6x45 Contender Rifle

[mtngun]

Today we tested the 6x45 to see if the headspace problem was fixed.

First up, a retest of yesterday's IMR4350 load:

-- 84 gr. bore rider with 0.237" nose
-- 2.450" COL (0.015" away from contact)
-- 27 gr. IMR 4350 (that's all that will fit in the case)

-- chrono was on the fritz so I only got one reading, 2437 fps.
-- 10 shots in 4 3/8" at 100 yards, about the same as IMR4350 did yesterday.
-- all cartridges chambered easily and the the action never popped open, yea !

Not a great group but at least it was a group not a pattern.


Next, the same bore-rider except with WC844 powder:

-- 21.5 gr. WC844
-- Federal benchrest primers, because I had a partial box I wanted to use up.

-- 2514 fps
-- 2.8% velocity standard deviation -- that's terrible!
-- 10 shots in 8 1/4" at 100 yards (compared to 7.05" the last time I shot the bore rider with WC844).
-- all cartridges chambered easily and the action never popped open.

This is a pattern, not a group.


Next, the same bore-rider except with WC845.

-- I couldn't dial in a 2500 fps load because the chrono went on the fritz. So I just guessed at a powder charge.
-- 22.8 WC845
-- Federal benchrest primers

-- 2701 fps (the chrono recorded only 4 shots)
-- 3% standard deviation, but you can't trust SD for only 4 shots.
-- 8 shots in 7.8" (I only had 8 bullets left )
-- all cartridges chambered easily and the action never popped open.
-- the bore was clean as a whistle to the naked eye, and a tight fitting patch came out clean.

This is a pattern, not a group.

Conclusions and Lessons Learned:
-- the headspace problem seems to be fixed, yea !
-- the improved accuracy with IMR4350 seems to be repeatable.
-- it looks like the firelapping did reduce fouling because it used to begin fouling at 2600 - 2700 fps but today there was no fouling at 2700 fps.
-- WC844 still shot wild patterns, suggesting that the improvement in accuracy was due to IMR4350 and not due to the other changes
-- WC845 does not seem to be compatible with this barrel, either, though admittedly I was not able to test it at 2500 fps.
-- the Federal Benchrest primers that I used today were probably not the best for ball powder.
-- no conclusions one way or the other about the long bore riding nose other than to say there was no improvement with WC844, only with IMR4350.

Things to Try Next Time:
-- I took the chrono apart and cleaned the sensors again, but didn't see anything wrong with it. The chrono was 100% reliable before it got rained on, since then it has been iffy on 6mm though it works OK with 22LR and 357. Maybe the rain did some damage to the circuits? I'll give it one more chance before I give up on it.
-- The IMR4350 tests showed that powder makes a big difference so the next step will be to test a variety of powders.
-- if I find a powder it likes better, then I'll switch to experimenting with bullets, but for now will stick with the long bore rider.

[mtngun]

When I left off, the chronograph had been missing many 6mm shots, so I took it apart and cleaned it, but didn't really find anything wrong with it. Today I mainly wanted to shoot the 6x45 over the chronograph to see if the chronograph would behave itself. In the process, I experimented with several different powders:

I only shot one 5-shot group for each powder, so that's not enough to prove much. Still, it was enough to weed out the worst performing powders, like IMR3031.

Grains	Powder	Bullet Weight	Velocity ES	Group for 5 shots	Average FPS
23.0	Varget	68	24	6.5"	2504
25.3	Ramshot Big Game	78	41	5.75"	2450
25.5	WW 760	68	48	4.9"	2528
27.7	RL 19	78	59	4.45"	2377
23.5	WW 748	68	84	8.0"	2575
22.5	IMR 3031	68	115	11.0"	2636

Conclusions and Lessons Learned:
-- Varget had the most consistent velocity.
-- I couldn't stuff enough RL 19 in the case to reach 2500 fps.
-- I'm nearly out of Big Game so scratch it off the list.
-- That leaves WW760 and Varget as the the best powders of the bunch that are capable of shooting 2500+ fps.
-- In general the faster powders shot patterns while thet he slower powders shot groups (4" - 6", but still a group). This is consistent with Colonel Harrison's recommendation to use slower powders for high velocity cast.
-- If the Colonel Harrison rule is true, then it may be that I need more case capacity, so I can use a slower powder.
-- the chrono recorded all but one shot, and that one shot was at a can off to the side of my usual target board, so for now I will say that the chrono is fixed. Knock on wood, etc..

