How much over bore do you size?

[Cayoot]

I have a Marlin 1894 that I really like. Unfortunately, my 360180gb wont chamber in it as cast (unsized)

This is the first boolit that I'm going to have to size to get it to chamber in a .357. I don't usually size .38/.357, just TL then load.

Now that has changed. I'm going to purchase a sizer for my Star. I know that I should test to see where my carbine shoots best, but I don't want to buy 5 different sizers for my Star just to get one that works.

I slugged the Marlin last night. Slug came out right at .357 (that was a surprise!):drinks:

So tell me guys...in this old microgroove bbl, what sizer die size would be my best bet to start with? .359, .360, or .361?

I've read where you guys say that you have to size over more for the Micro groove bbls than for regular bbls.....but how much over?

Bary

[45 2.1]

Take some cases fired in the rifle your going to use those boolits in. Flare the fired cases to remove any vestige of crimp. You do notr want to expand the case body here. Take an inside caliper and measure the inside case diameter. Rotate the case on the caliper blades. A good scrapeing fit is what you want, as long as it will rotate and not lurch while your measureing it. That is the diameter you want.

[Cayoot]

And that should be adequate to give me a good "Grip" on the micro-groove rifeling?

[Scrounger]

I have a Marlin 1894 that I really like. Unfortunately, my 360180gb wont chamber in it as cast (unsized)

This is the first boolit that I'm going to have to size to get it to chamber in a .357. I don't usually size .38/.357, just TL then load.

Now that has changed. I'm going to purchase a sizer for my Star. I know that I should test to see where my carbine shoots best, but I don't want to buy 5 different sizers for my Star just to get one that works.

I slugged the Marlin last night. Slug came out right at .357 (that was a surprise!):drinks:

So tell me guys...in this old microgroove bbl, what sizer die size would be my best bet to start with? .359, .360, or .361?

I've read where you guys say that you have to size over more for the Micro groove bbls than for regular bbls.....but how much over?

Bary

.358; if that don't work, hone it out to .359, then .360 if necessary.

[45 2.1]

And that should be adequate to give me a good "Grip" on the micro-groove rifeling?

All that gives you is the largest boolit you should use. You will have to alloy or heat treat the boolit to the pressure level you intend to use. You need to try it out to see what works best in your rifle.

[Cayoot]

.358; if that don't work, hone it out to .359, then .360 if necessary.

Forgive foolish questions, but I'm a bean counter, not an engineer....

How do you hone it out?

[45 2.1]

http://www.castpics.net/

Honeing a sizing die under Research and Data.

[9.3X62AL]

One other avenue to explore to get a little cartridge clearance........different brass makes. Plated W-W brass is discernibly thicker than Rem unplated cases. A move like this might enable use of the fatter boolits needed to run well in the MG pattern.

[Cayoot]

Thanks guys, however my main question still remains unanswered:

Concerning Micro-groove rifleing in a pistol cartridge chambering, how much do you size over bore diameter as a starting point in your quest to get good accuracy?

Bary

[felix]

As fat as possible while cycling through the action from the magazine without any hangups. Once you find that magic boolit diameter and seating length with the boolit style on hand, then verify with magic marker all over the case where the boolit is (the neck portion) that the round can be seated by hand gently without scraping the color off. Chances are very good the color will not be touched, especially with a short action with a high angle insertion from the magazine unless the gun itself has been modified from standard. ... felix

Don't forget what Deputy Al said. Use the fattest/thickest cases that will be used in that gun for this endeavor. ... felix

[Blammer]

If it were me I'd start at .358.

I don't have a micro groove barrel but have a standard (forgot what it's called) and I have very good accuracy with my .358 dia sized bullets and my barrel slugs at .355... :)

[Cayoot]

If it were me I'd start at .358.

I don't have a micro groove barrel but have a standard (forgot what it's called) and I have very good accuracy with my .358 dia sized bullets and my barrel slugs at .355... :)


Your accuracy sizing is: .358
Blammer, so your barrel slugs at .355
That would indicate an increase .003

Your accuracy sizing increase .003
My as barrel slugs at: .357
So maybe I should start at/near .360

Just my bean counter logic taking over!:mrgreen:

[beagle]

Maybe I'm missing something here. I have a .357 M1894 Marlin and it's had maybe 20K plus rounds through it. It has that nasty micro groove rifling in it.

The 358429 seated over the shoulder and loaded over 11.8 grains of 2400 will punch into an 1 1/2" at 100 yards when I'm using a scope. This is sized at .358 and that's a measured .358" not what's on the sizing die.

I shoot loads of what I call .38/44 loads loaded in .38 Special cases in it as well as my two Ruger Blackhawks which like a bullet at almost .359". I keep about 20 boxes of this stuff loaded and grab it out of the same ammo can for either the Blackhawks or the M1894.

