Micro Grove and fire lapping

[MGySgt]

Anyone ver firelap a Marlin MicroGrove rifle? What were your results?????

Drew

[Catshooter]

Yep. Friend's 45-70 just would lead, no matter what we did. Finally decided to firelap it. Cured the leading completely.


Cat

[MGySgt]

Do you remember how many rouunds it took?

[longbow]

I didn't fire lap but lapped by hand.

I have a Marlin 1894 in .44 mag. that had a few quirks. I worked my way through and found out the hard way that the SAAMI spec for rifle barrels is larger than handgun barrels. DOH! I probably should have known that but didn't and available moulds cast at 0.429"/0.430" where I needed 0.432" minimum. So fatter boolits helped there but I still got leading. Then I read on the Marlin Owners Forum that some Marlin barrels have constrictions in them under dovetails and roll stamped lettering so I slugged the bore and ran the slug from one end to the other. Sure enough there were several tight spots!

So, I made up a couple lapping slugs and worked the tight spots until the lapping slug slid through easily then lapped from breech to muzzle working more strokes towards the breech than muzzle to try to make a slightly choked bore. I was a little concerned with lapping a microgroove barrel because there just isn't much rifling depth there but it worked for me. Accuracy improved and leading disappeared.

Not sure about fire lapping but I have to say that hand lapping really was not that difficult and did what I wanted.

Longbow

[dubber123]

Done a few, I know I did about 25-30 rounds on a 336 in 30-30, using 320 grit. Bore shines like a mirror, doesn't lead, and it shoots very well now. I believe I used a similar number in my 35 Rem with the same results. I probably have done others, but most have been conventionally rifled barrels.

[MGySgt]

As noted by longbow -- I too am concerned about the shallow Micro Grove and really don't want to barf this up. I really need to slug the barrel, I am already using .432 boolits as that is what my SBH likes after firelapping it.

[dubber123]

Firelapping works REALLY slowly, not much to fret over.

[Lakehouse2012]

Firelapping works REALLY slowly, not much to fret over.Any info out on the net i should read on this "fire lapping"? Never heard of it before and can see same issue on my new marlin 1895...

Sent from my SM-G920V using Tapatalk

[hylander]

I just hand lapped my 336 because of the really poor accuracy.
Will find out tomorrow if it helped.
If not, it will get a new barrel.

[MGySgt]

Any info out on the net i should read on this "fire lapping"? Never heard of it before and can see same issue on my new marlin 1895...

Do a search here - I am sure there are many threads here that deal in Fire Lapping. Midway sells the Wheeler Fire Lap kit, and Veral Smith has his own at LBT. I have both and used both on Ruger 44 mag and 45 Colt. It does smooth out the barrel, reduces leading, improves accuracy and makes cleaning easier.

But you can do too much annd greatly increase the dore diameter.

[Wagnerwerks]

This is on my to do list for my 1894 44 mag. There was a lot of info on Marlin owners.com.

[yeahbub]

I've pressure-lapped a number of barrels, some of them micro-groove and there are some differences, but not enough to materially change the lapping regimen. I don't use very coarse grit on micro-groove rifling, generally starting with 320 silicon carbide and finishing with 400 or 600. The results are mostly considerably better accuracy, since Marlin barrels seem to have the tight-at-the-breech and loose-at-the-muzzle characteristic with some regularity, but not all of them. They almost all shoot better now and clean more easily. Only one .44 mag I lapped didn't do better on target with cast, but was better with jacketed, and precisely why couldn't be determined before time ran out and the owner had it custom re-barreled. Another, more recent one does very well with cast and particularly well with paper patched. Generally, they'll take at least 20-50 lapping rounds, sometimes more depending on the degree and length of constriction, if that's the problem, or how loose it is at the muzzle. Some barrels have both problems, but it's still a lapping job. It's good to slug them more than once before you begin in order to be sure you're familiar with what that barrel feels like, since repeated slugging informs you of your progress will tell you when you're finished with the job. It's a whole 'nother experience when they slug smooth and consistent from end to end. You'll wonder if it's the same one you started with. Once consistent, a lot of the accuracy mysteries go away.

