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Old 04-30-2009, 05:14 AM
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Does anyone know the S&W factory design specifications and tolerance for bore diameter in the .357/.38 and .44?

What is the design bullet engagement in the rifleing for a lead bullet versus a jacketed bullet?

Hornady lists the bullet diameter for .357/.38 as .357" and for the .44 as .430"

I have noticed that my hard cast lead bullets from our local producer are .358" and .431".

The Hornady HP-XTPs in 158 and 300 grains measure out at .357 and .430.

These measurements indicate to me that the lead bullets engage the rifleing by .0005" and the XTP's do not engage the rifleing.

Why have the lead bullets engage the grooves and not the jacketed? I would think the copper is soft enough to do so. Maybe it is necessary for one but not the other. I see the lead bullet as holding back pressure leakage better, but also having more friction loss in the barrel.

The .357 and .430 bullets don't fit into the barrels of my 686 and 629, so the barrel diameter is obviously less, but I can't measure it accurately without a plug gauge. I guess this goes back to my first question. What is the factory shooting for on bore diameter and how much tolerance is allowed in manufacture?

Just curious as to how all this works together. I am that kind of person, unfortunately

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Old 04-30-2009, 05:14 AM
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Does anyone know the S&W factory design specifications and tolerance for bore diameter in the .357/.38 and .44?

What is the design bullet engagement in the rifleing for a lead bullet versus a jacketed bullet?

Hornady lists the bullet diameter for .357/.38 as .357" and for the .44 as .430"

I have noticed that my hard cast lead bullets from our local producer are .358" and .431".

The Hornady HP-XTPs in 158 and 300 grains measure out at .357 and .430.

These measurements indicate to me that the lead bullets engage the rifleing by .0005" and the XTP's do not engage the rifleing.

Why have the lead bullets engage the grooves and not the jacketed? I would think the copper is soft enough to do so. Maybe it is necessary for one but not the other. I see the lead bullet as holding back pressure leakage better, but also having more friction loss in the barrel.

The .357 and .430 bullets don't fit into the barrels of my 686 and 629, so the barrel diameter is obviously less, but I can't measure it accurately without a plug gauge. I guess this goes back to my first question. What is the factory shooting for on bore diameter and how much tolerance is allowed in manufacture?

Just curious as to how all this works together. I am that kind of person, unfortunately

Thanks
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Old 04-30-2009, 06:27 AM
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Quote:
I see the lead bullet as holding back pressure leakage better, but also having more friction loss in the barrel.
It is good that you are curious, and you have a lot of misconceptions.

I'll start out with this one part: plain lead bullets have far less friction than jacketed bullets. A soft swaged wadcutter can be easily driven through a barrel, but a stuck squib jacketed bullet is a real problem.... Also, look at your tables and notice lead takes less powder for equivalent loads.

I'll leave the rest for others, except to comment that much of this information can be found in several good books and manuals on loading. Try looking up "obturate."
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Old 04-30-2009, 08:20 AM
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"The .357 and .430 bullets don't fit into the barrels of my 686 and 629, so the barrel diameter is obviously less, but I can't measure it accurately without a plug gauge. I guess this goes back to my first question. What is the factory shooting for on bore diameter and how much tolerance is allowed in manufacture?"
More information for you. Most people measure the full bore diameter by doing what is called "slugging the barrel". A soft piece of lead such as an egg shaped fishing sinker is driven through the barrel and measured for diameter at the largest point. This process will give you an idea of what diameter cast bullet to use in your gun. You usually use a cast bullet that is .001"-.002" larger that the slugged diamter. If you're interested I think I have a link to some information regarding the process.
Cary
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Old 04-30-2009, 08:35 AM
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Model 14, I would do a search here of pin gauge or gauge pin, and cylinder throat for starters. This ground has been covered lots by thoughtful fuys. Note that pro bullet casters offer several different diameters so that you can purchase specifically for each of your guns, two different .44's, for instance. Also, jacketed bullets are not copper. They are yellow brass or some such alloy, containing copper but quite a bit harder. You are partly right in your surmise about copper itself though: Rainier, for instance recommends using lead loads for their copper plated bullets. I find they require a bit more tho to perform well.
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Old 04-30-2009, 08:37 AM
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Oops, thoughtful "guys". I should proof read more!
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Old 04-30-2009, 10:22 AM
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I looked up "obturate". It is the process of the bullet expanding to engage the rifleing. Okay, why is the unfired bullet larger than the bore, and more so with a lead bullet? The bore being smaller must be causing a swedging of the bullet and giving a better seal. Hornady lead bullets are the same as my cast bullets, e.g. .358", but the clad XTP is .357". Help me with the "lot of misconceptions", please. I have several reloading manuals, none of which adequately address my questions.
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Old 04-30-2009, 10:37 AM
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model14,
Here is a link to a great site with a lot of information on casting and shooting lead bullets. If you take some time there I think you will find some of your answers. I know I have gleaned a lot of information from the articles there.
http://www.lasc.us/CastBulletNotes.htm
Cary
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Old 04-30-2009, 11:45 AM
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I found this on the Firing Line forum:

