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Mountain Molds • Project: 357 pressure barrel
Page 1 of 2

Project: 357 pressure barrel

Posted: Thu Feb 28, 2008 5:55 am
by mtngun
from the old forum:

I picked up a petite 357 rifle barrel blank on ebay for not a lot of money.

It is home made. I would guess cut rifling, since that is how most DIY'ers make barrels. I haven't cleaned it and measured it yet, but at first glance, the rifling looks OK.

The plan is to fit it to a TC. I've never done that before, but in theory it shouldn't be too tough. We'll see. It's definitely a winter project, and maybe not even this winter.

It will be used primarily for pressure measurement. If you have been following my posts on pressure measurement, then you know that I've been puzzled by pressures in the 357 magnum. One of the problems with using my Marlin 357 for pressure measurement, is that it is not possible to locate the Marlin's strain gage in the ideal spot. On a TC, you can locate the gage in the ideal spot.

Also, strain gage critics complain that the receiver distorts the strain and causes serious calibration error. Ditto for barrel tapers. I haven't seen any evidence of that, but the problem will be ruled out on a TC since TC barrels are not screwed into a receiver, and there will be no barrel taper.

If it turns out that my presure barrel and my Marlin produce similar pressures, then that will give me a warm fuzzy feeling that the strain gage system is reliable. If they don't, then I guess I will still be puzzled.

I didn't buy a factory TC barrel because they have terrible chambers. Besides, TC doesn't offer a carbine barrel chambered for 357. Also, I wanted a rifle barrel so I can compare velocities to loadbook data for the 357 rifle, and to my Marlin's velocities. It's hard to make comparisons on handgun velocities because everyone uses a different barrel length, and some handgun test barrels are vented, and some aren't.

I will report back when the project is complete. That could be a long time.

Re: Project: 357 pressure barrel

Posted: Sun Jul 28, 2013 12:57 pm
by mtngun
Well, I warned you that it might be a long time before I finished this project. :lol:

Originally, I had planned to make my own barrel lug from scratch, but when offered a ready-made stub, it seemed like a reasonable deal.

In case you are wondering, the barrel is supposed to fit flush with the 0.810" diameter stub, but my $15 ebay barrel came to me with a 0.800" diameter, so it has a slight step where it meets the stub. Oh well, as long as it is functional
Image

Even with the ready-made stub, there's quite a bit involved in fitting the barrel, so it'll prolly take a few more weeks to finish this project.

Also, I needed a gun to develop 6mm target bullets, so I'm hoping to stub the stainless 243 take-off barrel and rechamber it for 6x45.

Re: Project: 357 pressure barrel

Posted: Sun Aug 11, 2013 2:50 pm
by mtngun
Today I chambered the barrel. I attempted to make my own chamber reamer and throating reamer, but was less than successful. The chamber reamer was a bit too soft and galled a little, which gouged the chamber a little bit. Fortunately, I noticed the problem after it only went in 1/4", so I abandoned that reamer and finished chambering with a boring bar.

I cut the chamber 1.290" long (my cases measure 1.285"), and put a 45 degree chamfer at the far end.

Then I throated it using a 0.3595" x 1 degree included angle throating reamer. The throating reamer had received the same heat treatment as the chamber reamer so it too was not quite hard enough and galled a bit. I was anticipating that, so I removed it frequently to stone down the galling. I think the throat turned out ok, but we'll find out when I shoot it. The taper starts just in front of the case mouth, so I can always throat it a little longer if the need arises to clean up this throat.

All chamber and throat dimensions are extremely tight. My Marlin's 180 grain loverider ammo will barely chamber, but none of my other 357 ammo fits. I'll eventually deal with that by making a nose sizing die cut with the same 1 degree angle as the throat, so that I can make any of my bullets a glove fit by running it into the nose die. But that's yet another project. :roll:

It took me quite a while to fit the extractor and to fit the locking bolts -- and yes, they do require fitting, it's not a drop-in kit.

This was my first time milling dovetails on a barrel (to fit the forend's barrel bolts) but I'm happy to say that went smoothly. The barrel bolts had to be filed to fit the dovetails so that took a little time, too.

Everything in the Eagle Arms kit has to be fitted. The bad news is that it takes time, especially the first time you do it. The good news is that you can set everything up for minimum tolerances, which is what I have been doing.

Somewhere along the way I finally cleaned the cosmoline out of the barrel and made a quick-and-dirty attempt to measure the twist. A tightly fitted patch makes roughly 3/4 turn traveling the roughly 17" of rifling (the barrel is 18 1/2" long). That would make the twist somewhere between 1-20" and 1-23", which should be perfect for 180 - 200 grain bullets. :) It has 10 lands and grooves, the bore is 0.347", and the groove hasn't been measured yet.

