[Sky C.]

Hello Mr. Stanton-

I'm new to this forum and am really enjoying what you have done with the site.  I was perusing some of the older posts regarding the .375 Winchester and note your recommendations for AA 1680 as being an excellent powder choice.

I have two questions I'd like to ask...

1.  Could you please confirm a load listed in one of your previous posts:

BTB .377" LFNGC / WW-375 brass / AA 1680 - 36.0 grs. / WLRP / 2123fps - Marlin 375 20" bbl.

In another posting you list:

BTB .377" LFNGC / WW-375 brass / AA 1680 - 30.0 grs. / WLRP / 2051fps - 20" bbl.

The load featuring the 36.0gr charge is considerably higher than that listed by Accurate Arms in their manual for a cast-250 bullet and I also note that the efficiency (fps/gr) is some lower by about 10fps/gr. comparing to your 30.0 gr load.
I wanted to check to see if this load was printed correctly or if there may have been a typo.


2. Question re: sized diameter of bullet and bore leading.  If a bullet is oversized compared to the groove diameter - is it more likely to lead?

I've slugged the bore on my .375 BB and have a groove diamter of .377",  The throat measures .3795".  I've been casting a bullet of my own design (.270" meplat, 310gr. GC design) that drops from the mould at .379" and have been shooting them at this diameter but am experiencing leading.  (primarily in the area just ahead of the throat)

Bullet BHN is about 12.5 (WW + 2% Sn, air cooled) with velocities running from 1500fps to 1750fps in a range of initial loads I've tried with different powders.  I'm truly surprised because my thoughts are that this is a fairly low range of velocities to experience this kind of problem.  Is it possible that the bullet being oversize vs. the grooves is the reason for the leading trouble?  Do you have any other suggestions as to where I may be running into trouble?

Any help you could offer will be much appreciated!!!

Thanks & God Bless-

Sky C.
Longmont, CO

 

[MikeG]

Sky,

Marshall has been pretty busy (quite a backlog of orders) so that's probably why he hasn't responded.

I'll do my best to help you out.

First, with ANY load that you find listed anywhere, work your way up slowly, preferrably with a chronograph.  That will tell you a lot about what is going on.

Cast bullets from different sources vary in alloy, hardness, lube, diameter, nose profile, bearing surface, how much powder space they take up in the case, and if they have gas checks or not, probably a few other things that I have missed.  So yes you will find load data that varies a lot.  Work up and if you are getting resonable velocities (ie about what you'd expect) with no pressure signs, then a variance of several grains of powder may not mean a whole lot.

In general, you want your cast bullets as big as will fit in the gun's throats.  So in your case 0.379" is correct, you can try smaller but leading will probably get worse.  You are probably going to have to go to a different lube or harden your bullets somewhat.  Solve the leading problem before you crank up the velocity.  If the bore feels rough when you slugged it, you may have to lap it as well.  Unusual for a gas check design to lead but could happen

Best results are generally found when the bullets are seated to touch the rifling when loaded.  If this doesn't match up with the crimping groove, may have to get a Lee factory crimp die so you can crimp at any length.

I'd try the longest possible seating first, even if you can't crimp (single load) and that might be a clue as to what will help.

 

[cast-n-blast]

SKY C,
       The first thing I'd do is harden those bullets up by water quenching, as it is the easiest way for the desired effect of a higher BHN(19-21). I believe I read you use LBT lube in an earlier post, so you're ok in that department. Then, as MikeG suggested, I'd seat those puppies out as far as possible to just kiss the lands. This serves 2 purposes. One, less bullet jump,for better accuracy, and two, more case capacity for more powder or less pressure. If leading is occuring in front of the throat, this is indicative of a rough bore in that area. Firelapping can and does work wonders.

          I personally use the RCBS .375 250 gr FN mold. They drop out at 270 grs and .377" when cast of straight WW. I've worked up to 2200 fps with AA1680, and fireformed .30-30 brass(more capacity,hence, more powder, less pressure). Groups of five run about 1.5", when shot from a cool barrel.

            Lord knows I'm no Marshall, But I've picked his poor brain to death talking and asking him questions about the .375. As a matter of fact, I hold him responsible for me buying 2 of the .375 Marlins. Never regretted it a second. Hope this helps you out.

                         Jeff

That mold of yours sounds very interesting. Oughta pack plenty of wollop ! Who made it for you?

 

[Sky C.]

Mike & Jeff-

Thank for the suggestions.  I must admitt to being a bit perplexed by this one.

a) Have already fire-lapped the barrel - when clean - it feels very smooth including in the throat region.

b) At the velocity range I've been at and higher - I have not experienced leading with an air cooled WW alloy, 12.5 BHN in other guns (a .348 Win on the smaller bore side and .45-70 on the higher side).  I WILL try hardening the bullets but really would prefer not to unless it becomes my last option.  The reason to want to stay on the softer side is that I want to use this on elk and I'd prefer to get some expansion if possible.

