Sizing bullets to cylinder throats

[curioushooter]

I never really paid much attention to this sort of thing until recently...when I read an article in Handloader that reccomedned sizing bullets to match revolver cylinder throats. Makes sense to me.

I pin gauged my S&W 624 (44 special) and all six throats will take a .432 pin but not a .433.

Is there rule for what bullet sizing die should be used? A .432? I suppose I should want a mold that throws at least a .432, too.

There is a very slight barrel constriction at the threads. Is there a way to lap this out without further enlarging the throats via fire lapping (which I've done to other firearms besides revolvers)?

[DHDeal]

I haven't read that particular article, but that is the general consensus. I started sizing to throat size as soon as I started casting handgun bullets as I had read so many threads stating that if you wanted accuracy and clean barrels you should (more or less). To me it made sense and it has been the case for me. Another good point you read is having the throats being as close to the same as another accuracy "trick" and it too has been the case for me.

Sometimes this bullet sizing gig can be a chore due to having very large throats. You can always size smaller, but you can't size bullets larger is a fact though🤣🤣🤣.

Your barrel constriction issue has been covered many many times. A blued barrel is easier to fire lap than a stainless barrel is also a general consensus. The Rugers seem to be more likely to have this than a Smith, or at least I pay more attention to single actions than double actions so I've read more about the issue there. I've been lucky with barrel constrictions and not so lucky with mismatched undersized throats.

[6bg6ga]

What happens to your theory when you have a throat larger than your barrel? I guess I'll continue to size bullets to the barrel.

[Tatume]

If the throats are not larger than the barrel, you can send the cylinder to DougGuy and he will fix it.

[USSR]

What happens to your theory when you have a throat larger than your barrel?

You still size your bullets to the cylinder's throat size. I have a couple of the early S&W Model 25's with the large throats and size my bullets to .455" even though the barrel is .451" - .452".

Don

[Greg S]

Size to throats and let the forcing cone sage the bullet down. If it is a blued gun, fire lapping with easily remove the barrel thread choke constriction if it is minor. Check Bear tooth Bullets website for details.

[curioushooter]

What happens to your theory when you have a throat larger than your barrel? I guess I'll continue to size bullets to the barrel.

You better hope your throats are larger than the groove diameter of the barrel. If they are not they swage the bullet down and it is undersized for the rest of the trip down the barrel.

With softcast bullets and most thin jacketed bullet in theory they obturate to fill the bore if there is adequate pressure. There are of course limits.

I've read every thread on this forum regarding lapping constrictions. I didn't find an answer to this, at least what I consider a satisfactory one: I have heard of folks putting abrasive in the barrel and then firing the projectile so that the throats never see the abrasive. Anybody work this out? I am not enlarging already larger throats or making them potentially different. Also, they are perfectly mirror glass shiny smooth. Any reputable folks out there that perform hand lapping?

[georgerkahn]

"My" rule of thumb has been to take a sized, lubed, bullet, and drop it into a cylinder. If the bullet falls through by its own weight, or a thump of revolver to my other palm -- then it's too skinny. A fatter bullet is needed! At the other extreme, if it takes more than moderate -- say, three or more pounds -- of pressure to get through -- then it's too fat, and needs to be resized -- I go ~ one thousandths at a time.
Annnd, if it can be pushed through with the eraser end of a lead pencil using roughly two pounds pressure -- then -- (imho) it's just right.
Nothing scientific here; and, I've never explored barrel diameter versus throat. I've many times slugged throats -- primarily to ensure all holed in a cylinder are the same size, as well as what it is. And, I've only has one revolver (a S&W Model 11 .38 S&W) which seemed to lead no matter what I did :( ---
But... all in all... this is what I do, and has worked for me.
geo

[Tatume]

[SIZE=3] "My" rule of thumb has been to take a sized, lubed, bullet, and drop it into a cylinder. If the bullet falls through by its own weight, or a thump of revolver to my other palm -- then it's too skinny. A fatter bullet is needed! At the other extreme, if it takes more than moderate -- say, three or more pounds -- of pressure to get through -- then it's too fat, and needs to be resized -- I go ~ one thousandths at a time.

Hi George,

This is an excellent example of direct measurement.

Take care, Tom

[curioushooter]

"My" rule of thumb has been to take a sized, lubed, bullet, and drop it into a cylinder. If the bullet falls through by its own weight, or a thump of revolver to my other palm -- then it's too skinny. A fatter bullet is needed!

