Testing The Micro Groove Barrel

[KCSO]

After hearing a lot of guff about hw inferior the micro groove barrels are with casr i decided to do a serious test. I had a 50 cal M/L barrel for my Encore and it was sitting unused. I also had a new Marlin micro groove barrel from a 336. I utrned down the 336 barrel and used it to line up a bull barrel 20" single shot for the Encore. The new barrel has a minimum chamber and is headspaced for the brass I will use for the test. The muzzle has a recessed 11 degree target crown and i have a 3x9 scpoe mounted on the barrel. Without any variables from magazine tube or bedding of the foreend this should show just how accurate a Marlin barrel can really be. I will be assembling loads and shooting the rifle with different cast bullets and different loads and we will see what we will see.

My first job was to empty some brass for loading so I shot up 25 rounds of 30-30 I had loaded with a 310 bullet and straight w/w for a Winchester 94. Now this was just emptying brass at 25 yards with a 3X settng on the scope and a piece of tape for a target. Lo and behold the toos soft too small bullets all went into 1" at 25 yards with NO leading. This may be interesting.

[btroj]

This should be very interesting.

[felix]

Microgrooves shoot better than deep grooves when the grooves do not get junky. Pay attention to the lube formulation for ALL the conditions. In practice, deep grooves shoot better longer because the junk has longer time to build enough to cause a severe problem. Deep grooves enhance boolit orientation during ignition, but produce enhanced fins which can break off during flight if not when they exit the muzzle. ... felix

[45r]

With my MG 35 rem marlin I had a 215GC Mtn Mold made boolit that has slightly fat bore-rider but after firelapping it fit perfect and lightly engraves.It shoots very well with Vitt-133.I don't even have to heat treat the boolits.I like the rifle so much I had the barrel cut to 16 inchs.It clover leafs at 60 yards and is my short range brush gun.It blows big holes through whitetails with its 72 percent metplat.

[Char-Gar]

A dozen years ago, I put five thousand cast bullet rounds through three different Marlin leverguns with MG barrels. When it was all over, I was 100% convinced that MG barrels will produce the same level of accuracy as a barrel with traditional rifling, as the same velocities and pressures.

The only difference was/is that MG barrels "tend" to be larger in the grooves and across the lands, when compared to traditional barrels. I chose the word "tend" carefully, as there are exceptions. This difference in internal barrel specs often means that bullets that give excellent results in traditional barrels won't do well in MC barrels. MG barrels (as do all barrels) require good bullet fit to throat, lands and grooves. Give them a bullet with the proper fit, and MG barrels are as good as any and better than many.

All of this stuff about MG barrels not doing well with cast bullets is just bunk that has been around for generations. It has been repeated so often, it is accepted by many as dictum. It is just another cast bullet "old wives tail", that refused to die.

[northmn]

My little Rossi 357 wil group about anything very tight at 25 yards but at 100 some laods pattern. I have seen smoothbores with roundball shoot very tight at 25 yards. My point being that in an accuracy test I would prefer to see longer range groups. I hate to crititisize someones hard work, but sometimes I see the work almost go for nothing when they test. This type of testing is very important and appreciated.

DP

[Char-Gar]

northmn --- All my testing was 100 yards bench rest.

[northmn]

northmn --- All my testing was 100 yards bench rest.

Sorry if I sound a bit nitpicking but I trust and appreciate that type of results and I generally use the old 100 yard standard myself.

DP

[fecmech]

Your Rossi has a 30" twist and I have 2 of them. They will shoot 120-130 gr bullets very accurately at lower velocities out to 200 yds(roughly 3 moa). Also the Lee 158 TL swc and Hornaday "clone" by BA bore do well out to 200 yds. The Lee 158 rnfp patterns and tumbles at 100 yds from both my guns at 1100-1200 fps and doesn't do that well at speed either. The Lyman 358429 with a healthy dose of 296 will group in 3-5" at 100 yds at around 1600 fps, which I don't think is too bad for a plain base at that speed.

[northmn]

I seem to be getting the Rossi to shoot but I just wanted to make a point about 25 yard testing which was mentioned. Again I do not want to be irritating and beat a dead horse, but short range testing on a shoulder weapon does not prove much to me personally.

DP

[thx997303]

If you re-read the OP, you will note that no testing has yet been done.

