Project: 357 pressure barrel

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mtngun
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Re: Project: 357 pressure barrel

Postby mtngun » Mon Sep 16, 2013 4:41 pm

Today I tested the glove-fit 200 grain spitzer. In theory a glove fit cast bullet is supposed to provide the ultimate accuracy, so I was expecting the TC 357 to set a new benchrest record. :lol:

I seated the spitzer to jam hard into the rifling (1.935" COL) and stoked it with 13.4 grains Lil Gun ignited by a CCI 500 primer.

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However, the glove fit spitzer did not even shoot as well as my Marlin loads that had to jump to the rifling. The 1.5% standard deviation was much higher than I like to see in a rifle, suggesting that it was not engraving/igniting consistently. That's the problem with the taper-inside-a-taper concept -- the fit is either super tight or loose, never in between, yet an "in between" fit is exactly what you want.
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So then I tried one of my 190 gr. Marlin bullets time seated out to engrave the rifling firmly, instead of jumping to the rifling like my Marlin loads do in this barrel. Despite using the same powder charge as my Marlin load (15.3 gr. Lil Gun), velocity was about 100 fps higher than the Marlin load, suggesting that the engraved bullet was creating higher pressures. Like the glove fit spitzer, standard deviation was higher than I like at 2.1%, suggesting it was not engraving/igniting consistently.

Accuracy with the engraved 190 was 2.85" at 100 yards, not as good as the Marlin load that had to jump to the rifling.
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After shooting 2 groups with the Marlin 190, the Mueller's eyepiece O-ring literally fell out of the scope. Without the o-ring, the lens was rattling around in the eyepiece. That may have been affecting accuracy, so after putting the scope back together I decided to retest some of the loads ..... continued on the next page.
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Re: Project: 357 pressure barrel

Postby mtngun » Mon Sep 16, 2013 4:59 pm

After fixing the scope, I seated the 190 grain Marlin bullet a little deeper, 1.673" COL instead of 1.688". It engraved lightly instead of engraving firmly.

Both accuracy and standard deviation improved with the "lightly engraved" load.

Accuracy averaged 2.1 MOA, vs. 2.26 MOA for the Marlin load, prolly not a statistically significant difference.

Velocity fell 15 fps compared to the firmly engraved load, but still about 100 fps faster than the Marlin load that jumps to the rifling.

Standard deviation improved to 1.1%, better than either the Marlin load (1.6%) or the firmly engraved load (2.1%).

"Lightly engraving" seems to be better than either jumping or firmly engraving.
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Then I retested the 200 grain spitzer, except I seated it a little deeper to only engrave very lightly (1.918" COL instead of 1.935").

Both accuracy and standard deviation improved with the "lightly engraved" spitzer.

Accuracy averaged 1.67 MOA vs. 2.8 MOA for the firmly engraved load.

Standard deviation was 0.8% vs. 1.5% for the firmly engraved load.

Velocity was 1702 fps, a 75 fps increase compared to the firmly engraved load. Apparently reducing the powder space increased pressure more than reducing engraving reduced pressure.

Once again "light engraving" seems to give the best results.
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By the time I finished these tests, the Mueller's o-ring had popped out again and the lens was rattling. One wonders if that affected accuracy of the tests ? Conclusions and future plans in the next post.
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Re: Project: 357 pressure barrel

Postby mtngun » Mon Sep 16, 2013 5:22 pm

EXTRACTION PROBLEMS: I thought I had fixed the extraction problem by setting the barrel back 1/2". Well, it does extract reliably with Marlin loads, but most of the loads I tested today did not extract easily. Apparently the pressure was higher due to the bullet engraving. The TC can prolly safely handle 50,000 psi with a decent 357 chamber (same pressure as the .223 family of cartridges commonly used in TCs) but this oversize chamber seems to run into extraction problems around 30,000 psi.

Sticky cases are a pain, so it has to be fixed. For now, I'll prolly set the barrel back enough to completely redo the chamber. There will only be about 16" of barrel left. Some people like the stubby carbine barrels, but I don't, so I'll prolly ask Santa for a new 357 barrel blank. :roll: In the meantime setting the barrel back will give me some much needed gunsmithing practice, so I might as well go for it. I want to get good at this gunsmithing thing so that I'll eventually have the confidence to work on expensive target barrels.

MUELLER SCOPE: It's under warranty so I guess I could sent it back, but I have no reason to believe that the replacement would hold up any better. I think the o-ring is too skinny and too flimsy to stay in place. A thicker o-ring would prolly fix it, so I might try to pick one up at an auto parts store. In the meantime I'll just keep putting it back together. It's a shame it has the o-ring problem because the glass and the adjustments are quite decent.

