Marlin 1894 throat

[levernut]

Veral,
My Marlin 1894, 44 Mag doesn't shoot cast bullets well above about 1300 fps.  I have tried oversize bullets and all the usual things but have not had much success.  It has the typical blunt Marlin throat so I would like to experiment with re-throating it.  I have an LBT mold, .434-280-LFN-GC and use LBT lube and H-110 powder.  I would like to shoot this bullet at 1650 fps.  What shape throat do you recommend?

[Veral]

  I think it is NOT a blunt throat, like the 45-70's have.  Both the 357 and 44 mag have long tapered throats to scoop up bullets shot from the speical cartridges.
 
The 280 gr LFN gc should be accurate at speeds to probably around 1900 fps or a bit over.  (I load a 300 gr to 1800 fps which is below max pressure.)

  Your the first customer to complain of poor accuracy with one of these rifles, so I'm suspecting that the bore is rough, which chews up the bullet and perhaps leaves it loose as it gets near the muzzle. 

  Don't rethroat until you have made a thraot slug and tried push through slugs to be sure the bore is straight and smooth.  (None are when new, and jacketed bullets won't smooth them out.)  The throat slug will tell you what the bullet has to deal with in getting started.  It could be tipping before it hit the rifling, if the chamber is greatly oversize.  You can tell how much by measuring a fired case to see how much larger it is than a loaded round.  The difference may be startling, and if it is great, it may be your whole accuracy problem.

  If you have lapped the bore and proven it straight and smooth using push through slugs, then do only the throat slug.  Of coarse, if I'm guessing wrong on something I've written above, set me straight.  And, as always, if you can't read your slugs well enough to trouble shoot the problem, send them to me.

  The fact that accuracy falls off when velocities reach a certain point leads me to believe the whole problem is bore roughness. 1300 fps is a very low velocity for that bullet / cartridge / rifle, to give up on accuracy.  --  I can't guarantee that pressures were exactly within industry standards, but I do recall driving my 250 gr gc LFN at a bit over 2200 fps with excellent accuracy, in my 44 Marlin, thisfrom a lapped bore. 

[levernut]

Veral,
Thanks for the info.  I lapped and slugged the throat years ago so I'll check the bore again to make sure there are no restrictions or rough spots.  I also shoot the max diameter possible and still chamber.  I believe it is a .433 or .434 diameter.

A bit more information; I can seat a 280 WFN to touch the rifling and the problems go away, but I cannot seat the LFN to touch the rifling and still keep it in the case.  At 1650 fps with a WFN, DV goes through the roof.  Does this substantiate your thoughts about alignment?

[Veral]

  When you reslug the barrel, keep in mind that driving a lead slug all the way through will tell you nothing about bore smoothness.  The LBT push through slugs are pure lead and have a tiny band which  offers so little resistence, once it is started, that it can be easily pushed through with a cleaning rod.  As it moves along the operator can feel every little bump and tight spot.  Lap until one goes through absolutely smooth frm breach to muzzle and the gun will handle heavy loads with accuracy, if a good bullet lube is used.

  If you can seat the WFN so it contacts the rifling you have a shorter than normal throat for these guns.  Don't change it.  It is already too long.  When you get the sluging done right and lap some more if required, hit us with your results and we'll finish up finding the problem if one still exists.

[levernut]

Veral,
I shot 80 more lap loads thru this Marlin (total 116 lap loads) and it still shoots the same.  I've fought this off and on for several years and have about given up.  Group sizes are 3.75 to 6.00 at 75 yards.  The first shot from each group was always a flyer to the right 4-5 inches.  In fact, the first shot of each group made a nice 1.00 group but it was always 4-5 inches to the right.  The only time this didn't happen with cast bullets is when I seated my 280 grain WFN to touch the rifling. 

If the bumps and restrictions are not gone after 116 lap loads then it's probably not going to be a shooter.

[Veral]

  I sure can't argue with your analization, but still believe there is a glitch which is being missed.  Please send me a half dozen sized and lubed bullets so I can do some fine measuring on them.  Perhaps I can find an answer in them.  When you send them, include your phone number, please, and I'll call you with my findings and opinions.

  You see, I rebuilt precision machinery for 25 years, and in all that experiance I found that precision is not a game of chance.  If something isn't right on any precision machine, it can be measured and fixed.  Guns are machines for precision launching of bullets.  My suspicion is that your bullet bases are not square.  Are you using Lyman sizer dies?  The stop plugs in these are never square, and can knock your gas checks off as much as .015 around the perimiter.  If you are using a Lyman sizer die, or if the stop plug doesn't show the fine radial lines of being lathe turned on the end, send it along with the bullets and I'll fix it.  I hope this is the problem.