The OP states that in order to do the tests, he needed to empty some brass, so he merely mentioned offhand, that the boolits he was removing from the brass shot well at 25 yards.

[northmn]

I am very interested in the tests and appreciate KCSO'S desire to make the tests and look forward to his results.

DP

[garry r]

A dozen years ago, I put five thousand cast bullet rounds through three different Marlin leverguns with MG barrels. When it was all over, I was 100% convinced that MG barrels will produce the same level of accuracy as a barrel with traditional rifling, as the same velocities and pressures.

The only difference was/is that MG barrels "tend" to be larger in the grooves and across the lands, when compared to traditional barrels. I chose the word "tend" carefully, as there are exceptions. This difference in internal barrel specs often means that bullets that give excellent results in traditional barrels won't do well in MC barrels. MG barrels (as do all barrels) require good bullet fit to throat, lands and grooves. Give them a bullet with the proper fit, and MG barrels are as good as any and better than many.

All of this stuff about MG barrels not doing well with cast bullets is just bunk that has been around for generations. It has been repeated so often, it is accepted by many as dictum. It is just another cast bullet "old wives tail", that refused to die.well you just answerda question i put in a new thread . my 1895 has a loose bore i geuss is what youd call it and i though of re barelling it with a traditional rifled bbl but if i could get a casr bullet to fit it would solve the problem then wouldnt it . mine shoots extremly low at 25 or 100 yrds both. i use reloader 7 powder cause that abd varget are all i can get around here . thanks for testing them out .

[Char-Gar]

Garry.. The Marlin MG barrels are not loose, they just require a different bullet to get the proper fit. I have one 1960 vintage Marlin Texas (30-30) that runs .310 (grooves) and .304 (lands). It proved a tough nut to crack. I finally had Mountain Molds, make me a mold that fit the barrel and it is a track driver now. Most 30 caliber MG barrels are not that large, running .309 X .302 give or take a thou. These MG barrels tend to run large all across the Marlin cartridge spectrum.

I always figured that was some production reason that Marlin MG barrels had these specs. With all of those grooves, that metal needs some room to move on out. But that is just a guess on my part.

[btroj]

Good explanation Chargar. Not loose, just different. We seem to assume that a barrel must meet a certain set of measurements or it is "wrong".
Feed a micro groove a bullet that fits it and you will find happiness.

Brad

[Char-Gar]

Brad.. Being a lover of Krag rifles will teach a fellow about barrel specs being all over the place. My first Krag runs .3095 in the grooves. My second Krag runs .311 in the grooves, while my third is a true .308. Townsend Whelen in his article "Days of The Krag", tells of having rifles in his Army Company that ran as large as .316 in the grooves.

Springfield Arsenal didn't pay much attention to such matters, because they were accustomed to making barrel for black powder bullets which were swagged and expanded to fit the grooves, whatever the dimension was, when the powder charge hit them on the butt. When smokeless powder came along, they had some real problems.

They brought Harry Pope into to help them make barrels for Palma Match rifles and old Harry was horrified at the variety of barrel specs on the Krags. He raised hell and the specs soon thereafter tightened quite a bit.

What this is all about, is that each barrel, regardless of rifling type, must be measured and treated as a law unto itself, if the cast bullet shooter is to find joy. When it comes to shooting cast bullets, there are no stretch sock one size fits all barrels,

When molds were still cheap on Ebay I bought a half dozen two cavity Lyman 311291. There are of various vintages and run from .309 to .315 on the body and .300 to .303 on the nose. With a good collection of body and nose sizing dies I can put together just about any combination to make any 30 caliber barrel shoot.

[btroj]

Do any military rifles have closely held rifling tolerances? I view them as the ultimate in" slug it first" rifles. Some of them are way different than what is expected.

I just hate seeing micro groove still being regarded as poor cast barrels. This old wives tale needs to be put to rest.

Brad

[northmn]

One of the things on your micro groove is that the Lyman reloading catalogs have always issued a warning that loads for a micro groove must be kept under 1600 fps. That type of warning in a good loading manual will keep the questions concerning microgroove coming.

