The 357 pressure barrel project resumes (again)

[mtngun]

A Bald Eagle shooting rest showed up. The Bald Eagle has some quirks that need to be fixed -- I'll post a thread on that when the time comes -- but for today I used it "as is," and it was definitely steadier and more comfortable with the TC than the other rests I've tried.

A rear bunny bag is in the works, but for today I had to improvise. The pic shows a couple of snowboot liners being employed as a rear rest. Definitely not optimal.


Once again I tried the 200 gr. spitzer, but with some differences. This time it was sized 1-diameter at 0.359", instead of 0.3575" x 0.8 degree taper like last time. Last time I seated it out to engrave the rifling, but this time I seated it deeper so that it did not engrave -- I've never had much luck with engraved cast bullets in a TC, it seems to cause ignition problems, among other things.

As you can see from the notes in the photo, I walked up the powder charge until I reached what I felt was the max safe load, based on the chrono and on case head expansion.


Results at 100 yards for the 200 gr. spitzer with 15 gr. Lil Gun, CCI #500, 1.790" COL, heat treated wheel weight, Rooster HVR lube:
-- 1748 fps, 0.70% standard deviation for 15 shots (decent)
-- 2.1", 1.45", and 2.0" at 100 yards. 1.85" average.
-- a few of the cases were sticky to extract, suggesting that maybe I should back off the powder charge.


Next up, a 160 gr. plain base based on the Sensible Keith design. Since my 160 gr. PB revolver bullet shot surprisingly well last time, I attempted to "improve" it. I kept the same front band length, the same meplat, the same nose length, but stretched the length by using deeper grooves and a bigger GtoB. My thinking was that a longer bullet would be more accurate, all other things equal. The "improved" bullet also holds quite a bit more lube, but that was not the point since there was no sign of excessive fouling with the revolver bullet.


You can see that the "improved" bullet is slightly longer than the revolver bullet.


I walked up the powder charge until the velocity was the same as the revolver load, 2000 fps. Since the longer bullet seats a little deeper, less powder was required to reach the desired velocity. Results at 100 yards for 17.8 gr. WW296, 1.513" COL, heat treated wheel weight, Rooster HVR lube, sized 0.359":
-- 4", 6.3", and 3.2". Average 4.5".
-- 1982 fps, 0.56% standard deviation for 15 shots (that's pretty good).


Conclusions and Lessons Learned:
-- the TC definitely likes the 1-diameter spitzer better than the tapered spitzer.
-- the TC does not like my "improved" 160 gr. PB bullet.
-- I can't draw any conclusions about 0.359" vs. 0.3575" since there were too many variables today.
-- the Bald Eagle rest definitely helped me, but the lack of a firm rear rest was still a problem.

Things to Try Next Time:
-- reduce the Lil Gun powder charge on the spitzer load
-- possibly try WW296 on the spitzer load -- I suspect WW296 has a slight advantage in accuracy, and more consistent velocities.
-- possibly try 0.3595" or 0.360" on the spitzer load.
-- try the old revolver bullet at 0.359"
-- try different weights of plain base bullets.

I would be tickled if I could find a load that shoots 1 MOA in this barrel. And if I can find a respectable plain base load, I would like to use it to do some lube and design tests with it.

Obviously it would be easier to get bragging accuracy with lower velocity loads, but that's not my style. I'm only interested in max loads.

[mtngun]

A rear bunny bag showed up. It did help to steady the rifle.



Today I tried a couple of new plain base bullets. First up a 200 grain spitzer.


14.8 grains 296, Rooster HVR, sized 0.359", heat treated wheel weight, Winchester small pistol magnum primer, 1.907" COL.

5 shot groups at 100 yards, in a 30 mph wind:
-- 2", 1.8", 2.4". Average 2.1".
-- 1640 fps, 1.2% standard deviation (poor)
-- the dispersion was predominantly vertical.

Next a 175 grain plain base spitzer (the design was 170 but it weighed 175).


16.0 grains 296, Rooster HVR, sized 0.359", heat treated wheel weight, Winchester small pistol magnum primer, 1.780" COL.

5 shot groups at 100 yards, in a 30 mph wind:
-- 1.8", 1.7", 2.1". Average 1.87".
-- 1789 fps, 1.1% standard deviation (poor)


Conclusions and Lessons Learned:
-- this barrel seems to shoot plain base just as well as gas checked.
-- the rear bag definitely helped, but the rifle is still "tippy" without a forearm.
-- the standard deviation is excessive
-- for now I will stick with WW296 powder since it seems to work as well as anything.

Things to Try Next Time:
-- make a wide forearm to eliminate "tipping"
-- try different seating depths
-- try sizing 0.360"
-- increase the powder charge a bit
-- try air cooled rather than heat treated wheel weight.