Now, the M1894 is just as accurate with .358" stuff as it is with .3585" stuff or even .359". Don't make any difference.

I'd sure try .358" and see how it shot. When you start pushing a cartridge to accept a "overbore" diameter bullet, all kinds of things happen. They become hard to chamber because of the overall diameter of the loaded cartridge and although it hasn't happened to me in the .357, I have had trouble seating oversize bullets in the .44 Magnum in regular dies at .433".

So, why create a problem. Size at .358" as there's plenty of dies available and see what happens. I'm bettering they shoot just fine and you'll see no difference in bullets sized to bigger diameters.

An additional problem that you encounter with OS bullets is that cases tend to size them down somewhat. I once pulled some .30 Carbine cast that were loaded at .311" and miked them after pulling. Gee whiz...they'd sized down during seating to .308"./beagle

[Cayoot]

Thanks for the advice Beagle...can I ask though...have you ever sluged your bore?

I'm just wondering cuz it seems that my bore might be a tad larger than others.

But, perhaps like you seem to be saying, I'm making much to do about nothing.

Bary

[felix]

True, dies have to be commensurate with the boolit diameter being loaded. I had to hone out my 44 maggie seater, and I am not going to relate the amount of time that took. RCBS dies are rock hard, and are much too hard for us hobby types. Professionals, OK, because they might need to produce 1M rounds with them. ... felix

[Blammer]

yea, that was pretty illogical... :D BUT before I slugged my barrel I assumed it was .357 and then use .358 and got great accuracy. SOoooooooooooooo... I was thinking I was sizing only .001 larger. Does that count!

On another note I have a 44 that slugs at .430 and I size to .430 and get great accuracy! go figure!

[Scrounger]

What he's saying is that if it works, it works. Keep it simple. If you tried .357 (or .358) and it worked, go with it, don't make life more complicated than you have to.

[Cayoot]

Great advice all...I was just hoping to avoid purchasing 3 or 4 sizer dies to find out what works.


I gues that there is no starting point that is better than any other.

[Buckshot]

..................Do a chamber cast. Mike it at the chamber mouth. Caliper the casemouth brass thickness, times 2 + .001"= What I would size to, if the slugs needed sizing that is.

..................Buckshot

[Cayoot]

Thanks Buckshot. I have some Cerrosafe...I'm going to try to cast the chamber this week.

[dubber123]

I too agree with the .358" die. Thats .002" over your bore, and likely will work great. If not, honing 1 or 2 thousandths larger is a simple matter.

[Cayoot]

Actually, it's only .001 over my bore of .357, so I'm going to try to measure my chamber in the two ways described here (Chamber cast and measure the inside of a fire formed casing and see what I come up with.

I was hoping someone would say something like "I find that going .003(or what ever size works) over bore is what works best in the Microgroove bbl"

But I think that there must not be any such rules.

Oh well, if we wanted easy tasks and medicore results, we would shoot J - word bullets eh?

[Bass Ackward]

Well, as usual, I am weird. I size all over the place with different bullet designs and hardness levels letting the gun tell me what I need. I have .357, .358, .3585, .3595 and .360.

If you are a hard shooter, (15 BHN and up) I'd go .358 for the first one. If you shoot softer, the .3585 would be my first choice to start.

[ktw]

I have an extra .358 Lyman H&I if you want to borrow it or discuss a trade for it.

-ktw

[chasw]

Ideally, you order a mold that drops bullets in your fav alloy at .359" Then you size/lube/gascheck them at .358" and shoot them in your barrel with its .357" groove diameter. - CW

[45r]

My Marlin 357CB shoots half inch 3 shot groups at 50 yards with boolits pushed through lee sizer at .359 and lubed in rcbs lubrisizer at .3595.Air cooled WW 185GC over 14.0 H-110 and CCI-550 primers.Both dies were lapped in Beartooth fire-lapping compound to those diameters with nylon bore brush wrapped with t-shirt cloth.Boolits drop out of the MTN MOld at .360(WW plus 2 percent tin at 740 degrees) and are not galled or distorted at all when sized in the smooth lapped dies and don't need to lubed before going through the lee push-through sizer.

[Larry Gibson]

Cayoot

Quickest way to happiness is to follow 45 2.1's advise; measure the inside of a couple fired cases (after flairing the case mouth only) and see what the expansion is with your chamber. If that is .360 or higher then a .359 0r .360 should do it. What is the inside measurement of your cases and the "as cast" diameter of the bullets?

Larry Gibson

[Cayoot]

You're right Larry, that does make the most sense. Then again, what 45 2.1 says usually does!

[Poohgyrr]

:coffeecom

I may be slow but even this old dog can learn new tricks....

Thanks for all the info.......

:drinks:

[jjamna]

Size mine at .358 I bet it shoots better than I can.