Marlin Cowboy -- Major Keyholes!

[Old No7]

How about this, an "on topic" post from me --if that's allowed...

You know, I was always told that as a "3rd-generation locksmith", I knew my way around locks and keys and all, but I never expected to have this much luck with keyholes!

The picture below will say more than my words can add, but I will give you the lowdown on the load that produced those keyholes:

* Marlin .38-55 Cowboy, with Ballard rifling (clean barrel)
* Once-fired Starline (long) brass
* WLR primer
* IMR3031, 32 grains
* Hornady 220 grain, .375", Flat Point bullets

I'm thinking those bullets aren't a very good match for the bore...



That group of 10 shots was fired at 50 yards, and none of the guys at the range had ever seen keyholing bullets group so well before! Me neither! (I guess that's where all the locksmith training kicks in...) Then a big discussion about the "velocity deviations" over a Chrony (which we didn't have) and the "terminal performance" of that load on deer followed, which was half in jest and just a little serious, until one of the guys said: "Well then, let's see what happens out at 100 yards..."

There was a 4" white rock just to the left of my frame/shooting lane on the backstop down range, so I took the 3 shots I had left, fired offhand at that rock. Well, no one had any calipers, but a couple of guys were observing the impact with spotting scopes, and they swear I missed the rock with all 3 shots -- yup, we expected that -- but they said all 3 rounds impacted in an area the size of a softball -- at 100 yards. Not too bad of a group for tumbling bullets, eh?

The only good out of all this is: (a) Now I know what bullet not to use, as the 375's are a little undersize, and (b) Now I get to play more and go develop another load.

Tight groups! (With no keyholes...)

Old No7

[1886]

Just a little undersized to the tune of about .004". Bill in Oregon sells the proper diameter bullet for your CB .38-55. Your brass choice is perfect. Good Luck. 1886.

[Ben_Rumson]

Interesting result...Did you make a sight adjustment for the 100yd shots?

[Thunder50]

The Marlin Cowboy guns can run as high as .381" and those .375 bullets just don't work in a bore .006" larger in diameter. My Cowboy 38-55 runs that .381" with a .373-.374" bore. With rifling only .001" at the most, per side, it won't work very well. I also have a NEF 38-55 that I rechambered to 38-72 and my .375" bullets also keyholed as bore sizes were almost as big as the Marlin. Going to some Hawk bullets at .377" worked just fine. He said with the velocities I was pushing them, they should "bump up" and work. Ended up with some 3/4" groups @ 100yds with the 280 gr bullets. He should have some lighter ones that would work . You might be able to paper patch them to a larger diameter and have the bullets you have, work also.

[Noah Zark]

. . . You might be able to paper patch them to a larger diameter and have the bullets you have, work also.

That's what I did, and the results were excellent.

Noah

[Ysabel Kid]

That picture ought to go into the dictionary under the heading of "keyholing". Talk about being worth 1,000 words!

[1886]

Just a little undersized to the tune of about .004". Bill in Oregon sells the proper diameter bullet for your CB .38-55. Your brass choice is perfect. Good Luck. 1886.

Old No 7, Sent you a P.M. sir. 1886.

[marlinman93]

Looks like the groups I got when I accidentally fired some .25-20 in my .32-20!

[Andrew]

Good gravy, them's some odd groups for sure.

[Tycer]

Nice group. Too bad you pulled that last one.

[Slick13]

The Marlin Cowboy guns can run as high as .381"

Why in the hell when jacketed bullets are .375 and .377 would Marlin make the bore that large?! What on earth where they thinking?!

To the original poster, good luck with your rifle. I'm still kicking myself for not picking up one of the sporting rifles Winchester was making in .38-55 right before Model 94 production stopped.

~Michael

[Griff]

Those 220gr .375 diameter bullets are made for the .375 Win., not the .38-55, which although VERY similar cases, ain't the same. .38-55 is sorta noted for having .379-.381 groove diameters. Once you find the right size bullet, tho', they're also noted for very good accuracy.

[Slick13]

Those 220gr .375 diameter bullets are made for the .375 Win., not the .38-55, which although VERY similar cases, ain't the same. .38-55 is sorta noted for having .379-.381 groove diameters. Once you find the right size bullet, tho', they're also noted for very good accuracy.

I know guns from 100+ years ago had variation in groove diameter, but there's no excuse for that nowadays. The cartridge was designed for a .377 bullet, and that's what the groove diameter should be so that the biggest cast bullet being needed would be .379".

