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M39 Custom - Tutorial w/ Instructions

45K views 43 replies 11 participants last post by  clarkmagnuson 
#1 ·
The M39 Project Tutorial

’67 M39 Custom stock, pillar post bedding, recoil suppression, Huber trigger, bolt and sear tuning, bore conditioning, scope mounting.
Full detailed step by step instructions.

The custom M39 project nears completion and as the weather improves, I have had the chance to test drive her enough to be satisfied with the results. It has a good 300 rounds or more through the bore now. Still waiting on the X-Caliber bipod, due to go into production any time now.
Bolt is on the way to Charity Littleton http://www.boltcheckering.com/ for a little dress up. Extra panels to be added on the flats on the top as well. Thinking about having the stock done eventually http://www.checkering.com/.

While I have not drilled a hole through a quarter at 200 yds with it yet, too much wind and being unable to hold it steady enough on a sandbag rest without that bipod, it has shown that it can and will do that. I have not touched the adjustments on the scope since I got it zeroed. Cold out of the case, it will reliably nail a golf ball at 250yds, first time, every time. Zero has not changed even a hair. I have seriously taken up golf, chip and putt at 250 yards, bouncing golf balls around on the berm until there is nothing left of them.
BTW: That’s with milsurp Polish 7.62x54R, the last cheap case I bought. One of the guys on the range says he can hand stuff some really accurate 54R. That I have to try!

Yes, I do admit to spending entirely too much money on this project, especially when the machinist ripped me on the scope mount, but it is still cheaper than any new production “sniper” with accessories you can buy. Satisfaction from building this “toy” has proved worth the time, money and effort!

Bear with me on the remainder of the tutorial as I am behind on the pictures and text and have some catching up to finish it.

pics: right side, left side, scope mount.
Playing card 200 yds, 1 shot 8-10 mph wind
Golf ball 250yds, 5 holes 8-10mph winds
Group 2/11 20 mph winds
Group 12/3 15mph winds
 
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#27 ·
Trigger Spring

http://www.surplusrifle.com/shooting2006/improvingm44carbines/index.asp

Follow the instructions in the above for lightening the spring by grinding to the indicated thickness.
Spring tension, and trigger pull weight have much to do with this tuning.
I have performed this on just about every Mosin I have with considerable improvements.
You can go a little too far, which I have not done to date, so it is a good idea to have a spare or two from Numrich in your parts inventory before you begin!

The easiest way to accomplish this is with the Dremel sanding drum.

The important part of this tweak, once you have achieved desired thickness by grinding both sides of the spring, is polishing the top surface where the trigger rides to mirror bright.

This is done by first hand rubbing with 1200 grit paper and then buffing with the Dremel and fine compound until all your grinding marks are completely polished out to mirror smooth.
On completion and final assembly, one tiny drop of Moly Fusion is applied to the surface to give the trigger a smooth as warm butter ride and protect the surface from rust.
 
#44 ·
Trigger Spring

surplusrifle.com

Follow the instructions in the above for lightening the spring by grinding to the indicated thickness.
Spring tension, and trigger pull weight have much to do with this tuning.
I have performed this on just about every Mosin I have with considerable improvements.
You can go a little too far, which I have not done to date, so it is a good idea to have a spare or two from Numrich in your parts inventory before you begin!

The easiest way to accomplish this is with the Dremel sanding drum.

The important part of this tweak, once you have achieved desired thickness by grinding both sides of the spring, is polishing the top surface where the trigger rides to mirror bright.

This is done by first hand rubbing with 1200 grit paper and then buffing with the Dremel and fine compound until all your grinding marks are completely polished out to mirror smooth.
On completion and final assembly, one tiny drop of Moly Fusion is applied to the surface to give the trigger a smooth as warm butter ride and protect the surface from rust.
1) Thinning of the Mosin trigger spring [sear] was all over the internet in 2009.
2) Buying a Huber trigger for a Mosin was all over the internet in 2009.
3) Polishing the Mosin trigger was all over the internet in 2009.

I discouraged those 3 changes in 2011 with this video



This diagram I made in 2011 is really just Hooke's spring law.

