Revisiting the Marlin 357

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mtngun
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Re: Revisiting the Marlin 357

Postby mtngun » Sun Jul 14, 2013 9:04 pm

After giving up on the longer COL project, I decided to go with a 180 grain, 80% meplat, loaded to 1.61" COL.  Just for fun, I did a shoot-out between 2 otherwise similar bullets with different GtoB's.
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Here is the accuracy results for the 2 bullets.  5 shot groups at 100 yards.  The 1.6 GtoB averaged 2.93" vs. 4.88" for the 3.0 GtoB, but believe it or not the difference was not statistically significant according to a t-test.  That goes to show how difficult it is to prove anything about accuracy. :lol:
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Here is a typical group with the 1.6 GtoB bullet. Many of the groups had diagonal stringing (typical for the Marlin), and many of the groups had 3 or 4 shots in a cluster, with 1 or 2 flyers spoiling the group (also typical for the Marlin).
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Powder Charge and Velocity
Powder charge for the accuracy tests was 16.7 grains WC297 . WSRM primers, HVR lube, and heat treated wheelweight.  I had hoped for 1800 fps, but it only averaged 1745 fps (3.0 GtoB) and 1751 fps (1.6 GtoB).   I suspect the velocities are a little low because the loverider bullets with big GtoB's are too "slippery" to make the powder burn efficiently. :cry:

After settling on the 1.6 GtoB bullet, I walked the powder charge up to 17.0 grains, averaging 1790 fps.   I think I need a less slippery bullet if I want to hit my 1800 fps goal. :lol:

Then I removed the Mueller scope and re-installed the 5D peep sight, and sighted it in for the 80% meplat. My eyes are not what they used to be so I struggle to put 3 shots in 3" with the iron sight. Point being, it's good enough for woods hunting, and the practical limitation to accuracy is my eyes, not the rifle or the load.
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Conclusions about GtoB and Loveriders and Itty Bitty Bands
-- the itty bitty bands seem to shoot as well as anything else I've tried.   They don't necessarily shoot better, but they don't shoot any worse, either.

-- the loverider design seems to shoot as well as anything else I've tried.   Not necessarily better, but not worse, either.

-- normal powders may not burn efficiently with the slippery loveriders.   Contrary to popular belief, more slippery bullets are usually slower, not faster, because smokeless powder needs resistance to burn efficiently.

-- optimal GtoB for accuracy seems to be between 1 and 1.5, though there are a lot of variables.

What's Left To Do ?
I may recut the 1.6 GtoB mold to make the 0.349" bands 0.351". It doesn't seem to affect the accuracy, but I want a little more engraving resistance to boost the velocity (the Marlin's bore is 0.347" so the 0.349" bands do engrave).

Then I may have to once again tweak the powder charge to dial in 1800 fps.

Otherwise, I've done all I know how to do with the Marlin, with regards to hunting loads. Perhaps a lower velocity plinking load would be more accurate with a scope, but I don't have any interest in low velocity plinking loads, and the Marlin is not going to wear a scope. ;)

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mtngun
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Re: Revisiting the Marlin 357

Postby mtngun » Sun Jul 21, 2013 10:15 am

Update:

I did recut the bore riding bands, but they came out closer to 0.350" than the 0.351" that I intended.

So then I retested the velocity to see if the fatter bands boosted velocities as hoped:

16.8 grains WC297, 1.610" COL -- 1764 fps average for 3 shots at 15 feet from muzzle.

17.0 grains WC297 -- 1795 fps average for 3 shots.

So no, I wasn't able to increase the engraving resistance enough to boost velocity. Perhaps this "slippery" loverin design would be more compatible with a slightly faster burning powder like #9 or 2400, but I have plenty of WC297, so I'll settle on load of 17.0 gr. WC297.

Eventually I hope to pressure test the load after I get a 357 barrel made for my TC. In the meantime I can only advise that this powder charge seems safe in my gun with my bullet design, but your mileage may vary. :lol:

jbquack1
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Re: Revisiting the Marlin 357

Postby jbquack1 » Sun Jul 21, 2013 3:39 pm

That is moving right along for a slug that big.I would think for woods range hunting, that would handle quite a bit.

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mtngun
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Re: Revisiting the Marlin 357

Postby mtngun » Sat May 23, 2015 4:12 pm

An update on the Marlin 357 in this thread testing powder coated bullets.


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