[TedH]

I tried some cast bullets in my 94 Big Bore today.  I was disappointed with results.  Accuracy was poor, about 4-5 inches at 50 yards.  There was considerable leading in the bore as well.  I was of the understanding that a bullet 1-2 thousandths over bore diameter was wanted.  My bore slugs .376, best I can tell.  I was using a 250 gr. bevel base bullet sized at .377 with a BHN of 16.  Powder was 30 grains of IMR-3031.  Do I need a slightly larger bullet?  Would a lighter powder charge help?  The load was right out of the RCBS Cast bullet manual.  Any other ideas?  Thanks, Ted

 

[IDShooter]

TedH,
   It's quite likely that the throat of your rifle is quite a bit larger than the bore diameter. Leading
in front of the throat area would be one indicator of this. I would try a larger diameter bullet if you have access to it. I haven't worked with a 375 before so I don't know if your load is hot or light, but experimenting up (if appropriate) and down with your powder charge may also improve your results. Let us know what happens!     ID

 

[MikeG]

Ted,

You might also try seating the bullet out to where it lightly touches the rifling.

This might end up with a longer OAL than will feed in the magazine, but try some single-loaded.  You probably won't be able to crimp them in the groove anyway, doing this.  If it works then you can hunt down a Lee factory crimp die and make your own crimp groove.

Also make sure that there is no copper fouling in the barrel.

 

[BCstocker]

Ted: That load in the RCBS manual was developed with a gas check bullet not a bevel base. They reported velocities just under 1500FPS. That is just about the velocity where soft bullets unprotected by gas checks start to cause problems in my experience. BHN of 16 would  indicate a kind of medium hardness and you'ld think it would be not too bad. Try the seating out trick previously mentioned and also try reducing your load 1 grain at a time and see what happens. I would also try Re 7 at the starting load recommended in that manual as well as progressively greater charges. If you are casting those bullets yourself you could  try lapping out your mould an additional .001-.002 as a little bigger than a .001 differential between bullet and bore usually works better. I have to say that other than for very mild loads I find gas checked bullets a lot easier to develop loads for. Leading also seems to be increased if the bore is not entirely clean of copper fouling so a good bore cleaner may be in order. Good luck in finding a workable combination.

 

[Sky C.]

Hello Ted-

I too am working on developing CB loads for my .375 Big Bore. I'd like to share a few thoughts about what I've found out so far...

I don't know you or how much shooting you've done with lever guns so if my comments seem elementry, please forgive me.

I've found that shooting lever guns off the bench for accuracy requires different techniques than shooting bolt guns. For starters - I've had best luck when using a sand bag front rest that is not packed to the point that it is hard. The guns are usually light weight and recoil off the harder rests in an inconsistent way for me. The softer bag really helps.

I've also found that lever guns tend to respond better to having the front rest placed as close to the receiver as possible. This position seems to be much better than further out on the forend or on the barrel.

Guns that recoil seem to respond better to being held onto tightly and pulled back into my shoulder firmly rather than to use a loose hold.

For accuracy shooting - using a bead sight is a serious challenge. I have experimented with a variety of different target shapes to try and find something that allows me to achieve a consistant sight picture. Obviously - your gun can only shoot as well as you can consistantly hold on the same point of aim. To date - I have not found many targets that allow me to achieve a consistant hold. The best so far is a large triangle oriented point down. The point is positioned above a very wide horizontal bar. The bar needs to be about an inch thinck at 50 yds. to be seen well. It should also extend a couple inches either side of the widest part of the triangle. The effect of this target in sighting is that the triangle allows you to locate a consistant hold from side to side. The horizontal bar is used to find a consistant vertical aim point.

All of the above is just some of what I've learnded about how to get the most out of my own shooting performance. I'm not hoppy with my results yet but I'm getting on the order of 1.25"H x 1.5"V at 50 yds. for 5 shot groups averaging around 1750fps. This with a 300gr. cast bullet, a tang mounted peep sight and the bead front.

As for CB's in the gun and leading - I am still trying to overcome this problem.

First some background. My bore sluggs .377" I have a custom bullet mould that runs .379", 300 gr. and is a gas check design. I made some measurements and found that there is considerable freebore for this chambering. My bullet needs to travel .270" before it reaches the rifling. Way too far to seat it out and even be able to chamber it let alone get it to feed through the magazine. I choose to load to max OAL which is also where the crimp groove is. The alloy I'm using is air cooled WW + 2% Sn. Lube is a mix of LBT blue and Darr formula. I use this lube in other calibers and find it sufficient to much higher velocities than what I'll be able to get out of the .375 Win. so am confident it is not the problem. Regarding hardness of the alloy - mine runs about 12.5BHN. This has performed well in my .45-70's at velocities to 1900fps and in my .348 Win. to velocities of 2200fps with no leading.

Initially I was getting extremely heavy leading. I used one of the lead remover kits for handguns where you pull a brass screen through the bore that is fitted to an expandible rubber mandrell... huge slivers of lead after only 5 shots.

At the recommendation of others on this forum and on the CB-L forum I then cleaned the bore - REALLY CLEAN. It helped some but I still got significant leading.

Some other gentlemen suggested that the bore for a CB gun actually needs to become seasoned - somewhat in the same way that a cast iron pan gets seasoned with use. A product was suggested that could be used to pre-condition the bore before shooting and between shots. The elixer is an automotive rust preventative material sold by the Eastwood company (www.eastwoodco.com) Part# 16017ZP. I got some and tried it. It has definitely helped. Now rather than needing to use a brass screen pulled through the bore. The leading is reduced and pushes out with a tight fitting patch.

I am still working to eliminate the problem completely. After giving the leading problem some further thought I have a suspicion that I may need to move to harder alloy. The reason I think so is because of that long freebore combined with a very fast 1:12 rifling twist. My thought is that the bullet already gets a good running start (.270") under a good deal of pressure before it first encounters rifling. When it does get there - the rifling twist is quite tight. I'm thinking it may be too much stress on the alloy and that it may be slightly stripping as it first enters the rifling. I have the heaviest leading in the area where the rifling starts and 4" to 6" in front of it. This would usually be associated with gas cutting at the bullets base but having a good bullet fit and a gas check - this simply should not be the case. That's why I'm thinking that my alloy may not be hard enough.

Once I run the next set of experiments with the harder alloy - I'll enter a post to let you know how it's going.

Good luck in your efforts - keep us posted on the results!

Sky C.
Longmont, CO

 

[Bartmasterson3]

It's sure good to have the forum back!

I don't know how smooth the bore of a Big Bore 94 typically is, but leading can be caused by a rough one. My experience with the 375 Win has been in a Marlin that has a sandpaper bore. Everything lead that goes through it causes leading...just have to scrub it out good every so often. Most of my load development for this round has been with hard bullets (20+ bhn) and checks. Re7 is the best powder I've used to date. Top velocity has averged about 2050 fps. This was with BTB 250gr LFN and 35.7gr of Re7 (SAFE IN MY GUN ONLY) in WW 38-55 cases seated to 2.560 OAL. Now that the national forest is open again (and I have a place to shoot) I've increased that charge somewhat and plan to shoot them this weekend. I believe that 2150 fps can be reached safely with these components.

If a rough bore turns out to be responsible you can try fire lapping. The BTB Tech Guide has step by step instructions for how to do this.