Handwriting Rectangle Slope Font Parallel


What I encouraged starting in 2011 was to 1) bend the Mosin sear .....or better 2) buy a Timney Mosin trigger.
 
#28 ·
Firing pin spring

http://www.surplusrifle.com/shooting2006/improvingm44carbines/index.asp

Once again, follow the instructions for shortening the firing pin spring.
This considerably improves bolt function making it much easier to cycle and cock.
I have done this to all the Mosins and the other M39 with similar results.
This bolt cycles like a knife through warm butter and only requires two fingers to effortlessly chamber the next round. The pin will strike with sufficient force to light off the primer. The only failure to fire instances have been true duds where even multiple strikes failed to light them up.

As to "lock time", I have found that combined with the other bolt tuning and sear polishing tweaks, lock time is considerably faster even with the shortened firing pin spring.
 
#29 ·
A brief intermission.
This is where I have to finish the rest of the tutorial.
More to come.
Sear and cocking lug tuning
Bolt and receiver tuning
Scope mounting
Bore conditioning
 
#30 ·
Wow! Very impressive work. I look forward to the rest of your tutorial, especially the part about the machinist ripping you on that scope mount...bottom half looks like an Accumount. Nice to see what is possible with the M39. I'd love to take my M39/SOV Repro to that level of accuracy, but I don't have your skills nor the cash to spend.
 
#31 ·
BORE CONDITIONING

How do you make a good and accurate rifle ten times better?
There are some tune up steps and treatments I have become a firm believer in, so much so that I have applied them to all my other “shooters”
Of course, the premise is that you are starting with a good bore with strong rifling that already shoots accurately.
I do not dismiss the accuracy of any rifle until it has been “properly” cleaned and conditioned and the crown and lap tuned up. I have had various milsurps that where fair to mediocre which suddenly gained a new life after the proper work and surprised me with new found accuracy.
I have “conditioned” rifles people swore were shot out and worthless only to obtain quite acceptable accuracy. In fact, I’ll be quite happy to buy that “worn out” milsurp for an appropriate pittance and gladly take it off your hands!

Bore Conditioning Cleaning

The first step in “conditioning” is a thorough scrubbing down to bare metal.
This is NOT running a few patches with Hoppes through it until the gunk comes out!
All traces of carbon and all copper and lead fouling must be completely removed.
DO remember to stock a supply of NEW brass brushes as, once crushed down and worn, they no longer reach into the grooves and you are only cleaning the lands!

There is a bit of Economics 101 here …
You can use many other products on the market in vast quantity with a huge labor and time investment. If they fail to do the job, your “conditioning” treatments will not be effective.
The below listed products are not the cheapest to buy but, when used in the order listed, you will consume small amounts of each stretching them far further than the other products for less money! There is also a huge reduction in the labor factor.

Chamber and Throat
Note that all steps below should be equally applied to the chamber and throat area, a part of the cleaning regimen often forgotten and ignored.
These areas need to be brushed during cleaning by finding appropriate size brass brushes that will fit tightly into them. The chamber is bigger than the throat so you will require several brushes. Crap in the throat is the usual cause of sticking empties that refuse to eject and the most common cause of broken extractors. Remember that the neck of the bullet expands slightly in the throat area upon firing to form the gas seal and considerable carbon and fouling will accumulate there. The easiest way to clean these areas is to place the brush on a short rod that will reach from the chamber end and chuck in an electric drill. Spin the brush for twenty seconds with the drill, change to the throat brush and spin that for twenty seconds.


Ingredient #1
The most essential cleaning product I use, in vast quantity, is Advanced Auto Parts Carb and Choke Cleaner. Although the price has taken a jump to $2.59 per can, it is still the cheapest solvent out there that works better than anything else I’ve found to date!
The contents of this product are designed to remove stubborn carbon deposits from engines.
It accomplishes the same job with the carbon deposits in a rifle bore.
Breaking up and removing the carbon also removes the trace metal copper and lead fouling that the carbon holds in place.
The Advanced Auto Parts cleaner has a slower rate of evaporation allowing more time to work with it. It will still eventually evaporate completely with no traces left behind.
It can damage wood finishes but is not as prone to dissolving them as many other products.
Whereas Gum Cutter will strip decades old paint in seconds after contact, this will not.
As one of the “cheapest” cleaning products that will remove 80% of carbon and fouling, it is worth always carrying a can with you to the range for a quick first clean up after shooting.