Abused/neglected rusted barrels also take more work, but they can be surprisingly good, though I never had a micro-groove barrel in that condition, so I can't say whether a rusty/pitted mg can come back.

[Big Mak]

I have a 2008 Marlin standard rifling (JM marked barrel) that absolutely hates .429 copper jacketed but plug a Missouri Bullet Co powder coated .430 lead bullet in the chamber and it hold 1.5" moa with iron sights at 50 yds.

[northernlead]

Good post,can you tell me where I can learn about how to hand lap.Thank you

[nekshot]

It has been talked alot here on this forum and the search mode should give you info. I did a few and all improved. I used the valve grinding mixture from napa or any car parts store. Usually a course and a fine tube.

[longbow]

Lapping is not inherently hard but you do have to be careful or you can ruin your barrel. In my case (like hylander) I figured if it didn't help my barrel I would get a new one so why not try?

You need some lapping slugs which can be cast in the bore or bullets that have been driven through the bore to impress the rifling on them, some valve lapping (grinding) compound, a brass or steel rod that will fit through a drill hole in the lapping slugs and a bore guide of some sort. Boolits driven through the bore will be pretty tight to start with so might be better to put lapping compound in the bore then run the lapping slug over it.

Here is a basic description of the process. Oddly I can't find a good detailed description:

http://www.shootingtimes.com/gunsmithing/gunsmithing_st_lappingbarrel_200805/

Here is something else that might help:

http://bisonarmory.com/content/RifleBoreLapping.pdf

Also, a point... don't push the lapping slug out of the bore! Once it is started, stroke until you feel smooth all the way pushing the lapping slug to the ends of the rifling at the breech and muzzle, so protruding but not right out. If you replace that lapping slug to use a finer compound or to use another repeat with the finer compound until you are happy with the results. Go Slow!

And... do not let the long rod touch the bore! Use a bore guide to keep it centered and not touching the bore.

Longbow

[MGySgt]

Shot the 1894 Marlin yesterday to see the velocity, I hadn't run that load over the Chrono when I worked that load up in late 90's. I was surprised, first it holds 3 in at 100 for 5 rounds.
The Chrono results - Average MV = 1658 with an extreme spread of 8. 265 grain. picture attached.
I was pleased, but I wanted to clean it down to bare metal so I could slug the bore to see if I really wanted to firelap it. If it is over .431 - I won't firelap it.
Still cleaning - it is taking me forever to bring it down to bare metal. Everytime I think I am done I run a NEW bore brush through it and the next patch is black with carbon and a few tiny flecks of lead, real small fleck's but they are still there. I will work on it again tomorrow.

[OverMax]

Was thinking of doing just to brighten the bore a bit. Have a model 36 closed receiver model. Changed my mind at the last minute. Just couldn't chance ruining a decent shooting old 30-30 having no problems. We both know that Micro Groove rifling isn't all that pronounced and might not handle a accidental too aggressive lap.

[MGySgt]

The firelapping kit I use is Veral Smiths from LBT. I have firelapped a number of 44 mag's and 45 colts, just not a rifle - Yet.

BTW I am still cleaning it. I may be getting near the end as I am getting some copper out now. This is a new to me rifle, I don't know what the original owner put through it, but I am prettyu sure it was jacketed. I haven't fired any jacketed ammo out of it.

[dubber123]

Was thinking of doing just to brighten the bore a bit. Have a model 36 closed receiver model. Changed my mind at the last minute. Just couldn't chance ruining a decent shooting old 30-30 having no problems. We both know that Micro Groove rifling isn't all that pronounced and might not handle a accidental too aggressive lap.

You'll die of old age before you "accidentally over lap" one. People seem to think a lot happens in a few shots, or 10, or 20. Nope, nope, and nope. You should be cleaning and inspecting the bore every 5 shots or so anyways. When you fire your first 5 and see NOTHING, you will relax a little :)

[MGySgt]

You'll die of old age before you "accidentally over lap" one.

dubber123 - that statement can be misleading. If you usee too aggressive of a grit you can make matters worse in as little as 10 or 15 shots. I use the LBT lapping compound because it has been throughly tested. Yes some individuals have use valve lapping compound and got wonderfull results from useing it. I am just not going to take a chance.

