The 357 pressure barrel project resumes (again)

[mtngun]

As usual, my shooting projects have been sidetracked by annoying stuff like making a living and building a house.

But I finally found time to get back to it (knock on wood). Let's hope this time I can stick with it long enough to get some of my gunsmithing projects more or less done.

To review: I want a TC carbine chambered for 357 mag, to use for both pressure measurement and bullet testing. The TC factory 357 barrels usually have a craptastic throat that makes them useless for serious bullet testing. Hence a custom barrel is in order.

Likewise, most standard 357 mag reamers are SAAMI spec with a "funnel" throat instead of a proper rifle throat. Hence a custom reamer is in order.

My previous attempts at chambering barrels with homemade reamers haven't gone well. The reamers required a lot of force to cut, one broke (it had not been tempered), and several dulled quickly. But the main problem was that they gouged the chamber and the gouges made it difficult to extract the case.

I often laid awake at night wondering what was wrong with my reamers.

I decided that 1) maybe I should try boring a 357 chamber rather than reaming. I'm not very good at making reamers but I've got lots of experience with boring stuff. 2) Maybe the gouging and difficult cutting was due to inadequate relief. In fact, my "D" reamers usually didn't have any relief at all, because I had been told by numerous sources that D reamers did not require relief (i.e., I believe Roy Dunlap's gunsmithing book recommended D reamers without grinding relief).

OK, so I set back my $20 357 barrel, refit it to the stub, bored the chamber portion (not the throat) with a boring bar, then polished the chamber with fine emory cloth. That turned out well.

I didn't bore the throat because 1) I didn't have a long enough boring bar on hand and 2) I was afraid the rifling would make the boring bar chatter.

So I used a homemade throating reamer. This time I freehand ground relief to within 1/16" of the cutting edge. Freehand grinding is "iffy" but I got lucky and it turned out as intended. I'm not sure if it was due to the relief, but this reamer cut effortlessly, unlike my previous "D" reamers.

FYI the throater was made from O-1, heated to 1600F, quenched in water, then tempered at 300 degrees in the kitchen oven. It has a 1 degree included angle, which in theory should be cast-friendly.



My $20 rifle barrel started out as 18 1/2" but because I had to set it back several times, it has shrunk to 14 1/2". TC pistols can be very accurate and some people love them, but for this project I want a rifle, not a pistol, so another 35 rifle barrel is waiting in the wings and this was just a practice run to get the kinks worked out of my chambering process. I didn't bother to "clock" the barrel and I'm not going to bother to attach a forearm.


I did fire a few rounds to verify functioning -- the empties extracted effortlessly, YEA! As long as I have the barrel set up I might as well mount a scope and see what the barrel will do on paper. First I'll have to load some ammo for it since the chamber (0.3795" ID) is too tight for the 357 ammo that I use in my other guns, which have 0.380"+ chambers. Hopefully I can get that done within the next week (knock on wood).

[mtngun]

I had a chance to shoot the 14 1/2" "practice" barrel, using the same loads that I've used previously, seated out close to the rifling, but not actually engraving. The tight chamber wouldn't swallow 0.358" bullets so I had to size them 0.357".

The 190 gr. Marlin bullet, 15.3 gr. Lil Gun, 1.620" COL.  1689 fps.  5.2", 4.1", and 5.1" at 100 yards, with mostly vertical dispersion.

The 200 gr. Spitzer, 13.3 gr. Lil Gun, 1.760" COL.  1513 fps.   3.9", 9.8", and 5.8" at 100 yards, with mostly vertical dispersion.


The good news is that extraction was effortless.

The bad news is that accuracy was poor. I don't know why -- the lack of a forearm? The 357" size instead of 0.358"? Short barrel awkward to shoot? Off-center chamber? Cold weather (it was 25 degrees)?

At any rate, the main point of this "practice" barrel was to practice chambering and to convince myself that I can cut a smooth chamber. That part was successful, so the next step will be to fit and chamber a Green Mountain rifle barrel.

[mtngun]

A Green Mountain barrel blank, fitted for a TC stub. Since this barrel is intended to be a bench testing gun, for the time being I'll leave the barrel full length (27") and full diameter. The only problem I forsee with the fat barrel is that I'll have to make a custom scope mount for it.