Things to Try In the Future:
-- retest Varget and WW760
-- try a lighter bullet, say 55 grains, with the theory being that less pressure will be required to hit my desired velocities.
-- recut the chamber to a 6-30. I had originally considered using a 6-30 chamber, but everyone said that the 6x45 was more efficient and could reach the same velocities with less powder. That's all true but the 6x45 achieves its efficiency by operating at higher pressure than a 6-30. If I used a bigger case then I might be able to reach my desired velocities using a slower powder at lower pressures, which should improve accuracy according to Colonel Harrison.
-- if the Colonel Harrison rule is true, then maybe I should be looking for a cartridge that requires a case full of 50 BMG powder to push my bullet to 2700 fps ? Maybe a 6mm-06? I don't know if anyone has ever attempted something like that with regards to high velocity cast ?

[mtngun]

Since last time I honed my 2-diameter nose die from 0.2366" to 0.2371", and cut a mold for a 57 grain spitzer.

The spitzer drops out as a 1-diameter loverin, but thanks to the magic of nose dies, it's easily converted to a tapered bullet that creates a glove fit with the throat and bore. By adjusting how deeply the bullet is run into the nose die, it can be arranged for the bullet to be touching the lands with only the gas check seated into the neck. This is the next best thing to breach seating. The general concept is associated with benchrest shooter John Ardito so I sometimes refer to it by his name.

Today's mission was to test the 57 grain bullet and to do more tests with the slow powders that performed best last time.

--57 grain Loverin, sized 0.245"
--23 gr. Varget
-- 2.160" COL, 0.015" away from contact
-- 2 different kinds of primers (still using up partial boxes of 30 year old primers )
-- 2455 fps
-- 2.4% velocity standard deviation (terrible )
-- 7 shots in 3.2"

Same load as above except Ardito-style
-- 2.290" COL, 0.015" away from contact
-- CCI #41 primers
-- 2447 fps
-- 1.74% velocity standard deviation (poor)
-- 10 shots in 2.85"

-- 57 grain Ardito
-- 27 gr. IMR 4350
-- 2.262" COL, 0.015" away from contact
-- CCI #41 primers
-- 2558 fps
-- 0.95% velocity standard deviation (so-so)
-- 10 shots in 1.75"
-- mean radius = 0.63"
-- radial standard deviation = 0.203"

-- same 57 grain Ardito load as above except with WW760 powder
-- 25.2 gr. WW760
-- 2398 fps
-- 0.86% velocity standard deviation
-- 10 shots in 2.3"
-- mean radius = 0.64"
-- radial standard deviation = 0.514"

-- same 57 grain Ardito load as above execpt with more WW760 powder
-- 26 gr. WW760
-- 2576 fps
-- 1.07% velocity standard deviation
-- 10 shots in 1.35"
-- mean radius = 0.47"
-- radial standard deviation = .17"

-- same 57 grain Ardito load as above except with more WW760 powder
-- 26.6 WW760
-- 2647 fps
-- 0.78% velocity standard deviation
-- 10 shots in 2.2" (1" horizontal x 2.2" vertical)
-- mean radius = 0.8
-- radial standard deviation = 0.14"


Conclusions and Lessons Learned:
-- this barrel prefers slow powders and light bullets. Perhaps because that combo produces lower pressures and gentler acceleration ?
-- WW760 seems to be the best powder so far. It was also the best in my hi-vel 30-06 loads.
-- IMR 4350 shows potential but you can't stuff enough into the case to reach my goal of 2700 fps.
-- it seems difficult to achieve low velocity standard deviation with the light bullet. It just doesn't have enough resistance to make the powder burn well.
-- based on only one comparison group, it seems the Ardito style is more accurate than the Loverin style, but I should really do more comparison testing before I make a final judgment.
-- the barrel was never cleaned today, and had not been cleaned after the previous shoot, either. At the end of today's shooting, I could not see any lead fouling with the naked eye, just some powder residue. I pushed one dry patch through to remove the powder residue, then it was clean as a whistle.