With a revolver I use 6 shots between each cleaning and inspecting (one for each chamber). Once I get done cleaning this Marlin I will use 5 rounds per inspection.

I have got most of the trash out of the barrel, but I am still getting what I think is a mix of carbon and bullet lube each time I use the bore bursh. Wet the barrel with bore cleaner (I use Montana Extreme) then run a bore brush down the barrel 10 times and follow with a wet patch - Black, normally 2 or 3 patches till no more black, repeat process. I did slug the barrel - it is .430 with 2 tight spots in the bore, I could push the slug past them with just a little force, so I am hoping that 15 to 20 shots will smooth them out - but we will see.

One of the tight spots is about 2 inches in front of the rear sight dove tail and you can see something on the right side of the barrel as you are looking at it from the muzzel. The wet patches use to bump against this spot so there was some build up of lead/carbon/bullet lube there. I don't feel it as much now as I did, but I can still see it witth a bore light.

[dubber123]

All I use is 320 grit. Many consider this too aggressive, but once you see the finish it puts on a bore, you may think otherwise. The grit begins breaking down finer immediately on it's trip up the bore. One of the best tips I was given is to pick out a tooling mark close to the muzzle. (easy on most Marlins) :) When you just begin to see this tooling mark being worked on, stop.

The way this works so well, is that the abrasive action becomes less and less as it heads towards the muzzle, and it puts a proper taper in the bore, meaning subsequent boolits or bullets get an ever tightening grip when they are fired. Reverse tapered barrels aren't unheard of, and good luck getting one to shoot. I agree that it's better to be careful, but my 1895 Cowboy took nearly 100 firelapping boolits, all 320 grit to cure that barrel of it's multitude of issues. Other than looking like a mirror inside, the rifling still looks sharp as new to me.

I'm sure you will have success with yours.

[MGySgt]

I have 18 rounds down the barrel and the bore size has not grown (as farr as I can tell that is). I shoot 6 and clean. Using BullEye powder and 155 SWC Keith Style. Yes It does lead that is why I clean every 6 rounds. (I know I said I was going to do 5 at a time but I had 6 I use for 44 mag fire lapping so......)

There are 3 tight spots in the barrel. They are getting easier to push a bore slug past.

Yes I have stuck some in the barrel (3 to be exact) settled on 2.5 grains with the boolit seated with the front griving band even wth the case mouth. Push the boolit in with my thumb except for one case I have to use the press.

I have the next 6 ready to go and the rifle has been cleaned.

[dubber123]

I have 18 rounds down the barrel and the bore size has not grown (as farr as I can tell that is). I shoot 6 and clean. Using BullEye powder and 155 SWC Keith Style. Yes It does lead that is why I clean every 6 rounds. (I know I said I was going to do 5 at a time but I had 6 I use for 44 mag fire lapping so......)

There are 3 tight spots in the barrel. They are getting easier to push a bore slug past.

Yes I have stuck some in the barrel (3 to be exact) settled on 2.5 grains with the boolit seated with the front griving band even wth the case mouth. Push the boolit in with my thumb except for one case I have to use the press.

I have the next 6 ready to go and the rifle has been cleaned.

Good deal :) I believe the last I did took about 30-35 to do with 320 grit. I did 5 and clean. Glad you are making progress.

[MGySgt]

Finished up today - 36 rounds total - final bore size is just under .431. Now I have to breakin the 'New' barrel. Shot 10 rounds of a plain base 250 Keith Style (wonders upon Wonders, they functioned through my Marlin - suprised me).

Cleaned it after shooting with dry patches and a bore brush - some leading but came out easy enough. I will load up some more rounds probably 250 Keiths with about 17.5 grains of 2400. Just need to shoot some and then clean it and shoot it some more before I shoot it with my hunting load for velocity and accuracy.

One test I have to do before I shoot it over my chronagragh is check to see if I loose any gas checks when the boolit leaves the barrel. The gas check is loose on the heal of the boolit after sizing at .432, but shooting it down the .430 barrel they stayed on - no holes in my chronograph. I really want to keep it that way. Don't know if I can replace it with another Ohler 35.