Re: Project: 357 pressure barrel

Posted: Sun Aug 18, 2013 8:03 pm
by mtngun
The TC carbine got an upgrade to a Boyd's thumbhole stock. The problem with the factory tupperware stock is that it's designed for iron sights and there's no cheek weld when you are using a scope. I love the pistolgrip stock for benchrest shooting -- you can use the grip to pull the gun snug against your shoulder, and the trigger finger angle is better so that the trigger feels much lighter compared to the tupperware stock.
Image

Rather than going with the Boyd's forend, I made a forend out of a scrap piece of oak (because oak was the only hardwood I had on hand). As you can see, the color of the oak forend does not match the color of the Boyd's stock. Oh well. ;)

My goal with the forend was 1) a wide flat bottom for benchrest shooting and 2) maintain the factory screw spacing. Unfortunately, I misplaced one of the forend screws and didn't have a spare, so for today there was only one screw holding the forend, and it did not hold it securely. More on that later.
Image

I haven't had time to make a mold or a tapered die for this barrel, or even to slug the barrel, so for today I used the Marlin's 180 grain ammo.

Remember how the too-soft chamber reamer galled and gouged the chamber a bit and I hoped it wouldn't create a problem ? Well it did create a problem. Fired cases were sticky. I tried a reduced load -- a 160 gr. PB at 1500 fps -- but cases were still sticky, so I knew it wasn't due to a hot load. Careful measuring suggested that there was a tight spot about 3/8" inside the chamber where the gouges were. The front of the chamber was 0.383" but the tight spot was 0.382", so the front of the fired case couldn't get past the tight spot. It wasn't the gouges themselves, but it seems they had pushed up some metal. I honed the tight spot with fine emery cloth until most of the tight spot was gone. Then I could extract most cases with my fingers, though occasionally one would still be stubborn. I'm sure if I continue honing the tight spot the extraction problem will eventually go away, the problem is that my benchrest chamber is turning into a sloppy Rossi-style chamber. :cry:

Here's the initial range results:

Marlin 180 gr. ammo -- 3.6" @ 100 yards, with vertical dispersion. 1800 fps.
160 gr. PB at 1500 fps -- 8" @ 100 yards. I dunno if these were air cooled WW or heat treated, they were just some bullets left over from some previous project.

So velocity was exactly the same as the Marlin, but accuracy was not what I expect from a decent TC barrel. The loose forend may have contributed to the vertical dispersion, so I tried tightening the single screw, but it didn't help much. Maybe the screw is bottoming out, or maybe it just needs the missing 2nd screw. :lol:

After the first round of chamber honing and re-tightening the single forend screw:
Marlin 180 gr. ammo -- 1.8" @ 100 yards, velocity had fallen to 1770 fps due to the larger chamber.

By the end of the day, the target had lots of little specs of Rooster HVR lube. I dunno if that means anything, but I don't recall ever seeing that much lube on the target at 100 yards.
Image

The next step was to firelap the barrel. The barrel itself is pretty smooth and did not need lapping, but I wondered if my homemade throating reamer had perhaps left a rough surface that could benefit from lapping ? Anyway, I fired 5 rounds with 150 grit followed by 10 rounds of 280 grit. The firelapping definitely washed the throat out a bit as measured by dropping a bullet into the chamber until it came to rest against the rifling. The 180 gr. Marlin bullet went in an additional 0.023", while the 160 gr. PB went in an additional 0.175". The latter seems extreme and might be due to measurement error, but nonetheless firelapping definitely pushed out the throat. That's OK because it was a short, tight throat to start with.

Retesting the firelapped barrel with the Marlin 180 gr. ammo:

5 shots 8" horizontal @ 100 yards, last 3 in 3/4"

5 shots 3.8" round @ 100 yards, putting my left hand on the scope instead of holding the forend like I usually do.

So firelapping did not improve accuracy and may have made it worse, not surprising since it pushed the throat out. I've never had much luck with firelapping.

Lessons learned and stuff to try next time:

-- while I probably can and will resolve the sticky extraction problem by honing out the tight spot, I'm never going to be happy with a sloppy chamber so I'll eventually set the barrel back and rechamber it. No big deal except that'll throw off the barrel bolts location. I'll prolly address that by making another custom forend with custom screw location. :evil: A PITA, but do-able, and I always have the option of starting over with another barrel, bearing in mind that this barrel only cost $15 and I consider it a learning experience. I want to do my learning on cheap barrels before I move on to match quality barrels. 8-)

-- Next time I make a TC barrel, I'll test-fire the barrel before cutting the dovetails for the barrel bolts. It would be much, much easier to set the barrel back if I didn't have to deal with the barrel bolt location.

-- I'll keep practicing at making chamber reamers until I get it right. I like to experiment with custom chambers and throats and it's much more affordable if you can make your own reamers.

-- I want to make a mold and a tapered die for this chamber. The 1 degree throat is what benchrest shooters use, but they use it with a matching tapered bullet, seated far out. I'm thinking a 200 grain semi-spitzer.

Re: Project: 357 pressure barrel

Posted: Sun Aug 25, 2013 4:12 pm
by mtngun
A little more progress today ....

A new reamer was made. It's 0.3800" at the case mouth and 0.3815" at the base of the case, creating a slight taper that should aid extraction. The body of the reamer is long enough to cut a 357 Maxi chamber should the need arise.

