Well folks, I've been reading for a long time how Marlin should get their act together and give the 38-55 a proper bore size. Digging out my original copy (1979) of Ken Waters “Pet Loads” to read what this well respected researcher had to say on the subject, I wasn't surprised to find the following.

When he wrote the original article for the May 1976 issue of “Handloader” Mr. Waters used three rifles, a Ballard No. 9 to represent weaker actions, a Winchester High Wall representing moderate strength actions, and a Winchester M 94 representing the stronger actions. Point is, he had two more 38-55 rifles than most of us have to work with.

Now, on to bullet diameter. Mr. Waters wrote “A most important consideration is bullet diameter, this being quite a variable factor among the different .38-55 caliber rifles. An oft-committed error in some of the older publications was the listing of .38-55's as taking bullets of only .375 diameter. I have yet to see a .38-55 with a barrel groove diameter that small, or even close to it! Both of our Winchester test rifles have .3785-.379 inch groove diameters, and the Ballard “Union Hill” slugs-and-mikes at a whopping .383 inch. Obviously, if cast bullets are to be spun for proper stability, especially with smokeless powder, they must be of a size to fill the bore to the bottoms of the grooves.”

From reading this, I believe we can assume that Marlin is indeed using the proper specs and holding them pretty close too, judging from what I've seen written about .378-.379 bores on almost all 336 CB's.

I'm going to post this on a few other forums too and would be interested to see your responses to the above.

My Marlin CB has .3785 which is in them boundries. It will shoot .377 to .379 cast quite well and .377 and .378 jacketed very well.

My Marlin CB has .3785 which is in them boundries. It will shoot .377 to .379 cast quite well and .377 and .378 jacketed very well.

Well hold on there pard.
Some winchesters and Marlins are running 380 from the factory. The winchester very old and the Marlin some what new. Your gun may be in between.

I used to think that this was common years ago to have differance's in bore's until I heard of some other calipeirs that were doing the same . Like a 35 Remington Micro grove @ .360 and a 44 Mag @ 431.

Yeah! the new SAMMI spec 's

It is that a lad needs to try a few off the rack to see how they are shooting . Then again you could solve this by casting your own.

I'm going to post this on a few other forums too and would be interested to see your responses to the above.

First - I'm pretty much a dedicated CB shooter and I got my new Marlin 336CB in .38-55 for this purpose. I'm sure most of you know that CB performance requires good bullet fit so I had done quite a bit of work measuring & etc. before ever heading to the range with my new toy.

Along the way - I spoke with Mr. Tim Looney at Marlin & he advised that their barrels run .378" - .379" on the new cowboy guns. He also noted that their measurement method was to use spade gauges which are similar to pin gauges only flat so they'll slide into the grooves. They are typically in .0005" increments. The largest gauge that'll slip in is "the measurement". Marlin's measurement of my barrel claimed .379".

However when I drive a lead slug into the barrel - I measure .3805". I believe the difference is due to the spade gauge requiring some degree of clearance to slip in & out without buggering up the barrel. The lead slug will upset for a more perfect fit.

In any case - the factory chamber was cut tight & a .379" bullet could not be loaded into the case and chambered. My rifle went back to Marlin & they opened up the chamber to "SAAMI Max". It will now accept a bullet of .380" which is performing pretty well. It will not accept a .382" bullet which is what I was originally aiming for. I don't have a size die for .381" so not sure where I run out of tolerance. In any case - it is doing pretty well accuracy wise with the .380" bullets and no hint of leading up to 1800fps range which is as warm as I'd planned on loading.

Best regards-

Sky C.

Well, I have not repeated my mantra for awhile, so here goes:

My 336 cowboy 38-55's grove diameter mikes at 0.380 inches in diameter. I have three sets of calipers and I slugged the bore several times, so I'm pretty sure of the measurement accuracy. I cast Lyman no. 375248 bullets of 1:40 (tin:lead) which drop out of the mold at 246 grains and a tad shy of 0.379 inches in diameter. I lube them with SPG by pushing them through a 0.379 die in a Lube-sizer. I load them over 42 grains of FFg Goex and a thin card wad. I compress the load with the bullet when seating it. The velocity averages 1170 fps ten yards from the muzzle. I've fired up to 81 shots (ran out of ammo) without cleaning and there was no obvious loss of accuracy nor much hard-fouling buildup.
I believe that the chamber was reamed to be small enough to hold a cartridge (like I load) center to the bore; lined up with the center- if you will. The burning of the black powder will obturate the soft bullet to fill the bore to grove diameter. And the grooves are cut deep, to 0.380 inches so they hold lots of black powder fouling and still grip the bullet well.

I figure that the 38-55 was designed to shoot ammo like I make. That's why I make it that way.
I bought the Marlin cb because I wanted a lever gun to hunt deer with while using black powder cartridges. I saw that Marlin made their cowboy 38-55 for exactly that (well, and cowboys too :))

Now, if you want to take that Marlin 38-55 out and shoot hard-cast or jacketed and smokeless powder through it, you will have to make adjustments. Thats fine and dandy, but please don't blame the gun or Marlin for a "poor chamber job" or the "wrong-size bore." Some of us like the rifle just like it is! :)

It's reasonably simple, if you want to shoot jacketed and hard cast .375-.356" bullets, find a .375W. If you want to shoot hand cast bullets of the right dieamter, then buy the 38-55. Even though they look nearly the same, don't try to make one into the other.

