Lead buildup at forcing cone

[vinnyg]

Hi,
I'm pushing 158 grain lead cast bullets that i resized to .357 and am not using a GC. I sluged the bore and i measured .356 on the high surface of the sluged lead bullet.
I'm loading 4 grains of uniqe behind 38 special brass sp primer and 5 grains of uniqe behind 357 brass spm primer. either way I'm getting lead build up after 30-50 rounds so I have to brush the hec out of the barrel every time i shoot.

The lead is building up at the forcing cone is this normal?

thanks in advance.
Vinnyg

[lurch]

What is the diameter of the cylinder throats? Lead in the forcing cone is probably from under size boolits there. If you don't want to slug the cylinder, try sizing to .358. That for the most part seems to be a better operating point for a lot of guns.

What is your alloy? Too hard can cause forcing cone leading as well as the boolit won't bump up in diameter and seal, causing gas cutting and lead in the forcing cone. Commercial cast boolits are notorious for this.

[vinnyg]

I just measured it and the cylinder throat is .358

I melted the alloy from pure lead came and added 60/40 solder for a tin mix and the BHN came out to be like 12.5 with the LEE hardness tester.

I also am experiencing a lot of smoke when i shoot because I used too much Lee Lube never the less I know that the build up is lead because the copper brush pulled a long sliver out when scrubbing the barrel.

[fredj338]

Try less solder & sizing to .358. That light a load is not obturating the base of the bullet & you are getting some flame cutting on the side of the base as it enters the throat, this is giving you leading. A softer bullet will upset sooner & seel the bore better at low pressures.

[jdgabbard]

My guess: First, your allow is a bit soft for the application. Second, your powder charge is a bit high for the boolits that soft. Since you're using near pure lead (with a little tin) you shouldn't be pushing them as fast as something that falls in the 10-12 bhn range, when you're alloy is probably in the 6 bhn area. From the 7th Edition Hornady manual for the 158g swaged boolits (swaged are pretty much pure lead.):

158g LRN, SWC, and SWC-HP
Powder Unique

3.3gr - 650fps
3.6gr - 700fps
3.9gr - 750fps
4.2gr - 800fps (max load)

357 Magnum Data for the same boolits with Unique

3.3gr - 700 fps
3.6gr - 750 fps
4.0gr - 800 fps
4.3gr - 850 fps
4.7gr - 900 fps
5.0gr - 950 fps (max)

From looking at your data, you're pretty much at max loads with what you're shooting. As far as soft boolits are concerned anyways. One thing that many have experience, with certain designs, the faster we push them the more inaccurate they become. There are always exceptions. Say H110 for example, it prefers hotter loads due to the way the pressure increases. But Unique is a faster powder, and you shouldn't have a problem getting the pressure up quick. I would say either back off your charge, or change your allow.

But hey, thats just my .02

[lylejb]

I recently had the exact same problem with light 38 loads, leading in the forcing cone / frame area, but not in the bore. I was using a commercial "hard cast" 158 swc.

It came down to exactly what Fred said, the bullet was not obturating, due to (in my case) high hardness of the bullet, and low pressure.

In my case, i wasn't casting yet so there was little i could do about the bullet, but i could, and did raise the pressure.

I went to a faster powder. This creates a sharper spike in pressure, and was able to obturate the bullet. THIS ENDED MY LEADING.

I was using AA#2 powder, i went to Trail boss. I think Bullseye would be even better, but couldn't find any locally. Any of the very fast powders should work, bullseye, red dot, 700x, clays.

Although i do like trail boss, my use of it was almost by accident. It was the fastest powder i could get locally at that time. In fact, it was the ONLY powder still on the shelf at my local store on the day i got it.

I really like the way it fills up the cases. 2.6gr of trail boss= 1/2 full. No more flashlight to see if there's anything in there!!

As far as your sizing, if your throats slug at .358, size no smaller than that.

I'm not sure what alloy lead came in made from, but your BHN is too hard for it to be pure lead. Pure lead is about 5-6 BHN, wheel weight alloy is about 12-13. Many people use wheel weight alloy for just about everything. your BHN is not bad if it is 12, but that's not pure lead. If it is pure lead, your BHN isn't 12. I would check it again to be sure. Here's a link to LASC's cast bullet notes. it has a chart of BHN for common alloys

http://www.lasc.us/CastBulletNotes.htm

You didn't say how much solder you added. 2%tin is enough to give good fillout, more is not always better. It takes alot of solder to add a little hardness, it just isn't worth the expense to me.

hope this helps

[lurch]

Concur with lylejb on the alloy. If it's 12BHN, it's not pure lead. Unless you added 10% tin, you aren't even close to that hardness IF you started with pure lead. That's some expensive cast boolits...

You are at a starting load level wit 4.0 grains in 38 brass based on pressure for a 38 spl revolver. Since you are also loading in 357 brass I assume you are firing both in a 357 revolver - correct? If so, the 38 brass loads will probably foul a bit more due to the extra distance to the throat. No guarantee there though, just the potential for it. I like to stick to 357 brass in my 357 for that reason.

