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Old February 27, 2018, 12:59 PM   #1
Snagman
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Cast bullet size

Quick question that I'm sure someone knows the "why" to it.
Why are the diameters for cast bullets always .001" larger than for a jacketed bullet?
From what I've read on several posts; people sometimes have feed issues due to the neck diameter on the rifle case being too big as a result. Seems to me the cast bullet would swedge easier and fill the rifling much easier than a jacket bullet.
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Old February 27, 2018, 03:24 PM   #2
reddog81
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.001 larger for cast bullets helps ensure a complete seal in the bore. Usually using the largest sized lead bullet that will fit into the chamber works as good or better than other sizes.

Lead will swage down easier - much easier, however if you're jamming lead or jacketed bullets into the throat the you'd better be careful.

Last edited by Unclenick; March 12, 2018 at 10:58 AM. Reason: typo fix
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Old February 27, 2018, 03:31 PM   #3
mikld
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Quote:
Originally Posted by reddog81 View Post
.001 larger for cast bullets helps ensure a complete seal in the bore. Usually using the largest sized lead bullet that will fit into the chamber works as good or better than other sizes.

Lead will swag down easier - much easier, however if you're jamming lead or jacketed bullets into the throat the you'd better be careful.
^^Yep!^^ On a couple guns I've gone .003" over groove diameter...
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Old February 27, 2018, 04:04 PM   #4
Paul B.
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".001 larger for cast bullets helps ensure a complete seal in the bore. Usually using the largest sized lead bullet that will fit into the chamber works as good or better than other sizes."

My preference is .002" over groove diameter in my rifle loads.

Lead will swage down easier - much easier, however if you're jamming lead or jacketed bullets into the throat the you'd better be careful."

I'll agree with you on jamming jacketed bullets into the rifle but not necessarily on lead bullets. My accuracy loads for the .308 Win and 30-06 require the nose of the bullet to be placed into the lands. It helps insure bullet are seated straight into the bore. My test for a proper size bullet nose is to insert the nose of the bullet I plan toe use into the muzzle of the rifle. If it is a snug fit or is slightly engraved by the rifling then they're good to go. Loose fitting bullets are rejected. Bullets usually used are Lyman's #311291 and #311284.
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Old February 27, 2018, 05:32 PM   #5
243winxb
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Quote:
people sometimes have feed issues due to the neck diameter on the rifle case being too big as a result.
I dont see this happening in a rifle chamber when the bullet is only .001" larger than a normal jacketed bullet.

Factory chambers are just not that tight.

There would be other issues causing the problems. IMO.
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Old February 27, 2018, 06:16 PM   #6
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I use .358 diameter (.38 Spcl bullets) coated lead in my 9mm. Accuracy is better than .356 lead.
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Old February 28, 2018, 02:53 PM   #7
Paul B.
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"I use .358 diameter (.38 Spcl bullets) coated lead in my 9mm. Accuracy is better than .356 lead."

I've slugged the barrels on three 9MM handguns, one foreign make and two domestic made guns. Two had .357" groove diameters and another .358. So much for 9MM barrels being .356". I prefer bullets sized .002" over groove diameter so I sized all my 9MM cast bullet .359". Works great in the .357" barrels and is decent in the .358" barrel. If you go that route, use a few dummy rounds to make sure the case neck is not now too fat. No problem in my guns but yours may be different.
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Old March 1, 2018, 11:28 PM   #8
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Its not just sealing the bore, though that is an important thing. And the lead swaging down easier isn't really the point, either.

Using a bullet .001-.002" oversize means there is more "bite" on the bullet by the rifling, something which the softer lead bullets need for accuracy.

Because lead is softer than copper jackets, a deeper bite from the rifling helps prevent stripping. Providing, of course that you are not driving the bullet faster than the alloy allows.

There is a balancing act between bullet size (dia), alloy hardness and rifling grip on the slug which limits the maximum velocity you can use without stripping, which results in loss of accuracy and most often leading the bore.
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Old March 12, 2018, 08:29 AM   #9
Snagman
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Thanks for the information
I'm looking at a .312" mold that has the bullet shape I'm looking for and was curious if I could successfully run that through a .309" resizing die and shoot it in my Blackout? I see all the .309" Lee molds make a bullet that is around .30" with the grooves being the only area that is actually .309". The front area of the bullet rides the bore while the grooves actually drive the rifling. I was thinking I might get a better accuracy if I resize a larger bullet so the entire bullet contacts and stabilizes in the rifling.
Any thought?
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Old March 12, 2018, 09:11 AM   #10
243winxb
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Lyman has said sizing down more than .003" can hurt accuracy.

The diameter of the cast bullet as it drops from the mold is effected by antimony content. More will produce a larger diameter bullet.

Molds are regulated by different alloys from each company.

Lee 10 lead 1 part tin. Lyman #2 alloy contains antimony and tin.

The bore riding part of the bullet will change in diameter with alloy. Some at castboolits may size the bore riding part also. http://castboolits.gunloads.com
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Old March 12, 2018, 11:07 AM   #11
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Good info
Thank you
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