DP

[NHlever]

Yes, it bothers me when Lyman, and others keep repeating old rumors. Lyman used to always size the cast bullets they tested right at what the caliber "should be", or .308 in the case of the 30-30. Early Marlin 16 groove micro groove barrels checked larger on average than the newer 12 groove barrels which I have found to be often the same specs as the "normal" barrels are.

[KCSO]

At 25 yards I will learn nothing as all the left over loads I have shot up so far are all in about 1" and no bulet tipping and no leading with any load so far. All the loads I am shooting up to get brass are bullets sized to 311 and as bullet size is most important I am not surprised so far. I did shoot up some M94 hunting loads with bullets going 2000 fps and they worked just fine at close range.

[JIMinPHX]

As I understand it, there are at least 3 flavors of microgroove out there. My .30 cal has about a dozen lands on it. I am told that is the coarse one. I am told that there are at least two other versions that have a finer pitch & therefore more lands. Mine shoots cast better than factory ammo at the same speed. RE-7 works well for my top end hunting loads & Unique does well for my 1200fps plinkers.

[missionary5155]

Good morning
Speaking about Krags.. I have 4 and the largest bore is one of those .315+ tubes. The others fall into the .312 + bracket. But once you get a fat enough cast boolit in them they are fine shooting tools.
Mike in Peru

[northmn]

In military rifles, one of the most consistant rifles is the Swiss. As to the Marlin micro groove, one writer mentioned that a problem with the early microgrooves was in the leade and that some bores were a bit rough. When they fixed some of these problems their other problems went away. It was not the microgroove itself that was the problem. This was in a lever gun magazine condrning the history of Marlins.

DP

[skeet1]

I just tried out my Marlin 336CS with 3X9 scope yesterday for the first time on paper. I had shot some soup cans before but it was just for fun and nothing serious. This time I shot the Lyman 311291 with a load of Unique. This made a one ragged hole about 1/2 at 60 yards, the longest yardage I can shoot on my home range. Bullets sized at .311 and no leading. Years ago I bought a Marlin model 94 in .357 when they first came out and tried to shoot the Lyman 358156 but at that time had no idea about sizing the bullets larger than .357. It was a dismal failure, I wish I had it back to try with larger bullets.

[EMC45]

I too look forward to more testing and will conduct some of my own. I heard the MG myth again re-hashed over the weekend at a levergun match. I don't believe it! All Marlin .22LRs have MG rifling and they shoot a pure lead bullet that is going pretty quick right? I also have a Camp45 and it has MG rifling. I have never had an issue with leading or inaccurate grouping. I have shot all kinds of cast through it and it has done fine. Too many people are prone to regurgitating the same old tired myths. I size my RCBS 309-180 FNs at .309 for my 336 30-30, the horror! They shoot just fine. I am gonna bench and Chrono them one day and we shall see. I may even shoot some plain base bullets....Gasp!:shock:

[NHlever]

Many years ago one of the gunwriters, and I believe that it was Layne Simpson got a "bull" barrel from Marlin with microgroove rifling. He did some pretty thorough testing in 30-30 I believe, and got some pretty impressive results. I guess he was trying to separate lever action accuracy (?) issues from the microgroove influence. Interesting stuff!

[w30wcf]

KCSO,
Thank you for starting this thread. About 10 years ago I decided to do some testing of micro-grooved barrels. Following is information that I posted at that time.

MICRO-GROOVE ACCURACY w/CAST BULLETS

Dear Marlin enthusiasts,

So much has been written about the accuracy, but mostly about the inaccuracy, of
lead alloy projectiles in these barrels, that I had to find out for myself. To start with, I consulted the Marlin Firearms book by Brophy and found out that there have been three(!) types of .30-30 micro-groove rifling.

We’ll call them a., b., & c. These are Marlin specifications but individual rifles may vary slightly due to tolerances:

a.) 1955 to 1957 - 16 grooves - .304” bore diameter / .308” groove diameter
b.) 1958 to 1968 - 22 grooves - .304” bore diameter / .308” groove diameter
c.) 1969 to present - 12 grooves - .302” bore diameter / .308” groove diameter

Several years ago I purchased a used Marlin 336A rifle with c.) rifling, and just recently, I have been able to test two earlier Marlins with the a.) & b.) rifling. Fortunately, I have found that by applying the same principles used for successful cast bullet shooting in conventional rifled barrels ( bullet hardness / design / bullet diameters correct to fit the barrel ), one can attain equal results in micro-groove barrels to over 2,400 f.p.s.!!

