How to slug a barrel??

[Flexy]

Hi, I'm new to this forum and newbie in bullet casting too. Might be that I've wrote this thread to a wrong category... but here it goes... I have a Marlin 1895, caliber 45-70 Gov. I loaded a few ~500gr bullets, but the accuracy was poor... Perhaps 3 MOA at ~50yards and ~80yards I stopped making holes in the paper altogether... I have read about casting bullets in general and to Marlins... I began to wonder if my bullets are too small for my gun. I used Lees 500grain molds, they are .457 molds...

OK, to the point. How do I slug the barrel? Do I run the slug thru the barrel, or "just dip" the slug at one(/both) end(s)?? I should make the bullets about .002" bigger than the groove diameter, I reckon?



Thanks!

[Sensai]

We need more data to be able to help. Welcome, by the way! As far as slugging the bore, you need to do both. Run one all the way through to check for tight spots and one about two inches into each end. There are great instructions in the stickies for "how-to" on doing this. Unless you're getting a lot of leading, I wouldn't jump to the conclusion that the problem is a too small boolit diameter. Is your rifle a "micro-groove" or standard rifling barreled gun? What load are you using with the 500gr boolit? 3 MOA at 50 yards is only about 1 1/2 inches, do you mean 3 inches at 50 yards? Are you sizing the boolits? Crimping? I feel like #5, "need more data".

[KCSO]

If you want to go whole hog get some bore diameter or thereabouts brass rods. One about 12" long and one about 24" long. Put a slightly undersized ball in the bore and use the rods and a brass hammer to upset the slugs in each sectionof the bore you want to measure. I use one set of rods for both 30 and 32 caliber slugs in rifles. In pistols I use my brass alignment rods and a stup to do the same if I need to. The idea of slugging breech and muzzle is to tell if the barrel was put on backward.

[Flexy]

We need more data to be able to help. Welcome, by the way!

OK, I'll slug the bore thru and both ends. No problem there then. Don't know about leading, only shot about 20 bullets so far. Atleast I did not notice any... It's a standard grooved barrel, 12 grooves IIRC. And I've used 35.5gr of Vihtavuori N120, according to QuickLoad it leads to ~33'000psi, 1500fps. Powder selection is quite limited... Vihtavuori is available and cheapest... And yes, I meant MOA, the best group was 3MOA, average of the other groups was closer to 4MOA. The noticeable thing I did not mention... I might have had one slight keyhole on the 50yards shots... and then missing the target altogether at 80yards started me to think about the bullet size. Sized bullets and gas checked them at the same time. Lee factory crimped the bullets to cases.

[Sensai]

The idea of slugging breech and muzzle is to tell if the barrel was put on backward.HA! Well I was thinking more along the lines of thread squeeze or throat errosion, but I guess you could be right![smilie=l:

12 grooves sounds more like micro-groove, but I could be wrong that is a big ol' hole. I'll have to check when I get home, but I think that my '95 has six. If you don't notice any leading after 20 rounds, your boolit probably isn't too small. You may just not have enough twist rate to stabilize that long boolit. I have not tried 500 gr in mine because I didn't like the accuracy lose I got going from 405 to 450. Mine seems to like the 405's better than anything else. I'll be interested to know what you come up with from the barrel slugging.

[williamwaco]

Normally, I don't slug barrels. I have found it be a waste of time.
I do it occasionally "just to see" but never when developing loads.
Perhaps with a little more experience, I will realize the error of my ways.
I have only been loading cast bullets since 1956.

If you think the bullets are too small, try a larger size, If it gets better, you were right. If it doesn't, try a larger size.

If you have a partial keyhole at 50 yards, that is a very strong indication that you bullets are too small.

The old wives tale about cast bullets need to be .001 over bore diameter is not correct. It never was.
Your bullets should be .002 to .003 over bore diameter.

Posts on the Marlin forum indicate your bore is probably .456 to .457
That would indicate your bullets should be .458 to .459

You didn't mention your current bullet diameter but if you are keyholing, I would go up .002.

Load up a dummy round with an unsized bullet.
If it will chamber with no effort required to close the bolt, load up 5 of them and try them.
If you need to apply more than normal force to close the bolt, the bullet is probably too large.

[Flexy]

Normally, I don't slug barrels. I have found it be a waste of time.
I do it occasionally "just to see" but never when developing loads.
Perhaps with a little more experience, I will realize the error of my ways.
I have only been loading cast bullets since 1956.


Well, I was not even a gleam in my fathers eyes at that time... So, just happy to get advice... :) In any case, I slugged the end of the bore and after that thru the bore. Idea was to not ruin the mold/sizer. Don't know how to put the material back to either of them after lapping... :) Results are within .4580" - .4585" in both slugs, measured at impressions made to the slug by the groove of the bore.



If you think the bullets are too small, try a larger size, If it gets better, you were right. If it doesn't, try a larger size.

If you have a partial keyhole at 50 yards, that is a very strong indication that you bullets are too small.

The old wives tale about cast bullets need to be .001 over bore diameter is not correct. It never was.
Your bullets should be .002 to .003 over bore diameter.



