Have been testing some loads in my .300 RUM, Remington LSS, 26" barrel. The barrel was cryo'ed and it had a trigger job, but is otherwise unchanged from the factory rifle. These are the velocities I chronographed at 70-75 degrees ambient temperatures:

200 grain Speer Spitzer, RL-25:

91.0 - 3106, 3126, 3140
91.0 - 3091, 3104, 3104
92.0 - 3180, 3163, 3178
92.0 - 3208, 3165, 3203
92.5 - 3173, 3163, 3165
93.0 - 3178, 3180, 3185

200 grain Speer, IMR 7828:

86.0 - 2986, 3024, 2934
87.0 - 2986, 2980, 3015
88.0 - 3116, 3104, 3083

200 grain Swift A-Frame, RL-25:

90.5 - 3118, 3155, 3133
91.0 - 3131, 3128, 3131
91.5 - 3121, 3131, 3163

I'm puzzled and a bit concerned that these loads are at or exceed published load data, with more than 100 fps higher velocities. (Alliant, for example, says the max load for the 200 grain Swift is 91.5 grains of RL-25, for a velocity of 3020 fps). I know the relationship between pressure and velocity is direct, but there are no pressure signs on my cases and no extraction difficulty at any of the above loads. In my pre-chronograph days, I would not have hesitated to increase these loads. Especially since best 100-yard groups -- 93.0 RL-25 (1/2"), 88.0 IMR 7828 (3/4") in the Speer, 91.0 RL-25 (1") in the Swift -- seem to be coming near the high end of these loads.

Should I be concerned on the basis of velocity alone and back off? I've chrono'ed Remington factory ammo (180 grain Nosler) at 3173-3247 in this rifle, so I have no reason to think my chronograph is reading high. Any advice or input would be appreciated.

Jim

Jim,
In my A-Square manual it says the max velocity for my .500 A-Square (adjusted for barrel length) of 2385 fps can be achieved with 118 grains RL-15. I achieve this velocity with 113 grains.

A very good example of why we should start low and work up. I shudder to think what would have happened if I had just dumped 116 or more grains in.

You have a completely modern set up and I do not think you will see pressure signs until you are well deep into the danger zone.

I load to the velocity in the book. This way I know I am safe. Anything over and I am on my own. I would recommend dropping to the same velocity in the book.
If you want to go faster add some inches to you barrel. Fowler's Gun and Machine on Huffman can set you up.

And then to confuse things, some bullets go faster than others.......

------------------
Gerard Schultz
GS Custom Bullets

Jim,

Your velocities are not too high.

In fact, I an disappointed to see that the 300 Remington is only delivering 3,120 to 3,185 fps for various 200 grain bullets.

I have a 300 wildcat based on an improved 8 mm Remington case. From a 26 inch Harris barrel I average 3,170 fps muzzle velocity with 81.0 grains of IMR 7828.

I was hoping the larger Remington case would achieve closer to 3,250 fps muzzle velocity for a 200 grain bullet.

Good Hunting !

Some barrels are faster than others and some chambers are tighter than others. If you truly have no discernable signs of high pressure I say keep going but go slowly with the IMR-7828 (Use .5 grain increments now) as it will "arrive" with little warning. You can go up in full grain increments with the RL-25. When you have time, you need to fire some factory rounds and then "mic" the pressure ring on 10 cases. Then see how your "new brass" handloads compare to this reading.
If you elect to do this, feel free to email me with your readings. You will soon develope a baseline for YOUR rifle, with which, you can better interpret where any new load is in regard to high pressure and stop before reaching a physical pressure sign.
I am being overly simplistic in this but you will see the merit of the system after using it for a while, especially if you tend favor a certain brand of primer and brass.

Nick

Nickudu, that sounds like good advice. This rifle's (and all the .300 RUMs, from what I've read) chamber has zero excess headspace; the cartridge headspaces on the shoulder and you can feel some resistance when you close the bolt. In fact, I'm going to have to get a neck die for this round, since you cannot partially re-size with a regular die without squeezing the shoulder a tiny bit forward, which makes it impossible to close the bolt.

The SAAMI max for this round is 65,000 psi. I fail to understand how pressures could approach that figure without primers and brass flowing enough to show signs on the case. Yet, even at the highest loads I've tried, the primers aren't even starting to flatten. My .300 Win Mag shows more primer flattening with factory ammo. I understand why a round like the .45-70 may exceed max pressures without showing signs on the case, but wouldn't expect this to be true of the much higher pressures of the .300 RUM.

To make things more confusing, various internet-published load data shows the max velocity for 200 grain bullets at anywhere from 3000 to 3300 fps. I'd settle for the lower end of that range if I could find accuracy, but as I said, most accurate loads seem to be coming when the velocity hits the 3100-3200 range.

Thanks for the input.

Jim

Before going any higher, try loading and shooting a single case 3, 4, or 5 times in succession with your hottest load. If you shoot a case five times and you don't have a loosened primer pocket or measurable head expansion, you're well within acceptable pressures by definition. The brass case is much weaker than the steel action, so as long as your brass remains safely intact, it's irrelavant what the absolute PSI is.

The lack of a flattened primer has more to do with minimum headspace than with pressure. With "normal" headspace (which I regard as excessive), the entire case is shoved forward by the momentum of the firing pin. The primer is then pushed rearward by its own explosion, or at least that of the powder, until it is stopped by the bolt face. Subsequent to that, the case stretches rearward until the head is stopped by the bolt face. If the primer has moved very far rearward from the pocket, then it spreads radially across the bolt face until the case head is shoved back against it, leaving the appearance of an extremely flattened primer.

On the other hand, when the brass is a "crush" fit in the chamber (and the primer pocket of the brass is of the proper depth), even high pressures will still leave primers with somewhat "rounded" edges.

The flatness of the primer is only an indicator of RELATIVE pressure when identical primers are used in identical cases which fit the chamber identically.

Even a pierced primer CAN be a result of poor firing pin fit rather than "excessive" pressures.

All this is to say that primer signs are usually a poor pressure indicator when taken alone.