Let’s dispell one myth which I have seen in print many times, and which goes something like this - ”The shallow micro-groove rifling does not grip the bullet as well as ballard or conventional rifling and can strip.” A typical .30 caliber conventional barrel has 6 grooves with a bore dia. of .300” and a groove diameter of .308”. So doing a little calculation, we find that the rifling is .004“ deep x 6 grooves = .024“ of bearing surface depth (b.s.d.).

By comparison we find that, in fact, all three forms of micro-groove rifling have more b.s.d. …
a.) .002” deep x 16 grooves = .032” b.s.d. or 33% more than ballard rifling
b.) .002” deep x 22 grooves = .044” b.s.d. or 83% more than ballard rifling
c.) .003” deep x 12 grooves = .036” b.s.d. or 50% more than ballard rifling

As we can see, bearing surface on the bullet is not a problem. A problem does exist in that on a.)& b.) type rifling, if you use a .30 caliber cast bullet designed with the standard .300“- .301 “ bore ride portion that is longer than ½ the bullet length, the .304” bore diameter is too big to provide support to the front of the bullet. In this situation, when pushed too fast, the bullet will yaw in the barrel, destroying accuracy. The bullet must fit the barrel.

Bullets that are .001 -.002 over barrel groove diameter on the driving bands will give the best results just as they do in barrels with standard rifling.

In all three types of micro-groove barrels, Lyman’s 311041 g.c. bullet as made by Oregon Trail bullets gave fine accuracy to 2,000 f.p.s. using 36 grs. of H414 powder. Over that velocity, the c.) rifling gave better results since the smaller bore diameter provided better support on the bore riding portion of the bullet.

Lyman’s 150 gr. Loverin style bullet works well in all three types right up to 2,400 f.p.s. since my mold drops bullets that are .002” over bore diameter for most of its length. Once again, bullet hardness, bullet design and a bullet that fits the barrel well are the keys.

Another myth: “Micro-Groove barrels are more prone to leading.” That is also false. Contributors to leading are rough barrel finishes and incorrect alloy hardness for the load being used, not the type of rifling.

My 336A had a rough spot a few inches in front of the chamber when I purchased it and it did pick up a bit pf leading there. 50 lapping rounds later and that took care of the problem. They also shoot plain based bullets extremely well.

Two weekends ago I attended the Cast Bullet Rifle Silhouette Championship in Ridgway, PA. One of the side matches was for lever action rifles at a distance of 330 yards. A fellow shooting cast bullets in a Marlin 336 rifle with micro-groove rifling won the contest shooting against other lever actions with ballard type rifling.

w30wcf

[EMC45]

KCSO,
Thank you for starting this thread. About 10 years ago I decided to do some testing of micro-grooved barrels. Following is information that I posted at that time.

MICRO-GROOVE ACCURACY w/CAST BULLETS

Dear Marlin enthusiasts,

So much has been written about the accuracy, but mostly about the inaccuracy, of
lead alloy projectiles in these barrels, that I had to find out for myself. To start with, I consulted the Marlin Firearms book by Brophy and found out that there have been three(!) types of .30-30 micro-groove rifling.

We’ll call them a., b., & c. These are Marlin specifications but individual rifles may vary slightly due to tolerances:

a.) 1955 to 1957 - 16 grooves - .304” bore diameter / .308” groove diameter
b.) 1958 to 1968 - 22 grooves - .304” bore diameter / .308” groove diameter
c.) 1969 to present - 12 grooves - .302” bore diameter / .308” groove diameter

Several years ago I purchased a used Marlin 336A rifle with c.) rifling, and just recently, I have been able to test two earlier Marlins with the a.) & b.) rifling. Fortunately, I have found that by applying the same principles used for successful cast bullet shooting in conventional rifled barrels ( bullet hardness / design / bullet diameters correct to fit the barrel ), one can attain equal results in micro-groove barrels to over 2,400 f.p.s.!!

Let’s dispell one myth which I have seen in print many times, and which goes something like this - ”The shallow micro-groove rifling does not grip the bullet as well as ballard or conventional rifling and can strip.” A typical .30 caliber conventional barrel has 6 grooves with a bore dia. of .300” and a groove diameter of .308”. So doing a little calculation, we find that the rifling is .004“ deep x 6 grooves = .024“ of bearing surface depth (b.s.d.).