Howdy Boreal-

Glad your Marlin is playing nice with BP loads. For me though - I prefer to avoid the headaches and expense of going the BP route. I'm not a hardcast fan at all. I cast all my own bullets and usually run a softish alloy somewhere in the range of 12-14 BHN.

Related to loading and performance with BP - the method of using small slugs and allowing them to bump-up I understand. Was curious though if you have ever done any loading with BP and bullets that started out as a good fit rather than depending on obturation? If yes - would like to hear your comments and observations about that. It would seem to me that this would be an even better and more reliable method for fine accuracy. I believe this was closer to the scenario that was achieved when using breech seating that has demonstrated excellent accuracy.


Thanks-

Sky C.

if you have ever done any loading with BP and bullets that started out as a good fit rather than depending on obturation? If yes - would like to hear your comments and observations


Thanks-

Sky C.

Well, not with the 38-55, but I shoot 45-70 and 45-120 single-shot target bp cartridge rifles which I use 0.458 and 0.459 bullets, but they are single-shot target rifles that I clean after every few shots. I have a whole different outlook for my bp cartridge lever guns.


If you're pushing soft bullets to 1800 fps with smokeless powder, I can see why you want them to be oversize. If bp gave me headaches, I'd do what
ribbonstone says and get me a 375 Win.

I'd say that I already use a bullet with a "good fit" for my 38-55, as it fits the chamber well and it obturates to the fouled groove diameter for lots of shooting before fouling in the grooves negatively affect accuracy (my guess). I forgot to mention that my 38-55 cowboy's bore diameter is about 0.372 inches, giving about 0.004(edited) in-deep grooves. Smokeless powder has never touched my cowboy 38-55, but you folks that use the stuff just go right ahead. Its not my place to judge. You can answer to the good lord when the time comes. :)

If you like a tighter bullet fit, maybe you could rebarrel to .375 Winchester.

I noticed that www.foxridgeoutfitters.com sells a 38-55 barrel for the Thompson/Center Contender Carbine. It is my understanding that it measures:
groove dia= 0.376-0.378 inches
bore diameter= 0.366-0.368 inches
0.09 in groove width?
1/12 in twist
And its chambered for the original 38-55 brass.

Since I'm a Contender fan, I would like to get one but I might feel kinda funny shooting BP out of a plastic-stocked Contender. :)

A Lyman #357248 cast a .378" bullet, but it wasn't enough for the .380" bore on this Winchester.

Scrathing and figuring, the .378" bullet was large enough to be mostly engraved by the lands, but not to bottom out....so I lapped the rear two bands (its a plain base) to .3805" of one cavity and gave it a try. Worked great, noticable improvment in accuracy and a decreas in leading, so I made the other cavity match.

Hunted around for an older .45-70 mold...found one (Lyman #457125 / 500gr.) that tosses them at .460". Also bought the Lee HB 405gr. mold, which gives a .459" daiameter bullet....but cast soft, the hollow base actauly does it's job. These two are used with black powder, so if either of them is cast soft (to about 1:15 tin:lead) they work fine.

Being "frugal" will cast wheel weight bullets and reverse-harden them (anneal them) for practice shooting. Is like oven hardening, but at the end, you turn the oven down in 25degree steps and let the bullets take a long time to cool.

A full sized bullet, with a chamber that has enough brass clearance to allow a clean release at ignition, does give better accuracy (for me) than the same bullet that relies only on pressure to "thump it up" to bore size. It's not much, and mostly it can be counted in "fliers", but the long term average groups favore the bullet that starts out closest to the size it's going to become when fired.

A full sized bullet, with a chamber that has enough brass clearance to allow a clean release at ignition, does give better accuracy (for me) than the same bullet that relies only on pressure to "thump it up" to bore size. It's not much, and mostly it can be counted in "fliers", but the long term average groups favore the bullet that starts out closest to the size it's going to become when fired.

Well, there ya go. :) My required accuracy is minute of deer at 125 yards or less. Am not a target shoter. Off the tailgate of my truck, I get two-inch groups at 100 yards

Just for fun, I'd like to mention that a few years ago, on the old Marlin Forum, somebody told me of a method they used to increase bullet diameter. He put a bullet in a vise and smash the two ends toward each other till the diameter increased above that desired, then the bullet was sized to exact desired dimentions. He mounted a "stop?" in the vise to get consistent results. I never tried that, but just for fun :) , I tried it in my own, more primitive, more fun method. I set the bullet on its base and on a C-ment floor and whacked it with a big ol' hammer. I did about ten of them before I got the hang of it, but they were surprisingly concentric, etc..

As you folks can probably tell, I've been making an effort to get away from the anal stuff in the last few years, and just have fun with my reloading and shooting. :D

My two favorite ways to hollow-point a bullet nowdays:
1)Place bullet on floor with nose up, use a sharp nail as a punch and hammer the nail into the nose to form a cavity. You don't lose any weight, as you do with a "universal hollow-pointer", etc.
2)For loaded ammo, carve an X into the nose with a huntin' knife. This method is the funnest.