More Things to Try:
-- stick with WW760 and the 57 grain spitzer
-- tweak the powder charge
-- tweak the seating depth
-- possibly try a filler to reduce the vertical dispersion
-- possibly try a different primer to reduce the vertical dispersion
-- try linotype rather than oven-treated WW. Lino is not harder or "better," but my theory is that because the bullet would weigh less in lino, less pressure would be required to reach my desired velocity. Less pressure = less bullet deformation.
-- try powder coat.
-- try sizing 0.246" instead of 0.245". If nothing else it might improve the ignition and help reduce vertical dispersion.
-- I'm still toying with the idea of recutting the chamber to 6-30, so I could reach the same velocities at lower pressures. But I want to keep playing with the 6x45 until I run out of ideas.

[mtngun]

A few more loads with the 57 grain spitzer, attempting to walk the powder charge up to 2700 fps:

0.2cc shot buffer on top of powder charge
-- 26 gr. 760
-- 57 gr. spitzer sized 0.245" x 0.238"
-- #41 primer
-- 2.261" COL (0.015" away from contact)
-- 2544 fps
-- 0.57% standard deviation (pretty good )
-- 10 shots in 3.2" at 100 yards

No buffer, increase charge
-- 27 gr. 760
-- 2.266" COL (0.010" away from contact)
-- otherwise same load
-- 2618 fps
-- 0.92% standard deviation
-- 10 shots in 2.6"

No buffer, increase charge
-- 27.5 760
-- 2.266" COL (0.010" away from contact)
-- otherwise same load
-- 2698 fps
-- 1.42% standard deviation (poor)
-- 11 shots in 1.85"


Conclusions and Lessons Learned:
-- the buffer did indeed reduce standard deviation, but for some reason it hurt accuracy.


Things to Try Next Time:
-- keep tweaking the powder charge & seating depth
-- 0.246" instead of 0.245"
-- perhaps try a different filler

[mtngun]

Today we tried tweaking loads with WW760 powder and the 57 grain and 78 grain spitzers. We also tried a new 46 grain spitzer.

All of today's loads used oven treated wheelweight, nose-sized, lubed with Rooster HVR, and a CCI #41 primer. The 46 and 57 grain bullets were sized 0.246", but the 79 grain bullet was sized 0.245".

Quickload believes this 46 grain spitzer requires a mere 22,000 psi to hit 2700 fps when pushed by WW760.

-- 27 gr. IMR4350
-- 2.180" COL (jam fit)
-- 2498 fps
-- 2.01% velocity standard deviation
-- 11 shots in 4.38"

-- 27.5 WW760
-- 2.171" COL (deeper than before, but still making contact)
-- 2683 fps
-- 1.13% velocity standard deviation
-- 10 shots in 2.5"

-- 27.7 WW760
-- 2.160" COL (0.003" away from contact)
-- 2757 fps
-- 0.82% velocity standard deviation
-- 11 shots in 3.75"

Conclusions about the 46 grainer:
-- doesn't seem to be a tackdriver
-- WW760 better than IMR4350
-- accuracy best with slight jam fit
-- barrel was clean other than powder fouling.

The same 57 grain spitzer that has been used previously. Quickload believes this bullet requires 25,000 psi to hit 2700 fps when pushed by WW760.

