sw 15-4 leading

[jonp]

I'm using Ben's 60/40 on a lee 358145 wc. Boolits dropping .358-.359 so I sized them .358 for consistency. The alloy is 20:1 about 10-10.5 bhn. I'm using promo at 2.4gr for a light target load.

My question is light leading. I shot 100 on Sunday without cleaning. I ran a dry patch through the barrel and took a look. I had leading in the first 1/2in or so with the rest of the barrel clean. No smears, ribbons etc. A little kroil and a brush got it out easily.

Can you drop the velocity and pressure low enough that the boolit won't seal causing the leading no matter the alloy? This is a very light load and the lack of leading farther down the barrel tells me the lube is fine

[JWFilips]

Been there: Don't size them...Try it again See if you see a difference!
I don't size for my Mod 15 Especially if I'm shooting soft alloy...JMHO!
Jim

[Petrol & Powder]

I know nothing of Promo but that sounds like a light load, maybe just a little too light.

[waco]

Try 3.0gr instead. Plus 1 on not sizing. Promo is Redot.

[GabbyM]

My Dillon powder through won't expand cases deep enough for wad cutters. I have to use the longer plug Lyman M die. Or else the cases swag the bullets down.

[jonp]

2.4gr Promo is below listed in some data but I found a couple of cowboy charts where it is barely on. I started sizing the boolits as some of them were dropping at .360-.361 for some reason. The majority were .358-.359 and I didn't want to measure each one. Enough are .358 that sizing to .359 would not be a good use of time.

The 9/10ths of the barrel not leaded is squeaky clean minus the powder. Not many unburned flakes but a little sooty. Without the leading I could probably shoot 200 without worrying about fouling too much.

So..can the powder charge be so low that the boolit will not seal no matter the alloy?

[lotech]

jonp- The charge can be too low, but that may not be the problem. I'm not familiar with your powder, but you might start by increasing the load in increments of two-tenths of a grain and fire ten rounds with each change, checking accuracy and possible leading along the way. I have two Model 15s, one from the late 'fifties and another from the late 'sixties. A .359" bullet doesn't shoot quite as well in either gun as a .358". I use Bullseye or 231, but I think your powder will work fine.

[btroj]

you just need a quicker seal in the bore. A larger bullet, maybe size .359 would do that. This depends on throat size as the throat will make the bullet whatever size they are no matter how much larger they apatart out. Also using a bit more powder could help as it could bump the bullet up enough to seal the bore quicker.

[Petrol & Powder]

I don't know anything about Promo but it sounds like your load is too light.
I think your bullet size is just fine, .358" works in all of my S&W revolvers. I agree that your sizing stem may be too small and the casing is sizing the bullet down. I would also go with Waco's suggestion and bump up that charge weight a little.

[Love Life]

How's accuracy hold up over long shot strings?

[GabbyM]

Have you tried pushing your sized .358" bullets through the cylinder throats? If they are snug or do not go through then you simply do not have undersized bullets. If they go in easily and maybe even wiggle a little then you need larger. No gages needed other than your sized bullets.

I'll re state. You need to take care not to swag down the bullet base inside the case.

For powder charge. Only reason you'd need a heavy charge for obturation is if your barrel was larger diameter than your cylinder throats. Or if you have variation in cylinder throat size and can't fit a bullet to all of them.

[GabbyM]

Text below is copy pasted from Wikipedia here: http://en.wikipedia.org/wiki/Obturation

With reference to firearms (http://en.wikipedia.org/wiki/Firearm) and air guns (http://en.wikipedia.org/wiki/Air_gun), obturation is the result of a bullet (http://en.wikipedia.org/wiki/Bullet) or pellet (http://en.wikipedia.org/wiki/Pellet_(air_gun)) expanding or upsetting to fit the bore, or, in the case of a firearm, of a brass case expanding to seal against the chamber at the moment of firing. In the first case, this both seals the bullet in the bore, and causes the bullet to engage the barrel's rifling (http://en.wikipedia.org/wiki/Rifling). In the second case, it seals the case in the chamber and prevents backward travel of gases against the bolt. The thin brass case easily seals the chamber, even in low pressure rounds like the .22 CB (http://en.wikipedia.org/wiki/.22_CB), but expanding or upsetting the bullet sufficiently for effective obturation requires sufficient pressure to deform the bullet material. The formula used to calculate the pressure required for solid base bullets is:
Bullet's BHN (http://en.wikipedia.org/wiki/Brinell_hardness_test) x 9.80665 N/kgf×106 mm²/m² = [N (http://en.wikipedia.org/wiki/Newton_(unit))/m²] = pressure in pascals (http://en.wikipedia.org/wiki/Pascal_(unit))Bullet's BHN (http://en.wikipedia.org/wiki/Brinell_hardness_test) x 1422 = pressure in pounds per square inch (http://en.wikipedia.org/wiki/Pounds_per_square_inch)[2] (http://en.wikipedia.org/wiki/Obturation#cite_note-2)The conversion factor of 1422 is mathematically derived in order to convert the pressure in kgf/mm² (the units used to measure BHN) to lbf/in² (the units used to measure cartridge pressure). That is:
Conversion factor = 25.4 (mm/in) x 25.4 (mm/in) x 2.2046 (lbf/kgf) = 1,422.Note that this number should only be used with cast lead plain-base bullets. It does not apply to jacketed or gas-check cast bullets. Below is a chart containing various bullet alloys, the BHN, and the PSI required to expand a bullet to the bore:



Material


BHN


Pressure



(psi)

(MPa)



Pure lead


5


7,110

49



1:20 tin/lead


10


14,200

98



1:10 tin/lead


11.5


16,400

113



Pure copper


40


56,900

392




Pure lead is very soft, and can be expanded or upset by most firearm cartridges, but the pressures required are higher than those encountered in most airguns. To allow obturation in airguns, pellets use soft alloys in conjunction with a thin, concave base designed to expand more easily. Some firearms ammunition, such as Foster slugs (http://en.wikipedia.org/wiki/Foster_slug) and hollow base wadcutter (http://en.wikipedia.org/wiki/Wadcutter) bullets, also use a hollow base to allow the bullet to expand and conform to a barrel's irregularities, even as the chamber pressure drops as the bullet travels down the barrel (see internal ballistics (http://en.wikipedia.org/wiki/Internal_ballistics)). For example, it is not uncommon for revolver (http://en.wikipedia.org/wiki/Revolver) barrels to have a slight constriction at the breech end where they thread into the revolver's frame; a hollow base bullet will expand to fill the larger diameter of the barrel after passing through the constriction.
To prevent excessive deformation in high pressure rifle (http://en.wikipedia.org/wiki/Rifle) and magnum pistol (http://en.wikipedia.org/wiki/Pistol) cartridges, lead bullets are often covered in copper or another harder alloy. These bullets are generally designed to swage (http://en.wikipedia.org/wiki/Swaging#Firearms_and_ammunition) to fit upon firing.

[bhn22]

Yes, your load is light for the alloy. Try to get up around 15,000 CUP, and also try the bullets unsized. As Brad mentioned, it sounds like you're having sealing issues.

[Char-Gar]

A bullet larger than the charge hole throat will come out the end of the cylinder the same size as the charge hole throat no matter what size it started. If you have no measured your throats, then do so. However most Smith and Wessons run .357 - .358 in the throats and your current .358 sizing diameter should not be the problem. It only would be a problem if you have larger than normal throats.

I know nothing about Promo, but it sounds to me like the alloy is to hard to obdurate the bullet base with your powder charge. So, as others have suggested, the fix is more pressure or a softer alloy. Either would work I should think.

[jonp]

To answer someones question who was kind enough to PM me with some help here is a picture of the box:

131988

145 is also stamped on the mold. It's a single cavity so it is not a question of if one of the cavities is different from the other.

I suspect sealing issues as some of you suggested. My question pretty much says it. The alloy calculator is a big help but lists Pb at 8 BHN which is high but I did get 20:1 using it to 10.5 bhn give or take. I don't have a program to figure pressure. This load is very accurate and I don't want to give up on it.

I'm going to drop the alloy BHN down to 6, 7, and 8 to see if I can make it work. I might just increase the loading as 2.4gr is right at the bottom of most of the things I can find although Handloads suggests a start of 2.1gr with a 148gr WC boolit.

As Per Alliant: Promo is the same as Red Dot and can use the same loading data BY WEIGHT NOT VOLUME.

I should point out one of the things in my OP that is slightly off. I was running them unsized as the 75k thread indicated until the leading then I went back and measured a random sample. When I found a couple at .360 and .361 for some reason I sized them all at .358 and re-applied more 60/40. .358 seemed to be the consensus from all of the reading on this handgun I've found. No-one suggested that they were really finicky but that seemed to be the recommended sizing so I went with that. I have not slugged the bore as I don't have a rod yet of the correct size. It's on my "to do" list

GabbyM: thanks for the bhn x 1422 = psi to seal. I've got that written down somewhere and forgot all about it. The loading of the 148gr WC at handloads suggests a pressure of 14,800 which if I have a 10.5 should be ok. Obviously it is not.