TAPERED BULLETS: The tapered bullet, seated to lightly engrave, shot better than anything else I have tried so far, so the concept seems worth pursuing. However ..... it seems to engrave harder on the first full diameter band than it does on the tapered section of the bullet. That's the opposite of how it should be -- it should engrave harder at the nose. In other words, the taper needs to be more gradual. I may be able to tweak that by honing the taper die. In the future, I'll try to deliberately make taper dies with a slightly more gradual taper than the throat, i.e., if the throat is 1 degree, perhaps the taper die should be 0.9 degrees ?

Also, the tapered part of the sized bullet seems to be out of round. I'll have to do some detective work to determine the root cause, and then fix it.

There are many other cast bullet experiments I'd eventually like to try, but for now I need to focus on basics -- a good chamber that extracts reliably, a good scope that doesn't rattle apart, and dialing in the taper so that it engraves in a more consistent manner.

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Re: Project: 357 pressure barrel

Postby mtngun » Sun Oct 06, 2013 12:48 pm

I haven't had time to set the barrel back yet, but I did verify that my tapered sizing die was nearly 0.002" out of round -- long story having to do with attempting to salvage a scrap die. :x So I made a new tapered sizing die. This time I made it with a 0.8" degree taper instead of a 1 degree taper. The new die was round, so that problem was solved.

I wanted to see if the round bullets improved accuracy, so I retested the 200 grain spitzer. This time I did not bother to size the cases since the bullet was a snug fit in the unsized neck. The unsized cases proved to be a mistake because they were very difficult to chamber.

Load was same as last time, 13.4 gr. Lil Gun, #500 primer, 1.918" COL. However, I dont' think the nose engraved when chambered -- it was hard to tell due to the unsized cased being so difficult to chamber. :(

5 shot groups at 100 yards -- 2.8", 2.0", 2.5". Average 2.43". Most of the dispersion was vertical.

Velocity averaged 1623 fps and 1% standard deviation.

CONCLUSIONS AND LESSONS LEARNED
-- the round bullets did not shoot as well as the out-of-round bullets :lol:

-- the unsized cases and difficult chambering made things worse, not better. I suspect the vertical dispersion and higher-than-normal standard deviation were due to the difficult chambering.

-- I think the limiting factor right now is the bad chamber, so I won't shoot this barrel any more until I can set it back and rechamber it. Hopefully the 3rd time will be the charm. :lol:

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Re: Project: 357 pressure barrel

Postby mtngun » Sun Dec 29, 2013 3:02 pm

In case you were wondering, my shooting/gunsmithing projects have been hold while I sorted out my lathe threading capabilities.

I don't have a manual lathe, so I'm "stuck" using CNC to fit barrels. CNC threading is a beautiful thing once you get it set up right and debugged -- but that has been easier said than done. :lol: I ended up having to switch to different lathe software (LinuxCNC aka EMC), I made some improvements to the lathe's tachometer and wiring, and did a lot of tweaks and debugging and testing to get the gremlins worked out. Finally it seems to be coming together. :D
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So maybe next weekend I'll be able to resume my gunsmithing/shooting projects. :roll:

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Re: Project: 357 pressure barrel

Postby mtngun » Tue Jan 07, 2014 3:22 pm

Update on the 357 barrel project:

The good news is that the barrel threading went extremely well. After cutting off the old chamber and refitting the barrel to the stub, it ended up 16 1/2" long. It's not my favorite length, but it'll suffice for the purposes of this project.

The bad news is that my homemade chamber reamer -- we'll call it reamer #2 -- broke. I think the cutting angles were wrong such that it took a lot of effort and a lot of friction to make it cut.

So then I made reamer #3, with different cutting angles this time. I was happy with the way the angles and the dimensions turned out, however it warped severely during the heat treating process. A little warpage is inevitable, but this was way too much. :cry: The resulting wobble would have thrown the chamber dimensions off.

So ..... I'll have to make yet another reamer, and try a different heat treatment process. Wish me luck. :D

Yes, it would be easier to buy a custom reamer, but where's the fun in that? Seriously, this is a budget project, and besides, the last custom reamer that I bought was a disappointment. I would prefer to learn to make them myself.
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Re: Project: 357 pressure barrel

Postby mtngun » Sun Jan 12, 2014 3:59 pm

So I made reamer #4, and this time I heated and quenched it while it was spinning in a drill press, instead of using the electric furnace like I usually do. According to internet wisdom, keeping it spinning prevents it from warping.

