Bullet fit the throat??

[johnnyjr]

How do you determine if the bullets fit your throat ??. How do you check this. And why can't you use a bullet that matches the diameter of a jacketed bullet ??. Seem to me if you powder coat a bullet and size it to jacket diameter it would or should work at least for low node. Thanks

 

[Bazoo]

For a revolver, slugging the throat and measuring is the easiest way to determine throat diameter. You don't have to size to throat diameter. If you have .434 throats and .429 groove diameter, you can size 430 and make decent usable ammo. It's possible accuracy will be acceptable, but it's also possible it will be horrible. If you're plinking, you likely will never notice the difference. I generally size to standard sizes and live with mediocre accuracy, provided that accuracy is halfway decent.

 

[Ian]

First question is, so far, unanswerable directly, generally, or universally.

The answer to the second question is that cast bullets, even.powder coated ones, cannot tolerate gas cutting and therefore must be large enough to fully obturate (seal) the bore. Copper jacketed bullets are often at or slightly below groove diameter to reduce friction and engraving pressure since they can tolerate a greater degree of gas escaping by them. Jax DO bump to seal somewhat, sometimes...but that's another story.

 

[bruce381]

I just use thump pressure to push bullet through the cylinder throats if it passes or has a slight drag ands is at or larger than bore Im good to go. more or less, sometimes have to open throats with reamer but that another story

 

[Petrol & Powder]

I am a firm believer that the throats of a revolver cylinder are the last sizing die the bullet will go through before it reaches the barrel.

A bullet may “bump up” a little but there’s a distinct limit to that effect.

Undersize throats on a revolver can be corrected by reaming (within reason) and you may gain uniform throats in the process.

Oversized throats leave you with fewer options and none of them are economical.

 

[Bazoo]

Larry Gibson over on cb.gl forum did some accuracy tests, and with his gun, he got better accuracy sizing to the groove diameter rather than the throat diameter, which for his case was oversized. So that goes to show that there is no hard rule on accuracy.

My results were the same, and I was researching it, which is how I came across his notes. For me, my throats are .431-432, but my groove is .4295 ish. I get better groups if I size .430 verses .431. That said, im not getting 1 hole groups. The best I've been able to repeat was less than 2" at 20 yards for 18 shots, and less than an inch for 6. I was having a good shooting day. With the larger bullets, the best i've done is about 2.5"

As far as leading, my gun has a slight constriction and has minor leading. I have been experimenting to get the least leading. And the .430 diameter bullets indeed lead LESS than the .431 bullets.

I don't subscribe to the theory that only bullets sized to the throats are accurate or won't lead. It's best to experiment.

 

[johnnyjr]

For a revolver, slugging the throat and measuring is the easiest way to determine throat diameter. You don't have to size to throat diameter. If you have .434 throats and .429 groove diameter, you can size 430 and make decent usable ammo. It's possible accuracy will be acceptable, but it's also possible it will be horrible. If you're plinking, you likely will never notice the difference. I generally size to standard sizes and live with mediocre accuracy, provided that accuracy is halfway decent.

Sorry, I left out it's 243 cal. My 243 jacket are 243 diameter. Just courious about different things. Thanks for your help

 

[JWFilips]

Bullet fit in the throat is the most important thing! Throats should dictate bullet size (not Bore Size)
I have an old 98 8 MM mauser that has a Throat of .338" But a normal 8 mm bore So In essence I need an 8.5 MM bullet to shoot accurately in this rifle ( and it does )

 

[johnnyjr]

Bullet fit in the throat is the most important thing! Throats should dictate bullet size (not Bore Size)
I have an old 98 8 MM mauser that has a Throat of .338" But a normal 8 mm bore So In essence I need an 8.5 MM bullet to shoot accurately in this rifle ( and it does )

So, how did you determine the throat size??

 

[bruce381]

wait i know this a chamber cast? or pound cast? thats all I got

 

[fiver]

pound cast.
look in Ian's basement for the procedure.
it isn't just used for diameter, it also shows the shape,,,, and that your trimming your cases too short.

 

[JonB]

there is this...

Article #4: Cast bullet fit and design

Disclaimer: The following information is the product of my own meandering experience and includes a few original ideas and concepts of my own and some that others have been kind to share with me, and is always subject to change as I learn more. It is in no way intended to be the last word, or...

www.artfulbullet.com

 

[Mitty38]

Well I pounded a soft lead ball thru my wife's SW 4 inch. 38 special revolver. All cylinders measured .359. Then I pounded one the length of the barrel. It came out .358 in the grooves.
Then thought I should size to .360.
But said heck with it, and tried the 38 special wad cutter, Alox lubed, loads I made for the Taurus in ..359. It shot them just as well, or better then the 6inch Taurus. With no leading
Guess you will have that.

