in the case, because anything less would not grip the bullet reliably. Well, the bearing length on my 155 gr. spitzer is only about 0.360" give or take, so subtracting 0.150" from 0.360" leaves 0.21". A 0.21" long freebore??? I dunno, that sounds pretty wild. But I'll think about it.

Before I recut the throat I want to give the current throat every chance to prove itself. There's still a few things I want to try:
-- a cardboard wad to possibly reduce leading
-- a soft wax wad, which I don't think will help but nonetheless it would be a quick and easy experiment.
-- a heavier bullet, say 170, with a longer nose-sized section than my current 155, more in keeping with the orginal Ardito concept of a long tapered bullet.

[mtngun]

Saturday's Range Results. I've pretty much decided to rethroat to a "snug slip fit freebore" but still have a few things I want to try before I take that leap. These are some of those things. A quick glance at the target shows that none of Saturday's experiments were successful. Some were just worse than others. It's tempting not even to report these results but I always say we learn as much from our failures as from our successes.

The green #number refers to the order that each group was shot.


Group #1) trying a soft check with the 155 gr. bevel base
-- 155 gr. bevel base
-- approx 25 BHN
-- 16.2 gr. Lil Gun
-- Win mag primer
-- sized 0.3575", nose sized "full Ardito"
-- 0.010" away from contact
-- HVR lube
-- 0.050" thick soft check made from Rooster Zambini Lube
-- 3.2 MOA
-- 0.99" mean radius
-- 1982 fps
-- 1.71% standard deviation
-- no leading, yea !!!
-- conclusion: soft check indeed eliminated leading, but accuracy was worse than normal and lots of velocity variation.

Homemade soft check made from Rooster Zambini Lube (it's a hard, non-sticky lube made for commercial casters). The sheet is simply pressed over the mouth of a charged case, then the bullet is seated on top of the check.


Group #2) trying a card wad with the 155 gr. bevel base
-- same as above but with card wad punched from manila folder
-- 4.22 MOA
-- 1.35" mean radius
-- 1966 fps
-- 5.74% standard deviation
-- light leading 2" ahead of chamber, no cleaner than without wad
-- conclusion: card wad did not help leading but hurt accuracy and lots of velocity variation

Group #3) 175 gr. PB, full Ardito, Lil Gun
-- 15.8 gr. Lil Gun
-- 175 gr. PB sized 0.359" x 0.349"
-- approx 25 BHN
-- seated right at contact point
-- HVR lube
-- chrono stopped working so no vel data but pretty sure 1900+ fps.
-- 2.44 MOA
-- 0.82" mean radius
-- light leading 2" ahead of chamber
-- conclusion: no better or worse than 155 bb load. Didn't fix accuracy, didn't fix leading.

Group #4) 175 gr. PB with WC297
-- 17.2 WC 297
-- otherwise same as above
-- 1931 fps
-- 0.72% standard deviation
-- 2.81" MOA
-- 0.82" mean radius
-- light leading 2" ahead of chamber
-- conclusion: no better or worse than 155 bb load. No better of worse than Lil Gun load. Didn't fix accuracy, didn't fix leading.

This was the same 175 gr. spitzer I tried earlier this year, but this time it got the "full Ardito" treatment.


The 175 grainer was seated right at the contact point, with the front band lightly grazing the rifling.


Group #5) 155 gr. BB with air-cooled wheelweight
-- 17.2 WC 297
-- sized 0.359", full Ardito
-- 1879 fps
-- 3.94% standard deviation
-- five shots in 4.14"
-- 1.53" mean radius
-- leading 2" ahead of chamber, worse than hard bullet
-- conclusion: worse accuracy, worse velocity, worse standard deviation, and worse leading with this soft bullet.

[mtngun]

While I was reloading for the TC357 the other day I had a senior moment and forgot to charge a case with powder prior to seating the bullet. Naturally it didn't go "bang" when the trigger was pulled. But ..... I was surprised that the bullet was lodged firmly in the rifling and had to be pounded out with a brass rod (hence the dinged nose).

It made me wonder -- with my normal TC357 load, is the bullet driven into the rifling by the primer, even before the powder burn kicks in ? Well I have no way of knowing for sure but for the sake of discussion let's assume that the primer does drive the bullet into the rifling, the next question is does the bullet enter the rifling straight or does it yaw?

