357 Mag Contender Barrel III

[mtngun]

I'm putting this in "hi velocity" for lack of a better category. It's hi velocity by 357 mag standards, anyway.

To review what this project is about -- most factory 357 rifle barrels have a sucky "toilet bowl" throat instead of a proper rifle throat. I want to see what a 357 will do with a good throat. And if that works out, I'll put a strain gage on it and use it for pressure testing my pet 357 loads.

My previous attempts to cut the perfect 357 throat did not work out -- either there was a problem with my homemade reamer, or most recently with the 1/2 degree throat, it just didn't want to shoot.

Perhaps if I had tried lots of different bullets and lots of different loads I would have eventually found something that shot decent, but that's not what this project is about. We're looking for the perfect 357 cast bullet throat, or at least a pretty good one, anyway. And nobody is even sure what the perfect cast bullet throat looks like!

So I will set the 27" Green Mountain barrel back and start over with a fresh 357 mag chamber. This time we'll try a 1.5 degree per side throat, because that's a very popular design.

I'll reuse the 357 maxi reamer to cut the chamber. The throat gets a separate throating reamer -- I like doing it separately so I can control the throat independent of the chamber. Here's the homemade 1.5 degree reamer. The .347" pilot is a very snug fit in the Green Mountain barrel, and the 0.379" section will be supported by the 0.380" chamber. The idea is that the reamer can't help but cut concentric with the bore.


While some say that "D" reamers do not require relief, I've found that they cut much nicer if you grind relief.
]

That's as far as I got today, this project will take a week or two working in my so-called "spare time."

[mtngun]

The usual 160 grain plain base spitzer. I had sized the bullets 0.360" before oven treating, but as it turned out the 0.360" bullets made the cartridge neck too big to chamber easily , so I had to resize the bullets to 0.3595".

-- 17.1 gr. WW 296.
-- Winchester Magnum Small Pistol
-- HVR lube
-- oven treated wheelweight
-- 1.725" COL (0.018" off the throat, as best I could measure)
-- lightly crimped into upper lube groove.

Results:
-- 2022 fps (way too hot, most of the cases required assistance to extract)
-- 0.42% standard deviation (excellent)
-- 0.75" mean radius at 100 yards (decent, but nothing to brag about)
-- barrel looked clean to naked eye
-- bore scope revealed very light lead streak in one groove, beginning 2 inches or so past the throat.

Complications:
-- 2nd group was shot with no cheek contact. Mean Radius = 0.81", Radial Standard Deviation = 0.85", Extreme Spread = 2.9".
-- 3rd group was shot with light cheek contact. Mean Radius = 0.70", RSD = 0.33", Extreme Spread = 2.2".


Conclusions and Lessons Learned:
-- the 1.5 degree throat is a decent throat. I don't know if it is the optimal throat, though.
-- This throat is not going to safely reach 2000 fps like the "bad" throat did. The COL is 0.105" shorter than the "bad" throat, so it effectively has less powder capacity. Plus the barrel is now 25" vs. 27" before.
-- it seems to shoot better with cheek contact than without.
-- why the excellent standard deviation? I credit the fairly deep seating, the light crimp, and the consistent fit in the throat.

Things to Try Next Time:
-- back off the powder charge until cases extract reliably. I'm guessing it'll end up at 1950 - 1975 fps.
-- try different weight bullets
-- size bullets 0.3585" (today's bullets sprung back to 0.3595" in a 0.3590" die, but the same die yields 0.3585" for air cooled wheelweight).
-- possibly tweak the COL, though I didn't have any chambering issues with it 0.018" off the throat.

[mtngun]

Last time the first-guess powder charge was too hot and extraction was difficult, so today we backed off the powder charge and experimented with different seating depths.

Also let's try this 140 grain plain base spitzer. I had tried it before in the "bad" throat and accuracy was mediocre, but maybe it would do better in the "good" throat?


Load was 17.1 grains WW296, 1.725" COL (0.018" off rifling), oven treated wheelweight, sized 0.359", HVR lube.

Not great but better than it did in the "bad" throat. There was very light fouling about 2" ahead of the throat, but not necessarily enough to complain about.


Next the usual 160 grain plain base spitzer, except we reduced the charge 0.3 grains to 16.8 grains WW296. Oven treated wheelweight, sized 0.359", HVR lube, and a very light crimp.


Here's the "standard" 1.725 COL (0.018" off the rifling). Not much difference in accuracy compared to last weeks too-hot load.


