MBC 158 LSWC, seating depth & crimping questions.

C

Carmady

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I have some Missouri Bullet Company 158gr LSWC for .38 SPL, 12 BHN.

I seat the bullets without crimping, and follow that with taper crimping as a separate operation. COL is about 1.475" which puts the case mouth near the bottom red line in the pic. Then they get taper crimped at the cannelure (bottom red line).

Last night I discovered that the COL shrinks from 1.475" to 1.470" after taper crimping. I figured the taper crimping was forcing the bullet .005" deeper into the case, and started wondering if the cannelure was there for a roll crimp and shouldn't be used with a taper crimp.

I've been getting excessive leading with these bullets, and wondered if that could be from an insufficient crimp allowing the gasses to go around the bullet and cause the leading.

I found a post on the net where a guy said he taper crimps in the middle of top driving band. See top red line in the pic. He didn't specify whether or not his bullets had a cannelure, but I decided to make a few that way and test them. Seating the bullet for this approach reduces the COL to 1.410".

Please advise on where I should crimp these things.

Pic of the bullets:
 

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I don't think it matters much if your taper crimp moves the bullet .005".
I guess you could shoot some crimped your way and some his way and see which is more accurate or leads less. Unless you are loading maximum magnums, it won't matter on pressure.

Me? I roll crimp in the groove provided.
 
Simply crimp them under the top driving band and forget about the "shrinkage". You are NOT getting leading because of the OAL. Leading is almost always caused by undersized bullet base or driving bands which allow gas to go past the bullet as it's moving down the barrel. You also need to measure the chamber diameter, forcing cone diameter, and bbl. diameter. If you're squeezing the bullet down too much in the chamber or forcing cone and then sending it down a bbl. that is larger than either of these two spots, you're allowing gas to get by the bullet in the bbl. One other thought: is it actually lead you're seeing in the bbl. or simply residue from the bullet lube? OAL in a revolver is not significant as long as the bullet will allow the cylinder to rotate through the cycle to the next round. You can get leading if you're driving lead bullets to maximum velocities in some calibers. I get some leading on plain based bullets in my mag. handgun calibers when I push them too hard. If you're shooting 38Spl loads I doubt this is the problem.
 
For the life of me, I cannot come up with a scenario where anyone would have to use other than a slight roll crimp (in the crimping groove), on cartridges intended for a revolver. As for leading, check your cylinder throat size compared to your bore size.

You also did not mention the powder and charge weight you are using. Most leading is caused by too tight of throat size compared to the bore and just plain trying to push a bullet too fast for the alloy...the old 2.7 grains of Bullseye with butter-soft swaged 148 grain hollow based bullets never caused a leading problem for the old-time target shooters.
 
I wouldn't consider that a cannelure. That is a crimp groove for a roll crimp just like you are supposed to do with a revolver bullet.

You can use a taper crimp if you want, but I can't see any benefit. I can think of a dozen other culprits that are more likely causing the leading rather than the taper crimp.

Some people don't like to use the roll crimp because it takes longer to correctly setup the die but, if i'm going to spend the time to reload I figure I might as well do it correctly. The roll crimp die should smoothly move the brass into the roll crimp groove with no deformation of the bullet and no bulging of the brass. If setup incorrectly both of these things can happen and cause problems. Additionally the roll crimp die can be set to only remove the bell from the expanded case, a light crimp, a moderate crimp, or a heavy crimp.
 
For any bullet with a crimp groove or cannalure, I roll crimp (or use a Redding Profile Crimp). Some folks use a taper crimp on their revolver bullets, mostly wadcutters, for their low velocity target ammo. They feel the lighter crimp aid in accuracy by not distorting the bullet.

I'd suggest you reload a round like you normally do and then pull the bullet and measure it with a micrometer. Your crimp (that's hard enough to push the bullet deeper) may be swaging the bullet small enough to cause leading (of course you've slugged the barrel and measured the cylinder throats already?)...
 
"I don't think it matters much if your taper crimp moves the bullet .005".
I guess you could shoot some crimped your way and some his way and see which is more accurate or leads less. Unless you are loading maximum magnums, it won't matter on pressure.