So I loaded 10 rounds without powder, seating the bullet 0.009" shy of contact as I often do with "real" loads, painted the exposed bands with magic marker so engraving would show up better, and "fired" them to see if they yawed as they entered the rifling. Including my "senior moment" bullet, 11 out of 11 primer-driven bullets engraved the rifling evenly, without any yaw. All of them engraved the front band hard, and all of them rubbed the magic marker off the 2nd band.

Sorry for the crappy picture. I suck at taking closeups of small objects.


So what does that prove? Well, *if* the primer drives the bullet into the rifling on real loads, it proves that the bullets are not yawing as they enter the rifling. If any yawing is occurring, it must be occurring further down the barrel, perhaps when peak pressure kicks in. Again, *if* the primer drives the bullet into the rifling, and that's a big "if."

*If* the primer drives the bullet into the rifling and *if* the yawing occurs later when peak pressure kicks in, then what can I do about it? Well, a harder bullet, or a bullet that is 1-diameter rather than tapered should resist deformation better. If Colonel Harrison were still alive, I'm sure he would advise me to rechamber to larger capacity case like 357 Herrett and use a slower, gentler powder like 4198 or 1680 to reach my desired velocity. He was a big believer in using slow powders for high velocity loads.

Anyway, that's just one possible scenario and I don't know if it is the correct scenario. Just something to think about.

[mtngun]

Today I attempted to recut the throat to a "snug slip-fit freebore." I dunno if that is a good cast bullet throat or not but I'm trying just about every kind of throat until I settle on a favorite.

Anyway, my homemade reamer cut smoothly and concentrically but the freebore turned out smaller than desired. I was hoping for 0.358"+ for use with a 0.3575" bullet but it ended up closer to 0.357". I tried putting some tape on the reamer to make it cut a little fatter but only partially succeeded. The finished freebore starts out around 0.358" but gradually tapers to 0.357" or so. The slight taper is not necessarily a bad thing but the diameter is just too small.

The new leade angle is 1 degree because that's what the original "bad" chamber had and it shot better than any chamber since.

The smallest sizing die on hand, nominally 0.357", made an air-cooled bullet 0.3566" and a hardened bullet 0.3575." Unfortunately the only bullets I had available in quantity were hardened so for today I was stuck with the 0.3575" bullets which were too big for the freebore.

Showing how a 0.3575" bullet fits in the freebore vs. a 0.3566" bullet. Even the 0.3566" bullet cannot seat out as far as I intended.


I was not happy with the fit of the too-big bullets in the too-small freebore and resolved to make a new reamer to recut the freebore. But I figured I might as well try this too-small freebore. Even if it does not work well, it will still be another data point in the search for the perfect cast bullet throat.

Indeed the too-tight freebore did not shoot satisfactorily. I was aiming for 1980 fps because that's what my Lil Gun loads clocked before rethroating and I was trying to maintain that same velocity for an apples-to-apples comparison. It took several load tweaks to get the velocity dialed in.

All of today's loads leaded in the usual spot 2" beyond the chamber. While leading is always subjective, today's leading seemed worse than usual. It took a lot of scrubbing to get the lead out. In fact, at the end of the day I scrubbed for 20 minutes before deciding it would be easier to clean up by shooting a few gas checked bullets.


Conclusions and Lessons Learned:
-- the too-big bullets in the too-small freebore were a failure in every way.
-- my homemade reamers are cutting smoothly and concentrically, but it's still a challenge to get the dimensions spot on.
-- I continue to get the impression that Lil Gun leads slightly more than WC297.

Musings on Why The "Bad" Chamber Shot Better and Cleaner than Subsequent "Good" Chambers
-- the barrel has gone from 27" to 21.5", yet I am still using 2000 fps loads.
-- Quickload believes that pressure increased 4000 psi to maintain the 2000 fps velocity as the barrel was shortened. Did the extra 4000 psi push the load over the edge?
-- Quickload believes that if loaded to the same pressure as the 27"/2000 fps combo, the 21.5" barrel would only clock 1935 fps.

Things to Try Next Time
-- make another reamer and try again to create a 0.358" - 0.359" freebore.
-- cast more bullets so they can be sized to fit the freebore prior to heat treating.
-- try dropping the velocity to 1935 fps to restore pressure to the same as the 27"/2000 fps combo.

