Reloading 300 RUM

winch_warrior

I'm new to reloading. I'm trying to reload my 300 RUM. I have read where I might need a crimping die for this heavy recoil rifle. Is this true? I'm sure lots of people are reloading for this......what can you tell me? This is for my Remington 700.

HandLoad

Heavy recoil can drive bullets back into the cases while sitting in the magazine. Safest to you and your gun if you make sure they don't reduce case capacity at or near maximum loads. Remember, Reduced case capacity can make for pressures exceeding maximum.

winch_warrior

That brings up another question......Will a taper crimp hold as well as a rolled crimp?

RCrosby

In answer to both questions; i.e. do you need to crimp at all, and if so, will taper or roll be needed, you might want to start by trying the following. Carefully measure your loaded (uncrimped) rounds then load the magazine to maximum capacity and fire all but the last round. Remove that round and check the OAL. If its shorter than when you started, then you definately need to crimp. If not, repeat with same round in the last position until you're satisfied that the bullet isn't going anywhere. If it does need a crimp you can most likely get what you need with whatever seating die you're using, but you might want to see if Lee makes a crimping die for this round. They work great on the thinned walled rounds I've used them in like the 38-40/44-40's and should work well with your big bruiser as well. In short, do you need to crimp? Maybe yes, maybe no. Lots of variables like hardness of brass, dimensions of sizing die and expander plug, etc. You just have to experiment with your rifle to find out.

nononsense

winch_warrior,

I think the best effort is directed towards testing your loads in the rifle magazine. I've been shooting a .300 RUM for hunting since it came out and I've yet to use an intentional crimp. I've used standard RCBC dies as well as my own custom made dies without incident. I have measured the neck tension required and use that without fail to secure the bullets in the case neck. But that doesn't take away from the fact that lighter rifles and cartridges with maximum loads will generate more recoil than in my heavy rifles.

Be aware of three things:

Bullets without a cannelure (crimping groove) need to be taper crimped carefully so you don't damage the bullet jacket and core, affecting the accuracy of that bullet.

Never roll crimp a bullet without a cannelure.

Crimping in any form will raise the pressure of any particular load. Be sure to use a crimp consistently from the start while working up your accuracy loads so that pressure indicators are obvious.

From another source:

"Crimping is the controlled deformation of the cartridge case mouth to strengthen the grip on the bullet.

Crimping

* provides a smoother contour for feeding ammunition (especially in repeating arms),
* prevents bullet set-up during ammunition feeding,
* aids with ignition of the main charge by adding additional friction to retard the bullet as it exits the cartridge case when pressure builds.

Cartridge crimping tool

In centerfire revolver cartridges and some rifle cartridges, crimping is applied by a die with an internal shoulder that rolls the case mouth against the bullet, forming a roll crimp.

The presence or absence of a crimp and the depth to which the crimp is formed are dependent on the type of cartridge. Some cartridges (e.g., 9 mm Luger and .45 Auto) use the case mouth to stop the cartridge from feeding too deeply into the chamber of the firearm. These cartridges are said to headspace on the case mouth. Applying a deep roll crimp to these types of cartridges will likely cause poor accuracy and misfires; they can be successfully loaded without a crimp. However, a very light crimp (barely observable) can smooth handling burrs at the case mount and improve reliability, while providing the required headspace support. This subtle crimp (taper crimp) is applied with a die having a gradually tapered crimping shoulder.

Most factory rifle cartridges and all revolver cartridges receive a substantial crimp at assembly. Revolvers that produce noticeable recoil can cause uncrimped ammunition to lengthen. The effects of inertia during recoil can cause poorly secured bullets to slide forward, possibly causing a malfunction in revolvers. Cartridges can also elongate under heavy recoil in box magazine rifles. In repeating rifles, feeding can force an unsecured (uncrimped) bullet to move too deeply into the case to continue feeding properly.

Roll crimping is common for revolver ammunition; a different system is used for many rifle cartridges, including military cartridges. A roll crimped case is assembled with a crimp shoulder to reinforce placement of the bullet in the mouth of the cartridge case.

Collapsed Case

Collet crimping applies force perpendicular to the case axis. A tapered steel tube with partially slit walls, a collet has a step machined on its interior surface that corresponds to the position of the case mouth. The collet moves up and down in a hollow die. As the vertical position of the collet changes, the tapered exterior moves against the support die, forcing the fingers formed by splitting the walls to move inward. This applies pressure to the case mouth where it meets the internal step. Examining the case mouth can identify collet crimping. The crimp area will have short vertical lines between the compressed areas consistent with the number of segments in the collet.

Crimp Cannelure or Recess Location

Taper crimping is the least stressful of the three crimp methods and can be used with any bullet. Roll crimping and collet crimping require that bullets have a recess into which the case mouth can be deflected. Without this, crimping will damage the case and/or the bullet."

Best.