A friend from Sitka recently sent me his Model 70 in .375 H&H for load development. A muzzle brake had been installed before he got it and the barrel cropped to 22 inches. A scope only .375 H&H bear rifle.
Evidently Reloader 17 was available in AK for a while and we found we could get to 2440 with R-17 with 300 Partitions and 2500 with Swift 260gr A-Frames. We also tried R-15, H4895, IMR 4064, with similar or less velocity. The interesting part was that VV N-540 produced over 2700 fps with 260gr Swift A frames. I still was under the listed maximum on VVs data.
As my friend in Alaska says, the .375 H&H "is what it is." Bullets will perform magnificently at these middle velocities. The object is to do necessary damage on both ends of the rifle. Not a lot more.
If you have the Elmer Keith attitude, "the .375 H&H is a great rifle for mule deer" from which we can sumize that Elmer was somewhat insensitive to recoil, and the Sierra boattails can make the cartridge behave like a long range rifle.
What was impressive was the accuracy with a variety of Nosler, Barnes, Swift and Hornady bullets. If you do your part the rifle would consistantly shoot inside of an inch at 50 yards regardless of the load.
I was able to get some more testing done recently. I performed a seating depth test and a powder charge run up with the now discontinued Hornady 300g BTSP and H4350.
I also did a basic min/max run up with the 350g SMK and H4350, H4831, and RL17.
I am not to the point in testing where I have arrived at any definitive results, so I don't have any pics to share. I am hoping that my next round of tests will yield more useable results.
Prior to testing, I mounted a Zeiss Conquest 4.5-14x44 AO scope on my rifle. It made life much easier while testing loads from the bench.
For my seating depth test, I loaded three rounds each to COAL's of 3.830; 3.790; 3.750; and 3.710 using 78g of H4350, Norma brass, and CCI Magnum primers. I then fired the assembled loads in round robin fashion @ 100 yards.
The first two rounds from the group seated to 3.830 cut overlapping holes. I don't know where the third round went.
The first two rounds from the group seated to 3.790 were likewise touching, with the third round expanding the group to about 1.5".
The group seated to 3.750 formed a nearly equilateral triangle approximately 1.75" across.
The group seated to 3.710 formed another nearly equilateral triangle about 2.5" across.
Both the 3.830 and 3.790 seating depths look like they really want to shoot. I intend to re-test both COAL's at my next opportunity (probably in the spring).
For the powder charge run up, I loaded three rounds each @ 78.6, 79.4, 80.2, 81.0, and 81.8g of H4350 respectively, seated to a COAL of 3.830, and fired my OCW test @ 100 yards in round robin fashion. To my surprise, every group from 79.4 on up printed a neat triangle about 2" across. The 78.6g powder charge printed two rounds touching with a third round about 1.5" from the first two.
In an attempt to reduce the number of rounds I would have to fire in a single bench session, I had cut off the bottom two powder charges, expecting best accuracy to be found from the middle to the high end of the spectrum. That now appears to me to have been a mistake. The fact that the 78.6g charge printed two rounds touching and produced the smallest group in the powder charge run up, taken together with the results of the seating depth test, is strongly suggestive to me that best accuracy with this powder and bullet may indeed be found at the lower powder charges. Once I establish the preferred seating depth, I intend to do a powder charge run up from 77.0g (Hodgdon book min) to 78.6g in an attempt to find best accuracy from this combination.
If I am unable to find a sub-MOA combination, I intend to try RL-17 and RL-15. My efforts may be complicated by the fact that Hornady has recently discontinued the 300g BTSP (I hope this means there is a new .375 bullet on the way. An SST would be nice). I may have to substitute the Sierra 300g BTSP to continue my testing much beyond H4350.
Where the 350g SMK is concerned, I wanted to see how fast I could push this bullet from a .375 H&H with several different powders. I was looking for a less expensive practice bullet that would offer similar flight characteristics to the high bc Cutting Edge bullets, allowing for more long range practice for my shooting dollar.
A few months ago, I e-mailed Sierra for load information using the 350g SMK in the 375 H&H using H4350 and H4831. A Sierra tech replied with the following:
I really expected H4831 to be too slow to work well in .375 H&H, but I thought that the heavier bullet might perhaps work better with a slower powder. Either way, I felt that trying H4831 alongside H4350 would tell me something about what the optimum burn rate range is for heavy bullets from a .375 H&H.