What if the "Snug Slip-Fit Freebore" Fails ? Let's assume that I eventually recut the freebore to provide the perfect snug slip-fit yet it still shoots like crap -- what's next?
-- I could try to duplicate the original "bad" chamber. It had a 1 degree leade that began at a sloppy 0.364"+. I can't think of any reason that sloppy throat would shoot well, but it did.
-- I could fall back on gas check bullets.
-- I could salvage this chamber by recutting to Maxi or Herret. That still leaves the question of what kind of throat to put in it?

[mtngun]

A new reamer made. The freebore section began life at 0.360", but after heat treating, scale removal, and stoning, it measures 0.359". If it actually cuts 0.359" I'll be happy.

[mtngun]

Last time the 0.3575" bullets were too fat to fit in the freebore, so today we tried 0.3565" bullets. The fit was still too tight and they still had to be seated deeper than I wanted. In hindsight, I might could have seated them out further, more on that in the next post.


Well, they were less awful than the too-fat 0.3575" bullets, but still awful nonetheless. I don't see any potential here. They did not lead as severely as last week's 0.3575" bullets, but they still leaded some.


I figured these bullet would still be too fat to seat out far enough, and that proved to be the case, so I went ahead and recut the freebore with the new freebore reamer. Continued .....

[mtngun]

I set the reamer stop to make the freebore 0.21" deep. The freebore diameter turned out to be 0.360" as measured with a tri-mic, and there was no taper that I could detect. I can live with that. Viewed through the borescope, the new throat looks concentric -- how could it not be concentric with the barrel dialed in perfectly and the reamer pilot just as snug as could be? The finish is not mirror smooth but it's acceptable.

I had originally guessed that the bullet would need 0.0005" clearance in the freebore to be an easy slip fit. That proved to be wishful thinking, so today we tried 0.001" clearance with 0.359" bullets in the 0.360" freebore. Even with 0.001" clearance it takes effort -- say 10 pounds of force -- to push the bullet into the freebore.

My normal method of measuring the jam point did not work with this throat. If I pushed the bullet into the throat with about 3 pounds force, as per my normal method, it would stop at the entrance of the freebore. If I gave it a firm tap -- say 10 pounds or so -- then it would slide into the freebore. Even then, there was no definite stopping point. If you pushed it a little harder, it would move a little further. I gave up measuring the jam point and instead set a seating depth by trial and error.

This is what I settled on, 1.950" COAL. It took moderate resistance to close the action with this seating depth. The bullet was rubbing in the freebore even though in theory it had 0.001" clearance. All it takes is some residual bullet lube or a single grain of unburnt powder to create a tight fit. I did not do any optimization testing on seating depth, this was just my best guess for a starting point.

This is my "old" 162 gr. plain base spitzer because it was the only 359 bullet available to shoot today.


17.0 gr. Lil Gun was intended to clock 1950 fps but it turned out a little faster at 2021 fps, with waaaaay too much variation -- 2.42% velocity standard deviation. People often ask why don't I use a jam fit in the Contender? Well, this is what happens if the cartridge does not chamber easily -- you get inconsistent velocities.

Nonetheless this load shows some potential -- the horizontal dispersion is decent, and the vertical dispersion can be attributed to the extreme velocity spread. Next time I'll try tweaking the load to shrink the velocity spread.


Observations and Lessons Learned:
-- a slip fit freebore needs at least 0.001" clearance in a Contender, maybe even more.
-- once again the Contender demonstrated that it does not like a load that does not chamber easily.
-- this freebore throat shows some potential if only I can get rid of the velocity spread
-- today's load still leaded though not as bad as before. Still, any "hard" leading is unacceptable.

Things To Try Next Time:
-- try 0.0015" clearance by sizing the bullet to 0.3585", or even 0.358".
-- go back to WC297 because it seems to lead less. I chose Lil Gun today to "torture test" the new throats -- since Lil Gun leads more, it is a harder test to pass.
-- if leading persists I can try a coating or fall back on gas checks. But it's sure curious how this same barrel didn't lead with its' original "bad" chamber.

[mtngun]

Speaking of snug slip-fit freebores, here's the SAAMI chamber for the 300 Weatherby Mag, calling for a 0.3084" diameter x 0.35" long freebore, followed by a one degree per side leade.