I debated whether to bore the chamber, like I did last time, or to make yet another reamer. On the one hand, I'm good at boring stuff and am confident that I can produce a smooth finish that way. On the other hand, it's tough to dial in the barrel so that the bored chamber is 100% concentric with the bore. I'm wondering if the previous "practice" barrel's poor accuracy might have been due to the chamber being bored off center? With such a tight chamber as it had, even being 0.0005" off center would be sure to push the bullet to one side, since the cartridge had no wiggle room in the chamber to self-align in the throat.

A reamer with a snug fitting pilot has a better chance of producing a chamber that is concentric with the bore, so I took the risk of making another reamer. Like my previous reamer, today's reamer had relief ground freehand to within 1/16" of the cutting edge. It seemed to cut decent. As near as I can tell with the naked eye, the resulting chamber did not have any big gouges, yea!

The throat is the usual 1 degree included angle.


As for the Green Mountain barrel, I wasn't expecting a whole lot for the price, but it actually looks decently smooth. If I remember correctly it has a 1-20" twist, same as most 357 rifle barrels.

If things go well I'll finish fitting the barrel to the stub within the next week and test fire it to make sure that empties extract easily. If it passes that test, then I'll still have to make a custom scope mount before I can start punching holes in paper, so that may be a few weeks yet.

[mtngun]

I finished fitting the barrel to the stub and shot a few full throttle rounds to verify that they extracted easily -- they did, yea!

The next step was to make a custom scope mount, since the standard weaver mount is not compatible with the bull barrel. A mount was made out of a scrap piece of aluminum, but the barrel still needs to be drilled & tapped -- the mount is not actually attached to the barrel in this photo.

Hopefully tomorrow I'll finish attaching the mount. Then I'll need to load some ammo for it, so it may be another week or so before it will be punching paper.

For the time being I'm not going to make a forearm for it -- the bull barrel provides a fair amount of stability without a forearm.

[mtngun]

The weather has not been conducive to shooting but nonetheless I was itching to try out my new barrel, good weather or not.

I had built a little cover for my chronograph. Eventually it will have lighting and the goal is to be able to shoot in any weather, day or night, and still get consistent chrono results. For now I tried using a portable flourescent trouble light, but it was no go, it failed to see any of the shots. Oh, well.


I still don't have a proper rifle rest or even a sand bag. Today I started out using a Stoney Point rest, which I had acquired mainly for soaking up recoil on the 30-06. It does a good job with the recoil but otherwise is awkward and not particularly steady. So midway through today's shooting I switched to this "V" bag and an old pillow. That was an improvement over the Stoney Point but still not the greatest. Just pointing out that my range facilities are still a work in progress.


Unless otherwise noted, all of today's shooting was 5-shot groups at 100 yards, with a Mueller 4.5x14 scope set to 14x, and Rooster HVR lube. The outside weather was 20 degrees and light snow. It was 40-ish degrees inside the shooting shack.

The 200 grain spitzer had been sized nose-first in a 0.8" taper die, then pushed through a 0.358" die that actually sized to about 0.3575". Then heat treated and lubed. It was seated out so that the front band lightly engraved the rifling, at 1.995" COL. The fit was such that the TC action locked up easily, but nonetheless bullets could not be extracted once chambered. In theory that should be the cat's meow for a cast bullet. The powder charge was 15.5 grains Lil Gun ignited by a CCI #500.


There were ignition problems with the 200 grain load. 3 rounds did not ignite even though the primer had a normal indent. Several other rounds had funny looking primers that suggested excess headspace, and all groups showed vertical stringing. The rim's headspace on this barrel is actually fairly snug, so I can only guess that either there was something going on with the engraved bullet that affected ignition, or else Lil Gun doesn't burn well in cold weather? At any rate, ignition was definitely a problem with this load.

200 grain groups -- 4", 3.9", 2.5", average = 3.5". All strung vertically.

Next up was my 160 gr. PB revolver load, with a CCI 550 primer and enough H110/WW296 to hit 1300 fps in a snub nose revolver, 1900 fps in a Marlin, and I'm guessing 2000+ fps in the 27" Green Mountain barrel. I wasn't expecting the stubby PB bullet to shoot well at rifle velocities -- it shoots 6" - 8" in the Marlin -- but just wanted to see what it would do.


160 grain groups -- 1.8", 2.4", 3.2", average = 2.5". All groups had 3 shots in a respectable cluster, suggesting that it wanted to shoot. There were no ignition problems.


Next up was my 180 gr. Marlin load, with a CCI 550 primer and enough surplus 297 to hit 1800 fps in the Marlin. I'm guessing it would easily clock 1900 fps in the Green Mountain 27" barrel.

