Barrel leading

Barrel leading

Joined: November 5th, 2014, 6:52 pm

May 12th, 2015, 11:15 pm #1

Hi All

A while back I posted a message about poor grouping from a PPC barrel. I got several helpful replies suggesting remedies.

I put these into effect. Results were great - one hole groups at 25 metres. Yippee. But now I have leading problems around the forcing cone and a short way up the barrel, half inch or so. Leading occurs within 15/20 shots

I now have the same barrel which slugs at .355 and 1 in 10 twist. the forcing cone was cut 1 mm deeper than a Browns insert and still at 11 degree. The crown was recut to a recessed flat 90 degree about 3mm inside an 11 degree outer.

Loads used vary from 2.1 to 2.7 Viht 310: 2.7/2.8 Bullseye: 2.7 to 3.2 GM3

Bullets .355 to .358 HBWC with a hardness of around 9.

The one hole group was achieved with 2.7 Bullseye with a .355 smooth sided HBWC. I sat all six rounds inside a single black patch at 25 metres.

I read all sorts of reasons - too hard or too soft bullets; too fast or too slow; too big or too small diameter;

The leading occurred in my first batch of trials working up from 2.1 Viht (a fast powder above Bullseye but slower than Titegroup) using a .357 HBWC through 2.2; 2.3; 2.4 etc when I stated to get fliers and found the leading to be the culprit.

Can anyone give me the correct cause.

Cheers. Dave





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Joined: January 22nd, 2012, 7:12 pm

May 12th, 2015, 11:50 pm #2

What are your cylinder throat diameters?

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Joined: November 5th, 2014, 6:52 pm

May 13th, 2015, 10:15 am #3

I do not have that or the gun to hand but can tell you that when dropping/pushing a sized bullet of .357 through, none drop out. Two cylinders are more or less bang on 357 as the bullet needs a light firm push to out it; one pushes out easier; one needs more push; and two are tight and really need to be forced out. I can reasonably estimate that 4 are .357 with 2 plus or minus half a thou and the 2 tight ones maybe .356. I do have a reamer on order to equalize all throats.
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Joined: January 29th, 2015, 2:26 am

May 13th, 2015, 3:42 pm #4

Hi All

A while back I posted a message about poor grouping from a PPC barrel. I got several helpful replies suggesting remedies.

I put these into effect. Results were great - one hole groups at 25 metres. Yippee. But now I have leading problems around the forcing cone and a short way up the barrel, half inch or so. Leading occurs within 15/20 shots

I now have the same barrel which slugs at .355 and 1 in 10 twist. the forcing cone was cut 1 mm deeper than a Browns insert and still at 11 degree. The crown was recut to a recessed flat 90 degree about 3mm inside an 11 degree outer.

Loads used vary from 2.1 to 2.7 Viht 310: 2.7/2.8 Bullseye: 2.7 to 3.2 GM3

Bullets .355 to .358 HBWC with a hardness of around 9.

The one hole group was achieved with 2.7 Bullseye with a .355 smooth sided HBWC. I sat all six rounds inside a single black patch at 25 metres.

I read all sorts of reasons - too hard or too soft bullets; too fast or too slow; too big or too small diameter;

The leading occurred in my first batch of trials working up from 2.1 Viht (a fast powder above Bullseye but slower than Titegroup) using a .357 HBWC through 2.2; 2.3; 2.4 etc when I stated to get fliers and found the leading to be the culprit.

Can anyone give me the correct cause.

Cheers. Dave




Dave I don't know how many rounds you shot through the gun before you noticed leading at forcing cone but you will always have some leading in the forcing cone after a few rounds are put through it. A small amount of leading is normal and unless excessive should not affect accuracy, often times shooting wad cutters a fouled barrel will Ransom tighter than a freshly cleaned one.
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Joined: January 26th, 2014, 5:18 am

May 24th, 2015, 8:23 am #5

I agree with JP, you will always get leading, just a fact of life running with HBWC. Because they are swaged the projectiles are inherently soft, otherwise you would never swage them. If you have miked the cylinder lead (that bit which the proj glides through before it hits the forcing cone) and your projectiles are at least the same size as your largest diam chamber then you are then on the right track to some sort of accuracy, as long as your barrel is no larger diam than this measurement.

