9 MM Barrel Twist Questions

Not sure where to post this so I thought here first. Last Friday I was shooting pistols at the local range. I had a S&W Model 39 and a Beretta Model92. I was shooting at 15 yards in the off-hand position. All the m39 hits were in the 10 ring. The Beretta hits were key-holing. I was using a 147 grain round nosed bullet and 3.5 grains of Bullseye using a CCI Small pistol primer. Trying to figure out why the key-holing. Barrel twist? Best guesses are welcome.

AJ said:

Not sure where to post this so I thought here first. Last Friday I was shooting pistols at the local range. I had a S&W Model 39 and a Beretta Model92. I was shooting at 15 yards in the off-hand position. All the m39 hits were in the 10 ring. The Beretta hits were key-holing. I was using a 147 grain round nosed bullet and 3.5 grains of Bullseye using a CCI Small pistol primer. Trying to figure out why the key-holing. Barrel twist? Best guesses are welcome.

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Is the 147 bullet cast or jacketed? Big difference. I don't know what the twist rate on any 9mm handgun is, but you shouldn't be experiencing keyholing with a bullet of that weight unless it's grossly undersized in diameter.

You might start by measuring bullet diameter with a micrometer; a caliper won't work if you want an accurate measurement.

I have a Beretta 92F that I bought new in 1988. It's been fired a great deal, almost exclusively with cast bullets. If the cast bullet is of sufficient diameter, about .358", many cast bullets will shoot well. Jacketed bullets are much more forgiving; a .356" or so should work fine.

According to "internet searches", the Beretta has a 1 in 9.84 twist and the S&W is 1 in 16. It would seem the Beretta would stabilize the heavier projectile better than the slower SW twist, sorta like the 1/7 is better than 1 in 12 for heavier and longer 5.56mm. I got nothing more. Joe

What kind of bullet? Cast lead, swaged lead, copper plated, jacketed, polymer coated, etc.? Theoretically, the tighter twist should shoot tighter groups, but real life isn't always the same as theory. It almost looks like the Beretta was a .40 cal.

The bullets are cast lead and the Mitutoyo caliper shows .356 and the Starrett Micrometer it shows .356. The bullets were manufactured by National Bullet Co. of East Lake, Ohio.

AJ said:

The bullets are cast lead and the Mitutoyo caliper shows .356 and the Starrett Micrometer it shows .365. The bullets were manufactured by National Bullet Co. of East Lake, Ohio.

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Something appears to be wrong. .365" is way too big; they wouldn't chamber if they were that large. .356" will work, but accuracy would probably improve if they were a bit larger.

rockquarry said:

Something appears to be wrong. .365" is way too big; they wouldn't chamber if they were that large. .356" will work, but accuracy would probably improve if they were a bit larger.

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Typing faster than I should be. It is also .356 on the Starrett. Will fix the original post.

AJ said:

Typing faster than I should be. It is also .356 on the Starrett. Will fix the original post.

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I'm pretty sure your Model 39 has a tighter bore than the Beretta and that's why it is more accurate with the .356" bullets. My Beretta shoots cast bullets accurately, as long as they're .3575" to .358" in diameter. I don't know about other Berettas, but that may be the case with them as well. The large diameter bullets I use in the Beretta also do well in a Sig P226 and a Walther P4. I use Bullseye powder with a 150 grain round nose (Lyman .38 Special mould).

pharmer said:

According to "internet searches", the Beretta has a 1 in 9.84 twist and the S&W is 1 in 16. It would seem the Beretta would stabilize the heavier projectile better than the slower SW twist, sorta like the 1/7 is better than 1 in 12 for heavier and longer 5.56mm. I got nothing more. Joe

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Yes, it's slow twists and heavy bullets that don't get along so if those numbers are correct then it's something else. Keyholing is because the bullet is not spinning fast enough to stabilize. Period.

I've been working with 147 gr bullets and a Springfield 1911 all summer. So far the .356's are not optimum. .357 diameter performs better and even .358 does well but at the maximum powder charge weights I start to see signs of over pressure. I'm going with .357.

