Can I get better accuracy with a bullet closer to bore size?

[tazman]

First a little background. I own a 357 mag revolver.Taurus 7 shot tracker with 6" barrel. Bore has been slugged and measures .3572. Cylinder throats are consistent at .358 =/-.0002. I have been getting good accuracy from .358 sized boolits. I tried a few .357 sized boolits as a test with medium 38 special loads and the accuracy was phenomenal. One large hole at 20 feet and no leading after 60 rounds.
My question is, would this apply to my 9mm also?
I am currently sizing my boolits to .357 and getting good but not exceptional accuracy. My bore slugs at .3552 and seems to be smooth throughout, no tight spots. I am not getting any leading from the .357 sized boolits. I am just wondering if I might benefit from a size nearer to the bore size.
I am hoping all the experience and knowledge on this site can give me enough information to decide if I would be wasting my money on another sizing die.

I welcome all your input and experience.
Thanks in advance
tazman

[Larry Gibson]

I've shot a lot of cast bullets sized .356 through numerous 9mm's with excellent accuracy. If the groove diameter is .356 or smaller accuracy can be very good. As you have found with your .357 sized cast bullets in .358 throats with a .357 groove diameter barrel accuracy can be excellent even if the bullet does not "fit" the cylinder throats.

Larry Gibson

[DrCaveman]

I've shot a lot of cast bullets sized .356 through numerous 9mm's with excellent accuracy. If the groove diameter is .356 or smaller accuracy can be very good. As you have found with your .357 sized cast bullets in .358 throats with a .357 groove diameter barrel accuracy can be excellent even if the bullet does not "fit" the cylinder throats.

Larry Gibson

Wait, has the King been dethroned in this case?

I guess nothing should be taken for granted in the quest for accuracy, eh? Every situation & gun is a little different, it seems. Sure makes it hard to separate wheat from chaff.

Sure inspires me to just 'go try it', though! As long as basic safety guidelines are followed, it sure appears to me that the sky is the limit for experimenting and...there are no rules!

Sometimes the books dont have the answer.

[rintinglen]

There are rules of thumb, but not all thumbs are the same size.
Different guns respond differently, and what works for most may not be best for all. Lyman has recommended sizing to bore diameter for years. Most, including myself, have found that one or two thousandths larger makes for less leading. But not always. I had a S&W Model 27 that loved hardcast, commercial .357 boolits; the same ones that would line my Model 66 with lead. .358 sizer, and voila, the leading virtually disappeared.
The beauty of this hobby is experimenting to get that perfect load that makes your gun do what you want!

[Old Caster]

Tazman, it mostly depends on what size the bullets still are as they enter the bore. The smaller the case is, the more likely it is to swage the bullet down or as you know a cylinder can make them smaller than sized before getting to the bore. I feel that the harder a bullet is the better it is to have it right at bore size or very little more. I don't like them a lot larger than the bore and have had better accuracy if they are close and the smaller the diameter the more important it is. I think this is because there is very little disfigurement of a bullet that is .453 getting squeezed down to .451 compared to something that is .225 getting squeezed to .223. The smaller bullet is being upset more percentage wise.

That being said, I had very poor results shooting .452 and .453 45 ACP hard cast commercial bullets out of a match .45 barrel compared to .451 from the same barrel. With the same barrel, I can't see any difference between .451 sized bullets compared to .452 sized bullets that are cast soft but how big the bullet is as it leaves the case in each example is largely unknown. You can pull a bullet with an inertia puller and measure but that is quite difficult to do definitively especially to a thousandths of an inch.

I would say that it would be possible to be better if you sized smaller but first I think you should at least attempt to measure a pulled bullet to see what it is after being swaged by a case and crimp because you might find that it is already smaller than you think it is especially with a stiff case like 9 mm is.

[dtknowles]

I don't know how accurate your current 9mm loads are but I don't know any application of the 9x19 that really benefits from minor tweaks to accuracy. Three or even 4 inch groups at 25 yards are not much of a handy cap as long as it is 99.999 6 sigma reliable. I switched to .357 for my 9mm loads and now I see a occasional failure to feed to battery in my StarLite (BKM or sum such). I am about to go back to .355, I was not having problems with any of my 9mm's but bigger seemed better but it is not really. It was not more accurate. The only 9mm's I have that accuracy might really matter are my HighPoint carbine and my EAA Witness and still a fraction of an inch is nothing and more than I think you will get.

Tim

[MtGun44]

ONLY Mr. Target knows the answer.

All guns are a thing unto themselves.

Bill

[DeadWoodDan]

rule of thumbs also apply to the alloy and hardness. Don't go down this road until you are really commited to the firearm and are prepared to loose sleep.

[Iron Mike Golf]

Some thoughts:

1. I am assuming that you miked the bullets (.358 vs .357) and have verfied they are indeed being sized to those diameters and are also round after sizing.