-- 27.5 WW760
-- 2.270" COL (0.010" away from contact)
-- flash hole drilled out to 3/32"
-- 2686 fps
-- 0.99% velocity standard deviation
-- 11 shots in 2.5"

-- 27.7 WW760
-- 2.265" COL (0.015" away from contact)
-- flash hole drilled out to 3/32"
-- 2658 fps
-- 1.04% velocity standard deviation
-- 11 shots in 5.25"

-- 27.7 WW760
-- 2.265" COL (0.015" away from contact)
-- 2681 fps
-- 0.69% velocity standard deviation
-- 10 shots in 3.6"

-- 27.7 WW760
-- 2.275" COL (right at contact)
-- 2661 fps
-- 0.91% velocity standard deviation
-- 10 shots in 5.6"

Conclusions about 57 grainer:
-- no obvious improvement with 3/32" flash hole
-- best accuracy seems to be 0.010" away from contact
-- barrel was clean other than powder fouling.

The same 78 grain spitzer that has been used previously, except nose-sized and loaded Ardito-style, with only the gas check in the neck. The front band engraved the rifling ever so lightly. By the way, sometimes I may call this bullet 77 grains or 79 grains -- it varies depending on the exact batch of alloy I am using at the time.

Quickload believes that this bullet requires 34,500 psi to hit 2700 fps when pushed by WW760.

Note that I determine the jam fit point by poking a bullet into the throat with finger pressure, and using calipers to measure from the base of the bullet to the breach (very easy to do on a Contender). With this bullet, finger pressure was enough to engrave the front band ever-so-ligthly. That created problems as discussed below.

-- 27.7 gr. WW760
-- 2.451" COL (0.013" away from jam but lightly engraving front band)
-- 2623 fps
-- 0.56% velocity standard deviation
-- 10 shots in 2.1"
-- but 9 out of 10 shots popped the action open, suggesting the cartridge was engraving too hard.

-- 28 gr. WW760
-- 2.440" COL (deeper than before but still lightly engraving front band)
-- 2609 fps
-- 1.09% velocity standard deviation
-- 11 shots in 2.1"
-- but every shot popped the action open, so it was still engraving too hard.

-- 28 gr. WW760
-- 2.420" COL (deeper than before but still lightly engraving front band)
-- 2675 fps
-- 0.76% velocity standard deviation
-- 11 shots in 4.7"
-- 2 shots popped the action open, so it was still engraving too hard.

-- 28 gr. WW760
-- 2.400" COL (deeper than before)
-- 2639 fps
-- 1.04% velocity standard deviation
-- 11 shots in 2.95"
-- but every shot popped the action open, so it was still engraving too hard.

Conclusions on nose-sized 78 grainer with WW760:
-- this bullet had shot patterns with WC844 but shows potential with WW760.
-- gotta change the front band diameter so that it is a slip fit rather than an engraving fit
-- it may be that it needs to engrave in order to be accurate, but that just doesn't work in a Contender.
-- barrel was clean other than powder fouling.

All of today's results. No bragging groups, but no patterns, either.


The chrono worked perfectly until the very last string, when it missed a couple of shots and then the display went blank. Troubleshooting revealed that a rat had gnawed on the power supply wires, grrrr. I bet that was the root cause of the intermittent chrono problems I've experienced in the past few weeks?


Lessons Learned Today:
-- Previously I had assumed that the key to high velocity accuracy in this barrel was keeping the pressure low -- using light bullets and slow powder. But today I did not see a correlation between pressure and accuracy. All bullets shoot 2" - 5" when loaded Ardito-style and pushed by WW760. So it seems like the key is WW760 and the Ardito-style loading technique, not pressure. I don't know why WW760 is so much better than the other powders, but it was also my best powder in 30-06 hi-vel loads.
-- leading does not seem to be a problem in this barrel at 2700 fps.
-- all loads are darned sensitive to seating depth. Whereas 1-diameter bullets usually did best 0.015" away from contact, the Ardito-style loads seem to prefer contact. Unfortunately, Contenders won't lock the action reliably with a jam fit, so I have to err on the side of reliable chambering.
-- So far I have seen no clear advantage between sizing 0.245" vs. 0.246".
-- No clear advantage between the 3/32" flash holes vs. the standard flash holes, so I will stick with the standard.
-- the primer pockets on these cases haven't been cleaned since the 1980's , and it was tough to seat the primers fully, effectively increasing the COL on some cartridges.