In a perfect world, all firearms bores would be made exactly to specifications, as would all bullets.

Bullets are sized to exactly fit the groove diameter of the firearm in question. The lands engrave the outer few thousandths of the bullet or jacket in order to impart spin upon firing.

Of course, this is not a perfect world. Both barrels and bullets are subject to 'tolerances'; that is a '30 caliber' barrel has a groove diameter of .3085" and a land diameter of .308" plus or minus a few ten-thousandths. Actually, modern machining methods produce barrels of superb uniformity; which is not to say the occasional clunker gets through the quality control. Modern bullets are very uniform as well. Most of the major bullet makers produce hunting ammunition superior in accuracy to match bullets of fifty years ago.

Military weapons of the past have varied greatly in specifications. 9x19 and .380 ACP pistols are both 'officially' .356 groove diameter; however, major manufacturers in various countries have produced such handguns with barrels ranging from .354" to .362". And they all shoot the same bullets. Wartime production of ammunition varied as well.

As you might expect, a small bullet in a large barrel produces only marginal accuracy. In addition, if the bullet is hard enough not to obdurate sufficiently, much power is lost in the propellent gases 'blowing by' the bullet. Larger diameter bullets simply 'smoosh down' (that's a technical term) to bore diameter.

Revolvers pose another problem. Not only must bullets fit the barrel, they must first pass through the throat of the respective cylinder. So, for maximum accuracy, cylinder throats should be reamed out to .0001" larger than the bore groove diameter. Sizing revolver bullets is a futile excercise; they get re-sized several times between chambering and the bullet leaving the barrel.

Now; one more cock-eyed thing about bore and bullet diameters. The popular name for a round may or may not have anything to do with the actual size of the bore.

.38 S&W, .38 Special, .357 Magnum, Super .38, .380 ACP, and most all the 9mm something or others are all in the range of .354" to .362". Except for extreme bullet weight differences, the projectiles are pretty much interchangable. I've loaded and shot 90 grain .380 ACP bullets in .357 Magnum cases. I've loaded and shot 158 grain lead round nose .38 Special bullets from a 9x19 autoloader. I've loaded and shot 125 grain JHP .357 Magnum bullets from a .380 ACP (they were too long to fit in the magazine, so I had to single load them).

.303 British is actually .323". .303 Savage is actually .308". 7.7mm Arisaka is the same as .303 British. 8mm Mauser is actually .323", or .312" in the earliest loading. 6.5x55 Swedish Mauser, .256 Newton and .264 Winchester Magnum are all the bore diameter; .256" is the land diameter, .264" is the groove diameter and 6.5mm is the metric equivilent of .256". Then, .257 Roberts and .25-06 are both .257 groove diameter.
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Old 04-30-2009, 12:59 PM
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I just talked to the tech department at Hornady. A very nice gentleman took the time to explain all of this to me. Their plated bullets are made to the exact groove to groove diameter. In a perfectly made barrel with a perfectly made plated bullet, there will be zero clearance and zero engagement with the barrel groove surface, just sliding friction. The lands will dig into the bullet and force it to spin. Obviously there is a lot of friction drag associated with that. The bullet will obtruate some, but it is not necessary or designed for. The plated bullet is manufactured to groove to groove diameter plus or minus 1 or 2 ten thousands (he wasn't sure). (I suspect that that is S&W's tolerance on bore and groove diameter also).