Step #1: Spray and flush the bore liberally with carb cleaner.
Stoke vigorously with a brass brush a good twenty times.
Flush liberally again with carb cleaner and watch the black junk pour out.
Work a dozen or so patches, soaked in carb cleaner through the bore scrubbing well until they no longer come out black.
Repeat with the flush and brush and again with patches until you no longer get anything out.
This step usually only requires two cycles on a “conditioned” bore and about fifteen minutes.
 
#32 ·
Ingredient #2

Shooter’s Choice Bore Cleaner
http://www.shooters-choice.com/
I highly recommend ordering directly from the web site in the larger quantity bottles.
While some gun stores in the area do carry Shooter’s Choice products, they only have the small bottles and it is more economical to order directly off the web. While the large bottle is expensive, used in the small quantities here, you will get considerable mileage out of one.

We shoot a lot, which means we clean a lot! Over the years, we have tried just about everything on the market and just find Shooter’s Choice products to do a better job, for the money, than any other brand. Personal preference, choose what you want, but I will use nothing else!

Step #2
Following the carb cleaner, soak a patch in Shooter’s Choice Bore cleaner and thoroughly swab the bore. Let stand five minutes and then brush vigorously.
Flush again with carb cleaner and patches soaked with carb cleaner.
Patch again with bore cleaner and scrub with several more patches wet with carb cleaner.
Flush, brush, and patch again with carb cleaner.
Very little should be coming out on your patches by now. If not, repeat the cycle.
You should only require two or three patches soaked in Bore Cleaner.

Step #3 Ingredient #3
Shooters Choice Copper Cleaner
Many of the copper cleaner products on the market are extremely caustic with high levels of ammonia (ammonia dissolves copper – that is the blue that comes out on your patch).
Some of these products are downright damaging to your bore if not used strictly according to directions!
Shooter’s Choice Copper Cleaner is not damaging to the bore when used properly.
Soak a patch in copper cleaner and thoroughly swab the bore.
Let stand 1 (one) hour.
Flush, brush and patch with carb cleaner.
No blue or copper should be coming out on patches or still visible in the bore.
If not, repeat the cycle.

Step #4 Ingredient #4
Shooter’s Choice Extreme Cleaner
This is a more potent foaming bore cleaner. Somewhat effective at copper removal.
Insert the nozzle in the receiver end and spray until foam comes out.
Repeat from muzzle end.
Let stand 3 (three) hours.
Flush, brush and patch with carb cleaner again.
Repeat cycles until patches come out clean.

Step #5 Ingredient #5
Wipe Out Foaming Bore Cleaner http://www.eabco.com/WipeOut.htm
While this is probably the best product on the market, it is too expensive to use for regular cleaning duties. The small spray can goes a long way but, it is not practical for routine cleaning chores. Wipe Out will dissolve copper safely and it is safe to let it stand for long periods, in fact it is necessary to let it stand for proper chemical reaction.
Insert nozzle from receiver end and spray until foam comes out. Repeat from muzzle end.
Let stand for 3 (three) DAYS. You can speed up the time and reactivity by placing over a heater vent but it must stand at least twenty-four hours to do the job.
Pay attention to the foam that runs out either end. If it is blue, there is still copper in the bore.
Flush, brush, and patch with carb cleaner.
If you are still getting blue, go back to step #3.
It is often necessary to apply a minimum of 3 (three) treatments of Wipe Out for “bare metal” conditioning.

The bore should now be completely cleaned to bare metal and ready to condition.
 
