Leading and Cylinder throat relationship?

[Murphy]

Hello guys,

I posted earlier in the week about having a leading problem with light to medium loads in my S&W 29 with a 4 inch barrel.

Keith Boolit, 9.0/9.5/10.0 of Unique, Wheel Weight alloy, Felix lube.

I slugged all 6 cylinder throats lastnight and found they came out at .430 dia. I used unsized bullet's that I placed in a vice and put the squeeze on to 'bump them up' and make sure I would get a true slug as best as I could. They all came out looking like they'd been through a sizing die.

Average boolit dia? .430

How does this correlate to leading? I've never really understood the cylinder throat/ bore dia. leading issue.

I haven't been back to the range with a different lube or powder just yet. I thought perhaps that getting a little more information to work with may be a wise move.

Suggestions?

Thanks,

Murphy

[felix]

Murphy, try for a more viscosity in the lube as per Larry Gibson. Lanolin increase and/or add some motor mica. The latter should be formulated by hand after the lube is solid and still warm. Mica drops to the bottom of the pan when the lube is becoming solid is the reason for the hand job. As an added benefit, the mica will clean up your forcing cone and will help smooth out any excessive frame hold onto the barrel. Another trick is to just coat the boolits with mica or baby powder. Sooner or later the leading will go away using this coating technique. I prefer to put mica into the lube itself. ... felix

[Dale53]

Murphy;
The theory is that bullets smaller than the throats can gas cut, causing leading. Elmer Keith's recommendations were to have the bullets big enough that you could just push them through the throats with a pencil (relatively light pressure).

Before you do anything else, try to use NRA Formula Alox lube. This is no reflection on Felix lube, but it is real easy to check out a new lube (apply it by hand if nothing else).

8.5 grains of Unique (in Magnum Cases) and 7.5 in .44 Special Cases - is an old recipe for a medium load (just about perfect for self defense, among other things). It also has a reputation (I find it is true) for excellent accuracy.

Dale53

[9.3X62AL]

The conventional wisdom is that the groove diameter of the barrel must be no larger than the throat diameter of the involved revolver. If the two dimensions are equal, then things are probably OK--I've had good results with a couple wheelguns so dimensioned.

I've had a couple that came with smaller throats than grooves--the more recent example being a Ruger Bisley Blackhawk x 7.5". Neither revolver shot well with cast overall, and the earlier gun got sold to a guy that liked j-words a lot--after I bemoaned its cast boolit shortcomings. I kept the Ruger, and recently opened up its throats to .453" to mate with its .452" groove diameter. I now run a .454" boolit into .453" throats that send the boolit into a .452" groove diameter--and the revolver shoots VERY well.

I would be sorely tempted to try .431" boolits in your 44. Be aware that a lot of S&W revolvers with the post-1981 "crush-fitted" barrels have a pretty definite constriction where the barrel screws into the frame, and a lap-out of some kind might be needed to resolve that problem. If leading starts about 3/4" ahead of the forcing cone, it could indicate such a restriction. I had a Model 586 x 6" that did that, and after shooting a truckload of j-words through the thing--it sort of resolved itself.

[BruceB]

I experienced severe leading with Unique powder in two different 9mm pistols many years ago.

Changing to Herco powder in the same guns, same boolits, same brass, same sizing diameter, same velocity etc etc eliminated the leading completely.

This was a really dramatic change in results. I don't know if present-day Unique would act the same in those guns, but I'd certainly give another powder a try, based on this clear tendency to lead barrels. I suppose that the above results have inhibited me from using Unique in the intervening DECADES, but I only started using it again when Vince in MO asked me to run some Unique trials in the .416 Rigby a year or so back.

I'd try a different powder, just for information's sake.

[Bass Ackward]

Keith Boolit, 9.0/9.5/10.0 of Unique, Wheel Weight alloy, Felix lube.


Murf,

While you are condemplating what I don't think has anything serious to do with your problem, I am going to give you something else to think about.

1. For equal weight bullets, a Keith style will throw more pressure than other designs. This is because it is longer than other designs of the same weight. More of the case volume is occupied by the bullet. What you are considering a light to medium load could be much higher pressure than you think if your gun has as tight of chambers as it does throats.

