Problems with my M-375 UPDATE

[Goat]

Earlier this year I bought a NIB Marlin M-375 that had the original tag of where it sold for $189.99. Unfortunately for me it cost more than that to come into my possesion but I think I did OK anyway. I was unable to shoot it for sometime because of health issues but I did finally get to play with it. every load with every bullet made vertical strings. About that time I was able to return to work and had little time to shoot. So I took it to a shooting buddy to let him try other combinations. He finally got to the point where there was nothing left to do but remove the forearm and magazine tube. That is when he found that the mag tube was forced onto the gun and he had to use a plastic wedge to get the tube off the mag hanger. We think that this is the likely culprit and he will shoot it in the morning without the tube or forearm in place. We both think that the mag tube is just slightly too long and material should be removed from the end closest to the receiver. What do you think?
Goat

[TedH]

I suspect you are exactly right. I had to do the same thing to mine, just shaved a little off the end next to the receiver. I also had a sticky firing pin that I believe was causing some stringing due to inconsistent ignition, might be worth a look on yours too. Even now, I get the best groups letting it cool for 5 min. between shots.

[BenT]

I passed on one this summer, because I read a post somewhere that the bores were a little too big, causing accuracy issues. So you might want to slug the bore if nothing else helps.

[TedH]

I passed on one this summer, because I read a post somewhere that the bores were a little too big, causing accuracy issues. So you might want to slug the bore if nothing else helps.

I have not heard that about the M375, although I have not ever slugged mine. Mine will shoot jacketed bullets very well, and here's a 100 yard group with cast bullets from a Ranch Dog mold.

[Ranch Dog]

I've had two rifles, plus one NIB that I never shot. Both of the shooters shot very well with jacketed or cast. These rifles have a long throat and I have seen erosion in rifles that have been fed a steady diet of jacketed bullets. There is quite a jump for the seated bullet to the bore so there is a bit of wear. I personally think that this was done to relieve internal ballistic pressures quickly. A proper lead bullet will fill the throat.

[txpete]

what did you size your bullets to?.I don't own a marlin in 375 but I heard they need to be FAT to shoot well.
pete

[TedH]

what did you size your bullets to?.I don't own a marlin in 375 but I heard they need to be FAT to shoot well.
pete

I've only tried them at .379" because that is what Ranch Dog recommends with his mold for the Marlin. I suspect they need to be that large to fill the throat and get a good grip on the shallow microgroove rifling. But .375" jacketed bullets shoot good too.

[Goat]

Rifle was fired without the forearm and/or mag tube and groups shrank to 1-1/2" at 100 yards. Looks as if the tube or the forearm or maybe both are causing the vertical stringing issues. Point of impact at 100 yds changed by almost THREE FEET! Material will be removed from the tube to relieve the pressure it was causing. I'll update this with the final outcome as it develops. Thanks for all the input.
Goat

[TedH]

Good deal!

[pokey]

Rifle was fired without the forearm and/or mag tube and groups shrank to 1-1/2" at 100 yards. Looks as if the tube or the forearm or maybe both are causing the vertical stringing issues. Point of impact at 100 yds changed by almost THREE FEET! Material will be removed from the tube to relieve the pressure it was causing. I'll update this with the final outcome as it develops. Thanks for all the input.
Goat

huh. i'll be durned.

[Noah Zark]

Had almost the same problem with an early production Winchester 94BB in 375 back in the early 80s. A friend sold me the rifle really cheap ($200) because it patterned, he said. Sure enough, he wasn't kidding. I ended up stripping off the magazine tube, forend, band, etc. The group shrunk from 10-12" down to 1.25" to 1.75" depending on load. The recess in the underside of the barrel for the mag tube cap screw was drilled off-center and would torque the mag tube to one side. I enlarged the recess and aligned the mag tube, band, etc. and the groups are consistently under 2" and sometimes under 1.5" if I do my part with a particular handload using 31 gr of 3031 and a Moyer's cast bullet.

Noah

[Goat]

Mag tube was shortened and the gun reassembled then shot again for groups. The tight mag tube was indeed the problem since groups are now 1-1/4" to 1-1/2" at 100 yds with the 220gr Hornady and AA1680 at a chronographed 2300 fps. I think I need to go hunting with it now...
Goat

[Griff]

Congrats Goat. That's my first recommendation for any "poor" shooting tubs mag gun. There CAN be other causes, but that clears up 95% of 'em IME.

[Noah Zark]

. . . The tight mag tube was indeed the problem since groups are now 1-1/4" to 1-1/2" at 100 yds with the 220gr Hornady and AA1680 at a chronographed 2300 fps . . .

Congratulations!

Noah

[Tycer]

I've got all my 94s set so they rattle a bit. Made a difference on about half of them. Blue Loctite is my friend.