C)  Leading toward the chamber end is supposedly most often associated with gas cutting toward the base of the bullet.  Given that I have a good fit in the throat & a GC base - I AM puzzled.

Loading to touch the lands - I'd love to but unfortunatly that won't happen.  There is quite a bit of freebore to this chamber (on the order of .250".  Seated out to touch the lands - the OAL is so long that the case can't even be ejected from the gun (Win M-94).

Any other thoughts or suggestions welcome.

As to the mould - had Mr. David Mos of Mena, AR cut it for me.  Lathe bored, cast iron.  It's a nice mould and turn around time was excellent.

Thanks-

Sky C.
Longmont, CO

 

[cast-n-blast]

Sky C.,
        With a meplat of .270", I wouldn't worry about expansion, as that nice flat nose will create a permanent wound channel about 1-1.5" thru and thru any elk, at the velocities you're pushing it, without any expansion at all. Something to think about.(I obtained this info. from the bullet casters bible, "Jacketed Performance With Cast Bullets" by Veral Smith. It can be purchased by going to sixgunner.com)

                       Jeff

 

[MikeG]

Hmm.... yes gas cutting near the throat shouldn't be happening with a GC bullet.  Strange....

Maybe a little more crimp, to build up pressures and maybe slug up the bullet just a bit before the powder gas gets loose.  How about a Lee factory crimp die?  With that size bullet, odds are that you are getting plenty of neck tension from the case already.

If you can't seat them to the rifling, then seat as long as you can.

Best of luck.... this one sure sounds perplexing, especially as you have already lapped the bore.

 

[cast-n-blast]

Sky C.,
        Without knowing the history of your gun, I've narrowed down the  leading problem, just forward the throat,to two possible reasons. One, the gun was shot alot, previously, with jacketed rounds, and due to poor bullet fit(.375 jacketed bullet, .377 bore) in the throat and groove areas, gas blowby occurred, eroding your barrel area, just ahead of the throat. This would make this area extemely rough, something more fire lapping could improve. You know a rough surface wreaks havic with cast bullets.

           The second, and better of the two scenarios, is heavy copper jacket buildup, that was not removed, prior to shooting cast. Every trace of copper jacket fouling needs to be removed. Copper fouling is usually worse in the area ahead of the throat, due to the gas blowby. Although the barrel may appear clean from the muzzle end of the barrel, traces can be present near the breech end of the barrel. Do the old copper solvent patch test.

             Jacket fouling acts as an agent for the lead to adhere to the bore.Think about it, a copper washed steel gun barrel, hot tin-lead alloyed bullet, a nice wax or grease based bullet lube for flux, and presto, all the ingredients for a soldered gun barrel.

             A harder cast bullet would be more resistant to the heat involved, and may take care of the problem itself. Something else to try after the copper solvent patch test.

              Hope this helps. Please let us know if this works. My curiosity is aroused.

                              Jeff

 

[Sky C.]

Gentlemen-

Thank you for your comments and advice.

Mike-

Crimp:  Good idea.  However, already using Lee Factory Crimp Die with a heavy crimp.

Seating the bullet out farther:  Definitely will try.  Have not yet experimented with how long I can go and still get to function through the action.

Jim-

Interesting thoughts you bring up.  I purchased the rifle used at a show so don't know the exact history.  I do believe it was a jacketed bullet gun but based on overall condition of the rifle (appeared to be new) suspect it probably didn't see much use.  I suspect that the bore is not showing signs of erosion however I don't have a borescope and so don't really know.  When clean (???) the bore seems very smooth in the area ahead of the chamber.

Jacket fouling:  You know - I really hadn't given the barrel a serious initial cleaning before I began shooting CB's.  Coincidentally though at the end of my last range session - I cleaned out the copper while still at the range and shot a handful of factory loads.  This was more to get a reference for making case expansion measurements for watching pressures as I continue load development but also to get a relative baseline for accuracy.  (Factory accuracy performance is pretty darned good - but I'm planning on this being essentially a CB proposition only.)

Anyhow - upon returning home I did go to work to seriously clean the bore following those jacketed rounds.  For only a handful of shots - there was sure a lot of indication of jacket fouling.  I worked it over fairly good with Shooter's Choice copper remover and then swapped back to Ed's Red, then to RB-17, then to Flitz,... patched out the bore with dry patches between to keep from creating some kind of really nasty concoction in the bore.  The thing is however, I worked with each of the products until the bore was showing "clean" only to find when I switched to the next that it would go to work on something else in the bore and indicate some type of fouling.  The gun has sat for the week now and I'm thinking I'll pull it out and start over again to see if in fact - I really do have the bore clean.  Nothing would be finer than to find that this is the problem and for "Beauty" to settle down and "act nice".

I'll report back after some more work.

Thanks again-

Sky C.