I was surprised that the Weatherby freebore calls for only 0.0004" clearance. Cast bullets seem to need more clearance due to their imperfect dimensions and residual bullet lube.

Getting back to cast bullet clearance in the freebore. The Contender is unhappy with 0.001" clearance, at least using my favorite hard, tacky HVR lube. More things to try concerning freebore clearance:
-- try a softer, non-tacky lube to see if it chambers more reliably
-- make a 0.358" x 0.359" nose die, that would leave the base 0.359" for a good gas seal but size the rest of the bullet 0.357" for easy chambering in the freebore.

[mtngun]

Today's goal was to try to shrink the horrible velocity variation, which is due in part to resistance when chambering.

I made a nose die to size most of the bullet down to 0.358" for an easier fit in the freebore while maintaining a 0.359" base for a good gas seal. Or at least that was the theory anyway.

Here's how it turned out when seated just off jam.


The 0.358" x 0.359" bullet did chamber easier than last weeks 0.359" bullet, but there was still a bit of drag and there was still no definite "jam" point.

I measured the jam from breach to base for several 1-diameter 0.359" bullets, pushing with 3 pounds of force:
-- 1.060", 1.064, 1.003, 1.063, 1.018, 1.057, 1.029, 1.039. Average= 1.042".

Then I measured the jam for several 0.358" x 0.359" bullets, again pushing with 3 pounds of force:
-- 1.222", 1.218, 1.225, 1.213, 1.232, 1.225, 1.203, 1.216, 1.209, 1.191, 1.208, 1.221. Average= 1.215".

The bullet was 0.775" OAL, so adding that to the 1.215" jam yields 1.99 COL to just barely reach the jam point.

For starters, we repeated last week's charge of Lil Gun to see if the nose-sized bullet was an improvement.
-- 17 gr. Lil Gun
-- Winchester mag primer
-- 1.973" COL (0.017" away from jam)
-- 1997 fps vs. 2021 fps last time
-- 1.55% velocity standard deviation vs. 2.42% last time
-- ES=3.53" vs. 3.12" last time
-- MR=1.08" vs. 0.88" last time
Conclusion: the nose-sized bullet chambered easier and the velocity variation was less horrible, otherwise no improvement.

Reduce the velocity and seat a bit deeper for less chambering resistance
-- 16.6 Lil Gun
-- 1.963" COL (0.027" away from jam)
-- 1947 fps
-- 1.76% velocity standard deviation
-- ES=4.02"
-- MR=1.18"
Conclusion: no improvement in accuracy and it still leaded.

Switch to WC297, which usually leads less:
-- 18.0 WC297
-- Win mag primer
-- 1962 fps
-- 2.48% velocity standard deviation
-- ES=2.82"
-- MR=0.86"
Conclusion: perhaps slightly better accuracy and slightly less leading, but the velocity variation was still awful.

Today's target. Note that the horizontal dispersion was 1 1/4" - 2 1/8", which is decent. But the lousy velocity variation is causing vertical fliers -- fast shots land high, slow shots land low. So the #1 priority is getting the velocity variation under control.


Leading is always subjective. What looks dirty to one person may look OK to another person. I find that even when using a bore scope leading is still a judgement call. My gold standard for judging leading is simply to push a tight fitting patch through. If there is "hard" leading, you'll probably see slivers of lead on the patch, and there will still be visible leading in the bore. But if there was only "soft" leading, there should be no slivers of lead on the patch, and the patch alone will probably leave the bore clean. All of today's loads flunked the patch test, though WC297 seemed less guilty than Lil Gun.


To add to today's fun, one of the Eagle Arms bolts broke. I swapped in the bolts from my 6x45 barrel and continued shooting, though while swapping bolts I noticed that the Bellm bolt spring seemed to have taken a set. In fact, the action popped open 3 times today, for the first time since I installed the Bellm spring.


At the end of the day I examined the bolt spring more closely. Yep, it has taken a set. In fairness to the Bellm spring, I'm not sure that the Eagle Arms stub compresses the spring as much as a TC barrel? In any event for now I solved the problem by cutting 3 coils off an old spring and inserting those 3 coils in before the Bellm spring.


Continued in the next post .....