Just chronographed the Remington Safari factory load, which uses a 300grain Swift A frame bullet. From my Sako Safari grade measured 10' from muzzle it was doing 2431fps.

My handload using the same bullet and 76 grains IMR4350 was doing 6' slower.

Both loads shot v.accurately but I was a bit surprised that they didnt go faster! Maybe it was the weather, about 40 F!

I have observed the same thing.
When Remington first brought that .375 H&H load out, I chronographed it at an honest 2530 fps in a 24" M70. I had the occasional pierced primer, and all showed signs of XS pressure, cratering of the primers, brass extrusion marks from the ejector cut on the bolt face, etc.

Canuck had an extractor blown off his rifle (M70) IIRC and had to deal with Remington on that.

Maybe he was one of many who got their attention. Correct me if I am wrong, Canuck.

Anyway, the next batch of .375 H&H Remington loads with 300-grain Swift A-Frames was clocking 100 fps slower for me, and no pressure signs.

I think the issue is that those Swift bullets are built stiff (thick partition) and have long bearing surfaces and may have been at upper limit for diameter, all adding up to increased engraving resistance and pressure spike compared to some other bullets.

Swifts are great bullets, but they may not go as fast as some other makes, for a given pressure level.

Somchem specifies a min/max load of 2,282 and 2,515 fps for the .375 H&H with a 300gr PMP RNSP bullet, using S335. The PMP factory load clocks 2,428 fps whilst the Federal load gives 2,530 fps. Thus PMP felt safer to stay under the max load just like the Highland AX ammo at 2,487 fps. The Sako load of 2,431 fps seems to be very much in line with the PMP load. The old Barnes -X bullet is both longer than the Swift A-Frame bullet and harder to seal the bore being a mono-metal bullet and can be loaded to 2,480 fps (Somchem max = 2,480 fps), so I am sure it can be done with the softer Swift bullet as well. However, we should consider some other aspects as well.

a) A critical design aspect of the .375 H&H is its short free-bore that makes for a steeper peak pressure in an already high-pressure cartridge - unlike the design parameter of the 9,3x62 mm. In addition, every rifle system is different and that accounts largely for differing muzzle veloities. Tollerances differ ito chambers and barrels. It is not uncommon that one rifle can yield 100 fps and more than another. Some barrels are cut tighter than others. Some rifles have 'loose' chambers.

b) Some people want to milk their rifles for the last drop of velocity, as if an extra 100 fps will make a notable difference. Given the above, why border at max or exceed max loads with the .375 H&H? Imo there is actually no need above 2,400 fps and there should be no reason to feel disappointed if you are getting 2,431 fps and 2,425 fps. The accuracy sweet-spot should really be the focus point. In the latest African Outfitter we can see differences in retrieved Barnes-X bullets - overtretching of mushrooms due to a mere 100 fps more. Impact velocities between 2,100 and 2,200 are as much as we need and bullet performance will be better.

c) Edward A. Mutanas, author of Lyman’s Reloading Handbook, criticized reloading books and manuals that list ‘marginal’ propellants rather than ‘best’ propellants for a specific cartridge, as the novice or gullible reloader might get the idea that most propellants do more or less the same work in a loaded round of a specific cartridge and bullet weight. Professional laboratories will run tests at ambient, elevated and suppressed temperatures to consider the stability of propellants. He states that as he has fired more than a million rounds in test loads and he therefore appreciates the amount of work involved to isolate best propellants for specific applications. He published an article in the American Hunter of Jan 1994 – Handloading: Picking a Powder. I wish to quote him on some pertinent points he made:

“One publisher fails to list IMR 4064 for the .375 H&H Mag. Yet this powder is a perennial favourite, delivering a good blend of ballistic uniformity and velocity with high accuracy levels and no undue compression of the propellant charge. In fact, this powder has been used in the past by a major ammo maker, in ‘factory loads’ for this very cartridge. This same data source lists IMR 4831 (as do others) for the same application with no mention of the bullet seating depth problems that may be encountered due to this bulky powder's requirement of more space in the case."

Warrior