Hey all, slugged my old Marlin 336 30-30
w/micro groove bbl....

Throat = 0.304" dia
Muzzle = 0.3085" dia

No wonder it wouldn't shoot much better than a 4" group at 100 yards.....

Scrubbed the snot out of it with shooters choice, hoppes, JB.... tried again, same thing....

So My poor sad 30-30's got a messed up barrel some how.....

It was my 1st gun, so don't really want to get rid of it..... But it doesn't shoot worth a darn, so it is really no fun.

So... with this much choke at the throat

A. Would fire lapping do enough without totally ruining the rest of the barrel?

B. Would it be better to try out lead lapping instead?

C. Would it just be better to bite the bullet and get a new barrel on it?

Custom lever smiths out there? Any do custom barrels for Marlin levers...

Thanks

John

quote:

Originally posted by TruckJohn:
Hey all, slugged my old Marlin 336 30-30
w/micro groove bbl....

Throat = 0.304" dia
Muzzle = 0.3085" dia

No wonder it wouldn't shoot much better than a 4" group at 100 yards.....

Scrubbed the snot out of it with shooters choice, hoppes, JB.... tried again, same thing....

So My poor sad 30-30's got a messed up barrel some how.....

It was my 1st gun, so don't really want to get rid of it..... But it doesn't shoot worth a darn, so it is really no fun.

So... with this much choke at the throat

A. Would fire lapping do enough without totally ruining the rest of the barrel?

B. Would it be better to try out lead lapping instead?

C. Would it just be better to bite the bullet and get a new barrel on it?

Custom lever smiths out there? Any do custom barrels for Marlin levers...

Thanks

John

First thing I would recommend is to let a gunsmith familiar with these guns look it over. Sometimes there are things an experienced eye can spot that may disclose a problem. I would consider that first before doing anything that might be irreversible.

first question, are you reloading or shooting factory ammo


how tight is the stock fit?
you can skimbed the forearm, this sometimes help

your barrel is slightly oversized... hawk bullets, those not for big bores to me, are soft enough they may shoot better

jeffe

Couple of possibilities:

1) It is very very common for marlin barrels to have tight spots. These can be usually be lapped out.

2) It is very very common to get undersize measurements when slugging a barrel. The slug abrades as it slides through the barrel. I have gotten up to 0.010" undersize. In fact, I slugged my marlin barrel over and over again and rarely got the same measurement twice. I am not impressed with the reliability of slugging a barrel.

quote:

Originally posted by popenmann:
2) It is very very common to get undersize measurements when slugging a barrel. The slug abrades as it slides through the barrel. I have gotten up to 0.010" undersize. In fact, I slugged my marlin barrel over and over again and rarely got the same measurement twice. I am not impressed with the reliability of slugging a barrel.

You can get reliable results if initially, after you lube the bore, and, after you insert the lead slug, you place a rod on each side of the slug and drive one towards the other like a hammer and an anvil. This forces the lead out and tight against the bore. Other wise the lead can distort on entry and produce false readings.

I think you can send microgroove barrels to Marlin and ask them to rebarrel it to a standard rifling barrel. I don't think it will cost you too much. I have read of others doing this in any event.

Brent

Wouldn't even the best slugging just produce an accurate reading of wherever the bore is the tightest?

Anywhere else, how would the slug "slug-up" to fit the loose spots?

And, if there are several tight spots in the bore, isn't the slug likely to only give you the diameter of the smallest of them?...it still isn't likely to tell you WHICH one of the tight spots was that diameter, is it?


It IS possible to taper-lap the barrel, with practice, so that the muzzle ends up the tightest point of the bore. Basically, that involves more strokes toward the breech end than at the muzzle end. But the muzzle is still going to be as oversized as it is now...it's just that the closer to the breech section(s) will end up being even more over-sized. Of course, with either cast bullets or your own bump-die for re-forming commercial jacketed bullets, you can make those slugs to fit the over-sized bore with very little added effort.

It's not brain surgery. Pretty much anyone can do it. Like anything else one is learning, though, it pays to go very, very slowly and carefully when you first try it. And remember the old carpenter's rule: "Measure twice and cut once."

yep.. unless something really odd happens, the slug is goign to represent the smallest part it went through.. though malm's idea is cool

jeffe

Yes, if you hit a tight spot that would be a problem and should put a halt to your troubleshooting.

It ain't gonna shoot if the muzzle is larger than the breech. If you slug a lot of barrels you will feel things that an air guage doesn't show. You have to slug it in one continual motion without stopping. The feel is more important than the measurement. It is very important to know where the tight spots are.
Butch

Although without slugging the barrel myself, I would bet that firelapping, or having your gunsmith lap the throat would help improve accuracy. Another problem could be the muzzle crown. Cutting the barrel back a little and recrowning could help it greatly, considering its age.

By the way, do you use a muzzle guide when cleaning the barrel? If you don't, some of the reason the muzzle seems larger could be wear from cleaning rods.

