Cast Bullet Association Blog Rss Feed

Optimum .30 Caliber Case Capacity for Lead Bullets

By John Ardito

(This article originally appeared in issue #48, March-April 1984)

I started shooting cast bullets in 1973 using a standard .308 Winchester, and if it wasn't for reading Ken Waters "Pet Loads" article in HANDLOADER #44, I would never have heard of the .308X1.5" cartridge. To prove to myself that the .308X1.5" is the best cartridge for lead bullets that we have to date, I decided to do an experiment.

By using one Hart barrel for all my testing, I could eliminate the possibility of one barrel being better than another. Step two, was to have six special reamers made up in .125" increments, starting at .308X1.250" through.308X1.875". All of these reamers had my special tapered throat .3125" to .300". All testing was done in the evening under ideal conditions.

My original intent was to start with the .308X1,250" reamer, and after 1,000 rounds of my best loads, rechamber the same barrel .125" deeper until I reached the full .308 Win, cartridge length of 2.015". I soon found that too small a case causes problems. The .308X1.250" case caused excessive pressure before I could get to 1800f.p.s. Using slower burning powder did not solve the problem, however, because I could not get enough into the case. Accuracy was only fair. The .308X1.375" case allowed me to get to 2000 f.p,s. before I ran into the same problem.

Next came the .308X1.5" case. This case allowed me to get 2200 f.p.s. with a 200 grain bullet, and no pressure signs. I even had space for slower powders, but maximum velocity with accuracy was 2200, The.308X1.625" was next. Pressures were lower, but I still could not achieve velocities over 2200 f.p.s, with accuracy. Accuracy in this case size was as good as the 308X1.5".After 1,000 rounds in the .308X1.750", I could for the first time see my average group size open up approximately .100" , The ,308X1.875" case showed another in-crease in group size of .100" . The full size.308 case wasn't any worse than the .308X1.875" .

I am not saying that you cannot shoot small groups with the big cases, because I got quite a few, but for consistent small groups I found the 1.5" and 1.625" best. I will try to explain why I think this is our best cartridge for lead bullets.

The .308X1.250' was the smallest case (left). used in Ardito's test: The full size .308 Win. case (right)

2200 f.p.s. seems to be the limit of any lead alloy bullet capable of shooting 10 shot groups under .600"consistently. The .308X1.5" case capacity is perfect in this respect. It will shoot a 200 grain bullet, using 26.5 gr of RL-7, at 2200 f.p.s. utilizing 90% of the case capacity. This is a hot load, and would recommend its use only in a strong action like the Remington 40X or M-700. When you think about it, the velocity is really very high from such a small case, especially from a 200 gr bullet. The full size .308 military match ammo, using a 173 gr bullet, is only 350 f.p.s. faster at 2550.

Cast bullets with long ogives, like the military M118-173gr, do not shoot as accurate as flat or round nose bullets. The pointed bullet does not have as much bearing surface in the bore and tilts to one side when fired. It then travels down the bore and out the muzzle, out of balance. This happens to some extent with all lead bullets, and is the major reason for the one flier in most groups.

To help eliminate this problem, I use a separate throating reamer, which is tapered. This same reamer is used to make a tapered bullet die. The die is used after the bullet is cast, lubed and gas checked. The tapered throat is 1.000" long, and starts at .3125" and goes to .300". The tapered bullet, except for the gas check, sits in this tapered throat and is aligned dead center with the bore. When fired, there is a smooth gradual transition from the throat into the bore. This procedure has improved my groups more than anything else I have tried in the last ten years. This system is so consistent that if my 5 shot groups get bigger than .400" or ten shot groups are bigger than .600" I get concerned. One ten shot group fired on my home range was taken to a benchrest match, and measured .343". One CBA score target was used to shoot 5 consecutive 5-shot groups, that averaged .278", with the smallest being .178".

There are many other things that come into play in order to shoot groups this small. These are listed below.

LOADING

My loading technique is a little different than most shooters, but is the same whether I'm shooting for practice or in a National Match. All loading is done at the bench, during the time allotted for the match. I use only one case until it wears out the primer pocket, which usually takes all of 2,000 shots. The reason one case lasts so long is I do not size the case. A hand tool is used to deprime and prime the case. Then the powder charge is thrown using a Culver converted Lyman measure. Now, you are probably wondering how I hold the bullet in the case, since I told you that I do not size my case. My chambering reamer has a special neck. The standard neck diameter dimension is .345". My reamers neck diameter is .350". When a case is fired in this chamber, it expands the case neck to.349" on the O.D., and .3125" on the I.D. This allows me to seat my .3125" diameter bullet in the case just up to the end of the gas check. No hand tools are needed to seat the bullet into the case. It is a hand-push fit, and the bullet can not be shaken out no matter how hard you try. It takes less than ten seconds to load a new round, and I have never run out of time of felt rushed to complete a 10-shot group.

BARRELS

First, you need a bench rest quality barrel. I like Hart barrels the best. I find the slowest twist that will stabilize the bullet the best. I use a 1-14" twist, and to my surprise, it stabilizes my long 200 gr bullet at 2200 f.p.s. A 1-12" twist would be my second choice. The slower twist does less harm to the bullet. A 1-9" twist gave me my worst groups. I had to drop velocity over 300 f.p.s. in order to get close to the same accuracy.

ACTIONS

Next would be a good strong action, with plenty of bedding surface with no magazine cutout, unless it is sleeved.

STOCKS

I have always used wood, but have just received my first fiberglass stock blank, and will have it finished by nexts pring for testing. I think the actual bedding is more important than what material the stock is made from, but time will tell. I use Devcon F for bedding all my rifles.

POWDER

I have yet to find anything better than ReLoder-7 for lead.

PRIMERS

Federal Lg. pistol primers gave me the best accuracy.

BULLETS

This is where most lead shooters go wrong. There are only a few good .30 caliber bullet designs that can be bought off the shelf. The best are the RG-4, 311335, 311299, 311284, 311290. These bullets are all of about the same weight, and have long forward bearing surfaces for support when fired. They all have short round or semi-flat noses. The forward bearing surface of the bullet should never be smaller than .301". Another reason I like these long, heavy bullets, is they retain more of their velocity at 200 yards than lighter bullets do. If you use a lighter bullet or a bigger case, you do not gain anything, because the maximum velocity for bench rest accuracy to date is 2200 f.p.s. with lead bullets. I have yet to find out why this is the velocity limit. I have used alloys harder than lead, but this doesn't seem to be the answer. Barrel leading is not the problem, so I guess the lube is OK.

Good Shooting,

John Ardito

Big Thanks to Glenn Latham for sending this Article in to be posted on the Blog!!

]]>