375 Rum inconsistent pressure signs

[Calvin45]

I'm sorry but that sounds like he just help speed up throat erosion. IMO.

Nah man it's like knowing a fire is coming and burning off the stubble in advance so there'll be no fuel to burn and it dies. Can't erode a throat that's been "pre-eroded"!

 

[scpaul]

Is there some place where I could see an engineering drawing or something similar?

 

[Paladin300]

I'm sorry but that sounds like he just help speed up throat erosion. IMO.

Actually I think the opposite is true. It allows you to seat the bullet further out. When used in combination with an Ackley Improved cartridge or something like the RUM or a LAPUA AI it generates 100-200 fps more. I can actually get about 250 fps but the accuracy is at around 2800 with 300 grain pills. I have a little over 800 rounds through mine and we just had it checked and it shows little to no signs of erosion. Consistently shoots .5 moa or smaller. I am having a 280 AI +p built.

 

[Lefty7mmstw]

Switch away from Magpro. We were having issues with that powder years back with delayed and all around crappy ignition. 9 outta 10 chance the powder is the problem. Heck, we even tossed some of it as we didn't want it around anymore.

 

[K.E.C. Darkside]

Switch away from Magpro. We were having issues with that powder years back with delayed and all around crappy ignition. 9 outta 10 chance the powder is the problem. Heck, we even tossed some of it as we didn't want it around anymore.

I don't mind the powder burning the throat out, if it is doing the job I won't, consistently. But to purposely bevel out the throat of your barrel, just does not make sense to me. IMO.

 

[scpaul]

I have an unopened pound in my stores for testing. I've had it for some years. Is there a lot number or other way to identify the problem batch. I really don't want to use it for 4 of July fireworks.

 

[Rum Man]

Actually I think the opposite is true. It allows you to seat the bullet further out. When used in combination with an Ackley Improved cartridge or something like the RUM or a LAPUA AI it generates 100-200 fps more. I can actually get about 250 fps but the accuracy is at around 2800 with 300 grain pills. I have a little over 800 rounds through mine and we just had it checked and it shows little to no signs of erosion. Consistently shoots .5 moa or smaller. I am having a 280 AI +p built.

I'm getting a 375 Rum put together here shortly ...after reading your post I'm going to get the +P done to this new Rum .
Thanks !

Rum Man

 

[Paladin300]

I'm getting a 375 Rum put together here shortly ...after reading your post I'm going to get the +P done to this new Rum .
Thanks !

Rum Man

Who is doing your work?

 

[MagnumManiac]

I don't mind the powder burning the throat out, if it is doing the job I won't, consistently. But to purposely bevel out the throat of your barrel, just does not make sense to me. IMO.

So, how quickly is a .500" long throat that has added angles to the rifling going to erode? Just FYI, the +P does not extend the throat length, it only changes the ANGLES in the LEADE of the chamber.

Cheers.

 

[Rum Man]

Who is doing your work?

Local guy up here in Michigan.

Rum Man

 

[chrisb97]

During initial load testing I followed cutting edges recommended bullet seating procedures and ended up with my seal tite band right up close to the case mouth. I initially started off with magpro at 94 grains and worked up to pressure signs at 99. In between 96.5 and 97.1 the groups closed up to half inch and going further they started opening back up. My chronograph was reading 2690 and at top end loads was pushing 2750. I am using a forster benchrest seating die and full length resizing every time. I'm gonna get ahold of my gunsmith and see if I can get the measurements for the throat and how far up he cut the lands for the 350 matchking to be seated at 4.1". When I load a bullet in a partially resized case to get an oal measurement it looks like my seal tite isn't touching the bore and the olive makes contact with the lands first, but the seal tite might just be pushing into the bore with not enough resistance, hence why I'm gonna get ahold of my gunsmith

 

[Paladin300]

Local guy up here in Michigan.