Me? I roll crimp in the groove provided."

Thanks for the reply. I have the 3-die carbide set from RCBS, the third being a taper crimp die with a seating plug; the same die sets for .38/.357, .380 ACP, and .45ACP. I've never had a roll crimp die, and always taper crimped lead.

I've been shooting them from a 642 and a LCR. I just found out the bullets will pass through the LCR's throats, but not the 642's.
 
"Leading is almost always caused by undersized bullet base or driving bands which allow gas to go past the bullet as it's moving down the barrel."

That's why I suspected the iffy crimp was contributing to the leading, by letting the gas around the side. I measured a few bullets and they're just under .358". Thanks.
 
For along time it has been my understanding with handguns that the crimp is needed to make the pressure. It's always been a roll crimp I believe. Long as I've been shooting cast bullet's you'd think I really understood one from the other.

That groove between the red lines is the crimp groove. Notice how it is made? Suggest's to me a roll crimp is needed. I don't have a clue why anyone would use a taper crimp. My guess is that it's used for rifles. But I have a couple rifle's I'm shooting cast in and the crimp groove is there so I crimp.

Don't know about commercial cast bullet's but I'm wondering if powder coat might stop the leading?
 
"For the life of me, I cannot come up with a scenario where anyone would have to use other than a slight roll crimp (in the crimping groove), on cartridges intended for a revolver. As for leading, check your cylinder throat size compared to your bore size.

You also did not mention the powder and charge weight you are using. Most leading is caused by too tight of throat size compared to the bore..."

I don't have a roll crimp die. I only .38s I've loaded in the past were lead 148gr HBWC which use a taper crimp; and a different brand of 158 LSWC which didn't have (iirc) a groove for a roll crimp, and got taper crimped like a 45 Auto lead bullet.

I checked the throats and found the bullets don't pass through the 642, but do pass through the LCR.

For powder charges, I was trying to get close to the FBI load:
Power Pistol/5.5gr
Unique/5.2gr
231/4.3gr
HP-38/4.3gr
That was the first time with those bullets, about 25 rounds of each with the 642, and the leading was bad so I decided to try one load per range session to isolate things...

HP-38/4.3gr, 58 rounds with LCR, heavy leading
Unique/4.7gr (down from 5.2), 50 with 642, medium leading
Unique/4.7gr, 50 with LCR, medium leading
Power Pistol/5.2gr (down from 5.5), 50 rounds with 642, medium leading

I was loading with 4.3gr of Unique when I noticed the taper crimping was pushing the bullet further into the case, haven't shot those yet.

Thanks to everyone for their replies.
 
I don't have a roll crimp die.
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All the major brands...all the .38 Special dies I know of, come with the roll crimp feature. It is optional however, as to how you adjust your seating die whether you use it or not.

Whoops! I see that there are taper crimp dies (RCBS) in .38 Special...evidently I have grown old and they have pulled some more new stuff on me again...coming up with ingenious solutions to nonexistent problems.
 
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I ran a lengthy series of tests with my 357MAX using crimped vs uncrimped bullets in a Low Wall rifle. With few exceptions, crimping made no difference in accuracy at 100yds and POI was nearly identical. The only powder I found to have any significant difference was W296, where the groups opened up somewhat with no crimp. Even then, the uncrimped loads shot fairly well. In some cases, the uncrimped rounds actually shot better. My conclusion was that crimping does a lot more to hold the bullet in place than it does improving accuracy or consistency.
 
Please advise on where I should crimp these things.
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Right were you're crimping those things - at the crimp groove.

I load and shoot a lot of the MoBuCo's 158 LSWC's, BNH-12 (and the 18's too; but mostly the 12's). AND . . . I taper crimp them - just like you.

I will tell you that without a doubt - and I have pages of chronograph data to prove it - that taper crimping them will produce a plenty consistent round. That is, assuming you're not using some exotic propellant that requires a magnum primer, and heavy roll crimp - like W296 or HS-6 - that sorta thing.