#33 ·
TUBB’S FINAL FINISH BORE CONDITIONING BULLETS

http://www.davidtubb.com/ff_tests.html
http://www.davidtubb.com/finalfinish.html

Read the technical specifications and the testimonials!
Believe what it says or not. I believe!
Having seen what these polishing bullets do to the bore and the improved accuracy, I am sold on them. Some calibers can be obtained in loaded cases, others like 7.62x54R (308 diameter) must be hand loaded.
For $34.95, what else can you buy so cheaply that will make a considerable improvement in your shooting?
For 7.62x54R hand loading, you will need decent Boxer primed brass. One of the cheapest solutions is Privi Partizan http://www.prvipartizan.com/. Just buy 50 loaded rounds and shoot them off. The brass will be pretty clean, without tumbling, for reloading and they will stand up to many reload cycles. Nice brass!

The loaded Final Finish bullets are fired ten rounds at a time progressing from one grade of grit to another, coarse to very fine.
Between each grit, thoroughly clean the bore following step #1 and step #2
After all fifty rounds, the bore should be very bright with distinct rifling.
It is now polished.

Bare metal condition again following all the cleaning steps and get down to bare metal with no residue of any kind remaining in the bore.

MOLYFUSION TREATMENT

http://www.shootersolutions.com/mol12ozkit.html

Once again, read the technical specifications and testimonials on the web site.
Believe or not! I believe!
Although I have no way of proving claims of improved accuracy, I can certainly swear how effective this product is when it comes to cleaning!
The product is PERMENANT! It binds with the actual metal and the only way to remove it is by grinding. It is a super lubricant! It is very good for treating any surfaces you want super slick, as in sears and bolts! One kit is enough to do many, many guns!

After complete Bore Conditioning and a treatment of MolyFusion, cleaning time will be reduced by 2/3! Very simply, crap no stick! Copper and lead fouling is vastly reduced as it no longer adheres to the bore. Guns, shot heavily all day, come clean in just a few minutes with cleaning steps #1 and #2. Just step #1 with carb cleaner removes 80% of accumulated carbon deposits.

CAUTION!!!
Do NOT allow MolyFusion to enter the chamber and throat area!
Read the cautionary statements in the technical specifications.
A certain amount of friction is required between the case of the bullet and the walls of the chamber and throat. Removing that with MolyFusion can cause very DANGEROUS stress on the bolt. This is absolutely essential for semi-automatics where recoil operation requires a certain amount of delay caused by friction.
Unless you want to risk wearing the bolt, make and insert an appropriate DUMMY round into the chamber during application and do not allow your mop to enter the chamber. A dummy can be made by stuffing an empty case with cigarette filters allowing one to protrude slightly from the neck. The filter material will absorb any MolyFusion that seeps into that area.

To treat the bore, buy a new mop. Apply a few drops of MolyFusion at a time with a toothpick until the mop is saturated. Stroke the bore with it several times, rotating the mop as you pull it out to ensure all surfaces get evenly coated.
Let stand 24 hours.
Flush and patch with carb cleaner.
Repeat twice more.

A proper and thorough application will turn the bright shiny bore a dull gray.
Than means it has bonded with and adhered to the metal.
While MolyFusion is permanent, it is advisable to repeat the extreme bore conditioning cleaning and application of MolyFusion twice yearly if you shoot a lot. The kit comes with oil mixed with MolyFusion that is good for a light oiling of the bore before storing. The small amount of MolyFusion in the oil will refresh and preserve the original treatment as well as effectively preventing rust. Read the testimonials and tests on corrosion prevention properties of MolyFusion. I have not seen any rust come out of bores that have been treated.

Note: Apply the MolyFusion AFTER doing the lap and crown.
 
#34 ·
LAP and CROWN

The muzzle end of the bore is the most critical factor in accuracy!
You have polished and conditioned the rifling in the bore to the best you can hope to achieve with it but the slightest nick in the crown will spray your bullets all over the place!

At the precise instant where the bullet disengages from the rifling, there is a huge high pressure volume of expanding gas behind it from the burning powder. As that gas begins to exit the muzzle behind the bullet, it must exit in a perfectly even and concentric circle.
Look up “smoke rings” and smoke ring generators on the web and watch the videos demonstrating how the smoke ring is formed. Note that it should be a perfect donut ring rolling back in on itself. The gas exiting behind your bullet must behave in similar fashion!
The slightest nick or ding in the crown can disrupt this gas flow leading to turbulence.
At the point of the turbulence, the gas will exert more pressure on one side of the tail end of the bullet causing it to yaw in flight. Yawing bullets do not fly true!

