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XWrench3
09-16-2009, 06:58 PM
i slugged the bore of my microgroove 30-30 marlin (actually a glenfeild), because of the leading i was having. many folks talk about these being oversized. but not mine! it measures 0.3075" with grooves measuring 0.302". so i guess i will try running them with gas checks, and see what happens. if i try to run these without checks again, i will make sure to cast them air cooled 50-50 ww / pb. in stead of straight water droped ww's.

Bret4207
09-16-2009, 07:06 PM
It was my impression that what they said was you need to use a boolit that's somewhat more oversize for the bore than with conventional rifling. You'd still need to measure the bore.

Shoot, I'd be happy you got a fairly tight one. Seems most guys here have the opposite problem. Good for you!

MtGun44
09-16-2009, 11:57 PM
What diam have you tried? I'd expect about .310 or .311 to work well.

Bill

StarMetal
09-17-2009, 12:04 AM
i slugged the bore of my microgroove 30-30 marlin (actually a glenfeild), because of the leading i was having. many folks talk about these being oversized. but not mine! it measures 0.3075" with grooves measuring 0.302". so i guess i will try running them with gas checks, and see what happens. if i try to run these without checks again, i will make sure to cast them air cooled 50-50 ww / pb. in stead of straight water droped ww's.


That's backwards isn't it? You mean bore is .302 and grooves are .3075...right?

Joe

XWrench3
09-17-2009, 04:47 AM
That's backwards isn't it? You mean bore is .302 and grooves are .3075...right?

DOPE! yeah, right.


What diam have you tried? I'd expect about .310 or .311 to work well

so what you are saying is that i need more that .001" oversize? like .002 or .003? at this point, all i have tried was .309" boolits. tonight, i opened up my sizer to .310, and i dipped the boolits in my homemade lube. plus they had a base coat of thined L.L.A.

armyrat1970
09-17-2009, 06:30 AM
DOPE! yeah, right.



so what you are saying is that i need more that .001" oversize? like .002 or .003? at this point, all i have tried was .309" boolits. tonight, i opened up my sizer to .310, and i dipped the boolits in my homemade lube. plus they had a base coat of thined L.L.A.

Yeah you did have that backwards.
What gr. boolits are you using and what type of velocity are you getting from them? .001 to .002 over is usually good for cast boolits. Your pressure and velocity can determine if you need a gas check or not. I believe under 2000fps a check may not be needed. Of course others may have a different opinion and looking for leading will tell. Maybe the pressure can make a difference though. It takes experimentation to figure the correct boolit hardness given velocity and pressure. Even without a check. If your boolit is to hard and you drive it to fast it can just skip over the lands and cause leading issues. Many feel a hard boolit driven fast will not cause leading but not so.
What were your first test with what alloy and what velocity?

243winxb
09-17-2009, 07:32 AM
Size to .311" using 6% antimony, 2% tin. air cooled,with gas check. Micro groove rifling can not handle a plain base bullet, you will have a better chance with the gas check. IMO

runfiverun
09-17-2009, 11:33 AM
i've done okay to about 1400 with a plain based boolit in a marlin.
it was 18" below poa at 50 yds though.

44man
09-17-2009, 01:04 PM
It all comes down to GRIP. Marlin rifling is so shallow that oversize boolits are used to jam boolits into the rifling as tight as possible, not because the bore is oversize.
Making the boolit harder will give better grip. If you get good groups with jacketed why in the world would you shoot soft lead and try to equal velocities?
Then Marlin did something GOOD??????? Made Ballard rifling for cast boolits but HEE, HEE, they tricked us because it is still only .003" deep.
They do not intend for any of us to shoot reloads, only jacketed factory stuff.

StarMetal
09-17-2009, 01:12 PM
It all comes down to GRIP. Marlin rifling is so shallow that oversize boolits are used to jam boolits into the rifling as tight as possible, not because the bore is oversize.
Making the boolit harder will give better grip. If you get good groups with jacketed why in the world would you shoot soft lead and try to equal velocities?
Then Marlin did something GOOD??????? Made Ballard rifling for cast boolits but HEE, HEE, they tricked us because it is still only .003" deep.
They do not intend for any of us to shoot reloads, only jacketed factory stuff.