In the case of their lead bullets (swaged), for the .357 they are made .001" over to take advantage of better sealing due to the interference fit with the groove surface. THe lead is soft enough to compress the diameter to the groove diameter. Also, obtruation definitely occurs adding to the sealing effect. The down side is that their relatively soft lead bullets will lead (smear)the barrel if driven much over 1000 fps. They get good efficiency for target work (less powder, less recoil) because of the good sealing, but are not good for the higher velocities needed for hunting. As you add hardening materials to the lead, there is less leading at the higher velocities, but efficiency is lost due to less sealing effect. At some point the hardened lead bullet starts to act like a plated bullet. Of course a lot of engineering goes into the terminal ballistics, and I am sure that effects the materials used and how they will behave in the barrel. Hope this helps those who want to learn why things are the way they are. To me, it makes reloading and shooting more fun.
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Old 04-30-2009, 01:09 PM
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In revolvers, you also have to consider the possibility of oversized cylinder throat:

QUOTE:
Revolvers

"In a revolver the throats are the areas in each cylinder chamber immediately ahead of the portion of the chamber where the brass case rests and into which the bullet projects. If the bullet is sized so that it is a gentle force fit in the throat, all else being equal, your accuracy potential will increase greatly.

Measure the throat diameters and slug the barrel. If you have a gun that has throats smaller than the groove diameter, (fortunately, an infrequent condition) there is not much hope for reasonable accuracy. From an accuracy standpoint, revolvers will not tolerate an undersize lead bullet rattling down the bore.

When you slug your barrel, note if there is a tight spot or area anywhere in the barrel. Pay particular attention to the back of the barrel where it enters the frame. A tight spot here is common and can size down your bullet. This situation can be remedied by lapping the bore.

Proper bullet fit in a revolver can do wonders. I can beat all my shooting buddies any day of the week; not because I am a better pistol shot, but because I fit all of my ammo to each particular gun - a decided advantage. I learned this way back when the Redhawk first came out. Through a series of very fortunate circumstances, I ended up with a matched set of the first year run. With their badly oversize .434" throats and using conventional ammo, the very best that I could get from them was 2" machine rest groups. By fitting bullets properly, they will now do 3/4" groups all day, even with full house loads. This dramatic improvement was realized in all my revolvers and I became a better shot overnight than I ever thought that I would be. It really is worth the effort.

Some revolver chambers have all six throats that are virtually identical, while some vary 0.0006 - 0.0007". Most hold 0.0003 - 0.0004" variation which is good enough, in my experience. Very carefully running an oversize soft slug through all six throats will give one the diameter of the smallest throat. This diameter is optimum for bullets fired in that gun.

You may very well find that your bullets shoot better with no sizing. My bullet sizer is virtually retired these past 15-20 years. Many bullets, as they fall from the mold, are already undersized for many modern production revolvers.

Tip - I fit most of my revolver bullets so that they will be a push fit into the throats and then load the cartridges so that bullets reach way out into the throats for good initial guidance; that is, with the bullet and bore axes perfectly collinear.

For those who load their rounds so that the bullets crimp at the crimp groove, rather than having them extend way out into the throat, oversize bullets, even those that are larger in diameter than the throats, can provide a definite advantage. There will be virtually no gas cutting, no matter what the bullet alloy."
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Old 04-30-2009, 01:32 PM
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Thanks, OKFCO5, thats good info. I am going to be doing some measurements myself.
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357 magnum, 380, 629, 686, crimp, hardening, hornady, model 14, projectiles, redhawk, savage, swedish mauser, wadcutter, winchester

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