Colt trooper MK III, undersized bore?

[rtracy2001]

OK, so a little background.

I acquired this MK III for free as the trigger was broken (some idiot used it for a hammer and bent the trigger guard.)

I re-formed the trigger guard and replaced the trigger, since then it has been a great shooter. Factory ammo has never been a problem, jacketed or lead. Well a while back I got bit with the casting bug, and since that time I have collected, purchased, scrounged and otherwise acquired enough equipment to stat casting a few boolits. I started out with a Lee TL358-158-SWC and a Lee sizing kit in 0.358". I went with the 0.358" size because all of my factory lead ammo measured 0.358" diameter.

Now the trouble

Well today I slugged the barrel of that MK III and the slug measured 0.353" to 0.354" well under my 0.358" boolits. I didn't believe it, so I slugged a second time with the same results. My as cast boolits (0.360") fit in the cylinders and stop just short of falling through. After sizing (0.358") the boolits will fall through the cylinders with just a little jiggle. The sized boolits enter about half way into the forcing cone before they stop. I loaded up a couple of 357 mag dummy rounds with my cast boolits (as cast) and they will chamber fine in all cylinders.

Am I screwed? or do you think this will be OK to load them up? :confused:

[StarMetal]

OK, so a little background.

I acquired this MK III for free as the trigger was broken (some idiot used it for a hammer and bent the trigger guard.)

I re-formed the trigger guard and replaced the trigger, since then it has been a great shooter. Factory ammo has never been a problem, jacketed or lead. Well a while back I got bit with the casting bug, and since that time I have collected, purchased, scrounged and otherwise acquired enough equipment to stat casting a few boolits. I started out with a Lee TL358-158-SWC and a Lee sizing kit in 0.358". I went with the 0.358" size because all of my factory lead ammo measured 0.358" diameter.

Now the trouble

Well today I slugged the barrel of that MK III and the slug measured 0.353" to 0.354" well under my 0.358" boolits. I didn't believe it, so I slugged a second time with the same results. My as cast boolits (0.360") fit in the cylinders and stop just short of falling through. After sizing (0.358") the boolits will fall through the cylinders with just a little jiggle. The sized boolits enter about half way into the forcing cone before they stop. I loaded up a couple of 357 mag dummy rounds with my cast boolits (as cast) and they will chamber fine in all cylinders.

Am I screwed? or do you think this will be OK to load them up? :confused:

No, Colt 357's and 38's tend to run a tighter bore and groove. Go ahead and shoot them and compare them to your factor ammo.

Joe

[dubber123]

Sounds like you are OK to me. If .358 falls through, I would actually be inclined to size them a bit larger. If you didn't know the bbl. was that tight, I don't think you would have ever been able to tell a difference from the factory ammo. Let us know how you make out.

[Hardcast416taylor]

I still have my 4" Colt Trooper Mk 3 that I carried for a "few" years. I used about everything that even looked like either .38 spcl. or .357 ammo thru it. I shot 148 gr. wc ammo alot for practice, up to some 175 gr. rn lead stuff in .357 brass. I found the gun to be as accurate as I was and more so on its part Our dept. load was a 158 gr. jsp Rem. ammo, alot of that was put thru it as well when expending old ammo. I had no problems hitting what I was aiming at out to 40 yds.Robert

[HeavyMetal]

Colt revolvers have always had the "rep" of tight bores!

I have an old Police Positive Special that love the Lee 125 Gr RNL sized 357. A co worker has a 6 inch Stainless Python which likes the 88 gr Golden Saber 380 bullets, go figure!

I'd stay with what your shooting and pay attention to pressure signs, of course you never start out with the hotest load listed in the manuals so you should have n issues.

[Bucks Owin]

Yep, Colt's normally run .355" or so and apparently your's is even tighter. They also have a reputation for fine accuracy! Go figure huh?....FWIW, Dennis

[MT Gianni]

The reverse would be bad with a .360 bbl and .354 cylinder throats. You want the sizing to occur in the bbl and forcing cone and it will. It may be that "book" maximum loads reach a higher pressure in your gun than in another. I would work for accuracy loads rather than screamers but it is a strong gun and should handle a lot.

[rtracy2001]

Thanks for the replies, I will load some up and see what happens. I usually start in the lower third of the book bands and work up (or down) from there. It may be a while before I get to go out and test fire them, but I will let you know how it works out.

RT

[9.3X62AL]

The Mk III Troopers are strong as can be, and both of mine were VERY accurate. They tend to loosen their extractor stars, and a micro-drop of epoxy will re-anchor them for about 1500 rounds.

As you have seen, the internal mechanism is MUCH simpler than the V-spring action. It is also a LOT more rugged. I ran over 10K Magnum rounds through one of the Troopers, most of that double-action, and its timing was absolutely unaffected by the work. The Mark IIIs were one Colt revolver that WAS NOT susceptible to timing issues from extensive D/A firing.

[AbitNutz]

I have a Colt Python and it runs .354-.355. It is silly accurate. Just for $hits I loaded up some 90 grain bullets designed for a .380 for some very low recoil practice loads. They too were silly accurate. I decided to see how fast I could push an 88gr Speer hollow Point. Everything works great...right up until the bullet breaks up in midair. The target looked like it was hit with bird shot. Go figure...

[LeMat]

The Mk III Troopers are strong as can be............, the internal mechanism is MUCH simpler than the V-spring action. It is also a LOT more rugged.............. The Mark IIIs were one Colt revolver that WAS NOT susceptible to timing issues from extensive D/A firing.

Can the same be said for the MKV's? I've got a Peacekeeper that I'm still a bit nervous about shooting extensively as I've already had to replace the ejector rod spring.

[9.3X62AL]

Can the same be said for the MKV's? I've got a Peacekeeper that I'm still a bit nervous about shooting extensively as I've already had to replace the ejector rod spring.

No time with the Mk Vs here. Can't help with those examples.