375 ultra mag

[Corey James]

Yes. Standard .375 RUM but custom barrel but SAAMI Chamber. 26" M24 Benchmark Barrel on REM 700 RUM Ultra Action

 

[nmbarta]

I have used 350 gr. 375 and 400 gr. CEBs.... I am getting 3,055 fps with Sierra 350s now with 26" barrel. This build will be a 29" Benchmark M24 barrel and not looking to hit much pass 3,080 fps in my testing. 375 RUM AI is a great caliber it is no 37XC, so my expectations are reasonable based on prior builds.

That's pretty crazy! I shoot a 350 rmb out of my .375 cheytac @ 3075 and don't have much for room to go up. Takes `133 grains of retumbo and a 29" barrel to get it there.
It would be nice to get that performance out of a smaller platform. Is that a max load?

 

[Corey James]

That's pretty crazy! I shoot a 350 rmb out of my .375 cheytac @ 3075 and don't have much for room to go up. Takes `133 grains of retumbo and a 29" barrel to get it there.
It would be nice to get that performance out of a smaller platform. Is that a max load?

Right at max of 113.5 grains Magnum. Zero signs of pressure so I have room to move up some but accuracy now is excellent. The 350 grain Sierra at 3.915" COAL are awesome out to 1100y tend to not hang in past 1500y, but this was a heavy barrel Weapon build to be shouldered when necessary and Safari style as built. M24 29" contour barrel at 1:9.4 twist

 

[Whitetail312]

Right at max of 113.5 grains Magnum. Zero signs of pressure so I have room to move up some but accuracy now is excellent. The 350 grain Sierra at 3.915" COAL are awesome out to 1100y tend to not hang in past 1500y, but this was a heavy barrel Weapon build to be shouldered when necessary and Safari style as built. M24 29" contour barrel at 1:9.4 twist

Why do they not hang? Even at sea level that bullet doesn't go transonic until 1900 yards... what's the issue?

 

[yorke-1]

Some of those numbers for a 26" 375 RUM seem a little suspect. I've been shooting a 375 RUM improved variant for quite a while with a greater case capacity than just an AI version and some of those velocities are optimistic even in my chambering in a 30" barrel with a 4.100" OAL. And those are from loads that I know are pushing pressures pretty high.

 

[Corey James]

Some of those numbers for a 26" 375 RUM seem a little suspect. I've been shooting a 375 RUM improved variant for quite a while with a greater case capacity than just an AI version and some of those velocities are optimistic even in my chambering in a 30" barrel with a 4.100" OAL. And those are from loads that I know are pushing pressures pretty high.

It was my typo it was a 29"

 

[Corey James]

My barrel is also a progressive twist barrel

It was my typo it was a 29"

It was my typo it was a 29"

We always post our range results with accurate chrono numbers... just as we did when we built our 28" 338-340 based on the 340 Weatherby Magnum.... we averaged 250 fps faster than a 338 Lapua burning 11 grains less powder using 250 gr and 300 grain bullets... we understate our velocities by 75-100 fps https://photos.app.goo.gl/bsCL2ry8wVc9SZRR6

Our 375 RUM AI numbers will be posted soon.... we are building a new 29" M24 Contour Benchmark Spiral Fluted barrel at a fixed 1:9.4" twist. We will run 300 grain lead core and copper Barnes LRX and CEB bullets in our testing.

 

[jw375]

I'm going to stick with the RUM +p chambering. I believe I can get 2800+ out of the 350 smk and that's more than enough for me

I agree. The 375 RUM +P chamber from Shawn Carlock will get you past a mile with 350gr SMK's, the velocity you're looking for and no fire forming or custom dies. I can easily get 2800fps+ with my 27" Benchmark. Use a Wyatts box. A drop tube for the powder charge when going over 101gr. makes things easier. Recoil is substantial, but manageable with the right brake. I have no regrets. Been shooting this since 2011. the 329gr Hammer is outstanding in this chamber as well. Even more velocity gains(IMO, not just due to the light wight) and less torque/barrel whip and pressure.

 

[Corey James]

I feel 375 is quite anemic for 1 mile but then again at 1750 yards it pulverized my 338 Lapua easily. I love the 375 RUM as is far better than any 378 Wby Mag or 375 CT.

You are dead right 2800 fps with 350 SMKs is plenty fast! My favorite target round but for some reason my 1:9.4" Twist hates 350s vs the Barnes LRX. I cant imagine that twist is too fast for the 350 Sierra but must be issue with lead core

 

[Corey James]

I use a Terminator 4 Brake My recoil is mild

 

[Corey James]

I agree. The 375 RUM +P chamber from Shawn Carlock will get you past a mile with 350gr SMK's, the velocity you're looking for and no fire forming or custom dies. I can easily get 2800fps+ with my 27" Benchmark. Use a Wyatts box. A drop tube for the powder charge when going over 101gr. makes things easier. Recoil is substantial, but manageable with the right brake. I have no regrets. Been shooting this since 2011. the 329gr Hammer is outstanding in this chamber as well. Even more velocity gains(IMO, not just due to the light wight) and less torque/barrel whip and pressure.

What optic are you running? I have tried the following and just do not like any of these so far.

Schmidt Bender 5-25x56mm
NF ATACR 7-35
Leupold 5HD 5-25x56mm

Issues with eyebox and the SB for the price very disappointed with shooting past 1,000y

Any ideas?

 

[Whitetail312]

I agree. The 375 RUM +P chamber from Shawn Carlock will get you past a mile with 350gr SMK's, the velocity you're looking for and no fire forming or custom dies. I can easily get 2800fps+ with my 27" Benchmark. Use a Wyatts box. A drop tube for the powder charge when going over 101gr. makes things easier. Recoil is substantial, but manageable with the right brake. I have no regrets. Been shooting this since 2011. the 329gr Hammer is outstanding in this chamber as well. Even more velocity gains(IMO, not just due to the light wight) and less torque/barrel whip and pressure.

I can't wait to have this build done, what are you seeing with the hammers? 2900 or so? I'm going to develop a load with the for my hunting load and use the SMK's for my target rounds.

 

[yorke-1]

It was my typo it was a 29"

Something isn't right about the information you're throwing out here. Please be very careful telling anyone that 105gr of Ramshot Magnum with a 350gr SMK is a safe load in a SAAMI 375 RUM. Especially if you're getting nearly 3000 fps from a 29" barrel. I'd be more interested in Pressure Trace data on that load than chronograph data.

 

[Corey James]

Something isn't right about the information you're throwing out here. Please be very careful telling anyone that 105gr of Ramshot Magnum with a 350gr SMK is a safe load in a SAAMI 375 RUM. Especially if you're getting nearly 3000 fps from a 29" barrel. I'd be more interested in Pressure Trace data on that load than chronograph data.

As always never take load data from other custom builds. Agreed.

I base experience of 29 years building and never condone using anyone's "posted" or otherwise their data without knowing the build specifications, chamber, throat, etc.

Good point to emphasize but those are the numbers and I am not the least concerned with pressures being developed. The 1:9.4" twist does promote a high spike in pressure but starting with my base loads with a 1:12 v. 1:14" I am not the least concerned.

If it is accurate is more important than speed... if you need more speed build a better caliber.