I did a careful measurement of the cylinder throats on my 629-4 MG today using an expanding ball tool and a micrometer. It seems that they are .4293 give or take a tenth or so. My bore groove slugs out at .4296-.4299. It would appear that I need to have the throats reamed out a bit. I have seen a link here to a fellow who calls himself Cylindersmith, has anyone used his services and is he still doing it? Another question. When I shoot .430 jacketed XTP bullets out of this gun what is it doing to the cylinder and to the pressures getting through the throat? If I have the throats reamed out to .4305 will the gun have problems shooting .429 jacketed bullets accurately?
44 Mag Throat Diameter
- Thread starter elundgren
- Start date
Register to hide this ad
I don't see a problem here requiring reaming. I would leave it alone unless you are having accuracy problems.
Titegroups
Member
You could have it reamed out a bit but I think you'll be wasting your time. Your looking at .0007 which is insignificant. If you are capable of measuring that accurately to begin with. Remember you have 40,000psi pushing that bullet through. Throat dia. is a known problem in some revolvers, in some calibers, not yours.
Well, it is good to know that it probably isn't needed. Back at the beginning of time I was a mechanical inspector, 1st articles and what not coming from machine shops so I am pretty sure about my numbers, particularly the throat diameters. Since the bore has 5 grooves that dimension is a little harder to be sure about but the fit of the slug through the throats, (very tight, goes through with a light hammer tap but not by pushing), leads me to think my figures there are good also. My main concern was in shooting cast bullets so I think I must just load and shoot a bunch to get a good idea. Thanks.
cylinder throats.
I've been lurking here for years but post very little. I prefer to learn but this is a subject I'm very much in touch with. I carry plug gauges in my range bag at all times and at gun shows when I'm looking to buy. My personal experience runs the gamut from early p&r guns up to current Performance Center guns. Most every p&r gun I've measured has been in the range of .432 - .435 and none of them were consistant good shooters. Sure there were some good groups but just when I was happy wth the load bullets would start flying all over the target. After 3 or 4 different 29's and 629's I wasn't a very happy camper and I had alot of money tied up. I settled on a 629 with .432 throats and custom cast and sized .432 240gr. bullets. Then a fellow club member bought a used 629 classic and the throats measured .429. I was really excited with this discovery and volunteered to sight the gun in for him. The groups were fantastic. We used a .430 240gr. cast bullet. I lucked into a chance to buy a 629 Classic for a good price so I sold my original 629 and bought the Classic. It shoots excellent with .430 cast bullets and .429 throats.I then had a chance to buy a 629 Stealth Hunter. The throats measure .4285 and it's a tack driver with the .430 bullets. Over the past 2 years I've measured 90% of the guns that come through the doors at the pistol range and from the Classic series onward the throats all measure .429. All the Performance Center guns I've measured are right at .4285. I'm sure there's a limit here but as far as my experience goes the tighter the throats the better the gun will shoot. I've also done this with .45 Colt, .38 Special, and .41 Magnum with the same results. Remember this is for cast lead bullets. Jacketed or copper plated is a whole different animal due to the difference of friction between the two metals. The throat size is not nearly as critical with copper. Just my .02cents worth.
I've been lurking here for years but post very little. I prefer to learn but this is a subject I'm very much in touch with. I carry plug gauges in my range bag at all times and at gun shows when I'm looking to buy. My personal experience runs the gamut from early p&r guns up to current Performance Center guns. Most every p&r gun I've measured has been in the range of .432 - .435 and none of them were consistant good shooters. Sure there were some good groups but just when I was happy wth the load bullets would start flying all over the target. After 3 or 4 different 29's and 629's I wasn't a very happy camper and I had alot of money tied up. I settled on a 629 with .432 throats and custom cast and sized .432 240gr. bullets. Then a fellow club member bought a used 629 classic and the throats measured .429. I was really excited with this discovery and volunteered to sight the gun in for him. The groups were fantastic. We used a .430 240gr. cast bullet. I lucked into a chance to buy a 629 Classic for a good price so I sold my original 629 and bought the Classic. It shoots excellent with .430 cast bullets and .429 throats.I then had a chance to buy a 629 Stealth Hunter. The throats measure .4285 and it's a tack driver with the .430 bullets. Over the past 2 years I've measured 90% of the guns that come through the doors at the pistol range and from the Classic series onward the throats all measure .429. All the Performance Center guns I've measured are right at .4285. I'm sure there's a limit here but as far as my experience goes the tighter the throats the better the gun will shoot. I've also done this with .45 Colt, .38 Special, and .41 Magnum with the same results. Remember this is for cast lead bullets. Jacketed or copper plated is a whole different animal due to the difference of friction between the two metals. The throat size is not nearly as critical with copper. Just my .02cents worth.