Yes, this approach is no doubt sound, but I would prefer purchasing ONE sizing die an no others. That is why I want to know what the rule is regarding throats. The throats are consistently .432+ Should I get a .432 sizing die? Or a .433? Probably wont matter much.

My M19 has a .357+ throat. I size those bullets .358 and they work great. Never bothered to check the bore on it because it shoots just fine. It is a P&Red Smith, however; the 624 is not.

[Tatume]

If your technique is sound, then 0.432" is the correct diameter for your cast bullets.

[megasupermagnum]

If that was the only 44 I owned, I would size to .432". Since all my other guns take a .431", I would use a .431". I don't know your own situation. You can fire lap your gun with a fire lap kit. It's kind of a PITA, but does work well. It will only lap your tight spot.

[Bass Ackward]

Unless you are going to clean after every cylinder full, measure / test after a shooting secession. (which usually changes the measurement.) And I have 5 sizers for 44 caliber because hardness & design affect the final diameter. If you shoot only 12 BHN or below, you can get away with one. Using a single size can lead to false conclusions about hardness & leading as you will often read here.

[curioushooter]

You can fire lap your gun with a fire lap kit. It's kind of a PITA, but does work well. It will only lap your tight spot.

How is that possible? My understanding of fire lapping and the nature of abrasives is that the most ABRASION will happen immediately forward of the case mouth (the throats). The abrasive will break down and be less sharp as it travels down the bore. This is why it works so well for rifles (which I have fire lapped many). It results in a slight taper from breech to muzzle since the abrasives cut the most at the breech and the least at the muzzle.

[Outpost75]

I'm with CuriousShooter on this one. Fire lapping causes wear of forcing cone and cylinder throats, but does little or nothing to mitigate a thread choke. A round-hole broach is the factory method to repair thread choke unless you pull the barrel, cast a lead lap and then uniform the barrel dimensions, chase the threads and reinstall the barrel, cementing with 242 Loctite so that the looser threads will stay tight without putting a hoop stress on the barrel.

[megasupermagnum]

The fire lapping hits the constriction, which is pretty much right away. After that it will be sized down, and no longer effective. Do this enough times, and it should result as you say, in a slight taper from one end to the other. Most importantly, it can lap out the constriction.

[megasupermagnum]

I'm with CuriousShooter on this one. Fire lapping causes wear of forcing cone and cylinder throats, but does little or nothing to mitigate a thread choke. A round-hole broach is the factory method to repair thread choke unless you pull the barrel, cast a lead lap and then uniform the barrel dimensions, chase the threads and reinstall the barrel, cementing with 242 Loctite so that the looser threads will stay tight without putting a hoop stress on the barrel.

I only did it once to a blued steel S&W, and it 100% cured it. A pin gauge slides all the way through with no resistance. Cylinder throats were not effected, at least not significantly. I don't know about the throat, it looked fine to me. That gun is now gone, but it shot great after that. I hear stainless guns are a whole other deal, being incredibly hard.

[DHDeal]

Far from the expert, but depending on alloy, you might not get away with one sizing die.
I know from my casting and sizing that a softer alloy (20/1 I use as this example) will not spring back and will be smaller due to this. My harder alloy WW + tin will spring back some. I measure with a good micrometer and not a caliper.

Georgerkahn's method is what I do, more or less.

Are you lubesizing or PCing your bullets is another good question.

Good luck on the thread choke and I believe Outpost75 knows what he is talking about, but on some of the other forums experts have suggested doing the firelap drill.

[Larry Gibson]

I'm one who disagrees with the philosophy of "always size to the cylinder throats". I did considerable testing using a Ransom Rest and testing at 50 yards along with shooting off other rests at 25 yards found if the bullets were larger than .002 - over the barrel groove diameter then accuracy really wasn't improved and sometimes was worse. A lubed cast bullet coming out of a .429 groove diameter barrel is going to be swaged down to .424 - .427 because it also has to ride over a thin layer of lube. Thus a bullet starting out into the barrel .002 - .003 over groove diameter is getting sized down .005 - .006 under a lot of pressure very quickly. That can do some bad disfiguring of the bullet, especially the base.

