38-50/55/70 Bullet Diameter?

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SSShooter
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38-50/55/70 Bullet Diameter?

Post by SSShooter » Tue Sep 24, 2019 6:50 am

My new Shilen 38cal barrel measures 0.3753" with my vernier (slugged with a 20-1 bullet). Am wondering, casting with 20-1 lead, if I should order a 0.376", 0.377" or 0.378" mold to start with..............? Hate to spend the money on the wrong mold. What's your thinking and why?
Thanks.
Glenn

beltfed
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Location: Central Wi

Re: 38-50/55/70 Bullet Diameter?

Post by beltfed » Tue Sep 24, 2019 7:47 am

I suggest start with the idea of using a harder alloy for your bullets
especially if you are looking at long tapered ogive such as Elliptical, or even long "money" nose.
At least 16+1.
Then you will need to check out whatever ctg /Brass and chambering reamer dimensions
before you try to answer the question of the bullet/mold diameters with the chosen alloy.

Generally, good to have bullet a couple thousandths
larger than groove diameter.
For the most part, it is Very important to have bullet drive bands to fit fire formed brass
and any freebore in chamber. A bore ride front body should ride on the lands, not be engraved by them.
If the bullet is too small for the FF brass and freebore, you will get gas cutting.
Example:
I just went thru a first round of shooting available bullets thru my 38-50RH:
I have on hand two molds: they both cast bullets at about 0.376-0.377.
Groove dia via chamber cast is about 0.3773" or so. Fire formed brass is about 0.379" I.D.
First result: fair to decent accuracy.
BUT LEADING with initial smokeless loads and no wad under bullet .
This equates to gas blowby and cutting.
Now, I am into Paper Patch bullets with patch to 0.379 base bands and patch to land of about
0.366-0.367"


beltfed/arnie

beltfed
Posts: 1844
Joined: Sun Jun 03, 2007 10:07 am
Location: Central Wi

Re: 38-50/55/70 Bullet Diameter?

Post by beltfed » Tue Sep 24, 2019 7:56 am

And, of course, Black Powder and 0.060 LDPE wad under bullet.
beltfed/arnie

martinibelgian
Posts: 1476
Joined: Thu Oct 26, 2006 1:20 pm

Re: 38-50/55/70 Bullet Diameter?

Post by martinibelgian » Tue Sep 24, 2019 12:31 pm

Yes, but sometimes..... I decided to open up my .308 sizer to .3085 in order to have a better fit in the freebore (.309) and case. Result? Mediocre accuracy. Which became better when I went back to .308 sizing.

art ruggiero
Posts: 537
Joined: Fri Nov 30, 2007 4:00 pm

Re: 38-50/55/70 Bullet Diameter?

Post by art ruggiero » Tue Sep 24, 2019 1:37 pm

can't believe .001 makes a difference with black powder art

bruce m
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Location: australia

Re: 38-50/55/70 Bullet Diameter?

Post by bruce m » Tue Sep 24, 2019 2:59 pm

beltfed wrote:
Tue Sep 24, 2019 7:47 am
I suggest start with the idea of using a harder alloy for your bullets
especially if you are looking at long tapered ogive such as Elliptical, or even long "money" nose.
At least 16+1.
Then you will need to check out whatever ctg /Brass and chambering reamer dimensions
before you try to answer the question of the bullet/mold diameters with the chosen alloy.

Generally, good to have bullet a couple thousandths
larger than groove diameter.
For the most part, it is Very important to have bullet drive bands to fit fire formed brass
and any freebore in chamber. A bore ride front body should ride on the lands, not be engraved by them.
If the bullet is too small for the FF brass and freebore, you will get gas cutting.
Example:
I just went thru a first round of shooting available bullets thru my 38-50RH:
I have on hand two molds: they both cast bullets at about 0.376-0.377.
Groove dia via chamber cast is about 0.3773" or so. Fire formed brass is about 0.379" I.D.
First result: fair to decent accuracy.
BUT LEADING with initial smokeless loads and no wad under bullet .
This equates to gas blowby and cutting.
Now, I am into Paper Patch bullets with patch to 0.379 base bands and patch to land of about
0.366-0.367"


beltfed/arnie
what he said.
but nothing is cast in stone.
bruce.
ventum est amicus meus

Coltsmoke
Posts: 1362
Joined: Sun Jul 04, 2010 8:55 am
Location: GA.

Re: 38-50/55/70 Bullet Diameter?

Post by Coltsmoke » Tue Sep 24, 2019 3:21 pm

I would go with a .376 dia. If you go with a bigger dia. the lead on the base band where the rifling pushes through is moved to the rear of the base and forms little fins hanging off the rear of the base. The bullets do that anyway, why add more to it. A bigger dia. bullet has to squeeze down smaller and can contribute to friction leading on top of the rifling in front of the chamber. If a .376 bullet needs to bump up a thousandth I don't think it will have a problem doing so, but with your measurement I don't see why it would have to do that. Just my opinion, but you know what they say about opinions. :lol:
Swamp Man Shelby Stanza for President!!

SSShooter
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Location: Jersey Shore

Re: 38-50/55/70 Bullet Diameter?

Post by SSShooter » Sat Sep 28, 2019 2:15 pm

Coltsmoke wrote:
Tue Sep 24, 2019 3:21 pm
I would go with a .376 dia. If you go with a bigger dia. the lead on the base band where the rifling pushes through is moved to the rear of the base and forms little fins hanging off the rear of the base. The bullets do that anyway, why add more to it. A bigger dia. bullet has to squeeze down smaller and can contribute to friction leading on top of the rifling in front of the chamber. If a .376 bullet needs to bump up a thousandth I don't think it will have a problem doing so, but with your measurement I don't see why it would have to do that. Just my opinion, but you know what they say about opinions. :lol:
Yes.......... think you are correct. Been doing some digging thru my 38cal shooting info of some years back and see that of the three bullets I shot then in a 38-56 (325gr, 340gr and 360gr) the one mold that was 0.376" gave the best results in a 0.367" x 0.375" barrel, so that's where I'll start.
See you at the RBGC at the end of Oct for 4 days of fun & games.
Glenn

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