fredj338
Member
It depends on the groove dia of your bbl & what size lead bullet you want to shoot. If you are shooting a 0.431" lead bullet, the smaller cyl throat is going size it down & you will get leading & marginal accuracy. Polishing out to the dia of the bullet you are going to shoot &/or groove dia is perfect. I have a machinist friend do mine, he specializes in ID/OD polishing, easy to do, takes about 15min for the whole job. It will not affect your jacketed bullet shooting at all. Many S&W rev have larger than groove dia cyl & they will only shoot jacketed w/ any real accuracy.
A recent RBH I bought had tight 0.450" throats I was shooting 0.452" bullets. Accuracy was marginal & always leaded the first 1" or so, why not, the bullets were coming into a 0.451" groove 0.001" too small. After polishing to 0.4515", leading is almost completely gone & accuracy is twice as good @ 25yds. Yeah, it can help quite a bit.
Last edited:
I have several Smith 629's that have cylinder throats that measure.4285. Since I also have Smith's and Rugers that have throats that measure .431, I size all my boolits to .431. The .431 boolits shoot extremely well, (if occassional 5 shot groups of less than 1"@25 yds with a scoped Classic DX is good!) and I get little or no leading. Sure makes life simpler than wringing my hanky about "proper boolit to match throats" diameters.
fredj338
Member
Then you are fortunate as it doesn't work that way for many lead bullet shooters.
Ok, it certainly makes sense that if the throat size is less than the groove dia. then gasses will get by and melt lead and deposit it in the barrel. But, it doesn't seem to do it for everybody. There is an awful lot of pressure behind the bullet, maybe not 40,000 psi, at least not in the loads I am using but surely at least 25,000 psi. Is that enough to deform the bullet and seal the bore? Seems that the answers are not simple.
amazingflapjack
US Veteran
That depends on the BHN of the bullet you are shooting, a choice that is also important, depending on the other factors. Flapjack.
Titegroups
Member
SAAMI spec for 44mag is 36,000psi. As you can see opinions and results vary greatly with everyone sure they have the right answer. In my opinion with max pressure and bullet expansion occurring soon after ignition and probably before the bullet passes through the throat that no bullet expansion occurs after the bullet passes the cylinder gap so whatever size the throat is the bullet should remain that diameter through the barrel. I don't think there's enough pressure left to expand the bullet once it reaches the barrel. If I'm wrong on that then it adds another layer of complication to throat size. Is it possible lead is soft enough to still expand and copper won't?
Last edited:
fredj338
Member
A copper jacketed bullet won't obturate, neither will a very hard lead bullet, so throat size may or may not matter to accuracy, but can play havoc w/ leading. The only way to get the over size, throated S&W 45colts to shoot well is shoot jacketed or a very soft, oversized lead bullet.
Perhaps my "good" results are due to the hardness of my alloys? I use boolits that measure Bhn 11, which I cast myself and adjust my alloys to reach that by the use of a Saeco hardness tester. It seems to me that a lot of folks run into leading and accuracy problems with diameters due to their use of commercial or home grown "hardcast" or quench cast boolits, whatever "hardcast" is defined to be.
I've always maintained that shooting cast boolits ain't a science, it's an art, and I'm still learning after playing around with them for 48 years!
I've always maintained that shooting cast boolits ain't a science, it's an art, and I'm still learning after playing around with them for 48 years!
