Follow up to mbc 240 gr 44 mag leading

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roval

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A few weeks ago I posted about my problems with leading in my 44 mag SRH with 7.5 inch barrel. I was using 12.5 gr 800 x which chronoed at about 1300 fps.

The bullet diameter was .430. I've since tried 12 gr of 800x which still resulted in leading. I had attempted to try measuring the throats with my caliper with poor results. So I bought pin gauges which arrived today.

It turns out that my SRH has .431 throats. I haven't slugged the barrel but will the .430 bullet in a
.431 throat cause the problem?

I haven't bought a new batch of bullets yet so I will look for .431 bullets online.
 
I don't load that but I use AA # 9 and a 240 gr Brinell 18 bullet and don't have a leading problem. I did have some leading using AA #2 but I think it was burning too hot.
 
Yes. An undersized cast bullet will lead the throat of your revolver. Perhaps in your case you might cast them .432? Size really does matter when one is discussing cast bullets.
 
Unfortunately I don't cast. I placed an order last night with Oregon laser cast as they are sized .431 they aren't powder coated and the are more expensive than mbc. Only got 500 for now. though, if they had 250 would have gotten that instead.
 
I'd say your throats are just fine. Too tight is far worse than a hair oversize.

A very good read on leading comes right from Missouri Bullets:
https://www.missouribullet.com/technical.php

Brad explains there that for best results you need to match the pressure of your load against the hardness of the bullet you want to use. It isn't really velocity, though they're often related.

IMR says a 13.4 gr. charge of 800x under a 240 gr. bullet will produce 39,600 CUP pressure. The formula Brad gives says you'd need a bullet of 30.9 Brinnell hardness to handle that much pressure. :eek:

No wonder you're getting leading. 0.9 gr. less powder, or even 1.4 gr. less is probably not dropping off pressure far enough to get down into the range where an 18 Bn hard bullet is going to work best.

While a problem many people run into is bullets which are TOO hard for the pressures they're really producing, that's not the case for your load. If you can get some 24 Bn lead bullets, they might be cool with your 12 gr. load of 800x.

(Not only that, but IMR doesn't really list a load of 800x below their top load of 13.4 gr., and when they don't give you a "starting load" that's usually a sign that that particular powder doesn't play well with reduced loads. So for your situation I'd get off of 800x entirely.)

So, just looking at the IMR/Win/Hodgdon family, I'd try any of these:
CFE Pistol
AutoComp
Universal
231
HP-38
SR 7625
Trail Boss
Titegroup
Clays
 
Since a .431 pin gauge goes in (and a .432 doesn't ?), they are at least .431, so a ".431" bullet might be a tight fit in your throats, but as they chamber and as long as the grooves are less than that, you should be OK. Are your pin gauges + or - ?
 
Must know the Grooves, Man

The key here is what Walkalong alluded to - groove diameter as it relates to both throat size and bullet diameter. Other things like pressure and bullet hardness will absolutely contribute to how much leading you will see, and where it happens, but bullet fit in the grooves is most important.

My personal belief is that you will never completely avoid leading, but it does not have to be terribly bad if you match the load, the bullet hardness, and the sizes. Lots of "experts" disagree with me and claim that they get zero leading, and/or that coated bullets never lead (I have proven that they do). You will just have to do your research, do your testing, and make up your own mind on what to expect. Do learn how to actually see leading in the barrel beyond just shining a light in the bore. Of course, you may already know all of that.

The lead bullet needs to be slightly larger than the grooves, .001 or .002 larger. And the cylinder throat MUST be at least as large as the grooves, and best if a bit larger. If the throat is smaller than the groove diameter, then your starting bullet size makes NO difference - the small throat will cause the bullet to be undersized before it ever gets into the barrel. Good luck figuring it all out - sometimes it is not easy.
 
The .431 pin goes in but the .432 doesn't. The tolerance es are supposedly .0002 +/-.

I do have other powders to try. 2400, unique, 296 and 4227. But haven't shot a session wheRe I only used one of those powders and checked the leading.

I just don't want to waste the 800x yet but I'll probably sideline it. Once I get the .431 bullets I will load a few with 12 gr just to see if that will lead it up as well before moving on.

If the pin gauges are accurate they are a good deal at 80 bucks. I had bought and plan to return muzzle loading Hornady round balls as they already cost 12 bucks for a hundred. I know I only need a few balls but they don't sell them individually. Although I've already measured what I can measure with it... the throats of my 2 gp 100s.
 
I wouldn't be in a rush to try either 2400, 4227, or 296. Those are all pretty standard "magnum" powders and are going to be pushing cast bullets pretty hard. Unique would be a really good choice, but at a much lower velocity.
 
The pin gauges should be rated either:

plus .000, minus .0002,

or plus .0002, minus .000.

Just curious.
 
using those pin gauges to determine bore diameter is an excellent way to find out if you have a bore restriction. just don't force the pin down the barrel. add the land height to get groove diameter.

murf
 
Looked at the box they are .oooo/-.0002.

Murf can you explain how I can get the groove diameter with the pin gauge. . I can easily measure the bore but I'm at a loss as to how to come up with the groove diameter.

Sam1911 I didn't get to thank you for your long post will revisit that page from mbc.

Btw if I get done measuring all I could think of. my lgs gunsmith expressed interest in buying my set for cost. This way I'll only be out shipping if I decide to go that route. Win win
 
grooves are normally .004" tall (you can measure the groove and bore diameter of your barrel with your calipers (subtract to get land height)). add two land heights to the bore diameter to get groove diameter. if your barrel has an odd number of grooves this won't work, but you can assume a .004" land height and add them anyway to get your groove diameter.

your srh has six grooves, so this should work for you.

murf
 
I just Googled it and got tormach 250 pc set from .250 to 0.500 for $80.

I measured the bore diameter and it was 0.416 so the groove diameter assuming lands of .004 should be 0.424. Does this sound right?
 
roval,

your groove diameter should be around .429", so either your lands are quite a bit taller than .004", or your barrel is dirty. you need a really clean barrel to do this test.

murf
 
So based on the diagram the bore diameter of ..416 was just slightly off the saami. 417 bore diameter. So the lands must be much more than .004 for the revolver. They do look higher than my 1911s lands. I'll slug the barrel one of these days
 
A good simple method to check fit of a cast bullet in a revolver's throats is to simply drop a sized bullet down into the cylinder, and it should BARELY work it's way out, or need to be very lightly coaxed through with a pencil or dowel. Check all chambers to reveal any diameter differences.
 
that's what i get for assuming all lands are the same height. saami drawings show .006" for your 44mag. next drawing shows .004" for the 45acp.

learn something new every day!

roval, did you find any restriction when you gauged the barrel?

murf
 
All the chambers were equal. When I showed the gauges to my lgs gunsmith I measured the chambers of an old smith 38 special for sale in the used section from the late 40s and all the chambers equally measured .358 just like my 2 yr old gp100 as compared to my other gp100 6 inch blued half lug(late 90s to 2000s) that measured , .357. Pretty easy tool to use but I'm running out of things to measure.
 
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