So, after those groove diameter measurements, you agree that I should make the bullets to .460 and see if that's enough?



Posts on the Marlin forum indicate your bore is probably .456 to .457
That would indicate your bullets should be .458 to .459

You didn't mention your current bullet diameter but if you are keyholing, I would go up .002.

Load up a dummy round with an unsized bullet.
If it will chamber with no effort required to close the bolt, load up 5 of them and try them.
If you need to apply more than normal force to close the bolt, the bullet is probably too large.

IIRC, I had bullet size of .457, pretty close to the nominal of the Lee 90376 (leeprecision.com/mold-dc-c457-500-f.html)... I'll be lapping the mold and loading up a couple of rounds to see what will happen with the distances earlier...

[Flexy]

12 grooves sounds more like micro-groove, but I could be wrong that is a big ol' hole. I'll have to check when I get home, but I think that my '95 has six. If you don't notice any leading after 20 rounds, your boolit probably isn't too small. You may just not have enough twist rate to stabilize that long boolit. I have not tried 500 gr in mine because I didn't like the accuracy lose I got going from 405 to 450. Mine seems to like the 405's better than anything else. I'll be interested to know what you come up with from the barrel slugging.

The lands and grooves are around .06" in width. I still think that this is not micro-groove, but I ain't saying anything for sure...not enough experience under my belt. :)

I'll propably be downsizing the bullet weight after I get this to work properly. I feel that I don't need/want the fastest of loads, but rely more on the hefty weight and caliber... Even that in mind, 500gr might be an overkill for moose... Perhaps that is good for bear, casted hard... If I ever get the chance to deliver one to the said adressee... :D

[Sensai]

Before you go lapping the mold, check the unsized diameter of the boolits "as cast". Lee says that their molds are advertised size -0,+.003. I don't know how true that is in real world space, but I've never had one cast smaller than advertised size. Point being, you may have your right size without sizing. Did you scape out any leading when you slugged the barrel?

[Flexy]

I did check also before sizing... and the mold is advertised as .457". Sizing felt more like "scraping" of excess of pan lube away... I presume I got the smallest within 3 thousands of tolerance. No problems there, got to try to lap the mold and the sizer bigger, now that I have slugged the groove diameter.

I noticed that if I don't resize the cases, then my bullets just fall against powder. Max factory crimp is not enough to hold them. Should I just resize the neck of the case a little, so that bullets are tighter? Or is this a symptom of using .457" molds, when I perhaps should be using .459" molds?

[Sensai]

No, it's normal for the boolit to be a loose fit in an unsized case. I don't get a feel for exactly how loose it is, but you want the case to expand enough to release the boolit on firing.

[williamwaco]

Well, I was not even a gleam in my fathers eyes at that time... So, just happy to get advice... :) In any case, I slugged the end of the bore and after that thru the bore. Idea was to not ruin the mold/sizer. Don't know how to put the material back to either of them after lapping... :) Results are within .4580" - .4585" in both slugs, measured at impressions made to the slug by the groove of the bore.

This wording bothers me. The high points on the slug correspond to the low points in the bore thus the groove diameter. If you are measuring the low points on the slug, that corresponds to the top of the rifling. If that measurement is .458 your measurement is inaccurate of your bore is quite large.

So, after those groove diameter measurements, you agree that I should make the bullets to .460 and see if that's enough?

You didn't mention what you measured with. If it was a caliper, I still recommend trying .458 or .459
If it was a micrometer, try them unsized before you lap anything. You cannot unlap.


IIRC, I had bullet size of .457, pretty close to the nominal of the Lee 90376 (leeprecision.com/mold-dc-c457-500-f.html)... I'll be lapping the mold and loading up a couple of rounds to see what will happen with the distances earlier...

I find that most of today's molds drop smaller than "nominal". If your mold is dropping at .457 or .458, you should try beagling before you lap the mold.

[KCSO]

On cut rifled barrels especially the cut is just a fraction deeper where the cutter first bites in and so barrels are very slightly tapered. The good barrels come marked for the breech and the muzzle. Accuracy isn't as good if the bullet gets looser as it travels down the bore.

[Lead Fred]

.460 works great in my GG. Id not be shooting 500 grainers though it tho.
When I went from 405s to 425s, things got a bit stout.
Anything bigger I save for the Buff Classic.

The lee 457 stuff worked ok in the single shot, but not in the lever

[Flexy]

Lapped the mold and the sizer die, resulting in about .4605 after sizing. Shot a couple at the range, starting from 75yards. Nice group of 2 inches, if not counting one flyer. Knew that was a bad shot right when it left the barrel... Then I shot 5 at 125yards. 7 inches if counting one flyer, 3 inches if not...

Overall satisfied, because the keyholing is cured and accuracy is where I expected. Earlier hitting the target at 75yards was not a sure thing... Now I need to practice more to get rid of the flyers and size up my 450 and 400 grain boolit molds as well. Lapping the molds is time consuming and one really needs to restrain oneself not to use coarse grit media... which lengthens the time but end result is more round..