.40S&W boolit size .001 or .002 over bore?

[Jayhem]

I'm casting for a Sig P229 .40 S&W.

I slugged my bore and the slug came out as .400 by my Lyman caliper. My Lee 175 gr. TC boolits drop at about .402 and I have been sizing down to .401. I get light leading with 12-15 bhn boolits at .401 and around 25K-30K PSI loads (according to my Lee reloading manual)

My question is, since the .40 is a higher pressure cartridge would I do better with my boolits .002 over groove diameter instead of the .001 over I've been loading? A tighter fit to minimize gas blow by leading? I'm getting light leading streaks on the lands and some streaks near the chamber throat.
I tumble lube with Lee Liquid Alox and load to OAL of 1.140

Open to all comments.

- J

[HammerMTB]

You've got nothing to lose trying it!
The only thing to check is to see that rounds will chamber easily with the extra .001", but I'd bet they will.

[Jayhem]

The only thing I'm worried about is if it's .402 it's going to a lot tighter fit into the case. Currently it seats in the case perfectly with minimal case bulge and chambers perfectly. I guess it can't hurt to try is right.

[Shiloh]

My LEE sizing die is opened up to .4016. It is for a LEE TLSWC mold, the only mold I have for a .40
I am pleased with the accuracy I get.

Shiloh

[Jayhem]

My LEE sizing die is opened up to .4016. It is for a LEE TLSWC mold, the only mold I have for a .40
I am pleased with the accuracy I get.

Shiloh

How did you get it opened up? Is that what it sized to from the factory or did you have it lathed out? Do you know what your Lee mold boolits cast at? Mine always drop at .402, WW with 2% tin and WQ'd.

[sqlbullet]

Have you seated and crimped a bullet and then pulled and measured it? This is one test that often is overlooked but is important. Your .401" bullet might be down to .400" or a little less if the case mouth isn't expanded enough, or if too much crimp is applied.

Also, does the leading you mention build up over time? Does it come out with a pass or two of a brush? Leading, to my mind, is a build of of lead deposits that have and affect on accuracy or are overly difficult to clean.

I shoot this same bullet from 10mm. I can put 200-300 down the tube in a session and not notice any degradation in accuracy. There are some lead streaks in the bore, but nothing a couple passes with the brush doesn't clear right out. I load even my practice loads at well above the velocities a 40 S&W can safely push.

[9.3X62AL]

Mic your die set's expander plug diameter. Die sets "assume" the use of jacketed bullets in many cases, and the expander plug's stem can measure @ .395"-.396". Even a boolit as hard as 12-15 BHn can be reduced when subjected to seating into a case mouth .005"-.006" under boolit sized diameter.

I had a Beretta 96 as my first 40 S&W pistol. It had the same slight leading tendencies your SIG pistol displays, using the Lee TC 175 boolits with conventional lube groove/sized & lubed in a Lyman 450 @ .401". It was accurate, and the leading didn't build up--it was a sort of "steady-state" condition--but it annoyed me. My SIG P-226 in 9mm had the same habits/tendencies. Neither barrel formed a "lead mine"--but I didn't like it as-is.

I got out the mic and calipers, and saw that expander plugs in both die sets "favored" use of jacketed bullets per their dimensions. Just for grins, I bought a Lyman Multi-Charge Expander Die set, with its powder-through-expander capability that also effectively subtracted a die step for my semi-progressive (turret variation) loading regimen. The "tale of the tape" on the Lyman expander spuds showed them to be significantly larger than those found in the RCBS die sets. I loaded lots of ammo in both 9mm and 40 S&W, the only changes being the use of the larger expander spuds. Leading was gone, for all practical purposes--just a slight gray "wash" was present after 150 rounds.

OK, says I--that was progress. What other process(es) in the reloading cycle am I doing that could be causing a reduction in boolits' sized diameter? After an appropriate amount of brain-storming, deliberation, divination, and conjuring--it hit me. Taper-crimping. Especially if done with the idea that "if a little is good, then more must be better". I regard taper-crimping of autopistol cast boolit loads as being a necessary evil--to be applied in only that amount that straightens the case mouth flare back out AND NO MORE--and done as a distinct die step from (after) boolit-seating. This last "tweak" eliminated the gray wash from my 9mm and 40 S&W barrels. Completely.

We as casters go to great pains to match our castings to the internal dimensions of our firearms. All of that effort is wasted if care isn't exercised to assure that seating these boolits doesn't spoil all that good work. Think of this as another ideation of the old carpenter's saying "Measure once, cut twice--measure twice, cut once".

[Jayhem]

Interesting. didn't think to measure the expander die bullet and see what diameter it is actually expanding my necks to. I expand until I can just start to see the flare and when I do the cast boolits go right in with light effort and then are taper crimped just enough to get the case walls straight again.

The leading I am getting is only a few streaks and doesn't get worse the more I shoot as far as I can tell. I do have some pitting in this barrel because I bought the pistol from an ex-police officer who carried it for several years and likely didn't clean it enough. I may have to buy a new barrel if pitting is the cause of my leading issues.

The leading I'm getting requires soaking in Kroil overnight and brushing with a bronze brush to get it clean again.

[thegreatdane]

What other process(es) in the reloading cycle am I doing that could be causing a reduction in boolits' sized diameter? After an appropriate amount of brain-storming, deliberation, divination, and conjuring--it hit me. Taper-crimping. Especially if done with the idea that "if a little is good, then more must be better". I regard taper-crimping of autopistol cast boolit loads as being a necessary evil--to be applied in only that amount that straightens the case mouth flare back out AND NO MORE--and done as a distinct die step from (after) boolit-seating. This last "tweak" eliminated the gray wash from my 9mm and 40 S&W barrels. Completely.