I also found with cylinder throats .003+ larger than barrel groove diameter a harder cast bullet that did not obturate .001 - .002 larger than barrel groove diameter gave better accuracy than a bullet sized .003+ over barrel groove diameter. I also find leading in the throat and barrel to be more a function of the alloy, lube and powder used than "fit" to the cylinder throats.

Yes, I know many will disagree here but that's what I've found. I shoot .430 sized bullets in my Ruger and Hawes 44 Magnum revolvers with excellent accuracy and no leading. The Rugers throats are .432 and the Hawes are .433. I actually shot 5000+ cast bullets (COWWs) sized .429 and lubed with Javelina through the Hawes with excellent accuracy and no leading before I read I was doing it all wrong. Testing has shown bullets sized .431, .432 and .433 shoot no better (the .433 shot poorly as the barrel groove diameters are .429 in both revolvers) than the .429 and .430. I use .430 sized 44 bullets now simply because that size shoots best in my 44-40 Chiapa M92 which, of course, does not have cylinder throats.

As to the "constriction" I have fire lapped a couple revolvers and it did work as with megasupermagnum. However, I've also found that simply shooting a couple hundred jacketed bullets with top end loads for the cartridge usually accomplishes the same thing.

[curioushooter]

I'm one who disagrees with the philosophy of "always size to the cylinder throats".

Sometimes your hand is forced, Larry. In my case the throats were nicely consistent at .432+ (none would take the .433), but the only Lube-sizer dies available are .429, .430, and .431. So I got a .431 and told Arsenal to make me a Lyman 429421 clone mold that will cast at least .432 (probably their standard dimension).

I had never really given much consideration to this until I read an article (by Brian Pearce) in Handloader. All I "knew" is that the throats better be bigger than the groove dimension, or accuracy will most likely disappoint.


I've also found that simply shooting a couple hundred jacketed bullets with top end loads for the cartridge usually accomplishes the same thing.

This was not a new revolver, and had lead fouling in the barrel when I bought it. It is a 44 Special (S&W 624, which is stainless) so factory JHPs are probably going to be not powerful enough to smooth it out anyway. Most factory 44 JPHs measure .429 and it is dubious if 44 special has enough pressure to obdurate them. The guy I bought it from was quite old and claimed to have taken deer with it years ago, so I figure he probably was a caster/reloader. After cleaning the tittle of lead fouling out of the barrel the pin gauge almost slipped past the "constriction" indicating it is indeed minor.

Anybody consider the idea of applying the abrasive to the area of constriction and then firing a cast bullet into the abrasive? This would save the throats. It would also seem to be a bit easier than rolling the abrasive into the bullet with the steel plates.

[Tatume]

We have a fellow here who will make any size you want, at competitive prices. PM Lathesmith for details.

[Tatume]

That said, 0.431" bullets will work nicely in your 0.432+" throats.

[murf205]

Curious, shoot the .431 boolits before you do anything else. If the accuracy is not what you are looking for and it doesn't lead the barrel, you can always go up to the .432 or down to a .430. You are right to start in the middle measurement and you just might not have to do anything. I have a friend who has a Ruger SRH 454 with .451 throats and a .453 barrel and it shoots like a rifle with no leading at all. That is certainly contradictory to all the theories past and present but I have shot that gun as much as he has and it is a fact that it does not lead. Some of the loads were 260 gr boolits cast with range scrap and they are fairly soft. Admittedly, they were powder coated, which will let a barrel run a bit faster before it leads, but these were 1800fps and it's no wimpy load for a 260 gr. When I slugged the barrel of this gun, I could feel some restriction in the frame area too so it has all the bad qualities a revolver should typically not have to shoot well-but it does.

[KVO]

I've hand lapped a few barrels as well as fired lapped a couple. Fire lapping is definitely more fun and less tedious. You have much more control hand lapping and can feel tight and loose spots -like thread choke- and easily stop lapping when you feel everything even out. You already have most if not all the equipment you need for hand lapping with your casting pot, ladle, etc. PM me if you'd be interested in a more detailed walk through. Bear in mind that when fire lapping you are working the throats to bore in a ratio of 6:1 so the throats take less of a hit during the operation. My personal opinion is that I would not try applying abrasive inside any part of the bore and shooting over it for fear of either bulging the barrel or excess and uneven wear like creating a wash out or loose spot directly in front of the constriction or rough spot you are targeting.

