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Re: Revisiting the Marlin 357

Posted: Sun Jul 14, 2013 9:04 pm
by mtngun
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.

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:

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).

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.

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. ;)

Re: Revisiting the Marlin 357

Posted: Sun Jul 21, 2013 10:15 am
by mtngun

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:

Re: Revisiting the Marlin 357

Posted: Sun Jul 21, 2013 3:39 pm
by jbquack1
That is moving right along for a slug that big.I would think for woods range hunting, that would handle quite a bit.

Re: Revisiting the Marlin 357

Posted: Sat May 23, 2015 4:12 pm
by mtngun
An update on the Marlin 357 in this thread testing powder coated bullets.