Along with H4350 and H4831, I also tried RL-17. Conventional wisdom has it that RL-17 is close enough in burn rate to H4350 to use the same starting load for a given bullet/cartridge combination. Most reports I have seen indicate that RL-17 tends to reach its max anywhere from about one grain below max for H4350 to about two grains above book max for H4350. With that in mind, I loaded my test rounds for RL-17 using the H4350 data that I obtained from Sierra.
For my velocity run up, I loaded five rounds at one grain increments from min to max for each powder, with the bullet seated .040" from the rifling (with a COAL of 3.9"+), and fired the rounds over a chronograph into a dirt bank about 50 yards away.
With H4831, velocity topped out around 2300 fps. As I expected, the rounds loaded with H4350 were faster, topping out at 2406 fps with no pressure signs.
RL-17 delivered a bit more velocity along with a couple of surprises. It was obvious that RL-17 was building pressure more quickly than H4350 in the first couple of rounds as the starting velocity was higher and climbed more quickly from shot to shot. The third shot delivered 2436 fps, already above where H4350 had topped out. The fourth shot showed about 50 fps LOWER velocity than shot #3 and the chronograph did not register the fifth shot. Interestingly, a friend who was observing the test stated that the fifth shot sounded noticeably "hotter" than the others.
Based on what I had read in a link I posted earlier in this thread, I was watching for a velocity drop off between increased powder charges as the warning sign to back off when using RL-17. Truthfully, I had not expected to encounter the drop off so soon in the powder charge run up. I had expected to encounter that at a much higher powder charge. As it turns out, actual max appears to be somewhere between 70g and 71g of RL-17 with a 350g SMK. In this instance, RL-17 appeared to behave as a faster burn rate powder than H4350.
In order for the 350g SMK to work for my purposes (long range or ELR), I needed to be able to launch it at 2550 or above. I am pretty sure I could get it to 2450 with H4350, but that is about it. However, the 15 SMK's that I put into the dirt bank dug a 6" diameter hole that went several feet into the ground and impressive dirt clod showers accompanied every impact. None of my 300g loads produced such results. The 350g SMK appears to pack quite a punch at short range.
One other thing of note was load density with the three powders tested. H4831 produced 100%+ load densities with every powder charge. I was crunching powder every time I seated a bullet.
Though I did not crunch any powder with H4350, I could not hear powder moving in the case when I shook the loaded rounds, which leads me to believe I was achieving near 100% load densities.
In contrast, using the same powder charges with RL-17 as I did with H4350, there was a lot of empty space in the case after seating a bullet. I could hear a lot of powder movement in the case when shaking a loaded round. Had I needed to seat the bullet deeper to fit an action shorter than the full length Magnum Mauser action that my CZ550 is based on, I believe I could have done so using RL-17 without a performance penalty. That is something that may be worthy of note for anyone shooting the .375 H&H in actions like the Remington 700 or Winchester Model 70.
Given you have room for more powder with RL17 have you considered RL19? In 300 WinMag we have found switching to RL19 from a good load in 4350 can deliver a useful increase in speed. Density of RL19 allows for some more powder. 75gr of 4350 is replaced by 79gr of RL19 in the 300 WinMag.
You should reconsider the ream job to 375 WbMag. Same brass made better. Because it is less tapered and the neck's double radii the case life is improved. Hornady's #8 manual lists an increase from 76.3gr of IMR 4350 in the H&H to 87.7gr IMR 4350 and 200fps more velocity in the Weatherby. Same case, better shape, +200fps, what's not to like?
I am bummed by Hornady's dropping the 300gr SpBT. Hope something else comes out of them. Maybe with a better BC.
Try working up the Nosler 260gr Accubond. The numbers are very promising in my 375 Ruger. 285 yard zero and 3022 fps MV (!!!) it rises no more than 4" @ 160yds and delivers 2000ft lbs (the big ton) @ 630yds. That zero (285yds) is 11.3" down @ 400, 28.6" down @ 500yds and crosses 60" @ 620 yds. You should come very close to 3000fps with the right loads with the Nosler.
Glad I'm not the only one stretching the 3/8" bore...
The issue with RL19 isn't case capacity, it's burn rate. It will not behave the same in a larger bore as it does in a .300WM. In a larger bore, the volume for expansion of powder gases increases more rapidly as the bullet moves down the bore. That requires faster powders relative to a smaller bore with a similar case capacity.
I have confirmed to my satisfaction that powders slower than H4350 actually reduce velocity in the 375 H&H during my tests with the 350g SMK, which included H4831. RL19 is in the same burn rate range as H4831 and highly unlikely to offer enough increase over H4831 to overcome the 100fps advantage of H4350 and the nearly 150fps advantage of RL17 in the H&H case.