By comparison we find that, in fact, all three forms of micro-groove rifling have more b.s.d. …
a.) .002” deep x 16 grooves = .032” b.s.d. or 33% more than ballard rifling
b.) .002” deep x 22 grooves = .044” b.s.d. or 83% more than ballard rifling
c.) .003” deep x 12 grooves = .036” b.s.d. or 50% more than ballard rifling

As we can see, bearing surface on the bullet is not a problem. A problem does exist in that on a.)& b.) type rifling, if you use a .30 caliber cast bullet designed with the standard .300“- .301 “ bore ride portion that is longer than ½ the bullet length, the .304” bore diameter is too big to provide support to the front of the bullet. In this situation, when pushed too fast, the bullet will yaw in the barrel, destroying accuracy. The bullet must fit the barrel.

Bullets that are .001 -.002 over barrel groove diameter on the driving bands will give the best results just as they do in barrels with standard rifling.

In all three types of micro-groove barrels, Lyman’s 311041 g.c. bullet as made by Oregon Trail bullets gave fine accuracy to 2,000 f.p.s. using 36 grs. of H414 powder. Over that velocity, the c.) rifling gave better results since the smaller bore diameter provided better support on the bore riding portion of the bullet.

Lyman’s 150 gr. Loverin style bullet works well in all three types right up to 2,400 f.p.s. since my mold drops bullets that are .002” over bore diameter for most of its length. Once again, bullet hardness, bullet design and a bullet that fits the barrel well are the keys.

Another myth: “Micro-Groove barrels are more prone to leading.” That is also false. Contributors to leading are rough barrel finishes and incorrect alloy hardness for the load being used, not the type of rifling.

My 336A had a rough spot a few inches in front of the chamber when I purchased it and it did pick up a bit pf leading there. 50 lapping rounds later and that took care of the problem. They also shoot plain based bullets extremely well.

Two weekends ago I attended the Cast Bullet Rifle Silhouette Championship in Ridgway, PA. One of the side matches was for lever action rifles at a distance of 330 yards. A fellow shooting cast bullets in a Marlin 336 rifle with micro-groove rifling won the contest shooting against other lever actions with ballard type rifling.

w30wcf



Great write up!

[lonewelder]

EMC45

My glenfield shoots pb boolits so well I am doing away with my regular GC plinking load.I'm going to start bumping up the speed on the pb to see how far it will go.

[EMC45]

EMC45

My glenfield shoots pb boolits so well I am doing away with my regular GC plinking load.I'm going to start bumping up the speed on the pb to see how far it will go.

I have some ideas for my 30-30 (336SC) too. I have a neat little Keith lookalike 32 SWC. It is the RCBS 32-098. I may run some of these through my sizer at .309 and see how they do. Also have the Lee 100gr. RN .311 mold and I HAVE sized a good bit of these to .309 for my testing. All PB too. I am gonna try some PPing as well. I also have a Savage bolt 30-30........Time to get out and do some shooting....

[Char-Gar]

w30WCF.. Thanks for the repost. Information like that needs to see the light of day from time to time. In spite of all of the work some of us have done with the MB barrels, the myth persists. Seem like killing Count Dracula is easier than doing this myth in.

[KCSO]

What I have found out so far is pretty well known already. Fill the throat and the gun will shoot. Accuracy goes down as bullet size decreases. If the throat is full loads to 2000 fps will still shoot into under 2" at 100 yards. We are snowed in again and range time has been limited but I will be posting more hard data as soon as I can get 100 yard targets.

[pdawg_shooter]

I paper patch only for my rifles, and the only difference is the MG barrels take a little stronger paper. 16# green bar printer paper works for everything. I size .001/.0015 over BORE diameter and patch up from there.

[T-Bird]

My '70's era marlin 336 35Rem. mg barrel shoots the RCBS 200gr boolet better than I can see (about 2'' group at 150yds) I shoot a 3x9x40 scope.Trifocals are tough with irons. T-Bird

[Smoke-um if you got-um]

Trifocals are tough with irons. T-Bird

You are a true master of understatement, my friend..........:bigsmyl2:

Mike