[blackthorn]

I will preface this by saying I have never hand, or fire lapped a barrel. That said, applying a bit of hillbilly logic---Jacketed bullets are HARRRRRd and I suspect that once pushed past any tight spot are highly unlikely to bump-up. So, coating just the obstructed spot(s) and then firing jacketed bullets (at reduced velocities) should work very well. Once sized-down by the obstruction the bullet would remain smaller for the rest of its trip down the barrel, missing all but any other tight spots. It would likely carry some of the lapping compound further into the barrel, but if one were to clean every third or fourth shot it should not cause any unwanted wear.

[Petander]

Curioushooter,

I just got a M29 that needs some maintenance. I wanted to shoot it but didn't find much of my old 44 stuff, I sold my last 44 in 2003 when I got into 500.


I found a Lee 255 SWC mold and a Lee .430 sizer. I made bullets,coated them, 430 leaded and was not accurate. I opened up the sizer to .431, no leading and very good accuracy. Same load and alloy. I also just got a Mihec mold,dropping .432, shoots clean Hi Teked unsized, just confirmed today.

Even the .432 goes rattling through the throats. I will keep the .431 sizer as is for that SWC / alloy combination.

[onelight]

That is nice to be able to shoot them as cast and eliminate a step.

[USSR]

I also just got a Mihec mold,dropping .432, shoots clean Hi Teked unsized, just confirmed today.

I have yet to get one of Miha's moulds that didn't cast them larger than specified. That's good because you can always size them down, but sizing them up......

Don

[megasupermagnum]

I always see people recommend jacketed bullets. I tried about 300 of them. It didn't effect the constriction at all. Lapping, either firelapping, or hand lapping is the only way. Broaching is not a method a regular guy can use.

[curioushooter]

A fellow named Ken Mollohan who wrote for LASC (which presently only has articles against fire lapping written by Mike Bellm) described a clever way to fire lap yet save the throats and seems like it would be especially effective on revolvers. I read about it at Kitchen Table Gunsmith (https://ktgunsmith.com/firelapping.htm). Yet I cannot find any article actually written by the man. It seems like a good idea with a lot less BS involved. No crudding up cases with abrasive, no special cast bullets, not rolling on plates, no wear imparted to the throats.

[onelight]

I always see people recommend jacketed bullets. I tried about 300 of them. It didn't effect the constriction at all. Lapping, either firelapping, or hand lapping is the only way. Broaching is not a method a regular guy can use.
My experience to . No help on thread choke
I have found jacketed to help smooth rifling that has sharp burrs , my Rossi 92 for example would cut patches and looking down the bore you would see little pieces of material hung on them , jacketed does seem to help that . When that extreme you can feel a difference when cleaning after shooting jacketed . Won't make it feel like a quality finished barrel but better.
Another plus is making sure the gun is okay functionally before making any changes to it . If it won't work like it should with factory ammo I will send it back for repair or replacement before wasting my time on mods and working up loads for it.

[Larry Gibson]

With regards to shooting jacketed bullets what I said was; "simply shooting a couple hundred jacketed bullets with top end loads for the cartridge usually accomplishes the same thing. " "Usually" does not mean always.

Like many things we attempt to do, hoping for a solution to a perceived problem, shooting the jacketed bullets will not potentially change the barrel and/or throats in a manner that can not be undone. It has worked for me....usually...but not always.....to the point I have not fire lapped a revolver barrel in 20+ years...… To me it is always worth a try before fire lapping IF the constriction actually is causing problems of inaccuracy and/or leading. Many times (again, not always) a slight constriction actually does not cause any problems in many revolvers given the type of shooting done with them.

[onelight]

With regards to shooting jacketed bullets what I said was; "simply shooting a couple hundred jacketed bullets with top end loads for the cartridge usually accomplishes the same thing. " "Usually" does not mean always.

Like many things we attempt to do, hoping for a solution to a perceived problem, shooting the jacketed bullets will not potentially change the barrel and/or throats in a manner that can not be undone. It has worked for me....usually...but not always.....to the point I have not fire lapped a revolver barrel in 20+ years...… To me it is always worth a try before fire lapping IF the constriction actually is causing problems of inaccuracy and/or leading. Many times (again, not always) a slight constriction actually does not cause any problems in many revolvers given the type of shooting done with them.
I ain't a guy that thinks he knows more about any of this than you :grin: I don't claim my way of doing any of this is best only that it is the best way I have found so far for me
I always look forward to your posts .