You could go to .357 and/or up the powder charge. Another way to get it to spin faster is increased velocity. Might want to skip the relatively fast Bullseye and go with something a bit slower like Universal/Unique to get the velocity up. I've used 3.5gr of Bullseye in the Springfield and it shot as well as most loads with .357 diameter bullets. But as I recall at the moment that's a minimum load. If so try pushing it a bit harder.

As a side note, none of the cast bullet loads I've tried will shoot as well as jacketed bullets in the 9mm. But I've gotten close. I'm not a big fan of "good enough" accuracy but with lead bullets in the 9mm I might just have to accept that.

Of course the proper thing to do is slug your barrel. Then go .001 to .002 over that diameter and check that they will chamber of course.

Loading Cast Bullets in the 9mm Luger | Cast Bullet Association

glenwolde said:

Yes, it's slow twists and heavy bullets that don't get along so if those numbers are correct then it's something else. Keyholing is because the bullet is not spinning fast enough to stabilize. Period.

I've been working with 147 gr bullets and a Springfield 1911 all summer. So far the .356's are not optimum. .357 diameter performs better and even .358 does well but at the maximum powder charge weights I start to see signs of over pressure. I'm going with .357.

You could go to .357 and/or up the powder charge. Another way to get it to spin faster is increased velocity. Might want to skip the relatively fast Bullseye and go with something a bit slower like Universal/Unique to get the velocity up. I've used 3.5gr of Bullseye in the Springfield and it shot as well as most loads with .357 diameter bullets. But as I recall at the moment that's a minimum load. If so try pushing it a bit harder.

As a side note, none of the cast bullet loads I've tried will shoot as well as jacketed bullets in the 9mm. But I've gotten close. I'm not a big fan of "good enough" accuracy but with lead bullets in the 9mm I might just have to accept that.

Of course the proper thing to do is slug your barrel. Then go .001 to .002 over that diameter and check that they will chamber of course.

Loading Cast Bullets in the 9mm Luger | Cast Bullet Association

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Many give up on cast bullets in the 9mm before they find decent accuracy. Granted, it can be frustrating, but like other handgun cartridges chambered in a good quality semi-auto or revolver, a cast bullet that fits and is of the proper alloy for the load will shoot at least as accurately as the best jacketed bullet.

It took me a long time to find this out and I've lost track of the different bullet designs I've tried in 9mm, but the work paid off. I've always enjoyed load development anyway.

You can slug bores, but I've found a general rule that works well is to use the largest diameter bullet that will permit a loaded cartridge to chamber without difficulty. Using this approach, you can still stay inside the maximum recommended SAAMI outside diameter for a loaded cartridge.

Until very recently, S&W used a 1-18.75 twist in everything 9 mm/,38/.357. Due to whining, they changed the twist in 9 mm barrels to 1-10. I doubt that rifling twist has anything to do with the issue.

My C-9 3.5" pistol with a 147 gr. Speer TMJ at a oal of 1.165"
with 3.3~ grs of Bullseye is around 828fps and at POA with 1-1.8" rest groups.

My 5" barrel with the same load but the Berry plated RN bullet does 874fps
but it has very poor accuracy.

The Berry does better at 905fps or faster in my long barrel M92
with Green Dot or slower powders.

What is the bore diameter of the Beretta? If larger than 357, 358 it could be the cause of the key holing.

rockquarry said:

Many give up on cast bullets in the 9mm before they find decent accuracy. Granted, it can be frustrating, but like other handgun cartridges chambered in a good quality semi-auto or revolver, a cast bullet that fits and is of the proper alloy for the load will shoot at least as accurately as the best jacketed bullet.

It took me a long time to find this out and I've lost track of the different bullet designs I've tried in 9mm, but the work paid off. I've always enjoyed load development anyway.

You can slug bores, but I've found a general rule that works well is to use the largest diameter bullet that will permit a loaded cartridge to chamber without difficulty. Using this approach, you can still stay inside the maximum recommended SAAMI outside diameter for a loaded cartridge.

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I may give up. I'm not sure it's worth it. I've tried 115gr, 124gr, 147gr with half a dozen powders. The lead bullets aren't horrible but not as good as jacketed in the same weight. I'd call them "decent". Well the 115's cast were horrible. The rest were decent. If I test any given weight in lead it performs worse than the same weight in jacketed.

