Reaming, how far over bore diameter for lead.

[Thompsoncustom]

I'm looking into getting a barrel reamed or getting another reamer and wondering how far I can go over bore diameter without effecting accuracy. This is for a 9mm pistol so no super long accuracy required probably 50 yards as a absolute max.

I have a .356 clymer throat reamer now but I'm thinking I need a .357 or .358 reamer. I have 2 sizing molds for my 9mm bullets .3565 and .358 but I only use the .3565 anymore as I sold the guns that needed the .358.

The problem I'm running into right now is I want a longer OAL with some of my cast bullets and some of them caught the beginning of the throat and scrap the Hi Tek coating off. My PC bullets seem to be OK but I figured if I can make the throat diameter wider without messing up accuracy that should fix the problem.

[mdi]

Jes wonderin'; is there a specific reason you want a longer OAL? Why not just seat the bullet deeper?

[runfiverun]

throats are cut in degrees not diameters.
you are just cutting back the rifling [shallower] at an angle.

[Thompsoncustom]

Hmmm my .356 clymer says .001 over bore diameter right on the box. Doesn't say anything about the degree. I'm guessing the slower the taper the better for cast?

Well I load some really heavy 9mm like 160gr RN and 170gr SWC so a little more length would be nice.

[KYCaster]

The devil is in the details........

9mm GROOVE dia. is .356......bore dia. is ~.346 or so.

Are you reaming the chamber leade in a semi-auto or cylinder throats in a revolver?

Jerry

[DougGuy]

His reamer sounds like it is for an auto pistol barrel not a revolver.

Regardless of what anything is, once you choose one diameter, you must make the other diameter fit within it. By using the .356" reamer in the barrel throat you are consigning the coated boolit size to be no greater than .3558" for it to chamber without issues. Anything larger will not go into the throat.

Seating deeper is creating a second problem as a workaround to the first really, it doesn't "fix" anything, and you have to compensate your load data to make up for less case volume.

If you want to shoot .357" boolits in the 9mm, you need a .3575" throating reamer. If you plan on coating a .357" boolit, you need either a larger reamer or a custom made (hopefully piloted) lap that can scoch out the final diameter in the throat to accept the coated boolit. At any rate, if you want to seat the boolit into the throat, which is the proper way to do this, the throat has to be minimum .0002" above boolit diameter, and it has to be deep enough so that the rifling does not interfere with the chambered round. This way it will reliably "plunk" all of your loaded ammo without chambering issues and it will not damage the coating.

I am also finding that some bit of freebore or smooth throat in front of the chambered boolit is beneficial to both velocity and grouping, and it lowers initial pressures when the boolit can pull crimp and gain inertia before it engages rifling.

I do not yet have a 9mm or .40 cal reamer but I intend to add those calibers in custom sizes to the list of calibers I ream barrels and cylinders to. By springtime I should be able to do 9mm and .40 barrels.

If you slug your bore at .355" I would not go over .357" diameter including coating for the boolit. A revolver forcing cone is much more forgiving than the throat of an autopistol. If I slugged one at .355" I would try to get everything to work with a .3565" throat, if it slugged at .356" I would try to get it all to work with a .3575" throat, meaning the final diameter of a coated boolit would be no greater than .0002" under the throat diameter. I think you would not have problems with these numbers unless you get into some out of rounds loads, .0002" is not a lot of wiggle room. Your loads would have to be carefully assembled.

[Thompsoncustom]

That sounds great. My bore is .3555 and I size all my coated bullets to .3565 and even have a LEE FCD that I lapped out with some diamond compound to not undersize my .3565 bullets so I'm pretty set on that bullet diameter. Looks like what I need is a .357 throat reamer and I should be good to go.

[Outpost75]

You don't want to seat the bullet deeper in small cases like the 9mm because as little as 0.05 change can cause a dangerous pressure spike in some combinations. With M882 NATO ammo reseating the bullet only 2mm deeper raises pressure to proof level.

[leftiye]

Actually, ye're sposeta know that and work up loads so as to avoid the high pressures. Sounds like the load is being taken as gospel and copied exactly. Good luck keeping them there body parts.