2. So, the .358s are likely not being sized further by the cylinder throats, but are being sized to .357 by the barrel. Guess where the excess alloy on the base drive band is going. A little micro-skirt, yes? I wonder if the bullet base is uniform all the way around after exiting the muzzle and before pressure drops.

[tazman]

Some thoughts:

1. I am assuming that you miked the bullets (.358 vs .357) and have verfied they are indeed being sized to those diameters and are also round after sizing.

2. So, the .358s are likely not being sized further by the cylinder throats, but are being sized to .357 by the barrel. Guess where the excess alloy on the base drive band is going. A little micro-skirt, yes? I wonder if the bullet base is uniform all the way around after exiting the muzzle and before pressure drops.

Answer to question1: Yes I did mike them and they are round and the bases are sharp.

Question 2: I hadn't considered that. I find that very intriguing. I wish I had some way to recover a bullet after firing so that any "micro skirt" would remain intact.

Would a hard cast bullet (water dropped linotype) be more or less likely to do that than a softer alloy?

I guess I will have to get a smaller sizer and see if things improve.
I could go all the way to .355 since that is what my bore mikes. May just need to purchase a few bullets at that dimension and see if they work better.
Thanks for the replies everyone.

[tazman]

Old caster wrote:I would say that it would be possible to be better if you sized smaller but first I think you should at least attempt to measure a pulled bullet to see what it is after being swaged by a case and crimp because you might find that it is already smaller than you think it is especially with a stiff case like 9 mm is.

I pulled several of my cast bullets to check on that very thing during the original setup for the pistol. The cases are NOT resizing the bullets. I am using a very hard alloy currently(water dropped linotype) and a minimal taper crimp. Just enough to keep them from moving during firing. The bullets are the same size after being pulled as before I loaded them. The loaded rounds seat easily in the chamber with no forcing necessary.
Since I am currently sizing .002 larger than the bore, I was wondering if that was too large and needed to be closer to .355?

[MT Gianni]

Before trying to improve things you must know your base line or starting point. I also like to know what a gun does with factory loads or at least j-words. I find it rare that I can improve with jacketed groups with my cast. I may equal them and will kick them to pieces regarding cost but I like to know where I stand.

[Old Caster]

I think a harder bullet is a lot less forgiving than a soft one and feel that the harder they are, the more important exact sizing is. I also think that soft lube is more forgiving and relegate myself to put up with the sticky stuff all over everything even though hard lube is so easy to handle. If you are not swaging the bullet down with the case I believe that sizing smaller is at least worth a try.

[Cherokee]

You are using a really hard boolit (water dropped lino you said), I would go with the 357 for the Taurus. For the 9mm, go for 356 size. I use 356 for all my 9mm loads for several guns. Good accuracy and no leading.

[tazman]

MT Gianni wrote: Before trying to improve things you must know your base line or starting point. I also like to know what a gun does with factory loads or at least j-words. I find it rare that I can improve with jacketed groups with my cast. I may equal them and will kick them to pieces regarding cost but I like to know where I stand.

I have tried Federal fmj, cci Blazer, and winchester fmj which are not top of the line ammunition but should still work reasonably well. My cast boolits already outperform the factory loads. They just are not giving me the groups I get with my revolver.

Old Caster wrote: I think a harder bullet is a lot less forgiving than a soft one and feel that the harder they are, the more important exact sizing is. I also think that soft lube is more forgiving and relegate myself to put up with the sticky stuff all over everything even though hard lube is so easy to handle. If you are not swaging the bullet down with the case I believe that sizing smaller is at least worth a try.
Cherokee wrote: You are using a really hard boolit (water dropped lino you said), I would go with the 357 for the Taurus. For the 9mm, go for 356 size. I use 356 for all my 9mm loads for several guns. Good accuracy and no leading.

It sounds like the consensus is to at least try the smaller sized boolit. Since I am thinking along those lines as well(I admit it, I am not objective) I will give the .356 sizer a try. I may even buy a few Boolits already sized at .355 and give them a try as well. Worst case, I melt them down and recast them.

[Old Caster]

I would try .356 and I would at least try a softer bullet and soft lube. A softer bullet can get you into trouble though especially in a 9mm because the cases will swage a soft bullet down so that will have to be checked again if you do that. I expect that you will always be able to shoot your revolver more accurately because most likely it has a longer sighting radius and a better trigger.

[tazman]

I got hold of a .356 sizer yesterday and proceeded to resize about 20 of my boolits to .356. I loaded them up with the same recipe I used before that worked the best.
Flat failure.
No leading but the accuracy was terrible. Nearly 6" group at 20 feet. Not tumbling at least.
I tried the same load with the .357 boolits again and got the same result as last time so it wasn't just a bad day at the range.
I guess Sizing them that small won't work in this pistol.

One good note, I tried a couple of different powders and saw an improvement in accuracy. Not quite as good as the 357 mag but very close. I may be on to something there.