From what I've been told it's still button rifled, not cut. Probably why it's still shallow, even those you can button rifle deep.

Joe

brian
09-17-2009, 06:36 PM
uh...guys... the evidence is there in front of you. size the driving bands to whatever the throat diameter is (do a chamber/throat slug).

however, notice that the BORE is the same dia. as many 303 rifles..... microgroove barrels are shallow grooves. has nothing to do though with grip on the bullet wrt accuracy. if you shoot a long nosed bullet and it is a "nominal" one for 30 cal. likely the nose measures 0.300 maybe even 0.301. but in a 0.302 bore, that's a lot of unsupported nose, hence the accuracy issue. try a CB with a short unsupported nose section and that can be sized to throat diameter. Saeco #315. or find some 303 brit moulds and try them one at a time (314299) to see if accuracy improves. if the long nosed cb you're using can slip into the barrel at the muzzle, nose first, up to the first driving band, the nose is undersized for support and you won't get the best accuracy. in a 0.300" bored rifle ("normal') the lands will give good support to a CB with a nose diameter of 0.300 to 0.301. but due to microgoove internal dimensional differences, you need a nose section of whatever the bore diameter is (usually between 0.302 to 0.304) to support the nose. a very popular CB for a 30-30 is lyman 311041, but often the nose cast out at 0.300 to 0.301 and when fired in a "microgroove" barrel, accuracy is usually less than ideal, hence the bad rap wrt CBs and microgrooves.

also the throat cast or throat slug will reveal a lot wrt the leading issues. the marlin lever gun that i worked with extensively had the issue, which i didn't find until after the throat slug, where there was no distinct ending of the chamber and beginning of the throat. usually there's a step at the end of the cartridge neck end of the chamber which delineates the begining of the throat. in this marlin, there was no delineation. so i cast as large as possible. in my case i was working with the model 375 in 375 Win. so instead of casting 0.375" slugs, i was casting 0.383". i couldn't go bigger due to the chamber neck diameter limitations, but the bigger i went from 0.375 the less gas cutting and the less leading. due to what i thought was a very poor way to cut a chamber i eventually sold that rifle and moved on. but your throat slug might reveal a 0.313" throat. who knows. it might measure 0.312", or 0.314". whatever it measures, size to that diameter, and make sure the nose is at at least 0.302 if that's your bore diameter, and you should get much better accuracy and a lot less leading, all else being equal (use a good lube and a strong enough alloy for the pressures you intend to load to)

to recap, make sure the driving bands are size to your rifle's individual throat dimensions to help reduce leading. make sure the nose is well supported (if you can stick the nose into the muzzle up to the first driving band, it is NOT well supported) for better accuracy. use a good lube, and alloy with enough strength to tolerate the chamber pressures you intend to run.

Saeco #315 is out of their "traditional' mould catalog. it's a short nosed tapered design. a more experienced CB user i was lucky enough to meet told me that he liked suggesting that design to newbies as it was one of the easiest, in his opinion, to get to shoot decently in a wide variety of 30 cals. it may not be the most accurate in any individual rifle, but on average, it's a pretty easy design to get to shoot decently. i just loaned mine to a friend who is getting 5 to 7" groups at 75 yards out of his marlin microgroove 30-30. he was using the 311041 and he could drop the cb into the muzzle nose first up to the first driving band. i'll try and remember to report what he gets with the 315. he's doing a chamber cast with cerrosafe to find the diameter to size to (max throat diameter). i predict he'll get much better accuracy results with a well fit cb. we shall see.

Brian

RNyogi
09-17-2009, 06:46 PM
I've got a Marlin 336 in .35 Remington. I've been working up some loads, I'm using a ranch dog gas checked bullet sized to .359, over IMR 3031. I'm up to right aroung 2100 fps, good accuracy (only checked at 25 yds so far), and absolutely zero leading.
I love that gun!
It does have micro groove rifling. Greg

1Shirt
09-18-2009, 08:01 PM
.311 and Lee Fact. Crimp!
1Shirt!:coffeecom