.375 RUM accuracy Problems

[Bernedti]

Hello Guys

My custom .375 rem ultra mag, based on a .300 Win mag Winchster 70 that i finished 3 moths ago won't shoot Sub MOA

My current Load:
350grn Sierra MK
OAL= 3.957 inch
Powder: Reload Swiss 70 = 93grn
CCI Large rifle Mag Primers
Remington Brass

at the Time i'm at 2800 fps muzzle velocity

Quickload says that the pressure must be somewhere at 4600 bar / 67000 psi
But the Case shows no pressure sings at all ???

So o good friend of mine said that i sould increase the powdercharge that the neck of the Case will fit better in the chamber

I'm not really sure if this will work

What should i do

 

[watercam]

You did not say what size and shape your groups are, that would help. With calibers that large your rest plays a large part, especially your vertical component. Are you satisfied that the rifle is recoiling consistently? You have a fairly stout load, I would play with bullet seating depth before increasing your powder charge. When all else fails, mount a different scope to verify that the one you are using is able to handle that amount of recoil.

 

[wboggs]

How do you feed a 3.957" round in a Win 70 action? You must be loading single shot. What twist on your barrel? I would back way back on the loads and start with some target 300 gr bullets and see how they shoot. If they shoot well, then start back on your 350 gr loads. I assume you are using high grade dies.

 

[Bernedti]

Sorry that i forgot something

I'm singleloading yes
Rifle twist is 1:12
I'm using a Forster benchrest die set
At 100 meters the groups are between 1,5 and 2 inches

The Scope can't be the Problem
I tried my Kahles K624i and at that time I've mounted my Steiner military 5-25x56

I tried several seating depths and with 3.957" i shot the smallest groups

My best 300meter group till yet

the shot in the middle is from a .308

My 100 meter seating depth test
OAL is written on the targets in milimeter

The groups with OAL 100,5mm are little better than the 101mm groups but thy look nearly like the 101mm

 

[wboggs]

You have good dies. I bet you are close to the rifling with that long OAL. I would try some different bullets, 300gr. Sierra and/or Barnes X. One of them should shoot well with a proper load. Have you checked to see if a 1-12 will stabilize the long 350 gr bullet?
Bill

 

[Bernedti]

I'm not really close to the lands
The max OAL is 4.063"

I've checked that the 1:12 will stabilize the 350grn SMK, before i build the rifle
The stability factor should be somewhere at 1.85

 

[watercam]

OK, you know what you are doing. Other than trying different powders and bullets I would be stumped as well. The Sierra's should shoot. I assume your bedding is solid and barrel free-floated.
I would love to hear how this progresses, it is an interesting project. What is this rifle's primary usage?

 

[dkhunt14]

I like to find powder charge first. I also like the bullets in a couple of thousandths. I start with the bullets in and then find the powder charge. Most times that is where it shoots best. That 350 Sierra is a real long bullet. At 2800 I am not sure it would be stable. If I remember we shot a faster twist in the Cheytac case and it was a lot faster. Matt

 

[Bernedti]

I tried to build the rifle for the .350 SMK because i think that bullet has the best Price for that "performance" it delivers

I tried some different powders but every time i ended up with the same size of groups

The stock was milled 0.001" larger than the action
The recoil lug is bedded and the system was torqued in with some 0.001" thick steel band
I think there can't be any movement
The Barrel is free floating

The primary usage should be long rang target shooting but with that groups

by the way the rifle

http://abload.de/img/dscn0504hjkws.jpg

http://abload.de/img/dscn0505pcjk3.jpg

 

[Bernedti]

I like to find powder charge first. I also like the bullets in a couple of thousandths. I start with the bullets in and then find the powder charge. Most times that is where it shoots best. That 350 Sierra is a real long bullet. At 2800 I am not sure it would be stable. If I remember we shot a faster twist in the Cheytac case and it was a lot faster. Matt

So that i i see it right

you start with the bullet in Land or a couple of thousands of and find the right charge first?

Sorry my brain works not clear today (translate English to German)

The stability factor i calculated with 2700 fps is 1.85

 

[dkhunt14]

I would mill a little more out like .125 and Devcon steel bed the whole action even behind the tang.

 

[Bernedti]

Edit last reply

 

[dakor]

That bullet from my experience does not like to be in the lands load it .015 off the lands and start there. A 12 twist will stabilize these bullets and Sierra used a 375 H&H with a 12 twist to test the bullet before they brought it out and I also use the 350 SMK in my 375 H&H with a 12 twist with good results even at 1000 yards. I have a 10 twist in my 375 Ultra and with the 350 SMK I am using H-4831 for a powder. IMR-7828 shot well and gives 100fps more than H-4831 but IMR-7828 was not stable in cold weather and I would get low flyers so I gave up 100 fps for stability. With the 350 SMK both powders shot 1/2 MOA or better.

Here is what I would try if I were you load the bullet .015 off the lands and Get some H-4831 and start around 88 grains and work your way up. If you cannot get H-4831 try for R-22 or IMR-7828 both of those powders are good accuracy wise but are not very temp stable for where I live anyway.

 

[dkhunt14]

When we shot that bullet in a 375 cheytac it liked it in the lands 10. The gun would shoot 5 shot groups of 5 and under at 1000 yards. I believe we shot an 11 twist In the cheytac case and we shot them around 3100 or so with 5010. At that time the 350 was the only bullet we could get that would reach out there.. The other bullets would fall out at around 1350 to 1400 yards. Matt

 

[effendude]

Shooting heavy recoiling rifles is a special skill. Heavy bullets impart much torque to the rifle and that can show up on target. I would focus on getting promising groups at 100 yards/meters before I went back farther. Eliminate as many things as possible beofre changing a bunch of things.

Also your cartridge overall length has nothing to do with distance from the bullet ogive to the lands.

Good Luck,
Scott

 

[wboggs]

Do you have a match quality barrel? If so, you should be able to get a load that will shoot. You have excellent suggestions by those who are using long range .375 cals. from .375H&H to the .375 CheyTec.
Keep use informed so we can all learn from your experience.

 

[wolley]

I shoot A LOT and I could never get a rifle that recoiled that hard to shoot tiny knots. No matter what. Just sayin.