[mdi]

You don't want to seat the bullet deeper in small cases like the 9mm because as little as 0.05 change can cause a dangerous pressure spike in some combinations. With M882 NATO ammo reseating the bullet only 2mm deeper raises pressure to proof level. While I cannot question this post...

Just curious and for my own info.; I have always seen "...seat deeper and you'll get dangerous higher pressures" answers nearly daily when one asks about OAL issues. Yes in theory pressures will rise, but I could get his from space trash falling back to earth too, but how much will the pressure rise say, per each .010"? I'm thinking this is just a "Web Warning" and very few if any have any facts (measurements) and just repeat what they've read on a forum somewhere...

I'm aware of the "depends" thinking (powder type and charge, caliber, gun, bullet weight, etc.) and the reports of kabooms from bullet set back, but has anyone ever tested specific pressure rise per amount of reduced case capacity? Like how much will pressure rise in a 9mm loaded with a 124 gr. lead RN and a charge of 4.0 XX powder when seated .015" shorter than book OAL?

If this considered a hijack, my apologies...:oops:

[DougGuy]

While I cannot question this post...

Just curious and for my own info.; I have always seen "...seat deeper and you'll get dangerous higher pressures" answers nearly daily when one asks about OAL issues. Yes in theory pressures will rise, but how much will the pressure rise say, per each .010"? I'm thinking this is just a "Web Warning" and very few if any have any facts (measurements) and just repeat what they've read on a forum somewhere...

Whole lot more to it than just web gossip. Last year we had a lady shooter on here who blew up her 1911, and of course after about 300 "keyboard gunsmiths" pored over every tidbit of information she was able to give, came up with the theory that boolit setback from the slide stripping a round out of the magazine and it bumping the throat of the barrel on the way to being chambered, caused this. Scared the **** out of her, and luckily she wasn't injured but her gun was needing quite a bit of $$ spent to repair it. Root cause? Not enough neck tension or not enough taper crimp to keep the boolit from moving under normal pistol operation.

There really isn't a way to draw up a scale that shows how much pressure rise per linear inch of COA because powder changes burn rate and pressure curve characteristics with load density. Some powders may be possible to do a study and document changes in COA to a reasonable curve in pressure but other powders exhibit unpredictable qualities when load density gets above a certain % and unless you do a full blown study with a pressure barrel, you couldn't just throw an assumed system of reference at it. Bottom line, if you actually DID do this, you would likely find that each powder has it's own curve which is only accurate with the same boolit weight as the test was conducted with. Change boolit weight, you got a whole new curve for each increment of COA.

The smaller the case, the greater the change in case volume/load density per linear inch of COA, I can tell you that much for certain. The higher the pressure the cartridge operates with, the more violent even small changes can become, I can tell you that with certainty. In the case of the 9mm, it is a high pressure cartridge (36,500psi), and just from that fact alone, a .010" variation in COA would cause pressure to vary a WHOLE LOT MORE than the same .010" variation in COA of a .45 ACP load (21,000psi) which operates at roughly 40% less pressure than that of the 9mm.

It wouldn't take much setback from the boolit hitting the feed ramp to create a situation where you have in excess of 60,000psi in the 9mm when fired. By the same principle, you could get in trouble VERY easily in seating the 9mm boolit deeper in the case, and trying to compensate load data (or failing to compensate load data) to allow for this shorter COA.

[Forrest r]

While I cannot question this post...

Just curious and for my own info.; I have always seen "...seat deeper and you'll get dangerous higher pressures" answers nearly daily when one asks about OAL issues. Yes in theory pressures will rise, but I could get his from space trash falling back to earth too, but how much will the pressure rise say, per each .010"? I'm thinking this is just a "Web Warning" and very few if any have any facts (measurements) and just repeat what they've read on a forum somewhere...

I'm not sure if you're talking about something like this that ramshot puts out. They did tests on oal/pressure differences.

http://i162.photobucket.com/albums/t242/forrestr-photo/RamshotOALampPressure_zpslofavsku.jpg (http://s162.photobucket.com/user/forrestr-photo/media/RamshotOALampPressure_zpslofavsku.jpg.html)

[Bullwolf]

While I cannot question this post...

