Scratching my head with 300 RUM


Well-Known Member
Nov 26, 2009
I went to the range today which is at 5500 ft in elevation. This time I wanted to try out the 200 gr Accubonds with Retumbo and Ramshot's Magnum powder. When I got to the max loads, this is where things got strange with the Sendero

200 gr AB with 98 gr of Magnum powder gave me velocities of ...

AVG Velocity is 3,399. That seems fast, perhaps too fast? 2 out of 5 shots showed signs of too much pressure by slightly sticky bolt and half moon shape on the rim of the case. The temp was 48 degrees. When I hunt it might be 80 degrees so should I back off a grain or two?

200 gr AB with 95 gr Retumbo gave me velocities of...

AVg Velocity is 3,269. This seems about right on without any pressure signs.

Both had about the same accuracy. Has anyone else experienced high perfromance from Magnum like this before?
IMHO forget the temperature, I would back off 2 grains now!
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From your reactions, guess I'm happy to be alive :)

This is the first time I've reloaded and had pressure signs. Kind of scary!

For clarification... not the first time reloading, just first time with pressure signs.
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It's a good idea to have several load manuals for comparison and I always start below max loads and then work my way up slowly while looking for any signs of over pressure.
At 95 grs.Your .5 grs from maximum with the Retumbo 95.5 is a compressed load!
based on the data from website
I find they list higher grs. than my Hornady and Lyman reloading books.
Starting load is 89.0
Back it down
Don't have the Magnum powder data handy
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I use 95gr Retumbo, CCI250, 200grNAB and get 3280 with a custom built 27" Lilja. I would say you're running pretty hot to get that out of a 26" factory barrel.
I'm running 95 Grains of Retumbo, Fed 215M primer, Rem Case, 200 AB out of a custom built 700 Rem w/Hart barrel 26" and getting an average of 3220 with no signs of pressure at all. Your load seems a bit higher but that could be the chronograph's error on either yours or my set. I agree it does seem a bit fast from what I have seen from other rifles. Still its not all that bad if your not experiencing any pressure signs. Loose primers, hard bolt lift etc.
On the Ramshot Magnum I have not had any experience with it but those velocity's seem scary. Were you getting any pressure signs at all?????? Odd, really odd.
I have run 96 gr of Retumbo with 200 AB's in the 3200+ range with no pressure signs but I did have pressure signs with 96.5 gr. I always take chrony readings with a grain of salt. I have two that usually differ in the 20-50 fps range.

Just becareful with your pressure signs. If your primer pockets get loose quickly, you should be backing off. First thing I would do is see how your primers are seating.

I dont know much about Magnum, but those velocities are either awesome or scarry. May have to give it a try.

I would say you are over the top with Magnum. Your experience is different than mine. I got fabulous groups with 95 gr and 3100 fps with 200 AB in the 300 Rum. at 96.5 I seemed to pressure out and velocity was only 3140. I quit. Factory 700 BDL 26" bbl. I normally run rl25 for about 3150 fps with the 200 ab. Maybe you've got one hell of a fast barrel..he he
I dont think my chrony was off. When I saw 3400 fps I stopped and shot my .357 sig through it just to make sure it was displaying close to accurate numbers. When i shot the pistol it showed 1410 fps which is right on.

Today I will try the Magnum powder again, but at 96 grains instead of 98. I will also try RL25 and Retumbo.

Wish me luck.

I know it was on because I have used my chrony while shooting my pistol several times and before I purchased my chrony I would use my buddies with the same velocity. Unless, both chronies are off and the bullet manufactures posted data is wrong, then I guess your implication is right. I don't know if its right on :)
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