 

[Tomme boy]

Not many people here subscribe to what LARRY thinks or does.

 

[Bret4207]

How do you determine if the bullets fit your throat ??. How do you check this. And why can't you use a bullet that matches the diameter of a jacketed bullet ??. Seem to me if you powder coat a bullet and size it to jacket diameter it would or should work at least for low node. Thanks

You can do castings of the throat and see the shape and get the size. You want to come close to "filling the throat" as we say, but without jamming the bullet in so hard (if it's larger than the throat) so that you push pressure way high or the bullet won't come out with the case if you go to unload that round. With more pressure your bullet will, more or less, tend to obturate and fill the throat. But that's not a for sure and certain thing and not always controllable- but it IS part of dynamic bullet fit. It's all about fit! Read Ians stuff in the link above.

 

[quicksylver]

I take the path with the most fun, for my .30 cal . rifles I have four sizing dies .310 thru .313, the fun part comes when I load 5-10 rounds of each size with the same cases powder, primers etc shoot them and see what works best ONE WILL . No pounding, casting or measuring needed Mr.Target tells it all.

 

[johnnyjr]

I take the path with the most fun, for my .30 cal . rifle I have four sizing dies .310 thru .313, the fun part comes when I load 5-10 rounds of each size with the same cases powder, primers etc shoot them and see what works best ONE WILL . No pounding, casting or measuring needed Mr.Target tells it all.

Excellent idea.. I will do that.. thanks

 

[Snakeoil]

First question is, so far, unanswerable directly, generally, or universally.

I'm not sure I understand that statement, Ian. I assume you are talking about the OPs opening question.

I think there is an answer. Simply put, you measure the throat and measure your bullets. The universal purpose of the throat is to allow a loaded cartridge to chamber without resistance from the bullet.

I see that replies here are for both revolvers and rifles. But there are some qualifying statements that are missing that would allow an appropriate answer. Maybe that's what you are getting at. We don't know enough to answer the question.

I would think that to answer the question, the following would info would be required.

What velocity are you wanting to shoot
Gas check or plain base
Powder coated or plain cast bullets
Bullet alloy type

if it passes or has a slight drag ands is at or larger than bore Im good to go.

I suspect you mean groove diameter. The throat will tend to be larger than groove diameter. If it was a bore diameter, it probably would not chamber.

For gas check bullets my general rule, which has worked so far is for GC bullets, 0.001 to .002 over groove diameter. For PB bullets, groove diameter. I don't use PC so can't speak to it. I tend to use 20:1 for GC and 30:1 for PB.

On a rifle, to assure the bullet enters the rifling straight, depending on the rifle, you seat the bullet so that it either touches, slightly engraves or has just a few thousandths jump to the rifling. For a revolver, you are stuck with the bullets having to be at least flush with the end of the cylinder face.

 

[Brad]

For revolvers I want a mildly snug slip in the cylinder throats. That is what works best for me.

For rifles it isn’t that simple. I generally have an idea of what size I want to go from there. I don’t shoot for small groups so I don’t agree around with this much.

 

[Ian]

there is this...

Article #4: Cast bullet fit and design

Disclaimer: The following information is the product of my own meandering experience and includes a few original ideas and concepts of my own and some that others have been kind to share with me, and is always subject to change as I learn more. It is in no way intended to be the last word, or...

www.artfulbullet.com

Everything but the "how".

We had a pretty good thread started on defining fit in a rifle throat, what it means and what it looks like when it's good, bad, and ugly, but the person who was the impetus behind it faded away.

I, frankly, am too flabby in that part of the brain anymore to attempt tue description and too happy with the results I get with powder coated bullets to be inspired to delve into the topic of dynamic fit again in earnest. Lots of illustrations would be needed and in the end, only a handful of people in the world would get it, do it, and achieve the results proper dynamic fit can give you. This is further complicated by there being more than one philosophy of what constitutes correct bullet fit in a rifle throat, much depending on the person, their tooling limitations, and are their ultimate goals. Those who already get it learned the hard way, over a lifetime of dedicated experimentation, and don't need my two cents on the subject anyway.