If I can find a 1.5 MOA plain base load -- at full throttle velocities, of course -- then I could use such a load to do a bunch of lube and design experiments. I haven't done much work with plain base rifle bullets so that would be a good learning experience for me.

[mtngun]

Today I tried a new 160 gr. plain base spitzer, plus I tried some tweaks to the 175 gr. spitzer load.

The Green Mountain barrel now has a forearm, or actually a 3" wide sled. The sled is simply clamped onto the barrel so there is no need to drill and tap or cut dovetails to mount it. I don't have a 3" bag on hand so I improvised with some scrap foam and masking tape. It actually worked well enough and made the rifle feel noticeably steadier.


First up, the 160 gr. spitzer. It was intended to be 150 grains but actually weighed 157 grains without lube, so we'll call it 160.



Heat treated wheelweight, sized 0.360", Rooster HVR lube, 1.820" COL (just off the rifling but not actually touching), Winchester magnum primers, and 17.5 grains WW296. 5 shot groups at 100 yards.

-- 2.2", 0.9", 1.6", Average = 1.57"
-- 2005 fps, 1.3% standard deviation (poor standard deviation)

This barrel finally broke the 1 MOA barrier. If only I could do it every time!


Continued in the next post ....

[mtngun]

Next up the 175 grain plain base spitzer, with various load tweaks.

-- Sized 0.360" (last week I used 0.359")
-- COL 1.823" (last week I used 1.780" COL)
-- 16.2 gr. WW296 (last week I used 16.0 gr.)
-- otherwise the usual heat treated wheelweight, Rooster HVR lube, and Winchester mag primer

-- 3.15", 1.8", 1.8" for 5-shot groups at 100 yards.
-- 1879 fps, 0.48% standard deviation. That's a good standard deviation.

The first group -- 3.15" -- was a deliberate experiment with a different benchrest technique. Instead of pulling the rifle against my shoulder and holding on with both hands, as I normally do, I only used one hand and did not pull it against my shoulder at all. I'm going to disregard that group because I'm sure it was due to the different hold, not the load. So disregarding the 3.15" group, we're left with a 1.8" average vs. 1.87" last time.


Next:
-- air cooled wheelweight (instead of heat treated)
-- otherwise the same 16.2 gr. WW296, 1.823" COL, HRV, sized 0.360", and Winchester mag primer.

-- 2.7", 4.0", 1.85".   2.85" average for 5-shot groups at 100 yards.
-- 1846 fps, 0.88% standard deviation. (lower velocity and higher standard deviation compared to heat treated bullets )

Next:
-- powder coated wheelweight, using the shake & bake method, and "wet black" from powder by the pound.
-- otherwise the same 16.2 gr. WW296, 1.823" COL, HRV, sized 0.360", and Winchester mag primer.

-- 4.3", 2.4", and 3.0".   3.2" average for 5-shot groups at 100 yards.
-- 1838 fps, 0.77% standard deviation (lower velocity and higher standard deviation compared to lubed heat treated bullets.)

Note that my first attempt at powder coating did not go well, the powder did not stick well so I did it twice to get thorough coverage.


Conclusions and Lessons Learned:
-- the 160 plain base spitzer shoots as well as anything, so I'll focus on it next time.
-- no obvious advantage to 0.360" over 0.359", except that it may have lowered the standard deviation.
-- the forearm sled definitely helped to steady the rifle, but my benchrest technique still needs improvement.
-- air cooled bullets were inferior in every way to heat treated bullets.
-- powder coated bullets were inferior to bullets lubed with HVR. Though to be fair, I need to improve my powder coating process.
-- none of the loads fouled the barrel as best I could tell with my naked eye.

Things to Try Next Time:
-- tweak the 160 grain spitzer load
-- try to improve my powder coating process
-- try other coatings
-- perhaps try a 140 grain spitzer.

[mtngun]

More coating experiments today. First up, Valspar tractor enamel. The enamel added about 0.002" to the diameter. The same load as before for the 175 grain bullet -- 16.2 gr. WW296, Winchester small pistol magnum primer, 1.823" col, sized 0.360" after coating.


-- 1823 fps vs. 1879 fps with HVR lube last week
-- 0.79% standard deviation vs. 0.48% standard deviation with HVR lube last week
-- 2.6 MOA (3.1", 2.6", and 2.1") vs. 1.8 MOA with HVR lube last week.
-- no visible fouling to the naked eye


Next, Minwax water-based Polycrylic, otherwise the same 175 grain load. The polycrylic added only 0.0005" - 0.001" to the diameter.