When you think about what is occurring when you shoot a cartridge it is amazing that it works at all. It is a little like the physics of hitting a golf ball. With all the variables such as club angle, where on the face the ball is hit, speed of the club, etc, it isn't possible for anyone to do it but they do none the less.
fredj338
Member
I think a little of both. Many that shoot commercial "hard" cast will have leading issues. Casting your own allows size & alloy control for a better result, but casting is not for everyone & getting more expensive every year as cheap alloy dries up. Thank you the State of Kalif & the EPA.
Last edited:
catfish_dan
Member
- Joined
- Jul 21, 2013
- Messages
- 17
- Reaction score
- 1
Hi,
I have 629 MG and recently starting loading cast bullets since I live in Mass and getting components for ammo has become a real challenge.
My first batches resulted in some fairly extreme leading problems, 240gr SWC with 12g of Blue Dot. After half a box the grooves were no longer visible. This was a load worked up by a relative who had good results with it.
I first started looking at my lead alloy since this was a new load for me, and then asked my relative to put some through his Ruger. He had no issues at all with the ammo.
We then took a look at the throat dimensions and I was surprised to find the throat was so tight, similar to what the OP was reporting. After measuring the cast rounds (.430) it seemed awfully tight in comparison with the throat. The Ruger was relatively loose so much so that the .430 cast bullets could be dropped through the cylinder with ease whereas my Smith couldn't even get the bullets started.
To be able to shoot cast, should I be resizing the cast down to .429 or maybe even .427? I really can't afford to shoot purchased ammo, if I can even find it at the moment, so any recommendations would be appreciated.
Thanks,
Dan
I have 629 MG and recently starting loading cast bullets since I live in Mass and getting components for ammo has become a real challenge.
My first batches resulted in some fairly extreme leading problems, 240gr SWC with 12g of Blue Dot. After half a box the grooves were no longer visible. This was a load worked up by a relative who had good results with it.
I first started looking at my lead alloy since this was a new load for me, and then asked my relative to put some through his Ruger. He had no issues at all with the ammo.
We then took a look at the throat dimensions and I was surprised to find the throat was so tight, similar to what the OP was reporting. After measuring the cast rounds (.430) it seemed awfully tight in comparison with the throat. The Ruger was relatively loose so much so that the .430 cast bullets could be dropped through the cylinder with ease whereas my Smith couldn't even get the bullets started.
To be able to shoot cast, should I be resizing the cast down to .429 or maybe even .427? I really can't afford to shoot purchased ammo, if I can even find it at the moment, so any recommendations would be appreciated.
Thanks,
Dan
Dan, most folks seem to think the bullet should be sized to fit the throats (exit bores) of your cylinder, or maybe 0.001" bigger - as long as you can seat the loaded cartridges in the chambers without a problem. I think the theory here is that the base of the bullet can receive a lot of damage before it leaves the cylinder if it is not a good fit for the exit bores. I tend to agree with this. Whenever my cast bullet loads are properly sized for the exit bores of the cylinder, I have very little trouble with leading and poor accuracy. Just make sure your loads easily "drop in" to the chambers.
The OP's gun sounds fine to me. I would not make any adjustments to the exit bores.
The OP's gun sounds fine to me. I would not make any adjustments to the exit bores.
catfish_dan
Member
- Joined
- Jul 21, 2013
- Messages
- 17
- Reaction score
- 1
my current loads do drop in the cylinder fine, they are tight to exit though. Based on your comments, do you agree I should try and resize the bullets to .429? My main concern here is to reduce the crazy leading I'm getting. Am I following the right path? I'm not currently looking to mod the gun at all if I can help it.
Thanks,
Dan
Thanks,
Dan
jepp2
Member
A while back, he changed to only doing .45 cylinders. I had sent him a 32 H&R cylinder, but he was unable to ream the throats. So I got a Manson throating reamer and did my 3 cylinders myself. They turned out just fine.
I recently throated my 629-6. As you mentioned it was tight like yours is. I buy my reamers directly from Manson's rather than through Brownells. I do this mainly as they will put on the pilot I want, rather than an undersize one as those sold by brownells. After throating my cylinders were ~0.4315". I shoot 16 BHN sized to .431 and they are just a snug thumb press through each throat. I keep my pressure up on these and get really no leading with excellent accuracy.
As others have mentioned, there are MANY theories on what to do. I'm not going to say someone else is wrong, but I do know what works well for me.