Things to Try Next Time:
-- make the 79 grain front band a slip fit rather than an engraving fit.
-- try a fatter M-die spud such that the bullet can self-seat when the action closes, instead of causing the action to pop open. Currently my homemade M-die spud leaves the neck ID 0.2415", try 0.243" or 0.244" instead.
-- clean the primer pockets.

[mtngun]

I couldn't find my primer pocket cleaning tool so I made another one. Take a scrap case, flatten the neck with a hammer, grind to shape.


A 0.2444" M-die spud replaces the 0.240" spud. It remains to be seen whether the 0.2444" spud will produce the desired neck tension. I want it loose enough that a jam fit bullet will self-seat when a cartridge is chambered, yet tight enough that the bullet won't move unintentionally.

[mtngun]

Today's experiments did not go as planned because I spent most of the day fighting a problem with the Contender action popping open. I assumed the load was to blame but now believe it was due to the fit of the locking lugs, a common problem with Contenders. But I'll still post the data because sometimes we learn as much from things that go wrong as from things that go right.

All of today's loads used oven treated wheelweight, HVR lube, CCI #41 primers, WW760 powder, and Ardito-style sizing and loading.

78 grain spitzer, nose-sized 0.246" x 0.237"
-- necks prepped with 0.2444" M-die
-- 2.480" COL (front band engraved lightly)
-- 26.0 gr. WW760
-- 2417 fps
-- 0.69% velocity standard deviation
-- 11 shots in 6.4" at 100 yards
-- 4 rounds popped the action open

Same as above except seated deeper
-- 2.445" COL (front band still engraved lightly)
-- 2450 fps
-- 0.88% velocity standard deviation
-- 11 shots in 3.6" at 100 yards

Sames as above except seated deeper and more powder
-- necks prepped with 0.2455" M-die
-- 2.435" COL (front band still engraved lightly)
-- 26.7 gr. WW760
-- 2533 fps
-- 0.99% velocity standard deviation
-- 11 shots in 3.7" at 100 yards
-- 3 rounds popped the action open

Same as above except seated deeper
-- 2.405" COL (front band still engraves, just not as far)
-- 2538 fps
-- 1.02% velocity standard deviation
-- 11 shots in 2 7/8" at 100 yards
-- 7 shots popped the action open

Same as above except seated deeper
-- 2.380" COL (front band barely engraving)
-- 2555 fps
-- 0.68% velocity standard deviation
-- 11 shots in 3" at 100 yards
-- 6 shots popped the action open

Sames as above but different nose die, 0.246" x 0.2365"
-- 2.480" COL (only gas check in neck, front band was a snug slip fit in rifling)
-- 2456 fps
-- 0.81% velocity standard deviation
-- 11 shots in 4.8" at 100 yards
-- 3 shots popped the action open

Next up the 88 grain spitzer, nose sized and loaded Ardito-style


88 gr. spitzer, sized 0.246" x 0.2365"
-- 2.560" COL (front band a snug slip fit in rifling)
-- 26.7 gr. WW760
-- 2466 fps
-- 0.68% velocity standard deviation
-- the first 5 rounds popped the action open. At that point I paused to work on the locking lugs, more later
-- after stoning the locking lugs, the remaining 5 shots did not pop the action open
-- no group measurement because the POI shifted after doing the locking lug work

Same as above except more powder and longer COL
-- 2.575" COL (only gas check in neck, front band a snug slip fit in rifling)
-- 27.2 gr. WW760
-- 2556 fps
-- 0.79% velocity standard deviation
-- 10 shots in 8 1/8" at 100 yards
-- the action never popped open, yea !

Today's groups: the 78 grain showed some potential but couldn't quite get it's act together. The 88 grain shot patterns.