Now how do you check that - easy enough - take your target stand 15 feet from the bench and put newspaper across it and shoot thrugh the paper. If the gas check is going to come off you will have 2 holes in the paper for every round you fire. I will test with 10 rounds to see what happens

[MGySgt]

Well I have shot it for accuracy and velocity.
Very dissapointed.

Velocity dropped 30 FPS

Accuracy has gone to poop.

I really do not believe the barrel is gone. I really think it is the boolit I am useing. The loss of velocity may hve brought the boolit down past that magical speed to stay stable. If you look at my boolit real close you can see it is almost the profile of a wad cutter and to get good accuracy past 60 yards with them you have to drive them fast.
25 yards while chronographing the load was one ragged hole in the target.

I am going to re-work the load with Alliant Prower Pro 300-MP and H-110. I can get another 75-100 FPS out of them.

Drew

[dubber123]

I've not once seen accuracy decrease, but you may have to re work loads. I doubt VERY highly you did anyhing to harm your barrel.

[longbow]

I am surprised your bore is that tight. Marlins are known for "fat" bores though I can't say for sure they go over the SAAMI spec of 0.431" much or often, though my .44 mag. Marlin bore slugged at 0.4315"... but tenths of a thou are a bit elusive.

As a side note, I started out using the famed Lyman 429421 SWC Keith style because everyone said it was simply the best boolit for .44 mag... more towards revolvers I suspect but what did I know?

Not only didn't it feed well but accuracy was very mediocre and I got a lot of leading. Turns out that it cast exactly to 0.429" with WW. No, I didn't go the Lyman #2 alloy route. So the boolit was 0.0025" undersize. That explained leading and poor accuracy or at least partially.

Fatter boolits helped with accuracy and reduced leading but it wasn't until I slugged the whole bore looking for tight spots that I solved the leading issue. Once I hand lapped those tight spots out things improved a bunch with better accuracy and no leading.

I actually haven't shot the gun much since but I have it feeding the H&G #503 well and it likes the Mihec 434640 which is an RNFP design. Both have given quite acceptable accuracy out to 50 yards anyway. I have to sit down and do some serious shooting at 50 and 100 yards to see how it does.

I've mostly shot my lightweight 165 gr. plinkers in it since I did all that work!

Longbow

[MGySgt]

Dubber123 - I really don't think I hurt the barrel - like stated earlier the 'new' size is just under .431 and I size my boolits to .432. I have a few other molds for the 44 but they are clones of the 429421 Keith, they are both over .432 so the size will be good.

My Mountain Mold 265 gr GC just feeds so darn smooth and hits so hard with that big flat point I just want it to work. But if it doesn't I will change to one of my 429421 clones, they just don't feed as smooth, they will feed though.

Looking at QuickLoad today I found that LilGun might be the powder to try as it showed the highest velocity of any other powder I plugged in, Yes that included H-110/296. Going to a LGS tomorrow maybe I will pick up a pound. Wonder if LilGun needs Mag primers - I have some, just need to find out if it needs them or not, have to look up some loads that use it.

Drew

[MGySgt]

Longbow - I quit using the Lyman 429421 30 years ago because it leaded so bad due to it being under size. I have had a number of Mountain Molds that worked great, but like an idiot I sold them off for one reason or another. My current one (the 265 gr GC shown earlier in this thread) shoots great out of my Stainless SBH with a 4 1/4 in barrel - yes it has been firelapped. I was 'Trying' to make it work in the Marlin, it was designed with the Marlin in mind.

May have to sell it off too (still a great boolit for 50 yards and under) and find another one that has a wide meplate and is in the 260 - 280 grain range that would be a WFN or LFN boolit.

Drew

[dubber123]

I only ever had one that didn't show a marked improvement, a Marlin CB in 45-70. It shot a little better, but not a ton. It did reduce the leading by a bunch. I could shoot 2 full grains higher powder charge before leading started to creep in, so a substantial improvement there.

That gun was a problem child since day one, I'm glad I paid a lot for it :)