But .... it warped just as bad as reamer #3. :cry:
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I'm not ready to give up yet (but I'm getting close :lol: ). I want to try a couple of more things:

-- make the chamber reamer seperate from the throating reamer. That way there will be 2 short reamers instead of one long reamer, and the short reamers should not warp as much as a long reamer.

-- make a simple "D" reamer instead of the 5-fluted reamer. My thinking is that the D reamer will bow along the flat side, and that won't matter because only the cutting edge needs to be straight. I'm not crazy about D reamers because you have to feed them pretty hard to make them bite into the metal, and they chatter more than a 5-fluted reamer, however, they do get the job done.

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Re: Project: 357 pressure barrel

Postby mtngun » Sun Jan 19, 2014 3:03 pm

Reamer #5 was made. It only warped half as much as the previous two reamers, but it still warped noticeably. I marked the high spot on the runout and ground that high side off to make a "D" reamer. The theory was that the cutting edge would be straight, plus the D reamer should have enough flexibility to straighten itself out once inside the barrel.

The reamer pilot was a very snug fit in the bore -- the bore is 0.3478" and the pilot is 0.3475"+.

The chamber was reamed at 160 rpm, using plenty of cutting oil, pausing to clean chips frequently, and with the reamer allowed to "float" in an untightened drill chuck (the reamer was free to wobble inside the untightened drill chuck, the chuck was merely used for pushing the reamer forward).
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The good news is that the D reamer cut with minimal effort and not much chattering. :)

The reamer measured 0.3795" at the neck and the finished chamber measured 0.3803" at the neck, so apparently the reamer was still warped enough to cut slightly oversize, though not enough to complain about.

The bad news is that the finish was rough, apparently due to chips getting wedged between the reamer and the chamber wall. :cry:

I test fired some full house loads and all cases failed to extract easily, and had to be tapped out with a cleaning rod. So I lightly honed the chamber with fine emery cloth, and tried again. Cases still failed to extract easily. :(

As near as I can tell the main problem is a chip gouge on the case neck, where the arrows are pointing in the photo. That shiny ring on the case is where the case expanded in the chip gouge, and then rubbed against the chamber as the case was extracted.
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The gouge in question only extends 180 degrees around the chamber. I'm guessing it was caused by a chip getting momentarily wedged between the reamer and the chamber wall -- I can't think of any other explanation. :?:

As you can imagine, I'm pretty frustrated. :twisted: I wanted this barrel to be a learning experience, and it has been a learning experience, the problem is that I'm learning everything the hard way. :lol:

Thoughts, Theories, and Plans for Next Time:

-- my brief experiences with D reamers suggests that they are more prone to chip gouging than conventional 5-fluted reamers. That's one reason I attempted to make 5-fluted reamers.

-- it may be that the reamer warping is not that serious a problem because 1) the reamer does not rotate and 2) I suspect that it tends to straighten itself out in the barrel, to some extent. Still, who wants to take a chance with a severely warped reamer ?

-- conventional wisdom holds that you should clean chips frequently, but I'm wondering if the gouges are happening when I reinsert the reamer into the chamber? I brush the chips off the reamer, and blow out the chamber with compressed air, but there's usually an errant chip or two still clinging to the reamer, and possibly an errant chip inside the chamber. Maybe I should defy conventional wisdom and continue reaming until the chamber is full depth, and only withdraw and reinsert to set the last few thousandths of headspace?

-- pros pump oil into the muzzle end of the barrel to flush chips out the breech end. No doubt that is the more superior method and perhaps would have eliminated my chip gouging problem, but it's a fairly big deal to set up so most hobby gunsmiths like me don't bother. Besides this barrel was too short for the muzzle to stick out of the lathe headstock, anyway.

-- I may have to break down and order a custom reamer, since my homemade 5-fluted reamers tend to warp excessively. I suspect the conventional 5-fluted reamers would have fewer problems with chip gouging.

-- because I'm itching to resume shooting projects, I may attempt to fill the gouge with JB weld and then re-ream after the JB hardens. It may not work, but I don't have much to lose by trying.

-- I've got a 6mm x 223 barrel TC project in the works, but I don't want to ream that chamber until I get the bugs sorted out of my chamber reaming methods. So the 6x223 is on hold until either 1) I get my homemade reamers figured out or 2) I buy a custom reamer.


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