Fixing the Pop-Open Problem
At first I assumed the action popping was caused by my loads engraving too hard. But the bullets were just barely grazing the rifling, the action closed easily with a "click," and I verified that the locking lugs were engaging decently by painting them with a magic marker and observing the wear pattern. Something was not right. So I gave the locking lugs a good going over. I could never find anything obviously wrong, but nonetheless I stoned the lugs to make the contact angle a little gentler, something that has worked well on my other TC barrels. After stoning the lugs I fired 15 shots with no pop-open incidents, so let's hope that did the trick.

The Stock Cracked
While I was working on the locking lugs I noticed that the Boyds stock had cracked where the Contender frame bolts to the stock. Ruh-roh. I gouged out the inside portion of the crack, filled the gouge with epoxy, and also expoxied a brass pin across the width of the stock. Then I lightly bolted the frame into the stock (after slathering the frame with grease so it wouldn't stick to the epoxy) and will let it dry overnight. Hopefully the epoxied pin will stop the crack and the epoxy bedding might help, too.

The lamination did not fail, rather the wood itself cracked.


Conclusions, Observations, and Lessons Learned
-- today's experiments were confounded by the pop-open problem so I can't draw many conclusions.
-- I was not impressed with the 0.2365" nose. It did not solve the pop-open problems and accuracy seemed inferior to the 0.237" nose.
-- the 0.2444" M-die still did not allow bullets to self-seat.
-- I also tried a 0.2455" M-die and it still did not allow 0.246" bullets to self-seat.
-- I conclude that self-seating loads are not practical for a Contender, though they may work in a bolt gun.
-- I'm inclined to conclude that long bore riding noses are not practical in a Contender.
-- I'm starting to suspect that the Ardito sizing and loading method works best when the length of the tapered leade is proportional to the length of the bullet. In other words, if you have a long bullet then a long leade would be best. If you have a short bullet then a short leade would be best. That's just a theory and much testing will be required to prove it.
-- the chronograph worked flawlessly today now that the rat-chewed wire has been repaired.

Things To Try Next Time and Down The Road
-- retest the 78 and 88 grain bullets with a 0.237" nose (assuming the pop-open problem is fixed)
-- try adjusting the nose-size so that the bullet seats deeper.
-- retest the 57 grain bullet with a jam fit (assuming the pop-open problem is fixed).
-- possibly recut the 2 degree leade to 1 degree, based on the theory that a longer leade would be better for the longer 78 and 88 grain bullets.

[mtngun]

When I left off I thought I had fixed the popping-open problem by stoning the locking lugs. But this morning the popping-open problem was still there with the long 88 grain bullet. 11 out of 11 popped open.

So then I switched to the 57 grain bullet, but 1 out of 10 popped-open. At that point I was fed up with the popping-open problem and went back to the drawing board.

As near as I could tell, the locking lugs were making decent contact. I did a little more stoning on the locking lugs but can't say that it did much good because there was nothing visibly wrong in the first place.

Yet if I clamped the barrel in a vise, I could wiggle the buttstock up and down 1/4" at the recoil pad, because of movement at the locking lugs.

I repeated the test with the 357 barrel, it also could wiggle up and down 1/4" at the recoil pad.

I repeated the test with a factory 7-30 barrel, it only wiggled up and down 1/8" at the recoil pad. So apparently all Contenders have some slop at the locking lugs, some are just worse than others You probably don't notice it if you are shooting a pistol because the pistol grip doesn't offer much leverage, but it's definitely noticeable on a Contender rifle, especially with the heavy barrel blanks that I am using.

Why did the factory barrel have less slop than the Eagle Arms barrels? I tried swapping the factory locking lugs and spring with the Eagle Arms locking lugs and spring, and lo and behold, that made the Eagle Arms barrel lock up just as tight as the factory barrel. There seemed to be two differences 1) the factory bolt spring is much stiffer than the Eagle Arm bolt spring and 2) the factory bolts are a bit tighter in their slot than the Eagle Arms bolts.