Rum Man

I really like mine. I considered an edge when I built it, but the improved +p gives me the exact same or better performance, allows me to feed 265 ABLRs for hunting from the Wyatt's box (I still have to feed the Bergers and Flatliners single) and I can shoot factory ammo in a pitch, though my rifle really only likes Federal Premier Aframes. It does not much care for other factory ammo. but when we hand load for it, it shoots little tiny groups. It is a fun gun and if I was going to shoot something big in another zip code it would be the one. It is a 338 RUM Improved +P. It is probably my favorite rifle, with the APA FB Gen 3 you can Literally shoot it all day. When we first built it 4 or 5 years ago it was nothing for us to put 60 or more rounds through it in a session. I considered the 375 but went 338 because of bullet selection at the time. If I were doing a 375 I would twist it 1:9 or 1:8 so I could shot the big Flatliners in it. Good Luck!

 

[Paladin300]

So, how quickly is a .500" long throat that has added angles to the rifling going to erode? Just FYI, the +P does not extend the throat length, it only changes the ANGLES in the LEADE of the chamber.

Cheers.

This is taken from an article on the 338 Terminator which has a +p throat. It explains it fairly simply:

The Cartridge
The 338 Terminator is a monster. It's effectively a 338 Lapua Mag Improved +P. The brass is custom made for Defensive Edge, and it carries the "338 terminator" headstamp. The brass starts out as extremely high-quality 338 Lapua brass, and then it's fire-formed by Defensive Edge to push the shoulders forward a bit for its "improved" design. They sell the brass for $400 for 100 pieces.

This "improved" design with the shoulders pushed forward, and at a steeper angle, allows for more case capacity, which in turn allows for more powder. After seeing the high velocity and learning that the brass started as 338 Lapua Mag brass, I couldn't figure out how it was able to handle the performance without showing signs of pressure.

A conversation with the rifle's designer cleared it up and this is, in my opinion, the most novel part of the entire system … It has a unique chamber that allows for a more powerful round while minimizing the chamber pressure. More on this after some ballistics of the round.

The 338 Terminator has some impressive stats. The 338 Lapua Mag has been king for a while in the big-boy long-range cartridges. Then 300 Norma Mag came along and our military really started to like it because it outperforms the 338 Lapua Mag with less recoil. The 338 Terminator handily outperforms both (on paper).

I shot 1,000 yards with 5.9 Mils of elevation above my 100-yard zero and 1,250 yards with 8 Mils of elevation. That's a heavy bullet, traveling very flat, and packing a wallop on the target.

How did they get a 300-grain bullet traveling over 3,000 fps without serious over-pressure issues? The special chamber.

The Chamber
Defensive Edge has a patented chamber design wherein they use a special throat to handle the power of these monster rounds without dangerous pressures.

Instead of simply having an elongated throat and thereby having too much free-bore with a consequent adverse effect on accuracy (I'm looking at you, Weatherby), they have the rifling start at the throat, but they don't have the bore down to its final diameter yet.

There's a step wherein the bullet engages the rifling as it should, however, it isn't under full pressure yet because it isn't necked down to its final bore size until it can travel a bit. I described this as a graduated throat (to the dismay of the designer).

This really is novel — it allows the bullet to be controlled and start spinning without the abrupt start normally incurred with a standard chamber. My money is on this helping to increase barrel life too. After all, the throat is usually what goes first on a barrel because of intense heat and pressure generated by powder particles and friction from the bullet.

This unique throat design lowers pressure so much that a standard cartridge/load will not meet its normal performance expectations in this chamber. The reduced pressure prevents a cartridge from reaching the velocity it would normally, so this throat/chamber design is best suited for monsters like the 338 Terminator.

 

[chrisb97]

Switch away from Magpro. We were having issues with that powder years back with delayed and all around crappy ignition. 9 outta 10 chance the powder is the problem. Heck, we even tossed some of it as we didn't want it around anymore.

I've been thinking about trying rl26 instead. Using Gordon's reloading tool it shows good velocity with about 96% case fill at my OAL