The throat begins immediately in front of the case, starting at 0.360" and tapering to the 0.347" bore at a 1 degree included angle.

The homemade reamer is a little crude but it got the job done without any unpleasant surprises. We don't like unpleasant surprises. :lol:

I set the barrel back 1/2". That was enough to get rid of the gouges from the original chamber job, but not enough to clean up the entire chamber. So it ends up with a stepped chamber, 0.380" up front and 0.383"+ at the back. As long as it solves the extraction problem, I'm thinking the sloppy rear portion of the chamber won't hurt accuracy, especially if I partial size the cases. The important thing is to have a tight fit where the bullet sits.

I guess if extraction is still sticky, I set it back another 1/2" and try again. It's frustrating, but I'm determined to learn to fit barrels right so that I'll have my act together when it comes time to fit an expensive match grade barrel. ;)

Image

That's as far as I got. Things left to do:

-- cut the rim part of the chamber with a boring bar (my reamer doesn't have a step to cut the rim)

-- mill & drill the barrel to fit the extractor. Yeah, setting the barrel back requires doing that all over again. :roll:

-- test fire for reliable functioning

-- make a custom forend to fit the non-standard screw spacing, since the barrel bolts got set back along with the barrel. :roll:

-- make a tapered sizing die to match the 1 degree throat, that way I can size bullets to be a glove fit in the throat.

Re: Project: 357 pressure barrel

Posted: Tue Aug 27, 2013 3:27 pm
by mtngun
Taper die made, to match the throat.

In theory, you can take any cast bullet (as long as it is relatively soft, like air cooled WW) and size it nose-first in this die to create a glove fit for the chamber.

In practice, there will probably be limits on how much bullets can be sized and how far they can be crammed into the die.

It'll be a while before I have a chance to give it a test drive.
Image

Re: Project: 357 pressure barrel

Posted: Mon Sep 02, 2013 4:17 pm
by mtngun
Barrel back together and tested with 3 different full house loads (160 gr. revolver, 180 gr. Marlin, and 190 gr. Marlin). All three extracted easily, so the extraction problem seems to be fixed. Yea! :mrgreen:
Image

Fired cases measure 0.3795" - 0.3800" near the top, exactly what I wanted, so I'm proud of my latest homemade chamber reamer even if it is not beautiful. Beauty is as beauty does. :)

Stuff left to do:

-- make a custom foreend to fit the non-standard barrel bolt locations

-- test accuracy with my Marlin loads

-- make a 200 grain mold for this barrel -- I'll prolly make a pointy loverin and then use the taper die to take care of the fit.

Re: Project: 357 pressure barrel

Posted: Fri Sep 06, 2013 12:19 pm
by mtngun
The custom oak forend was made to fit the non-standard barrel bolts. As usual, the forend was deliberately made oversize and flat bottomed for benchrest shooting. I suppose you could carry it in the woods if you were motivated, but that's not really what it was designed for.
Image

To me the barrel is too short for best balance so maybe someday Santa Claus will set me up with a 21" bull barrel. :mrgreen:

Re: Project: 357 pressure barrel

Posted: Sun Sep 08, 2013 11:14 am
by mtngun
Testing the $15 barrel with Marlin loads:

190 gr., 75% meplat, 15.3 gr. Lil Gun
1.8", 3.9", 1.7", 1.65", average 2.26" (5-shot groups at 100 yards)
1669 fps, 1.6% standard deviation 15 feet from muzzle

Best group with the 190 grainer.
Image

180 gr. loverider, 80% meplat, 17 gr. 297 surplus powder
1.7", 2.6", 1.35", average 1.88"
1772 fps, 0.4% standard deviation

Best group with the 180 grainer.
Image

Even with the oversize target stock and target scope, the little carbine only weighs 7 pounds 9 ounces, so like any lightweight rifle the POI is sensitive to how you hold it. In other words, I'm sure the groups would have been better if I did my part. :lol:
Image

Considering that these Marlin loads don't engrave in the TC the way they do in the Marlin, I was pleased with how well they shot.

Things to do next time:
-- I made a 200 grain mold for the TC but haven't had time to load them yet. I'm hoping the 200 grainer will squeeze one MOA out of the $15 barrel.

-- I'll hold off on applying a finish to the barrel and mounting a strain gage until I decide whether the barrel is a "keeper."
Image

Re: Project: 357 pressure barrel

Posted: Sun Sep 08, 2013 3:03 pm
by mtngun
Here's the 200 grain loverin after sizing.

First, I sized the air cooled bullet nose-first in the taper die. Some trial and error was required to adjust the sizing depth -- the deeper you size it, the further out you seat the bullet. I just guessed at how far out to seat the bullet. If this bullet shoots well, I'll probably experiment with the sizing/seating depth to determine what is optimal.

Then I sized it in a 0.360" die.

Then it was oven-treated.
Image

Alternatively, I could have attempted to make the mold drop a bullet with just the right taper, but then I would be at the mercy of as-cast tolerances, and there would be no way to experiment with seating depth. IMHO, sizing is the only 100% reliable way to guarantee a perfect fit.