Malm, did you ever get the photos I sent .Did you get the PMs ? ....Just reverse the barrel to get the choke on the correct end then use it for goose !!

From some that I've seen, the bores of alot of levergun barrels become oversized from cleaning rod wear because they have to be cleaned from the muzzle end.

quote:

Originally posted by mete:
Malm, did you ever get the photos I sent .Did you get the PMs ? ....Just reverse the barrel to get the choke on the correct end then use it for goose !!

Yes I did mete and thanks!

quote:

Originally posted by butchlambert:
It ain't gonna shoot if the breech is larger than the muzzle.

Butch, did you accidentally say that backwards?

Lots of the best shooting barrels the world has seen in various periods of rifle history were barrels which WERE larger at the breech than at the muzzle. Harry Pope's barrels were made that way, and not too many people found them inadequate. The Ross competition .280 barrels were made that way too, when they were "cleaning up" most of the prizes at Bisley. Other respected makers have also reportedly found that having a little tiny bit of "choke" at the muzzle seems to help things along.

Alberta Canuck, You are so right. I need to read what I write before hitting enter.
Butch

I 'figgered' that was the case, Butch. Your name is well known as a very knowledgable rifleman in the circles I hang around in, so I was pretty certain it was just a slip of the keyboard.

Best wishes,

AC

So....
The general consensus is either:
1. Have it lead lapped correctly
or
2. Try fire lapping it.

before sending it back for a new barrel.

I have slugged plenty of barrels, and this is
the 1st one I have seen with a choked throat this bad..... and the sad part is that I have had it for the last 18 years.

Thanks

John

If you brought that rifle to me, and after looking it over couldn't spot anything out of the ordinary, I would push a tight fitting patch from the breech to the muzzle and feel for any irregularities. Next I would pour a cast of that portion of the bore, ahead of the throat, where the bullets seal is formed, and measure that.

Then I would slug, or, cast the muzzle end, using the technique I previously mentioned and compare it with the reading I got from the other cast and based on that, make a decision as to which route I would go next.

Often times we overanalize things and maybe this is one of them.

My point is simply that you don't know if any issues with the barrel are causing the incaccuracy. Yes it might be but I've had luck with Marlin by just sending them the gun and telling them that it isn't accurate and let them fix it.

They have one of the best customer service depts in the firearms industry and like others they not only take them in they also fix them.

Great company.

quote:

Originally posted by TruckJohn:
Hey all, slugged my old Marlin 336 30-30
w/micro groove bbl....

Throat = 0.304" dia
Muzzle = 0.3085" dia...
C. Would it just be better to bite the bullet and get a new barrel on it?

Custom lever smiths out there? Any do custom barrels for Marlin levers...

Hey John, You are going through a whole lot of speculation and fretting over a very easy and relatively inexpensive fix.

I have a 444Mar Guide Gun(rifle actually) with the weenie length barrel. I contacted Marlin and they told me the cost for a new 24" barrel would be $140 which included return Shipping. The only other cost to you will be the phone call to Marlin and the Shipping cost to them.

You might want to consider getting a barrel with the Ballard rifling from them. Darn nice rifles and I seriously doubt you can beat the Factory replacement cost.

Best of luck to you.

you might work on the basics, first...

quote:

Originally posted by jeffeosso:
first question, are you reloading or shooting factory ammo


how tight is the stock fit?
you can skimbed the forearm, this sometimes help

your barrel is slightly oversized... hawk bullets, those not for big bores to me, are soft enough they may shoot better

jeffe

From everything I've ever heard anywhere nobody can beat Marlin's price to replace the barrel on a Marlin

Usually the Microgroove barrels are pretty good, unless you are shooting cast bullets....

AllanD

Did some work on the barrel to see if I could find some improvement before spending $$$$$....

1. The throat was badly constricted. NO amount of goofing around with loads fixes this. Even agressive cleaning with JB didn't change it -- it was the steel that was the problem.

2. The rest of the barrel was slightly oversized, and belled out to ~0.309+ in the middle. You could feel a very very loose spot smack in the middle of the barrel.

After hand lapping out the restriction at the throat, then various fire lapping 10-shots at a time.... till the big nasty bell in the middle was mostly gone.....

The finished dimensions are 0.3095 at the muzzle, 0.3096/0.3097 at the throat.

I reloaded up some Rem 0.310" CoreLoct Round nose slugs to try out at the range tomorrow. I will tell you how it shoots.... I can't imagine it would shoot worse than it did.

Yep, It probably won't shoot factory ammo any more, but if it shoots good, I will leave it be. I can reload lots of ammo just fine.

Funny, but I have ran into 4 or 5 guys out at the range cussing their Marlin's with microgroove barrels. I really doubt it has anything to do with the "microgroove" rifling.... I would bet they have the same problem as my gun had.

Best regards

John

Maybe now after all your work it will at least throw the bullets in a consistant manner. Good luck!