+1. Light-Moderate taper crimping has solved my leading problems in 9mm and .380. Keep that case mouth to spec if not a tiny bit larger. You'll swage your meticulously cared-for bullet down undersized.

I believe it's important to note, as you back off your TC, please remember to check for the possibility of bullet setback. For me, I press the nose as hard as I can into the bench. If no movement, I call it safe and continue.

[Echo]

You mention that seating is fairly light-duty. Therefore, it's my bet that you aren't sizing down the 12-15 bhn boolits when seating - but it is still a good idea to seat, chamber, then pull a couple and see if that is the case. 'Assume, but verify'.

Two thousandths o'size should be no challenge for the barrel, but ensure that they will chamber reliably.

[Jayhem]

You guys mention pulling a loaded boolit. How exactly can I accomplish this without damaging the boolit circumference? can I just grab the nose of the boolit with pliers and tug it out?

[gray wolf]

bullet puller-- kinetic or Collet type.

[thegreatdane]

I prefer the kinetic ones cuz they don't scrape up the bullet.

[Bret4207]

Not to be picky, but in the interest of clarity your didn't mean "...over bore size?...", you meant over GROOVE size. The difference in terms has confused more than one noobie.

[sqlbullet]

The leading I am getting is only a few streaks and doesn't get worse the more I shoot as far as I can tell. I do have some pitting in this barrel because I bought the pistol from an ex-police officer who carried it for several years and likely didn't clean it enough. I may have to buy a new barrel if pitting is the cause of my leading issues.

If it doesn't affect accuracy, I wouldn't worry about it. There are plenty of threads here about guys that don't even try to get the 'streaks' out.

I only do because I it is my every day carry, and I carry JHP's.

[Jayhem]

Not to be picky, but in the interest of clarity your didn't mean "...over bore size?...", you meant over GROOVE size. The difference in terms has confused more than one noobie.

Thanks for clarifying. I know about groove/lands but I assumed most would know what I meant by "bore size".

[geargnasher]

Jayhem, I think 9.3X62AL really pinpointed your problem with your expander being, well, more of a "bellmouth" tool than a true "expander". Most die sets are made for jacketed bullets which aren't subject to being swaged down when seated in the case if the case is too tight. There is a safety reason for this, in automatics the bullets can get pounded deeper in the brass under recoil in the magazine if there isn't enough case tension on the bullet, and this can cause drastic pressure increases and sometimes "Kabooms".

When shooting cast boolits, often a much larger and longer expander plug is needed to stretch the case, not only the mouth, but the whole area where the boolit will be seated or the case can squeeze the softer lead like putty. If that happens, and most .40 die sets are notorious for having totally wrong expander sizes for cast, then your .401 boolit may actually be entering the throat of the barrel at .399 or even smaller, and this will most certainly cause leading.

Some other things to consider: Water-quenched clip-on wheel weight metal usually comes out between 19-22 BHN after it age-hardens for a week or two, so your mid-teens numbers are a little low. I haven't had much luck shooting 13 bhn air-cooled boolits much past 1000 fps without a little lead wash in the .40, generally my M&P likes them harder. Also, to answer your original question, no, I wouldn't go larger than .001 over bore size as an attempt to prevent leading, I would correct the problem with the expander first. My M&P has a chamber that tapers toward the front, and I have to actually swage the boolit a bit with the taper-crimp die to get them to reliably feed at .402", but .401" they work fine by just barely removing the bellmouth from the case. Once I fixed my expander issue the loaded diameter increased about .0015" where the boolit seated, and that was pushing the envelope already as far as chamber size goes. Your Sig is likely different, but I don't know how much or in what direction.

My experiences with the .40 is that, with higher-end loads, it likes very slow powders like Blue Dot or Longshot, hard boolits (so they don't skid the rifling so badly and get gas leaks/blowby/leading), and I had a custom expander plug made to .400" which lets the brass spring back to .3995 or so and still give me .0015" case tension while letting the boolits come back out of the case still being .401". Seating depth was another thing that took many trials to get just right so the gun feeds but still groups well. If you want to load milder stuff, treat it like a .45 ACP, use fast-to-medium pistol powders, air-cooled wheel weight boolits at 10-12 bhn, and keep pressures around 16K CUP and velocities around 800 fps.

Hope this helps,

Gear

[Jayhem]

Gear: Thanks for the good information. I have been searching the .40S&W threads on here and you have offered a wealth of information to the community, thanks!

I will certainly use this advice.

Just a quick question: Is there a .40 S&W expander die on the market made for cast boolits or would that be something custom made only?

[geargnasher]

Al mentioned using a powder-through-expander from a Lyman Multi-charge expander die set, that's the only one I'm aware of that's commercially available, but I admit I didn't search very hard, just had one made by a member here, JimInPHX to my exact specifications. Figured it was cheaper than buying one of every manufacturer's expander dies hoping I'd find one big/long enough. Go to the "testing" forum and look for a post by me titled "Spec sheet for Jim" and you'll see the drawings. You might contact him about making one, he did several for me and for at least one other member here. I imagine Buckshot could whip one out too, or any competent local machinist you might know. The specs I listed for the .40 expander were for a Lee Powder Through Expander die to work with the Lee autodisk measure, and to seat .401" boolits at 20 bhn with .0015" case tension. I use the Lee 175 TC and seat to 1.118" COAL in my particular gun. I think I turned the expander down from .401" to .400" after some experimentation with boolit tension and chambering, but I figured I'd better get one made bigger than smaller, kinda hard to add metal back to it!

Gear