While it's true that there is room to increase case capacity to gain velocity, the point of my quest is to maximize the capabilities of the H&H. That is why I do not intend to go with the Weatherby chambering. My original goals are well within reach and have actually been exceeded. The real challenge for me now is finding the accuracy level necessary to make it all work at long range.
I, too, am disappointed that Hornady has dropped the 300g BTSP. It was an excellent bullet. I am hopeful that Hornady intends to offer an improved bullet in its place in the near future. Will have to wait and see. If not, there are alternatives that will suit my purposes.
The reason that I have been using the Hornady bullet to begin with is that my earlier testing confirmed very similar pressure and velocity behavior to the Cutting Edge 300g MTH, which is ultimately the bullet that I wish to use for long range. Because the MTH bullets cost $2+/bullet, I am doing the majority of my development with the much less expensive Hornady bullet, which will get me in the ballpark. I can then fine tune the MTH from there.
That is the reason I have not worked with lighter bullets like the Accubond, though they have similar bc's and can be driven much faster. The Accubond has nowhere near the long range potential that the 300g and 320g MTH's do, and that is what I am ultimately chasing.
Once my experiments with the .375 H&H are complete, I have considered stepping up in case capacity a bit and have researched my options. I don't want to go really big because I want to stay with a carry weight rifle w/o a muzzle break. I have considered going to .375 H&H Improved, .375 Weatherby (pretty much the same thing), or something like a .375-.416 Rigby.
If I did any of those, I would like to do it on a CZ 550 Magnum action. From time to time, I see used CZ 550's in .416 Rigby or larger calibers for sale at bargain prices. I think that would be the starting point for my build.
The real kicker with this idea, though, is the limited selection of high bc bullets in .375. For the most part, .375 options are still built around being a close range smasher. Berger was working on a high bc .375 bullet, but that project has been suspended until they are able to catch up with demand for everything else they make. It is unclear what bullet weight was under development to begin with. If it was a 350g bullet, my experience so far tells me that more case capacity than I really want to go with would be required to make such a bullet useful. A high bc bullet in the 300g class would be more suited to the .375 H&H and .375 Ruger class rifles (those constitute the majority of .375's anyway), but I really don't know what the thinking of the bullet makers is regarding this. So far, the only high bc conventional bullet in production is the 350g SMK, which was really designed for the Cheytac cartridges. I have no interest in going that big.
All in all, I would have to see a big improvement in available .375 bullets before I would be willing to commit to a build involving a larger case. I just don't think it is worth the effort without better bullets to shoot. I like my H&H as is and wouldn't dream of reaming the chamber to something else. I would consider building another rifle, but that idea will stay on the shelf unless/until better components become available. Until then, I will work with and enjoy what I have.
Ultimately, I am convinced that the good old H&H will prove to have enough potential to make it a legit 1000 yard elk cartridge and perhaps even have enough capability to run with some of the more accepted ELR cartridges. Moreover, it is my hope that my experiments will draw enough interest among my fellow shooters on LRH to encourage some of the talented and experienced folks here to explore the capabilities of the .375's for themselves. Maybe that will help spark demand for better components.
Much of what you have set as goals parallel my goals. So I am seeking similar results.
GS Custom Bullets are now advertised on this site. They are, I believe the high BC 3/8" bore bullets some of us are seeking. They have a lower bore resistance than conventional bullets and can be driven quite fast.
You mentioned after this you might try something w/ more capacity. The cartridge you might consider is the 375 RUM. About what you want and compatible w/ the CZ 550.
In my work w/ the 375 Ruger I ran out of room with IMR 4350 & 300gr bullets. But RL19 is denser and where I had 80gr of IMR 4350 the same capacity holds 84gr of RL19. 4350 and 4831 are identical in granule size and have the same density. They are single base powders. RL19 is double base powder and therefore has higher energy density to boot. This advantage could put it into the ballpark you need. BTW 4350 is my go to rifle powder. All time favorite. So it pains me to suggest another. Superformance is a possibility as it is almost the same rate as 4350 but very dense. The space taken up by 80gr of 4350 can be replaced by as much as 86gr of Superformance. But as a "tailored" powder it either works or it doesn't. It delivers 100fps higher in 30/06 with heavy bullets and the 30/06 & 375 H&H are similar in pressure and expansion ratio. It is slower than 4350 and faster than 4831.
Please keep posting your results on this thread. I am following with bated breath (and a note pad w/ sharp pencil) your results with 300gr 3/8" bore bullets. Most hunters don't know how well this caliber knocks 'em down.