My Springfield 1911 will chamber everything. Clearly .358's were a bit tight. I would not be surprised if it chambered .359's.

Maybe it's hardness but if I have to cast my own out of straight Linotype to get it to work, eh, that's a lot of trouble (and expense) considering everything else I load for works fine with <whatever> alloy.

I may end up just sticking with jacketed bullets. Precision Delta's 124gr JHP (a HAP clone) aren't that much more expensive than cast. They're like $120/thousand.

glenwolde said:

I may give up. I'm not sure it's worth it. I've tried 115gr, 124gr, 147gr with half a dozen powders. The lead bullets aren't horrible but not as good as jacketed in the same weight. I'd call them "decent". Well the 115's cast were horrible. The rest were decent. If I test any given weight in lead it performs worse than the same weight in jacketed.

My Springfield 1911 will chamber everything. Clearly .358's were a bit tight. I would not be surprised if it chambered .359's.

Maybe it's hardness but if I have to cast my own out of straight Linotype to get it to work, eh, that's a lot of trouble (and expense) considering everything else I load for works fine with <whatever> alloy.

I may end up just sticking with jacketed bullets. Precision Delta's 124gr JHP (a HAP clone) aren't that much more expensive than cast. They're like $120/thousand.

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I'm certainly no cast bullet expert, but there is some indication that the softest bullet that will shoot at your desired velocity without leading the bore will be the most accurate. I've seen more in the way of proof that this occurs with rifles, but I suspect it's also the case with handgun bullets.

I normally use an alloy mix that's a little softer than Lyman #2 but a bit harder than wheelweight alloy but I think it would probably work even better if it was a little softer.

Inaccurate is one thing and can be worked on by load experimentation.
But the bullets landing sideways at 60ft would seem to say something else is in play,,
unless of course any other ammo thru the pistol shoots 'straight'.

Does a very close look at the bore of the Beretta show any hint of a poor rifling job, un-usually shallow, uneven cut, anything that strikes you as not being normal.

l had an old "War Hourse" that I finally had to just bite the bullet and

buy a new barrel for, in order to get it to shoot well again.

Good luck finding the problem.

The short for caliber 9mm bullets, even up to the 147 grain bullet, really need no more than a 1 in 16" rifling pitch to be accurate when the velocity is appropriate.

A lower than normal velocity for a bullet's length and weight and the rifling pitch of the pistol will promote tumbling. Perhaps this is the issue with your 147 grain cast bullets, although that fast twist in the Beretta should be stabilizing them.

It's interesting that the slower S&W twist is fine, but the faster Beretta twist rate is not. It should be the opposite. Odd.

AJ, FWIW I have loaded 9mm for a very long time. Over many years, and many types of 9mm pistols, one thing remained constant. I never got best accuracy using cast bullets. The common NATO type chambers and 1 in 10 twist are apparently not conducive to best accuracy with cast bullets. I haven't owned a Beretta in some time, but suspect they have the NATO type chamber. I did have one Hi-Power that routinely keyholed cast bullets, but with jacketed bullets was as accurate as the several other Hi-Powers I owned with factory barrels. I tried a number of profiles, weights, diameters, powders, velocity levels, etc., but never archived accuracy equal to jacketed bullets. I even tried cast bullets in pistols like the SIG P210, FN/Browning GP Comp Hi-Power, etc. Still no luck. A dedicated cast bullet barrel used to be available for the Swiss 210s, but I never went to the trouble and expense of obtaining one. Others have reported they've developed cast bullet loads that satisfy them as to accuracy, but I admit, with one exception, I never got there. The exception was the BarSto barrels I used in 2 or 3 Hi-Powers. Those did achieve a much better level of cast bullet accuracy than any of my factory 9mm barrels.

I have an old magazine article around here, if I could find it, detailing 9mm accuracy tests in a Hi-Power using the factory 1 in 10 barrel, and 5 or 6 barrels the author had Barsto make up with different twists, rifling leades, etc. He did make mention of cast bullet keyholing with the 9mms. Seems like he did report what might be necessary to achieve good cast bullet accuracy in 9mm pistols.

