Rifle: Custom CZ-550, barrel length 635mm (25")
Powder: Alliant Reloader 17
Bullet: Swift A-Frame 300gr
Brass: Norma, once fired, full resized
Primer: Federal GM215M
OAL: 87.2mm (3.433")
Crimped, but not in the crimping groove

Velocity check:
Factory Norma - Oryx 300gr - 781m/s ~ 2560 fps
Factory Federal - Nosler Accubond 260gr - 841 m/s ~ 2757 fps
Factory Sax KJG 10g (154.3gr) - 1069 m/s ~ 3505 fps

Reloads:
4.2g - 64.8gr - 677 m/s ~ 2220 fps
4.4g - 67.9gr - 709 m/s ~ 2325 fps

Both mild recoil (low pressure), but not the cleanest barrel after firing.
I will continue and hope to get better velocity.

Also tried 4.2g and Speer African Grand Slam Solid, heavy crimped in crimping groove - 680 m/s ~ 2230 fps

What do you think about it? I expected much higher velocities.

Jiri

My immediate reaction is that the burn rate of the powder is too slow for the size of the H&H case. That's causing the low velocities. But my second thought is that you're not using a bunch of powder either. I'd guess that you could probably use a few more grains safely.

Did you get any pressure signs?

LWD

LWD: It was mild. Feel of "low pressure". Even the heavy crimp to crimping groove on solid didn't disappear on case after firing at all. Very easy to open the bolt, primer at place looks fine. Simply no pressure signs.

RL17 is between RL15 and RL19, both well used for .375H&H reloading.

I believe that there is not enough powder and will try now 4.5g, 4.6 and so on, checking velocity and for pressure signs.

Jiri

That's good to know. Just eyeballing the load data on the Reliant website, I'd guess you can go up another 10% safely and maybe more.

LWD

Update:

4.6g - two shots: 748 m/s and 732 m/s
4.7g - two shots: 751 m/s and 740 m/s

No pressure signs. 4.7g load is about 100% filled case.

BTW much cleaner barrel (all powder burned or so)

Will try more next weekend.

Jiri

Update:

4.8g - two shots with 5 minutes between shots: 768.5 m/s and 766.4 m/s. At about 40 yards one hole - 2521 fps and 2515 (SD=4.2)

76 gr, OAL 3.5" - two follow up shots: 788 m/s and 794 m/s - 2585 fps and 2605 fps (SD=14 for follow up shots)

76 gr, OAL 87.2mm (just for crimping to crimping groove) and Speer African Grand Slam Solid bullet - 796 m/s - 2612 fps.

No pressure signs, bolt light to open, nice primers. Easy to full length size the brass.

It looks that RL-17 love compressed loads, very consistent at about 102%. I believe I can go up, but with around 76 gr it is the right velocity and I think accuracy will be perfect. Now, it is time to fine tune the load at 100m range.

Jiri

Update:

I tried two loads. Both 300gr Swift A-frame and 76gr of Alliant RL-17, but one with OAL 3.5" and crimped to "bullet body" and second with OAL 3.54 and crimped to crimping groove:



I placed chrono about 20yards from the muzzle (conditions at shooting range), so measured velocities are a little bit lower.
OAL 3.54, crimped to groove:

2486.5fps
2528.5fps
2512.1fps
2504.6fps
2498.7fps
SD=15.64391fps - not so consistent

OAL 3.5, crimped to "bullet body":

2478.3fps
2479.3fps
2471.1fps
2475.4fps
SD=3.67639fps - this is very consistent I think

Norma Factory:

2465.6
2460.3
2448.2
SD=8.91871fps - not as consistent as above

What do you think about it? Looks like RL-17 really loves compressed loads. Even my reloaded ammo is faster than Factory Norma, recoil is a little bit lower.

Looks good. Apparently, RL17 does like to be compressed. A lot of .308 shooters have had great success with it and the Hornady 208 A-Max.

Do you have any accuracy results on the differently crimped loads? I ask for a couple of reasons: first, a highly experienced friend doesn't think the .375 recoils enough to warrant crimping and second I've never liked crimping into the bullet body.

LWD

LWD: I will check it soon but I believe that velocity consistency is on par with accuracy. Crimping is just for "security reason" and crimping to body doesn't kill brass (it is not visible at all). I was shooting yesterday, but was very windy again so groups didn't say anything (so windy that it shoot about 6-7" to the right at 300m).

Pictures from shooting range. Chrono is far from muzzle (closer, there is no light). Primary target is 100m far and secondary 300m is far right.



Jiri

I used rx 15 in my 375 HH and used North Fork 300.
My rifle shot their 300 SP and solid to the same point of impact. The soft perfromed perfectly on buffalo.
was getting 2600 out of my cz