Just curious and for my own info.; I have always seen "...seat deeper and you'll get dangerous higher pressures" answers nearly daily when one asks about OAL issues. Yes in theory pressures will rise, but I could get his from space trash falling back to earth too, but how much will the pressure rise say, per each .010"? I'm thinking this is just a "Web Warning" and very few if any have any facts (measurements) and just repeat what they've read on a forum somewhere...

I'm aware of the "depends" thinking (powder type and charge, caliber, gun, bullet weight, etc.) and the reports of kabooms from bullet set back, but has anyone ever tested specific pressure rise per amount of reduced case capacity? Like how much will pressure rise in a 9mm loaded with a 124 gr. lead RN and a charge of 4.0 XX powder when seated .015" shorter than book OAL?

If this considered a hijack, my apologies...:oops:


If we didn't occasionally go off topic, I wouldn't learn half as much here as I do.


The old Hercules Powder Company had an article about this using Bullseye with deep seated 148 grain full wad cutters in 38 Special. I had just posted about this in another thread earlier today.

Here's a couple screenshots of the article from American Handgunner in Jan/Feb 1982.

http://castboolits.gunloads.com/attachment.php?attachmentid=105592&d=1371757632

http://castboolits.gunloads.com/attachment.php?attachmentid=105594&d=1371757626

http://castboolits.gunloads.com/attachment.php?attachmentid=105593&d=1371757629




- Bullwolf

[alamogunr]

Bullwolf: Is there an internet link to that article? I would like to read the entire article but the screenshot is too small for my old eyes.

[Bullwolf]

I didn't have an internet link to the article on hand, but a quick search found a .PDF scan of the entire January/February 1982 American Handgunner magazine on gunbooks.ca

To view it will require a PDF reader though such as Adobe Acrobat which is free to download if you don't already have it.

Page 8/9 is the start of the article, and it finishes up on page 69.

http://www.gunbooks.ca/ah/AHJF82.pdf


You can also use the keyboard keys [Ctrl +] to increase the view size in most browsers, and [Ctrl -] to shrink.

Some Windows based PC's will let you cheat a bit with the font size or a magnifier under Accessibility for view options. I'm not handicapped...just yet, but sometimes I have trouble reading small text as well.


- Bullwolf

[Thompsoncustom]

Actually, ye're sposeta know that and work up loads so as to avoid the high pressures. Sounds like the load is being taken as gospel and copied exactly. Good luck keeping them there body parts.

All the load data I use for my 160gr/170gr 9mm is developed and tested by me using Quickload and a Chronograph and I have yet to have any pressure issues but I would like to take things a step further.

I developed these loads for IDPA so they have to meet 125PF, but I have found that anything under 800FPS tumbles so that seems to more of the cut off than power factor.

I was looking to create the lowest recoiling round I could and it indeed does make a big difference. For example the 170gr in front of 2.8gr AA#2 make PF and has next to no recoil.

I've upgraded my IDPA gun from a CZ 75b to a CZ 75 Shadow and the throat on this gun is to narrow and to short to work with the 170gr bullets and the 160gr's have to be seated to deep. Ideally if I can get the Lee TL-358-158-2r to seat at 1.135 than I should be able to put 2.4/2.5gr's of red dot behind it at safer pressures and above 800fps.

[leftiye]

I was reacting to outpost 75's post, not to anything you wrote. I almost never look at LOA from the manual as a part of making up a load. Loads fit magazines, chambers, cylinders, and then you work up pressures. Very often LOA is determined by boolit crimp grooves or some other bullet/boolit feature and manual length is not possible to comply with. Then you see if they shoot well or not.

[mdi]

Finally, some honest to God facts! I had/have no problem with the "theory", but so many of the responses to this type question, I believe, are just parroting.

Thank you gentlemen!
Mike...

[DougGuy]

Bullwolf: Is there an internet link to that article? I would like to read the entire article but the screenshot is too small for my old eyes.

When you get one like that, hold down the Ctrl key and hit the + key until it gets big enough to read.. Don't forget to hold Ctrl and hit the - key to return back to normal size!