On the LASC page that lylejb referenced, it also states that the minimum pressure for getting obturation for a 12BHN boolit is about 17000psi (some will argue this, I'm just using it as a data point for illustration). Your load according to my references is not going to develop that pressure level in the 38 brass. I'm guessing for the 357, but it may come closer to making that pressure and have a better shot at obturating th bases and sealing if you size to .358 to start with. If your throats are .358, I'd try sizing to .359. Measure your sized boolits too - the numbers on the sizing die are sometimes not what you get. Alloy hardness plays a role here too, with softer alloys coming out smaller than harder.

[runfiverun]

alox and unique are a smoky combination.bigger boolit should help 359 would be my suggestion.
if you measure the inside of a fired case that will tell you about how big you can go.
apparently you can ignore my post on the other site.

[Rico1950]

Vinnyg,
Also like to add no mag primer necessary with Unique in the .357 loads.

[fredj338]

My guess: First, your allow is a bit soft for the application. Second, your powder charge is a bit high for the boolits that soft. Since you're using near pure lead (with a little tin) you shouldn't be pushing them as fast as something that falls in the 10-12 bhn range, when you're alloy is probably in the 6 bhn area. From the 7th Edition Hornady manual for the 158g swaged boolits (swaged are pretty much pure lead.):

158g LRN, SWC, and SWC-HP
Powder Unique

3.3gr - 650fps
3.6gr - 700fps
3.9gr - 750fps
4.2gr - 800fps (max load)

357 Magnum Data for the same boolits with Unique

3.3gr - 700 fps
3.6gr - 750 fps
4.0gr - 800 fps
4.3gr - 850 fps
4.7gr - 900 fps
5.0gr - 950 fps (max)

From looking at your data, you're pretty much at max loads with what you're shooting. As far as soft boolits are concerned anyways. One thing that many have experience, with certain designs, the faster we push them the more inaccurate they become. There are always exceptions. Say H110 for example, it prefers hotter loads due to the way the pressure increases. But Unique is a faster powder, and you shouldn't have a problem getting the pressure up quick. I would say either back off your charge, or change your allow.

But hey, thats just my .02
I have to disagree. The charge wts are low to med. pressure loads & the alloy, if it is 12BHN, is a bit hard. You can drive pure lead bullets to 850fps w/ little to no leading if sized right. The OPs bullet is too small & IMO, the alloy a bit hard for obturation w/ his lower pressure loads. That's how it seems to work for me anyway.

[Throwback]

Most answers are in the ballpark but as usual with cast there is more than one right answer.

A faster powder than Unique such as Bullseye, Tightgroup, AA#2 or even #5, Trail Boss etc. may be used and the problem will go away.

A harder or softer alloy may be tried with the Unique and may fix things.

Sizing .359 also will not hurt with .358 cylinders but changing the powder will make doing so irrelevant.

Bevel-based & gas check bullets without the gas check will lead at lower velocities than flat-based bullets or bullets with a gas check.

Finally, I will say that if any powder is going to lead a barrel and/or forcing cone, it is Unique.

[wallenba]

I just measured it and the cylinder throat is .358

I melted the alloy from pure lead came and added 60/40 solder for a tin mix and the BHN came out to be like 12.5 with the LEE hardness tester.

I also am experiencing a lot of smoke when i shoot because I used too much Lee Lube never the less I know that the build up is lead because the copper brush pulled a long sliver out when scrubbing the barrel.

I regularly shoot 38 spec. 150 WC's that are 14.9 BHN with 3gr of Titegroup, sized .358 lubed with Orange magic in my SW686. I get no leading. I think the alloy you are using is too soft. I would also check the gap between the forcing cone and cylinder as well as the timing if it is predominantly on one side of the cone.

[44man]

I have been doing a lot of shooting with light loads in my .44, from barely enough 231 and Unique to get them out of the barrel to near max for the powders. (245 gr RCBS SWC.)
I started with a soft boolit, air cooled and worked through water dropped WW metal to my hard alloy of WW with antimony and tin added. Air cooled to water dropped.
My bore is .430" and throats are .4324". The last boolits I tested were .4315" and tested 25 BHN.
There was never any leading at any point but as I worked through the hardness, groups at 25 and 50 yards tightened until groups were as small as I ever shot with a semi wad cutter. The harder boolit posting the smallest groups.
Take it or leave it as you will but groups with the hard boolits were much smaller at 50 yards then the soft boolits were at 25 yards.
Notice the boolits are still under throat size because the mold will not cast larger even after I lapped it a little. It was way too small at the start but never gave me leading. Accuracy is better after lapping but it could use more.
I will never understand why a fella will get super accuracy from his revolver using a jacketed bullet, then go to dead soft lead thinking it will work the same????
Some still confuse base expansion with obturation, you EXPAND the base TO obturate, you do NOT obturate the base. Either way you say it, my opinion is to leave the base alone and don't expand it. If you do because of the alloy, the boolit will smoosh at the forcing cone.
I don't know when this idea of shooting softer so the boolit expands will ever be put to rest! Everyone says jacketed and gas checked boolits shoot best but then make a PB into a putty ball.
Get the boolit to fit the gun and leave it alone, never change it's shape.
Here is what I mean. I needed to check my flintlock for early season. I have a .450" land to land and use a .451" ball with a .012" patch. I took one shot at 50 yards and another at the steel pig at 100. I centered the pig also.
Some of you will say "oh no", need a .440" ball and a .010" patch so it is easy to load (TC mentality) and the ball will "obturate" however I have news for you, the ball will "expand" and "deform" just like your soft revolver boolits.
No better demonstration then pure lead and what proper fit will do.