Next I tweaked the seating depth, 1.715" COL (0.028" off the rifling) and 1.735" COL (0.008" off the rifling).

Even though the 1.735" load was theoretically 0.008" off the rifling, a few rounds still required some effort to chamber, which is not a good thing in a Contender. Also, the velocity of the 1.735" load was higher, and a few of the 1.735" rounds were sticky to extract, suggesting that the pressure was a little higher.

All of the 1.715" COL and 1.725" COL loads extracted OK.


The deep-seated 1.715" COL had the best extreme spread. But since I only shot one group of each load, it doesn't prove much.


The deep-seated 1.715" COL had the best mean radius, and the 140 grainer was decent, too. Note that the "bad" throat averaged 0.55" mean radius with its pet load, so we haven't even caught up to the "bad" throat yet.


The deep-seated 1.715" COL also had the best Radial Standard Deviation (RSD). Supposedly RSD is a better indication of accuracy than either mean radius or extreme spread.


But the deep-seated 1.715" COL had more velocity variation than the others.

I expected the 140 grainer to have more velocity variation. It just doesn't ignite the powder as well as the heavier bullets


Next, Conclusions and Lessons Learned ....

[mtngun]

Conclusions and Lessons Learned
-- the deep-seated 160 seemed to do better, aside from having more velocity variation.
-- the 140 grainer did better than expected and is worth trying again.
-- 0.008" off the lands was sometimes hard to chamber and generally didn't do well.
--I've been shooting Contenders for 30 years and have never found top accuracy with loads that were a "jam" fit. Contenders prefer a load that chambers effortlessly, even if it means a jump to the rifling.
-- all of today's loads fouled oh-so-slightly about 2" ahead of the throat. It wasn't necessarily enough to be a problem, and didn't seem to get worse as more shots were fired. Still, it's interesting that the "bad" throat fouled less than this "good" throat. I suspect the 0.363"+ "bad" throat allowed bullets to enter the throat without shaving lead?

Things to Try Next Time
-- mount a strain gage.
-- try a firmer crimp on the 1.715" COL load. The lube groove lines up just right to make that possible.
-- shoot at least 2 more groups with the 1.715" load to establish a good baseline, since it seems to be my new "standard" load.
-- tweak the 140 grain load, perhaps trying 1.715" COL and a firm crimp.

There are a gazillion other experiments I'd like to do with this barrel -- different bullets, different lubes, etc., but my near term goal was to get it working reliably with a decently accurate load that I could use as a "standard" for experiments, and I've nearly accomplished that. Once I get my "standard" load dialed in I think I'll set this barrel aside for a while and move onto another new-to-me caliber.

[mtngun]

Retesting the 140 grain plain base spitzer, except this time seated a little deeper (1.715" COL vs. 1.725") and with a firm crimp.

-- 17.1 grains WW296, Winchester mag primer, 1.715" COL, firm crimp
-- 2052 fps
-- 1.12% velocity standard deviation (about the same as last week with a light crimp and 1.725" COL)
-- 1.35" Mean Radius vs. 0.73" last week
-- 1.77" RSD vs. 0.63" last week.
-- 4.1 Extreme Spread vs. 2.0" last week.
-- the barrel looked decent with the naked eye but a tight fitting patch revealed small slivers of lead. It was a little too dirty for my taste.



Conclusions and Lessons Learned:
-- the firm crimp and deeper seating depth made it worse, not better.
-- for the time being I will give up on this 140 grainer.

[mtngun]

Retesting the 160 grain plain base spitzer at 1.715" COL, except this time with a firm crimp.

-- 16.8 gr. 296, Winchester mag primer, sized 0.359", oven treated WW, HVR lube, 1.715" COL, firm crimp.
-- 1970 fps
-- 1.13% velocity standard deviation vs. 0.98% with a light crimp
-- Mean Radius = 0.96" vs. 0.70" with a light crimp
-- RSD = 1.34" vs. 0.43" with a light crimp
-- Extreme Spread = 2.85" vs. 1.63" with a light crimp
-- some cartridges were difficult to chamber. Those same cartridges were usually difficult to extract, too. I'm guessing that the hard crimp created a slight bulge.
-- the barrel looked clean to the naked eye, but I did not bother to check it with a bore scope.


Conclusions and Lessons Learned:
-- the firm crimp hurt accuracy.
-- the firm crimp may have also caused chambering problems
-- the firm crimp did not improve velocity standard deviation.
-- I will give up on using a firm crimp for the time being.