Not knowing what sort of press you are using I can only tell you what i did to dramatically shrink my groups.

I use a Dillon which uses a insert in the powder die to bell and drop powder in, unfortunately the inserts are great for jacketed projectiles, not so for soft lead. So what I did was have a long insert turned up .001 larger than the diam as the projectile I am using, theoretically expanding the inside of the case to .358 to the same length as my projectile.

The issue with HBWC as we know, is that they are soft, if you want to see how much of an issue you have, carefully pull a loaded round and mike up the projectile. Brass cases are squeezed down to SAAMI specs by the die, brass will compress and then due to it's nature expand slightly. Unfortunately this happens also when you expand the case, expand and then contracts. By pulling the projectile you can see just how much the case compresses the soft lead, if the head of the projectile is undersize then this causes the leading. With my increased diam expander die and longer length the projectile is being held by the crimp, not by compressing the projectile down to .354.

Leading was reduced dramatically, accuracy increased also.

Each brass manufacturer uses different thickness brass, Winchester is great in my gun, Lapua isn't, RWS at a pinch. Each manufacturer has a slightly different head thickness also... but that's for another post....

Hope this get's you thinking.
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Joined: January 29th, 2015, 2:26 am

May 24th, 2015, 2:46 pm #6

Tony Kents explanation of how and why is excellent. In great detail he explains how and why excessive leading can occur and offers solutions that may help to lessen the issue. This is why this FORUM is a good source of assistance to PPC and all shooters.Great Job Tony THANKS!
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Joined: August 21st, 2013, 3:31 pm

May 25th, 2015, 3:08 pm #7

Here is good article

HOME/MY BLOGS/REVOLVER LIBERATION ALLIANCE/
Preventing barrel leading
Monday, August 18, 2008 Filed in: Revolvers, Reloading, Ammunition

A reader asked me to comment on successfully shooting lead bullets in revolvers. It seems that he's been getting indifferent accuracy coupled with severe leading, and would like to know the "secret" to using lead in his gun.

I thought I'd covered this topic once before, but a thorough search of the archives failed to turn up the expected article. Guess I'll have to do this from scratch!

Please note that I'm not a "hardcore" cast bullet shooter. I don't cast my own, which means that I'm dependent on commercial sources for my projectiles. As a result, it's taken me longer to learn this stuff than it would have otherwise. Thus I'm no expert; but Ed Harris, who sometimes checks in here at the RLA, is - hopefully he'll see fit to comment. (Ed, if I get anything wrong please drop me a note - I'll make your response into it's own post.)

The first thing to understand is that your lead bullets need to fit the chamber throats of your gun. If, for example, your throats measure .358", your bullets should be no smaller than .358, and no bigger than .001" over that measurement. Smaller bullets won't be as accurate, and will let the erosive combustion gases blow past the bullet causing severe leading around the forcing cone.

(Many bullet makers will size their products to your preference; if they don't make that service obvious, just ask. A surprising number are happy to oblige, usually at no extra cost.)

The forcing cone of your gun must also be in good condition; roughness in that area will result in leading at that point.

Assuming that the gun part of the equation is in good shape, and the bullets are of correct size, the hardness of the bullet becomes the critical issue. Most bullet makers advertise really hard bullets as being the "cure" for leading. It sort of stands to reason, doesn't it? A harder lead won't smear as much as it goes down the barrel, and will leave less residue - right?

Guess what - it isn't true. In fact, it's completely off base!

Think about this: you probably have a .22 rifle hanging around. Most .22 LR bullets are plain lubricated lead - very soft lead, no less. Compared to your average hard cast bullet, a .22 slug is almost like butter - soft as can be. Yet I'll bet that if you looked at the bore of your rifle, you probably won't see much leading - if any at all. My .22 rifles will fire a thousand or so rounds between cleanings, and I've never seen lead in my bores despite the bullet traveling at 1,200 fps.

What's the reason? Obturation.

A bullet, under great pressure from the expanding gases behind it, grows in size to fit whatever hole (chamber throat, barrel bore) it is being shoved into. This phenomenon is called obturation. As the bullet obturates it seals the hole, and keeps the gases where they belong until the bullet actually exits the barrel.