~Michael

[KCSO]

Your Marlin will will need a 380-382 bulllet to shoot really well. I have not found a really good commercial bullet for the Marlin's so I use a cast gc 260 grain bullet from a Mountain Moulds special order. This will keep inside 4" at 200 yards when i am really steady and the light is good. In a jacketed slug you will need at least a 377 and a 379 would be even better.

[Bill in Oregon]

Guys: The original Marlin -Ballard .38-55 specified a .379 barrel. Marlin's fine Cowboy is true to the original specs and because the big bullet makers chose not to fool with a proper .379 slug, the Cowboy has fallen by the wayside. Believe me, with the right diameter bullet the Cowboy is a tack driver. With the right bullet and load, one-hole groups are the norm at 50 yards with a tang sight, and inch groups at 100 with a scope. Otherwise, it's like trying to get good accuracy with .308 bullets out of .303 Enfield. Ain't gonna happen.

[1886]

Guys: The original Marlin -Ballard .38-55 specified a .379 barrel. Marlin's fine Cowboy is true to the original specs and because the big bullet makers chose not to fool with a proper .379 slug, the Cowboy has fallen by the wayside. Believe me, with the right diameter bullet the Cowboy is a tack driver. With the right bullet and load, one-hole groups are the norm at 50 yards with a tang sight, and inch groups at 100 with a scope. Otherwise, it's like trying to get good accuracy with .308 bullets out of .303 Enfield. Ain't gonna happen.

Bill nailed it. Marlin built them right. It is their cartridge. Yeah groove diameters vary and they have varied for years but this does not mean Marlin did something wrong. I had a model 1881 built in 1889 that has a .379" groove diameter. Just like opening the Marlin chamber, big mistake, to use the wrong brass, to use cast bullets that fit the bore, this topic seems to get reignited every couple of months. Sorry for the crappy grammar. These rifles flat out shoot. I mentioned this before and it started a "prove it" campaign but MANY, MANY .38-55 Marlins wear Badger Barrels. The proper diameter jacketed projectiles are available for the Marlin CB just use them if you want to shoot jacketed. 1886.

[Old No7]

Thanks to all for your comments * -- I will be sure to post "better results from better bullets" when I get 'em. (Could be after duck & deer season -- be patient...)

* And that's what makes this my favorite campfire to hang out at!

Tight groups! (With NO keyholes!)

Old No7

[scr83jp]

How about this, an "on topic" post from me --if that's allowed...

You know, I was always told that as a "3rd-generation locksmith", I knew my way around locks and keys and all, but I never expected to have this much luck with keyholes!

The picture below will say more than my words can add, but I will give you the lowdown on the load that produced those keyholes:

* Marlin .38-55 Cowboy, with Ballard rifling (clean barrel)
* Once-fired Starline (long) brass
* WLR primer
* IMR3031, 32 grains
* Hornady 220 grain, .375", Flat Point bullets

I'm thinking those bullets aren't a very good match for the bore...



That group of 10 shots was fired at 50 yards, and none of the guys at the range had ever seen keyholing bullets group so well before! Me neither! (I guess that's where all the locksmith training kicks in...) Then a big discussion about the "velocity deviations" over a Chrony (which we didn't have) and the "terminal performance" of that load on deer followed, which was half in jest and just a little serious, until one of the guys said: "Well then, let's see what happens out at 100 yards..."

There was a 4" white rock just to the left of my frame/shooting lane on the backstop down range, so I took the 3 shots I had left, fired offhand at that rock. Well, no one had any calipers, but a couple of guys were observing the impact with spotting scopes, and they swear I missed the rock with all 3 shots -- yup, we expected that -- but they said all 3 rounds impacted in an area the size of a softball -- at 100 yards. Not too bad of a group for tumbling bullets, eh?

The only good out of all this is: (a) Now I know what bullet not to use, as the 375's are a little undersize, and (b) Now I get to play more and go develop another load.

Tight groups! (With no keyholes...)

Old No7

I was keyholing some cast bullets until another shooter told me to increase the powder charge none of the data in Lyman or Load Data mentions that light weight bullet you're using saw some weighing 243gr and up

[Slick13]

According to this http://www.sixguns.com/range/336cwby.htm Marlin cut the barrels of the modern guns to .378". If any are showing up that are as big as .381", I'd say shame on Marlin. There's no excuse for that variation. Could you imagine buying a .30-30 that measured .311"?!

~Michael

[jnyork]

. Could you imagine buying a .30-30 that measured .311"?!

~Michael

Yup, sure can, I have a 336a Marlin .30-30 with a .310+ bore, my friend has an identical rifle, both built in, I think, late 1940's, same bore measurement.