2. A Keith bullet requires more lube than other designs. Any bullet going down a bore leaves some lube behind that combines with the unburned powder that is left to help lube the next bullet down the bore. Some companies are even adding lubricants to the powder to cut metal fouling. The sharp shoulder on the Keith bullet keeps bore condition constant by scraping out this stuff ahead of the bullet as it moves down the bore. Therefore, each Keith bullet must carry enough lube to sucessfully perform the lube function for itself. If it does not, then you must use a higher grade of lube as Felix and others suggest. Or a harder bullet. Or a GC. Or all of the above. Man's gotta do what a mans gotta do.

One thing for sure is that once leading starts, it remains or continues to build. If there is a rough spot that is gathering the lead, it can never smooth up unless a new bullet can get to it. Do yourself a favor and take a rod with a bore brush along and brush where you are leading between cylinders. Lead will never be easier to remove than right after application. And this will expedite bore smoothing.

[fecmech]

According to the Lyman manual Murf's load is pretty low pressure by Magnum standards I'd guess somewhere around 20-25k. I have also experienced the same as Bruce B the Unique leading in the 9MM and in my case being able to run at 1200fps(in the 9mm)with the same bullet and no leading with both Herco and Blue Dot. I would try different powder if it was mine. Nick

[StarMetal]

I've been shooting Unique for over 30 years in all the various handgun calibers I've owned. Especially in the 45LC, 45acp, 9mm, and 357 mag. In the 9mm it is one of my favorite powders. There's no way I'd change it to Herco or something else unless someone gave me a ton of it free...that's how good Unique performs for me. This is in more the one 9mm too which include my hotloaded 38/45 wildcat. As of lately I've been using alot of it in my 30 Lugers. The only other powder I like in my 30 Lugers is WW 231. My results are totally different then Bruces...I do not see a leading problem in my 9mm's what so ever. I have no explanation of why there is such a difference.

Joe

[Bass Ackward]

According to the Lyman manual Murf's load is pretty low pressure by Magnum standards I'd guess somewhere around 20-25k.


Nick,

My version of a Keith can be seated to an OAL of 1.65 to 1.71 and still be in the crimp groove with varying levels of crimp. 10 grains of Unique with these seating depths amounts to 22,436 to 26,639. This is from Quickload. But the pressure from this load is way higher in my Smith than in my Redhawk that has larger chambers and throats. Shows up in the velocity too. It is still clearly safe and not what I was insinuating, but probably too much for ACWW in his case with Unique's burn rate range.

One 44 of mine works with 14 BHN and a Keith design using 8.5 grains of Unique. The Smith requires 20 BHN with the same bullet to achieve the same accuracy level with the same load. This is at the 8.5 grain level which is about 18,000 psi. My Smith has the new less than 90 degree "angled" rifling that Smith has been using for the last couple of years. I believe that rifling form requires a harder bullet than the old fashioned 90 degree type. Neither gun leads either which complicates the issue even more in Murph's case.

Whether I am correct about the reason or not, I need way harder bullets in my new Smith to achieve the same thing I did with my old ones.

[fecmech]

Bass- At the start of this thread I was sure the problem was throat size now I don't know and that was my reason for the powder change for the leading issue. My own experience which is somewhat limited has been that soft bullets (40/1 lead tin) driven at close to 1400 fps in the .44 with 50/50 alox leaded not a bit. Accuracy was not as good as Lino but pretty close to acww and in the 3 to 4" range at 50 yds. I'll be watching to see what solves Murphs problem.

Joe--I understand that there are a lot of people who love Unique and are very satisfied with it. I have never found it to do anything for me in handguns that I could'nt do better with something else. Nick

[John Boy]

Lyman ... Tip of the Month:

What leading in pistols or revolvers tell you about your loads
Generally leading that occurs towards the muzzle end of the barrel would indicate an excess velocity or lack of lube issue. Leading that occurs towards the cylinder (or chamber) can point toward several things. First, if the bullets are undersized compared to the throat diameter in the cylinder, they may be entering the barrel slightly off center which can cause leading. Next, if the alloy used is too hard to obturate (or upset the bullet base) gas can leak past the bullet base and cause leading. Light loads can also create this same situation because they do not produce enough pressure. Many people think a harder alloy is the answer to stopping leading, but at times a softer alloy can actually help.

[azvaquero]

Murphy --

Take it one step at a time. Can you tell me if there is leading inside the cylinder throats themselves? That question should be answered before we even get to whether there is leading in the barrel. If you can't get rid of leading inside the cyl. throats, throat/groove dia. relationship may not be the issue at all.