Anyway, when someone reports accuracy, or even keyholing issues with 9mm pistols, I can't say I'm surprised. Barring an issue with the barrel itself, perhaps you'll find that magic cast bullet combination, and all will be well. Best of luck with your efforts.

I read about half way down the thread and then skipped the rest, so pardon any duplication. There were some good advice and some not so good, but here’s my tale based on 40 plus years of cart bullet shooting in a wide range of rifle and pistol cartridges.

1) while it is true that slow twist and he’s y bullets can be a poor combination, it’s not that simple. The rifling only has to be fast enough to stabilize a given bullet of a given length (length, not weight is the critical factor) at a given velocity, longer bullets just tend to be heavier).

2) A long/heavy cast bullet in a rifling with excessively fast rifling twist can be a major problem under some circumstances as the bullet can essentially skid on entering the rifling. That can create excessive leading, which then exacerbates the skidding problem and increases the leading. It doesn’t take many shots to reach a point before your now virtually smooth bore leaded barrel starts key holing bullets.

3) lead hardness is a big factor. The conventional wisdom is that you need harder lead for faster velocities but that conventional wisdom is wrong, or at least a bit confused. The ally hardness needs to match the pressure of the load. For example you can take a .30 caliber bullet and cast it from wheel weights and tin and then water quench it and when it cures in 2+3 weeks you’ll have a Brinnell hardness up around 32. Really hard stuff, and it’ll lead really bad in a .30 caliber center fire rifle, as the bullet is way too hard to quickly obturate into the lands and grooves. While it is busy not obturating, hot, high pressure gas is flowing past the bullet and cutting lead off the bullet and then depositing it in the barrel.

Softer really is better (until it’s too soft), as the bullet must be able to expand in the throat and the bore to produce a good seal in the rifling. There’s a sweet spot in alloy hardness where the bullet both quickly obturates under the initial pressure of the load, but is still hard enough to not get stripped in the rifling.

This is where faster rifling is a disadvantage as it requires a harder alloy, especially if there is a long throat or leade that allows the bullet to pick up significant velocity before it enters the rifling.

For that reason, most serious cast bullet shooters want rifling on the end of the sufficient range to minimize the bullet hardness requirements. It’s one reason why a .38-55 with a slow twist of around 1-20 shoots heavy cast bullets much better than a .375 Win with a 1-12 twist. The .375 win can develop a lot more pressure, but you can’t use it as it’ll lead badly regardless of alloy used.

4) bullet diameter is the other big factor. Again the conventional wisdom says cast bullets should be .001 over groove diameter for best performance. Again, that conventional wisdom is often wrong. It’s an ideal, and a place to start but there is a lot more too it. The bullet has to obturate in the throat and leade, not the bore. If not you again get significant gas cutting and leading.

Using the .375 Win example again, Winchester used a very long and generous throat in the .375 Win chamber introduced in their BB94 so that it could in fact be fired with the longer, and larger diameter .38-55 cartridge. For the 200 and 250 gr jacketed bullets it was designed for it didn’t matter. However those large throat dimensions and long leade mean cast bullets have to be selected to fit the throat, not the bore. That usually means using a .379 or .380 diameter bullet to allow it to obturate in the throat and then size itself down to bore diameter.

If you shoot a .376” bulletin in it gas cutting will create leading long before it reaches the bore, and if you use an alloy soft enough to obturate in the large throat, it’ll strip in the fast rifling. It just wasn’t meant for cast bullet use,

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In short, bullet alloy hardness has to be properly matched to the pressure of the load, not the velocity, *AND* the bullet diameter has to be matched to the chamber dimensions, not the bore dimensions. Finally, the rifling needs to be fast enough to stabilize the bullet, but anything faster puts more stress on a cast bullet than slower rifling and creates a need for a harder alloy that won’t obturate as well. Those factors serve to create an increasingly narrow range where you can get good cast bullet performance, without having leading due to gas cutting on the “too hard” end of the spectrum and leading due to stripping in the rifling at the “too soft” end of the alloy hardness spectrum.