I load these for ICORE competition and they shoot tac-driver accurate. There is no need to roll crimp them. There's no harm in it, certainly (the groove is designed for roll crimping), but no need either. These 158's have plenty of surface contacting the case where applying a roll crimp is superfluous.

As far as leading goes; well, I've had a gut full of leading discussions. Not touching that part.
 
"Whoops! I see that there are taper crimp dies (RCBS) in .38 Special...evidently I have grown old and they have pulled some more new stuff on me again..."

My first set of dies, got them about 20 years ago.
 
"Right were you're crimping those things - at the crimp groove.

I load and shoot a lot of the MoBuCo's 158 LSWC's, BNH-12 (and the 18's too; but mostly the 12's). AND . . . I taper crimp them - just like you."

Thanks, that's reassuring. There's been no scorching of the case mouths, which I think I read was indicative of a weak crimp.

I've been learning a lot about stuff like leading, chore boy, bronze wool, since I started using MBC 158gr bullets. I'm not blaming the bullets, because the guns are also new in terms of round count, so it's the combination of the LCR and 642, and the MBC bullets.

According to my dial caliper the .38 SPL bullets are just under .358", which is what they should be. They won't pass though the cylinder throats on the 642. I also tried a .355/.356" MBC .380 LRN and it won't pass through the throats on the 642. That tells me the throats are too small, either made that way or leaded up. I'll take the brush and bronze wool to the cylinder again to make sure.
 
Thanks, that's reassuring. There's been no scorching of the case mouths, which I think I read was indicative of a weak crimp.
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Wrong. This "scorching" you're referring too is almost always caused by using a powder that doesn't burn well in the amount used for the bullet selected, or it's because you're using cast bullets and it's simply the lube residue on the case. Some powders are notorious for doing this and some are equally well known for not doing it. You're over focusing on crimp and what it might do. Look for a different powder for your loads. For one, Unique and cast bullets leaves soot on the case mouth all the time. It's just a dirty combination. In spite of that it still shoots well most of the time and the soot is irrelevent other than it's a pain to clean up without a tumbler.
 
Wrong. This "scorching" you're referring too is almost always caused by using a powder that doesn't burn well in the amount used for the bullet selected, or it's because you're using cast bullets and it's simply the lube residue on the case.
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Maybe I should have specified scorching on the outside of the case, if that makes a difference. I believe the explanation was along the lines that a weak crimp would not hold the bullet securely enough for the case to expand in the charge hole, and the absence of case expansion prevents a tight seal between the case and charge hole, and that's why some cases get scorched on the outside of the case mouths.

The 642 will be on its way back to S&W later today on account of the small throats.
 
Outside case scorching

About case scorching . . .

It's generally caused by insufficient pressure for the case to expand enough against the charge hole wall to prevent propellant blow-back. I think we all know that. But . . .

In the 38 Special world, given its low pressure specs, I wouldn't read a lot into it. Basically, outside case scorching is more or less normal for this cartridge. (45 ACP too)

Also, blow-back only means that at some point there wasn't sufficient pressure. It is possible that it occurred during the initial phase of combustion, but the case did take a seal as the combustion progressed.

I've been shooting 38 Special for decades. I've seen little rhyme or reason to case scorching, and overall, it seems rather prevalent for the cartridge. I stopped reading those tea leaves many years ago.
 
It seems you're getting some strange information on crimping, charges, etc., and the posts above are good accurate info. (forums are good places to get good information, but also a place to get confusing, misdirecting old wive's tales/opinions). While your gun is being repaired, perhaps some review of basics? Mebbe a text like The ABCs of Reloading, or perhaps the "How To" section of a good reloading manual? (Hornady has an excellent How To" section). Crimping is basic and although there are many opinions on what and how it's done, you can use old "rules of thumb"; any bullet with a crimp groove or cannalure gets a roll crimp. Bullets without groove or cannalure get taper crimped. There are exceptions of course, but for a newer reloader, this will get you through with very little trouble. As far as load levels and "scorching" (soot) cases, it normally does no harm to the gun or case, just stick with loads from your manual, starting loads or upper, near max. loads, and you'll be fine. After you gain knowledge and experience reloading, these thing will become apparent and you'll have no problems with them...
 
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