[jonp]

How's accuracy hold up over long shot strings?

Excellent. I've gotten great groups with the load

[bedbugbilly]

I agree with what Jim said - don't size 'em. My CM (1956 - pre 15) prefers unsized through it. If I size's - which I did when I first got it to .358 - I had traces of lead. Once I started leaving 'em "as dropped" (around .359) it stopped. The boolit mine seems to like the best is the LEE TL358-158-SWC over Bulls Eye or Red Dot.

If you are casting and leave them "as dropped" - they should be dropping pretty much the same so you will be "consistent" just as if you size them all. I tend to load on the lighter side of the data but have learned that sometimes I have to up it to get things to work right. If you load is light enough that it's not expanding things, you should notice some blow-back soot on your casings. Not that it is a terrible thing though - try 'em unsized and see what happens. Maybe that will take care of it with the powder/load you are currently using - if not - then adjust your powder and see what happens. Good luck!

[dubber123]

I have somewhere around 40 S&W's, about 90% of which are .35 cal. .358" works very well in all but the .38 S&W's,. I will also be willing to bet you have a thread choke right at the frame point. I have only in the last year begun checking this on my guns, and I find it pretty common. Firelapping fixes it, and has shown a very noticeable improvement in accuracy, on the order of an inch or better improvement at 50 yards.

[Love Life]

Excellent. I've gotten great groups with the load

If leading does not progress, and accuracy is not affected over long shot strings, then I wouldn't sweat the midget.

[Petrol & Powder]

Fire lapping would be WAY down on my list of possible fixes. A little more powder would be my first choice, followed by checking the expander stem on my die.
The throats should be checked with a sized bullet. I think an alloy around 10 BHn is fine, you could go a little softer but I wouldn't try that until I upped the charge weight a bit. While an unsized .359"-.360" bullet has been suggested it is pointless if the throats are sizing the bullet to a diameter smaller than that.

.358" works in all of my S&W's. The OP is using a very light load with .358 bullets with a very appropriate 10 BHn and getting good groups with minor leading. A little more powder seems like the logical ( and easiest! ) place to start.

[dubber123]

Fire lapping would be WAY down on my list of possible fixes. A little more powder would be my first choice, followed by checking the expander stem on my die.
The throats should be checked with a sized bullet. I think an alloy around 10 BHn is fine, you could go a little softer but I wouldn't try that until I upped the charge weight a bit. While an unsized .359"-.360" bullet has been suggested it is pointless if the throats are sizing the bullet to a diameter smaller than that.

.358" works in all of my S&W's. The OP is using a very light load with .358 bullets with a very appropriate 10 BHn and getting good groups with minor leading. A little more powder seems like the logical ( and easiest! ) place to start.

Out of my fair pile of .35 cal S&W's, the throats vary little from .358" The alloy is not too hard, not too soft. A light load should not lead if the boolit fit is correct. It is of course worth checking all the possibilities, but a mechanical choke point is quite likely, and I prefer to actually fix the problem versus band aid it. First is determine the real problem, second is fix it correctly. I'd rather spend an afternoon and do it right, than accept a barely acceptable patch to the problem. Jon will figure it out.

[Petrol & Powder]

I'm not saying that thread choke should be discarded as a cause but I would eliminate other factors before resorting to fire lapping. The gun is shooting well and the leading sounds to be minimal.

[jonp]

The leading is minimal but vexing. Comments here and from the pm's I've gotten from another member had me go back to the data I was using last night. Handloads.com as well as Alliants 2004 load data for a 148gr lwc (the mold is stamped 145gr but is dropping 148gr average so I used that data) lists 2.3gr Red Dot at 730 fps and 14,800 psi. This indicates 10-10.5 BHN to seal which is what I am using so I was scratching my head and is the reason for this thread. Last night I went to several other sources and no-one else is anywhere near that pressure with that load or even lists 2.3gr as a loading. 10 BHN should be up around 3.0gr Red Dot to work right. No wonder I'm getting some leading. I can either drop the alloy to 9 BHN and use 2.4gr or use 10.5 BHN Alloy and up the powder to 3.0gr. I'm going to do both.

I can only surmise that the number from Handloads.com came directly from the Alliant 2004 sheet which is what I have. Of course, since the leading was easily removed and occured only after 200rds then I could just ignore it and run keep an eye on it but no leading is better than a little leading.

Everyone that immediately pointed to the loading being too light were spot on. Good advice like this on something that popped right out to several people despite what the reference I have says is why this is a great site.

Thanks to everyone here and this is a good reminder for me to reference several manuals if one looks a little funny. I cross referenced 2 but that clearly was not enough.

jonp