[mtngun]

Retesting the 160 plain base spitzer except with 1.720" COL and a minimal crimp.

-- 16.8 296, Winchester mag primer, 0.359", oven treated WW, HVR lube, 1.720" COL, minimal crimp.
-- 1979 fps.
-- 0.84% velocity standard deviation for 20 shots, vs. 0.39% for 1.725" and 1.735" COL
-- note the vertical stringing.
-- Mean Radius = 0.85" for both groups combined, but one group was a respectable 0.58"
-- RSD = 0.47" for both groups combined, but one group was a respectable 0.25". For comparison, last week's 1.725" COL did 0.49" RSD.
-- Extreme Spread = 3.1" for both groups combined.
-- the barrel looked clean to the naked eye. The bore scope revealed a wee bit of lead in the corners of two grooves. The other grooves looked clean. There were no slivers of lead on a tight fitting patch.


Conclusions and Lessons Learned:
-- this load showed some potential but was hurt by vertical stringing and high standard deviation.
-- in general this bullet/barrel/chamber combination has been hyper-sensitive to minor load tweaks.
-- in general this 1.5 degree throat has not shot as well as the "bad" throat that this barrel started out with.
-- since last week I had replaced the improvised front bag (just pieces of scrap foam and a mouse pad) with a "real" front bag. Maybe it liked the scrap foam better than the real bag?

Things to Try Next Time:
-- a few fire lapping shots ???? Because this throat seems to foul a bit more than the "bad" throat. I can't see anything wrong through the bore scope but maybe there is a microscopic burr or some such thing?
-- maybe go back to Lil Gun ???
-- maybe try a different primer ???
-- maybe go back to 0.358" diameter ???
-- if it seems like I am grasping at straws, I am, because I've already tried all the easy stuff and already fixed all the obvious problems.

[dpm6264]

Hi Dan,
Interesting how on your recent testing the bullet string walk was very consistent over and over starting left and walking horizontal to
the right and then down and then finally back over left for the final shots of the group. I don't know if that means anything but I
thought it was curious that it strung the shots the same group after group. Thoughts?
Do you think you have drawn any conclusions on firm crimp vs light crimp yet. I have always been curious about weather the firmness
of crimps can make a difference or not.

Not proper for this thread here but I shot the 35 rem this weekend with straight sized bullets with the push through Lee and believe
it or not they didn't shoot really any better than the crooked sized ones. Go figure. More work ahead.

Doug

[mtngun]

Interesting how on your recent testing the bullet string walk was very consistent over and over starting left and walking horizontal to the right and then down and then finally back over left for the final shots of the group.

Oh the numbers 1 thru 10 on the target don't mean anything, I just assign each hole a number when I am measuring the coordinates because it makes it easier to keep track.

Do you think you have drawn any conclusions on firm crimp vs light crimp yet.

This particular barrel & chamber does not like a firm crimp. When I say "light crimp" usually all I am doing it "tucking in" the flared case mouth.

I shot the 35 rem this weekend with straight sized bullets with the push through Lee and believe
it or not they didn't shoot really any better than the crooked sized ones. Go figure.

Cast bullets are always full of surprises. But at least you have ruled out the sizing problem.

[mtngun]

I finally got around to making a throat impression for this barrel.

The verdict on the throat is that ...... it's perfect. I wouldn't change a thing.

Let me explain the logic behind this throat. The leade begins immediately with no freebore per se. The taper starts at 0.362" -- it's deliberately oversize so that bullets can enter the leade without shaving lead at the transition between the chamber and the leade.

I dunno if the 1.5 degree per side angle is optimal for a 357, but it's a very common angle on benchrest guns so it should be "decent."

You can't tell from the photo but the rifling marks are even all away round, suggesting that the throat is concentric with the bore.


I was actually hoping that the throat impression would reveal a flaw, something that would explain why this very good throat doesn't shoot quite as well as the "bad" throat that this barrel started out with.

Since I can't detect anything wrong, I'll leave it alone other than I do plan to shoot a few firelapping rounds, for two reasons: 1) now that I have a borescope I can see that while the barrel is on the whole quite nice, there are a couple of spots that consistently accumulate fouling and 2) to knock off any sharp corners or machining marks in the chamber and throat.

Things to Try Next Time
-- shoot a few firelapping rounds.
-- possibly try a 1.5 degree nose die so that bullets can be nose-sized and loaded Ardito style.
-- try WW680 powder (it's out of production but I have a pound sitting on the shelf that I might as well use up).