When analyzing a spready pattern from a gun that appears to be spraying all over the place with no consistency, it usually points to a problem with the lap and crown.
As compared to vertical or horizontal stringing with a consistent and repeatable pattern, crown and lap problems appear totally random. “Flyers” can frequently be attributed to crown and lap problems when the bullet gets tipped of course as it exits the barrel.

Most milsurp rifles will exhibit some form of crown damage from handling, use and storage.
Even new rifles can accumulate slight buildup of copper and lead fouling deposits at the critical lap juncture sufficient to cause “flyers” and spready groups.
It is important to very closely inspect this area with a strong light and a high magnification lens strong enough to observe even the smallest nicks and scratches.

If the imperfections and dings are small enough, they can easily be polished out without resorting to a re-crown job. Crown cutter kits are an expensive investment if you are not doing a lot of them, will still require polishing, and extremely expensive if performed by a gunsmith.
Polishing is usually sufficient to return the gun to accuracy if you pay attention to detail.

Step #1:
Closely inspect the crown and highlight any imperfections with a dry erase marker. When lightly rubbed off, it will leave visible traces behind in any nicks and dings.
The outer surfaces of the crown can be successfully polished and imperfections ground out using a Dremel with various grit compound ROUND wheels. The trick is matching the angle of the crown with the rotating wheel while rotating the barrel or Dremel so all areas are buffed evenly.
This is a little more difficult to do with a 45 degree target crown and you may have to alter a Dremel buffing wheel to the correct angle to match.

Step #2:
Continue to buff and inspect with each grit until imperfections have been buffed out and are no longer visible. Progress to finer grits up to final buffing with very fine red jewelers rouge (the small red Dremel container). For final mirror bright polishing, add a few drops of honing oil to the compound in the container and spin the buffing wheel in it to apply to the buffer. It should have a thin and oily consistency. This will remove bluing from the crown area. It is of no consequence to leave it “bare” and apply a thin dab of oil with your finger tip when done or apply MolyFusion which will prevent rust. The crown should be perfectly mirror bright all the way to the outer edges where it rounds over to the barrel shank.

Note that for deep or severe nicks and gouges, it may be necessary to round the end of a wooden dowel to the matching angle and use it to twirl a small piece of fine grit sandpaper. Common hardware items, such as an “eye hook” will often fit correctly over the outer surface. Being rounded, the eye hook can be coated with compound and used to polish the “round over” outer diameter.

Lapping

Here is the “secret” and most important part!
The critical juncture where rifling ends and begins the crown is the most important point.
This transition area must be perfectly even and concentric.

DO NOT, as is often suggested, perform this with a brass screw from the hardware store or any type of power tool or drill! It takes a very minimal amount of time and effort, by hand, with the right tool and without risk of causing extensive damage that will require re-crowning.

Order several caliber specific lapping tools from http://midwayusa.com/
Just search LAPPING on the site and it will take you to the page.
These are only $7.99 so buy a couple and discard them when worn.

The brass lapping tool is important for two reasons.
It is a rounded ball, unlike a screw which may not be perfectly concentric.
Soft brass is necessary so that the compound works into and adheres to the polishing surface of the tool. Without the proper softness in the brass, the compound will not adhere and “work” the mating surfaces.

Step #1:
Purchase a small tube of valve grinding compound at the local auto supply store.
Wipe the crown area with a patch soaked in carb cleaner.
Apply a small dab of compound to the ball of the tool and spread it evenly around.
Holding the tool between thumb and forefinger, twirl the tool back and forth for twenty or thirty seconds while rotating the angle with your hand so that it is constantly changing and not wearing an uneven groove in the ball head. Utilize the entire surface of the ball.
Wipe the area clean with a patch soaked in carb cleaner and remove all compound.
You should see a very narrow gray “ring” starting to appear between the rifling and the highly polished crown.
Repeat once or twice until you have a very distinct and even gray “ring” roughly 0.75-1mm wide.
Wipe the crown and the tool clean with patches soaked in carb cleaner to get off all rough grit compound.