If the bullet doesn't obturate, the very hot gases will rush past while it is in the bore. The lead where the gases pass is melted and deposited on the barrel's walls - producing leading. This kind of leading is the most difficult to remove, as it really "sticks" to the bore - as if it's been soldered there. In fact, it has!

It follows that we need to make sure that they bullet obturates in our bore. In order for a bullet to obturate, the metal used needs to be soft enough to deform easily under the amount of pressure being applied to it. If the bullet is too hard, it won't obturate and there will be no sealing.

So, the bullet has to be soft enough to obturate. Why not just make all bullets out of super soft pure lead - won't that cure the problem? No, it won't; a bullet that's too soft will also cause leading, as it won't be strong enough to maintain the necessary seal in the bore. It also won't be resistant to the heat generated by the friction of travel down the bore. Both result in lead left in the barrel.

The bullet has to be hard, but not too hard; soft, but not too soft! The variable is the amount of pressure generated by the firing cartridge.

The higher the pressure, the harder the bullet needs to be to resist excess deformation - but remember that it has to be soft enough to obturate properly. A mild .38 Special target load needs a softer bullet than a fire-breathing .357 Magnum in order to obturate; putting a too-hard bullet in a mild cartridge is as much a problem as a too-soft slug in a hot one.

Bullet hardness is rated on the Brinell (BHN) scale. Pure lead is 5 BHN; "hard cast" bullets can be close to 30 BHN. Somewhere in that range is the ideal bullet for any given cartridge; how do we find it?

As it happens, there is a way to determine the optimum bullet hardness. First, you need to know the amount of pressure your load develops. That's easy - your loading manual will have that information. (Pressure is listed in either CUP or PSI; they are slightly different, but for this particular question either will be close enough to get the answer we need.)

There are two formula: one for the ideal hardness, one for the maximum hardness.

Ideal hardness in BHN = Pressure / 1,920
Maximum BHN = Pressure / 1,422
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Joined: January 26th, 2014, 5:18 am

May 28th, 2015, 6:53 am #8

Sounds good JB, pretty much what we have both been saying. I wonder how many Dave was testing prior to getting the leading, I know that I have gotten carried away and before you know it there is a dozen groups of 24 down range, and yep, leading. I tend to shoot 24 shot groups at 50, 25 will take care of itself, the points are lost at 50. I shoot 24 as this is the size group I am going to get in that series, makes sense.

Each time I try another load a bronze brush goes in and the barrel and cylinder gets a good scrub so I can see my face in them.

I suppose we should talk about lube, the killer of all groups, too much or too little. I have in the past re-lubed some pills with moderate results, most just don't need the extra lube and the results can change dramatically. If they are using a good lube it should be enough, when the projectiles are swaged they use a swaging lube so the lead doesn't stick in the die, which isn't suitable to shoot with so an additional lube is dipped over the top. I've used knurled projectiles and smooth sided, mixed results with both.

Powders which are too fast will also cause leading as the flame is so hot it can melt the bases, my preference is Bullseye or WST.

Look at what I said in my last post, pull those projectiles and mike up the head. I can almost guarantee that they are undersized, the new expander solved my problems.

cheers

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Joined: November 5th, 2014, 6:52 pm

June 9th, 2015, 10:08 am #9

Hi everyone

Thank you very much for such detailed replies. I think the problem may have been such low powered loads used at the start that obturation failed and by the 16th shot leading had or was occurring. Secondly I have inconsistent cylinder throats ranging from .357 to .35575.

My friend and gunsmith has read all your comments and has decided to ream all throats to .357 and use .357 projectiles with 2.7 Vihtavouri 310 about the same or slightly faster than 2.8 Bullseye. All this into a .3545 barrel with a nice throat. I am also using various HBWC with a range of hardness.

Going to the range for some serious testing Thursday and Friday. Lets hope the weather holds. Well, after all, it is England
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Joined: January 26th, 2014, 5:18 am

June 9th, 2015, 11:00 am #10

Best of luck Dave. It's summer there so all should be good, shouldn't it

Winter and 27 here, will just have to contend with blue skies. Range time for me this weekend too, need work at 50.

cheers
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