Too much pressure in the 300 RUM?

[Alucard]

Hey guys, I have a question about pressure in the 300 RUM. I am loading 169.5 RBBT HP Wildcat bullet with a charge of 100.0 gr of Retumbo. I use Fed 215 Match primers. The cart overall length is 3.630" in my gun. I have a Rem 700 Police.

With this load, I have noticed that the primers are just slightly starting to crater. I can start to see the firing pin mark starting to make a raised crater. The primers do not seem to be flattening out, just cratering slightly. I shoot 1/4" 4 shot groups at 100 yards with this load.

Is this a sign of too much pressure? Or are the primers of softer materials and this is nothing to concern myself with? Thanks.

 

[Brent]

I would consider it a max load, or slightly over. It does depend on the firing pin to bore fit and you may be alright if it's just a sloppy fit, or conversely, you could be really hot if it's a tight clearance.

I would pay real close attention to ALL of the pressure indicators, like heavy bolt lift, difficult extraction, prominant ejector marks, primer pocket life.

I get to about 100gr Retumbo with a 178 A-Max and consider this a top load "in my rifle".

 

[1doug]

Hodgon states 103 as max charge for 165 grain bullets. However each rifle is diferent. 100 grain of retumbo should be a compressed load. This might cause some problems.

 

[Alucard]

I don't have much for the other signs of pressure. The bolt seems to open no problem, not stiff or sticking, the cases aren't buldged anywhere. There are some marks from the extractor, but nothing too major. I am sorry, but I don't know anything about the primer pocket life, so I can't say anything on that one.

d-a
I would assume that the load is compressed, but I have the bullets seated quite long, so there is still alittle more room in the case /ubbthreads/images/graemlins/wink.gif

Should I back this load off? The only reason that I am shooting this one is because it gives 1/4" 4 shot groups at 100 yards. It is a maximum load according to Seirra's latest manual. The minimum load shots great about - 1/2" to 5/8" 4 shot groups at 100 yards, but not as good. Also, the primers in that load do not seem to be cratering.

 

[CAM]

Alucard
I don't shot a 300 rum
But please watch the conditions that you worked up the load in and remember conditions change!
A max load at 32deg might be DEADLY at 100deg
to give up 1/8" for safety is a small price!
Good luck and have fun and be careful /ubbthreads/images/graemlins/smile.gif

CAM

 

[3sixbits]

Alucard: The best way to check for pressure for most of us is by case head expansion. Primers are a vary poor indicator of pressure and can not be relied on. Bolt lift is a good indicator as long as you can remember how the bolt closed before firing ie. high primer? Flattened primers, was the shoulder pushed back when you sized? Neck clearance with bullet seated this changes as the necks thicken with firings and with varying bullet dia. This is why the best way I know of is to go by case head expansion. This is a vary good way to eliminate lots of variables. What may be a safe load in your barrel might take another rifle apart. /ubbthreads/images/graemlins/wink.gif

 

[Alucard]

Thanks for the info guys. I did test the load in only +4 degrees Celcius. Might not be the greatest thing to do. Yeah, I think that I will cut the load back and save some problems. No need to damage a rifle for 1/8" more of accuracy /ubbthreads/images/graemlins/wink.gif Thanks again for the advice!

 

[Mysticplayer]

The other 'best' way to monitor pressure is with a chrony. If the velocities are within reason, odds are pressures are too. If you are way above (say over 5%), you can bet pressures are toasty.

With regards to primer pocket life, if your pockets get loose in under 4 reloads, your loads are very toasty. That is where I was running my RUM. Dropped loads a bunch and now am on my 7th reload with no issue. Primers looked the same after firing so don't really pay much attention to that anymore.

I also neck size so bolt lift will get harder all on its own. Again not that accurate of an indicator unless you need to hammer it open, then...

I shoot in BC so know all about the cold weather. Nice thing you are using Retumbo. It should not vary much when temps go up to +30C. Always start low and verify but I have shot the same loads in some very hot weather with little change either in POI or accuracy.

Enjoy...

Jerry

 

[3sixbits]

The main problem with using a chronograph to use as a pressure indicator is as the velocity drops off in an overload the pressure goes up. Where does this leave us? Is the cure to add more powder as the chronograph's readings indicate? It only gets worse as the pressure goes up, the velocity will continue to go down. Have any doubts? Call and talk to your chronographs manufacturer and seek technical assistance. I believe you will be surprised. /ubbthreads/images/graemlins/blush.gif

 

[rost495]

Is there any argument over the ejector marks? I've not seen ejector marks in any 223 case from the AR unless it had significant pressure. IE I don't think there is any question that ejector marks are a sure sign of a warm load?

 

[Fotis]

What about case head expansion?

 

[Alucard]

As far as case head expansion goes, everything looks fine. By the way, how would I be able to tell if the case head is expanding too much? I am new to the game of large cartridge reloading, and just recently started refining my techniques for better ammo. Thanks.

 

[3sixbits]

This method of head expansion has been in use by the shooting public for several decades and was introduced to the shooting public by Ken Waters. His method requires a 0-1" mic (the ability to read the tool) and pen & paper. Using the case head expansion method. A measurement of the sized and loaded ctg is taken before the area of the rim or rimless or belt. You list this reading in your notes, fire the ctg. and again measure as before. If the head expansion is in excess of .0003 you have exceeded the limits of safe pressure. Ken Waters was perhaps the greatest firearms writer of the last half of the 20th century. His book "PET LOADS" has the most prominent spot in my own library. His articles in HandLoader mag were perhaps the best I have ever read on the practical side of re-loading. Yes he had the ability to write in the clearest and most comprehensible manner of any author it has been my experience to have read. I recommend to all his writings!

 

[Alucard]

Oh ok, thanks 3sixbits. I have some sized cases on my reloading bench, and I still have the cases in question to the pressure. I will have to check that out when I get a chance. Thanks!