-- 1841 fps vs. 1879 fps with HVR
-- 0.84% standard deviation vs. 0.48% with HVR
-- 2.4 MOA (2.4", 2.3", and 2.5") vs. 1.8 MOA with HVR
-- there may have been a wee bit of fouling just past the throat, but otherwise the barrel looked clean


Next, Powder-By-The-Pound "Wet Black," dry shake & bake with plastic BBs, 160 grain plain base, otherwise the same 160 grain load as last week -- 17.5 gr WW296, Winchester mag primer, 1.820" COL. The powder coat added about 0.002" to the diameter.


-- 1965 fps vs. 2005 fps with HVR lube last week
-- 0.8% standard deviation vs. 1.3% with HVR
-- 2.6 MOA (2.3", 2.7", and 2.8") vs. 1.57 MOA with HVR
-- no visible fouling to the naked eye.


Conclusions and Lessons Learned
-- every coating that I have tried reduces velocity and reduces accuracy compared to HVR.
-- it's true that the coatings shoot clean, but so does HVR !
-- for the time being I am going to abandon coatings in this barrel and stick to conventional lubes.

[mtngun]

Next up, tweaking the 160 grain HVR load. Powder charge boosted from 17.5 to 17.7 grains, and COL boosted from 1.820" to 1.849". The longer COL lightly engraves the front band. Otherwise the usual load of heat treated WW, Win mag primer, sized 0.360."


-- 2006 fps vs. 2005 fps for last week's HVR load.
-- 1.4% standard deviation vs. 1.3% for last week's load.
-- 1.77 MOA (1.1", 1.9", and 2.3") vs. 1.57 MOA for last week's load.
-- the low fliers had low velocity.

Next up, a 140 grain spitzer. Same nose as the other spitzers, only the weight is changed. 19.0 gr. WW296, Rooster HVR, sized 0.360", Win mag primer, 1.835" COL -- just off the rifling but not actually engraving.


-- 2136 fps
-- 1.2% standard deviation (poor)
-- 2.83 MOA (3.5", 3", 2")
-- there may have been a wee bit of fouling just past the throat, but the rest of the barrel looked clean.


Conclusions and Lessons Learned:
-- the 160 grainer shows the most potential so I will focus on that bullet from now on
-- I was impressed that the plain base bullets could be driven to 2000 - 2150 fps without excessive fouling
-- the 160 grainer has a problem with standard deviation and vertical stringing
-- the TC does not like bullets seated to engrave. It seems to cause ignition problems

Things to Try Next Time:
-- refine seating depth for the 160 grainer
-- refine the powder charge for the 160 grainer
-- order a heavier hammer spring since the TC has a reputation for weak ignition

I'm thinking the 160 grainer has the potential to be MOA if I can eliminate the velocity variation.

[mtngun]

Today, a few tweaks in an attempt to reduce the velocity variation with the 160 plain base spitzer.

-- I removed the hammer extension, thinking it might be slowing down the hammer strike
-- the bullet was seated a hair deeper to 1.830" COL, just off the lands but not actually engraving
-- it was crimped a little bit harder than before, but I couldn't do a hard roll crimp because there's no groove in the right place.
-- unless otherwise stated it's the usual load of heat treated WW, sized 0.360", HVR lube, and Winchester mag primer.

15.9 grains Lil Gun.
-- 1.8 MOA
-- 1.43% standard deviation (poor)


17.7 grains WW296
-- 1.45 MOA
-- 0.99% standard deviation (poor, but compared to 1.3% - 1.4% with previous WW296 loads).


Conclusions and Lessons Learned:
-- WW296 seems to have a slight edge over Lil Gun.
-- perhaps the load tweaks reduced standard deviation a little bit, but there was no major breakthrough.
-- I'm about out of ideas. I could try a different brand primer, but I'd rather stick with Winchester because I have a bunch of them.
-- I could redesign the bullet with a crimp groove where it needs to be, but I'm not that motivated bearing in mind that this barrel will eventually get set back and recut with a tighter throat.
-- my goal was to find a 1.5 MOA load that I could use to test lubes and bullet design, so I have achieved my goal (barely).
-- I can't really complain about 1.5 MOA at 2000 fps with a plain base bullet.

Stuff to Try Next Time:
-- I'm ready to move on to lube and bullet design tests, using this 160 grain WW296 load as the test mule.

[mtngun]

Some progress on the shooting muffler and chronograph house. They are not finished but finished enough that the range is open!


I did some more shooting with the 357 barrel today but I am going to post that in the lube forum rather than here.

[mtngun]

The 357 mag barrel is now the 357 Maxi barrel so I'll just start a new thread for it. Maybe someday the 357 pressure barrel project will pick up where it left off.