The wimpy Eagle Arms bolt spring is definitely a problem. I dug through my collection of springs and found a Wolff spring that was about the same or slightly stiffer than the factory spring, and installed it in the 6x45 barrel. It made a noticeable difference, it even sounds different when you close the action.


I've ordered some Mike Bellm heavy duty bolt springs, I'm hoping that they'll be even stiffer than the Wolff spring.

As for the fit of the bolts, when you receive the Eagle Arms stub kit you have to fit the bolts and some stoning is required, as they explain in their instructions. As they came from Eagle Arms the bolts were so tight that you couldn't even put them in the slot, so you have to stone the bolts here and there to make slide freely in the slot. If you try to make the bolts fit too tightly, the bolts will get stuck in the slot and the spring won't push the bolts out. So you have to keep stoning a little more at a time until the bolts move freely. That's how they ended up sloppier than the factory bolt. However, in hindsight the tight bolts were getting stuck partly because the Eagle Arms spring was too wimpy to overcome the friction of the tight bolt. Oh well, live and learn.

After installing the heavier Wolff bolt spring, I only had one pop-open the rest of the day, and that was with a jam-fit load.

[mtngun]

I'm not going to say that the Contender pop-open problem is fixed because every time I think it is fixed, the problem returns to bite me in the ass. Realistically, action lockup is a weakness of the Contender design and always will be, some barrel/action combinations are just worse than others. Whenever I hear someone say that the Contender is a strong design I just roll my eyes. It's actually a very wimpy design.

Anyway, back to shooting. I'm short on time so I'm only going to provide a summary rather than a detailed report. Here's today's target, the lower right group is the 88 grain and everything else is various tweaks to the 57 grain.


88 grain bullet at 2500 fps -- shoots patterns (11 in 6.8"). I'm going to give up on the 88 for the time being.

57 grain bullet at 2700 fps -- shows some potential, but can't get rid of the fliers. Best 10 shot group was 2.9", worst was 7". Some groups had vertical stringing, others had hortizontal stringing, others were round.

I'm guessing the wobbly Contender action and 2 piece stock are partly to blame for the odd dispersion patterns -- very small changes in how you grip the rifle make a noticeable difference in POI. That's true of any rifle but Contenders are definitely more sensitive than rifles that have a one piece stock. Sure, Contenders are accurate with jacketed bullets, but high velocity cast is a different ball game.

Seating depth -- as velocity increases, it becomes more important to seat close to contact or even engraving slightly. Unfortunately, Contender actions will pop open if you attempt a jam fit, grrrr. Somewhere in the neighborhood of 0.005" to 0.015" away from contact seems the best compromise. Even then, all it takes is one unburnt granule of powder in the throat to create a tight fit and make the action pop open.

Things to Try Next Time
-- focus on the 57 grain bullet
-- tweak the powder charge
-- tweak the nose-size depth
-- hopefully the Bellm spring will be an improvement

[mtngun]

The Mike Bellm bolt springs showed up. I don't have a way to actually measure the spring rate, but we can estimate it using the spring rate formula.

Eagle Arms -- 0.032" wire thickness, 17 lb/in, 8.7 lb max load.
TC -- 0.036" wire thickness, 42 lb/in, 12 lb max load
Wolff -- 0.038" wire thickness, 53 lb/in, 14 lb max load.
Bellm -- 0.044" wire thickness, 130 lb/in, 20 lb max load.

The actual force applied to the locking lugs will also depend on the spring preload -- i.e. the Wolff spring has more preload than the Bellm spring because the Wolff spring is longer. I didn't go to the trouble to calculate the preload for each spring, so I can't give you a number for the actual force on the locking lugs. My seat of the pants impression is that the Wolff spring is a tiny bit harder to open than the TC spring, and the Bellm spring is a tiny bit harder to open than the Wolff spring.

If you have an Eagle Arms stub I recommend upgrading to the Bellm spring.

For now, I have a Bellm spring in my 357 mag barrel and the Wolff spring in the 6x45. I'll shoot them side by side this weekend and see if I can tell a difference, but I think they are pretty close.