180 grain groups -- 4.9" 3.3", 1.7", average = 3.3". There were no ignition problems.



Conclusions and Lessons Learned:
-- the fact that it shot surprisingly well with the stubby PB bullets -- at 2000+ fps, no less -- suggests that this barrel wants to shoot.
-- the fancy glove fit tapered bullet that engraved the rifling was a dog and a pain in the ass.
-- my primitive bench setup is definitely a limiting factor. Oh, I've shot plenty of good groups from improvised rests in my day, but it takes practice, and I'm out of practice. There is no doubt that a more comfortable, stable rest would help me.

Punch List for Future Shooting Sessions With This Barrel:
-- get the chrono working
-- mount a strain gage
-- get a real rifle rest and sandbags
-- get a stable stool for the benchrest. I've been using a wheeled office chair, which is nice at the reloading bench, but far too loosey-goosey for shooting.
-- make a broad forearm for the bull barrel.
-- try other plain base bullets, since this barrel seems to shoot PB just as well as GC.
-- try different seating depths with the 200 gr. spitzer. Maybe it would ignite better if it did not engrave the rifling?
-- try a simple 2-diameter spitzer, rather than the 0.8 taper.
-- make a throat impression and perhaps consider sizing to 0.359", or the biggest diameter that can chamber.

[mtngun]

In case you were wondering why I was using an 0.8 degree taper bullet in the 1 degree taper throat, this thread attempts to explain.

[mtngun]

Some chamber measurements, using pin gages. I stuck a pin gage into the chamber as far as it would easily go, and used a sharpie to mark the pin flush with the breech. It's not super precise but it's a quick and easy way to get ballpark numbers.

0.363" gage -- went in 1.4" deep
0.362" gage -- 1.434" deep
0.361" gage -- 1.466 deep
0.360" gage -- 1.494" deep
0.358" gage -- 1.580" deep

A 0.348" pin would not enter the muzzle, a 0.347" pin almost but would not quite enter (I wasn't going to beat on it with a hammer ), while a 0.346" pin would easily enter.

An expanding ball gage could be expanded up to 0.3473" and still spin easily. Let's call the bore 0.347"-ish.

So anyway, the main takeaway was that the throat just in front of the case is 0.362"-ish and about 0.18" long. That's a long oversize throat! Not good!

The reamer measured only 0.358" - 0.3585" just in front of the chamber, so how did the throat grow to 0.363". Well, reamers can cut larger than the reamer itself. My homemade reamers warp during heat treatment and warping tends to make the reamer cut larger.

It's also possible that I unintentionally enlarged the throat when I was polishing the chamber with fine emory -- though I don't think so. Fine emory only takes off a few tenths and I deliberately avoided running it into the throat.

Conclusions:
-- I should use the largest diameter bullet that will chamber easily, which will probably be 0.359" (it'll be limited by the cartridge OD).
-- in the future, I'll avoid using emory cloth to polish a straight chamber, and instead make a solid lap. The lap will not be able to enter the throat. (Emory cloth should not be a problem on bottleneck chambers).
-- in the future, I'll use a throating reamer to cut the throat in a separate operation, instead of cutting the chamber and throat with one reamer. That way, I can gradually cut the throat a little at a time until the diameter in front of the case is just right. I'll probably have to make some sort of gage to measure the throat while it's in the lathe.
-- at some point in the future I may set this barrel back and try again -- it's 27" long so if I set it back I'd still have 25" -- but for now I really really really want to do some shooting, so I'll shoot this chamber for a while and see what I can wring out of it.

[walstr]

Greetings;

Fluorescent illumination is not steady, but rather 'changes' at 120 CPS. That confuses your light sensors in the chrono. Use either a 120VAC incandescent or try DC powered LEDs. I'm prototyping a portable LED light source for my "sky screens" if/when its too dark outside to sense boolits, but still light enough to shoot safely.

[mtngun]

Fluorescent illumination is not steady, but rather 'changes' at 120 CPS.

Correct. Since my last post I have done some internet research on the subject. It depends on the chrono, but my CED prefers infrared light. Most incadescents and some LEDs emit enough infrared to do the job, but to play it safe (I hope) I ordered some infrared LEDs.

You can buy a storebought light system from CED but it is not cheap.

[walstr]

"...my CED prefers infrared light. Most incandescents and some LEDs emit enough infrared to do the job,..."

Didn't know IR sensors were involved. My chrono 'spec sht.' certainly doesn't mention that level of detail. Your dedicated Chrono Village Hut is too cute! Again, thanks.