Step #2:
Using the fine red compound, thin with a little honing oil and smear a dab on the ball of the tool.
Repeat the procedure until the “ring” comes up mirror bright.
Invert the barrel and spray liberally from the receiver end with carb cleaner.
Patch from the receiver end with patches soaked in carb cleaner, discarding as they exit the muzzle so as not to draw it back into the bore, until all compound has been removed.
Coat the lap and crown with oil or MolyFusion.

Lapping is such a critical component of accuracy that every gun I shoot gets lapped!
I have had this “cure” several very sporadic shooting and well worn milsurps and halve group sizes or eliminate “flyers”.
We carry the tool and the compounds in our range box and have often done a quick lap job on someone’s poor shooting rifle with immediate and dramatic improvements!

It may need to be repeated!
Keep an eye on your lap and crown and whenever the “ring” is no longer mirror bright, give it a little touch up with the lapping tool! Don’t forget to inspect for dings and scratches whenever the muzzle comes into contact with something while handling or shooting.

Note that lapping also works with counter bores and muzzle brakes!
For any removable muzzle brake, lap the barrel where the rifling ends as well as the inside and outside of the brake.
For a rifle with a counter bore, find a tool small enough to reach down inside the counter bore and do that as well as the muzzle end at the crown.

Pic: Lapping Tool
Pic: crown with dings before polishing
Pic: crown after polishing
 
#35 ·
Awesome project!! Im buying an M39 of my own from online within the next couple of days. I'll be getting a '67 unissed with "new bore". I'm really hope to follow your thread and do most if not all of the things you described. I very much look forward to any updates on the progress of this rifle as well as (hopefully!) some detailed instructions on how to do it. Thanks for all the helpful advice.
 
#37 ·
It seems like you know what you are doing..........I have a M-N 91/30 now but I have been looking at the m39 to turn into a sporter......I have a problem with my hands as I am older, pulling back the safety on the M-N.....I have found that Timney makes a triger assembly with a saftey on it that can be installed into the 91/30. So my question is, will that same triger group from Timney fit into the M39.........I am looking for a shorted rifle to get into the bursh a litter deeper. And The m39 looks like the way I want to go, If this can be done..Thanks
 
#41 ·
For a "brush gun" ,short carbine, I won't part with my "custom" M44. It came to me from Bubba, sans bayonetand lug already ground off. Similar treatment with a new Boyds stock, bedded, LimbSaver butt pad and 12oz mercury recoil tube in the stock. Tuned and tweaked in similar manner. With sling, it is something you can throw on your back for a trek through the woods.
Snaps to shoulder very quickly and points very fast. Great for standing shots fromthe shoulder as the weight is shifted to the rear so sights come on target fast. It was a post war production so the bore was excellent. Mojo adjustable rear sight and fiber optic front blade makes for quick target acquisition. Bolt cycles slick as warm butter. Accuracy is great at 200yds from the shoulder and standing with it is not laborius.
The M39 is a prize "bench shooter" and way too heavy for much else.
The M44 would be my "go to" for a "hunter" ( if I hunted with rifle) I still enjoy making "snap shots" from the shoulder with it now and then.
 
#38 ·
For those of you who may want a pristine barreled m39 action, I have a 1944 in new condition. It's a HEX receiver, and is really nice. Has a few spots where the bluing is off, but otherwise perfect. Asking $275. Contact me soon as there is a gunshow next weekend in New Bern, and it's going with me if not sold here.

Contact me direct at the following email dhenzler@sonic.net
 
#42 ·
Nice thread, I can't see the images, but that may be do to a filter at work. Some things I picked up, while building this. Pine Tar Oil mixed with Linseed oil will over time start to darken. If the part didn't come with the Pin or screw, well have fun finding the correct one. I like the Accu Mount as I think it is a close to correct as I will ever get for what I can afford, but I am not a huge fan of the scope. I think the money would of been better spent on finding a Vintage Zeiss, Wetzler, or Khales. The canvas scope cover is okay, but the leather strap is cheap, and will break over time. I do some leather work on the side so I plan on redoing the cover.
3774302
3774303
3774304
*no Finnish rifle were harmed making this rifle. Built from parts.
 
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