[fredj338]

Hmm. If the cyl throats are larger than bore dia + 0.001" then I am fine shooting bore sized + 0.001" bullets. The issue for me is throats smaller & swaging the bullet down before it hits the barrel throat. That is where I get leading & accuracy issues.

[swheeler]

Hmm. If the cyl throats are larger than bore dia + 0.001" then I am fine shooting bore sized + 0.001" bullets. The issue for me is throats smaller & swaging the bullet down before it hits the barrel throat. That is where I get leading & accuracy issues.

barrel throat in a revolver? you mean FORCING CONE??

[Biggin]

Since ya'll are on the subject I'd like to ask a question. I been shooting my 357/38s lately and on every one of them I'm getting some leading in the forcing cone. They are all getting the same load. A 150grn RCBS swc size to .358 over 4grns of 231in 38 cases. In my Smiths I'm getting good accuracy and no leading in the bore. In my rugers I'm getting soso accuracy and no leading on the bores. They all get some leading in the throats. My question is " is this normal? " A .357 jword bullet basically falls right through the throats and a sized .358 boolit requires some pressure. The ruger throats doo seem a bit tighter than the Smiths. And no I haven't slugged the barrels of any of them and I don't have any pin gauges yet. Thanks for any suggestions.

[Biggin]

Ps. I'm using what I believe to be cow as tested by the nice guy that tests lead on this site. Bne? For some reason I can't remember his name.

[swheeler]

By some if you mean very minimal yes that is normal "for MY revolvers with plain based bullets" I also get some lead on the front of the cylinder also with these same loads which is 158 gr and 4.3 gr w231

those 358-158-rf are cast of coww cut with pure to 8-9 bhn

[Biggin]

Thanks swheeler . Yes it's minimal leading I can get most of it out as long as I clean after shooting. The forcing comes on all of them are factory and seem very rough to my eyes. I wonder if smoothing them up would help any at all I don't know. Im a lifetime shooter but still fairly inexperienced with shooting cast.

[243winxb]

My old Lyman said size to groove diameter. After slugging, i ended up with .358, .430 & .452" for Colt GC acp & .451" for an S&W 645 , 45 acp.

30 caliber rifle .309" or .310" Works for me in many different firearms.

Larry Gibson got it right.

[243winxb]

I'm one who disagrees with the philosophy of "always size to the cylinder throats". I did considerable testing using a Ransom Rest and testing at 50 yards along with shooting off other rests at 25 yards found if the bullets were larger than .002 - over the barrel groove diameter then accuracy really wasn't improved and sometimes was worse. A lubed cast bullet coming out of a .429 groove diameter barrel is going to be swaged down to .424 - .427 because it also has to ride over a thin layer of lube. Thus a bullet starting out into the barrel .002 - .003 over groove diameter is getting sized down .005 - .006 under a lot of pressure very quickly. That can do some bad disfiguring of the bullet, especially the base.

I also found with cylinder throats .003+ larger than barrel groove diameter a harder cast bullet that did not obturate .001 - .002 larger than barrel groove diameter gave better accuracy than a bullet sized .003+ over barrel groove diameter. I also find leading in the throat and barrel to be more a function of the alloy, lube and powder used than "fit" to the cylinder throats.

Yes, I know many will disagree here but that's what I've found. I shoot .430 sized bullets in my Ruger and Hawes 44 Magnum revolvers with excellent accuracy and no leading. The Rugers throats are .432 and the Hawes are .433. I actually shot 5000+ cast bullets (COWWs) sized .429 and lubed with Javelina through the Hawes with excellent accuracy and no leading before I read I was doing it all wrong. Testing has shown bullets sized .431, .432 and .433 shoot no better (the .433 shot poorly as the barrel groove diameters are .429 in both revolvers) than the .429 and .430. I use .430 sized 44 bullets now simply because that size shoots best in my 44-40 Chiapa M92 which, of course, does not have cylinder throats.

As to the "constriction" I have fire lapped a couple revolvers and it did work as with megasupermagnum. However, I've also found that simply shooting a couple hundred jacketed bullets with top end loads for the cartridge usually accomplishes the same thing.

I have not seen this in recovered bullets?
swaged down to .424 - .427 because it also has to ride over a thin layer of lube. I need to check it out.

My pistol bullets are sized to groove diameter. 358,452, 430

[Larry Gibson]

That is with a lubed bullet. PP'd and PC'd bullets are another story.