Need help troubleshooting 300 RUM pressure issue.

[MontanaRifleman]

Your 300 RUM is being a real fuss-bucket. Seems like you've covered all of the more common possible causes. You're getting such an extreme increase in pressure with repetitive firings that the causes I've experienced in the past wouldn't even account for it.

Since the pressure is quite consistently increasing with each additional round fired after starting with a clean bore, I can't help but conclude that something is layering onto the bore with each additional shot fired that's restricting the bore or increasing bullet/bore friction and creating elevated pressures. But I've not experienced anything like this before, let alone heard of anything of the kind. So while this rationale seems the most likely cause, I have no explanation or recommendation.

Nitriding should reduce bore/bullet friction rather than be any cause of increased friction. You've already put quite a few rounds down the bore for me to think it's got anything to do with residue from the nitride bath. Hope you're able to determine the cause. Or if not, that the pressure variations diminish so you can get on with load development and start enjoying your rifle.

I tend to agree that since the pressure issue is a changing dynamic it must have to something to do with a changing bore condition brought about by firing the rifle. That said, these rifles are not fouling all that much. The 6-284 and 6.5 WSM take less than a dozen patches and the RUM has taken about 6 to 3 patches the last 2 times I've cleaned it. My routine is to drop a few drops of BTE down the muzzle, scrub with a nylon brush and let it soak for about 30 mi then wet patch it out until color fades. With the 6-284 and WSM, this takes about 3-4 patches per srub/soak for a total of less than a dozen patches. The last time I cleaned the RUM, the 2nd patch after after scrub/soak was pale. After the 2nd scrub/soak, the 1st patch was light colored and the 2nd patch was clean except for some trace carbon. So if the bore is changing, why so little fouling coming out? A real mystery to me.

 

[MontanaRifleman]

When the 300 rums gave me pressure trouble which was often, I switched to H50BMG and had the best results. You'll loose some velocity but to be realistic, do you really need 3200'sec from a 230? It's sexy for sure but is it needed or worth it?

I tried Retumbo and that didn't change anything... except with the 6-284 and 6.5 WSM. And then they seem to shoot well with 33 after.

Not really interested in trying another powder at this point, especially with limited components available.

Time to go do some shooting.

 

[trophyhunter1000]

What type of primer are you using? I had a problem that was just like yours in my 7mm ultra. My friend said the primer I was using was a little to cold for the load (can't remember load data) but I bumped up to a hotter primer and backed down the load and danged if it didn't cure it. My guess was that due to the primer not being hot enough with the first loads the excess powder was leaving alot of residue on the lands and in the throat thus jumping the pressure up. With every shot i took the higher the pressure would go plus th MV would steadily go up about 10 to 20 fps every round. Hope this helps.

 

[MontanaRifleman]

More good news at the range yesterday. I loaded up near max load strings in the 6-284 and 6.5 WSM for pressure/velocity and accuracy testing. That went fairly well. ES's were not great but over all very stable shooting with no pressure issues. Accuracy was so so. got one .58" group out tof the WSM. The 6-284 appears to have a scope or mounting issue.

I loaded a string of 230 Hybrids over 96 gr of RL33 for the RUM. Velocities as follows...
3061
3119
3097
3113
3071

the ES wasn't very good but when i took took the Magneto off to group them, I shot a nice .52" (.21" ctc) not so ragged hole out of the $800 nitirded crow bar.

 

[Outlaw6.0]

Well now, that ain't half bad. 100yds I'm guessing? Step that bad boy out to 300 . 1x brass or new?


t

 

[MontanaRifleman]

My analysis to date.

The 6-284 and 6.5 WSM seem to sorta "get over" whatever pressure issues they had. That said, the max loads in volume of powder are slightly lower, by maybe a couple of grains, than the original work up pressure/velocity testing, but are showing the same pressures and velocity. So no loss in velocity performance. The lower charge weights are good as they the max loads are no longer so compressed as they originally were.

In the RUM, I am seeing about equal pressure/velocity with 96 gr of RL33 as I did with 100 gr of RL33 in the original pressure/velocity testing. So something has happened in the bore to cause this and I just don't know what it is. My smith thinks i have removed about 2-3 tenths of a thou of steel from the bore with my lapping. If so, the nitride should be completely gone and would not be a factor.

Here are the 3 pressure work up strings I shot on separate days.

96.... 2937...........2988..........3017
97.... 2963...........3037..........3043
98.... 2962...........3075..........3097
99.... 3037...........-----.........3138
100.. 3105...........-----..........3182
101.. 3121...........3174.........3203 blown Primer
102.. 3162...........3186/3217 heavy bolt on 3217
103.. 3192 slightly sticky bolt

Yesterday's 96 gr velocities averaged about 3100 and are close to max. 98 grains is over max as already demonstrated with a blown primer. I will try 97 gr next and see what happens there for curiosity.

Bottom line, somewhere in the time I got these barrels back from nitriding to now, something happened inside them to change their dynamics.

 

[MontanaRifleman]

What type of primer are you using? I had a problem that was just like yours in my 7mm ultra. My friend said the primer I was using was a little to cold for the load (can't remember load data) but I bumped up to a hotter primer and backed down the load and danged if it didn't cure it. My guess was that due to the primer not being hot enough with the first loads the excess powder was leaving alot of residue on the lands and in the throat thus jumping the pressure up. With every shot i took the higher the pressure would go plus th MV would steadily go up about 10 to 20 fps every round. Hope this helps.

Thanks for the input Trophyhunter. I have alwayss used 215's for the RUM cartridge and they have always worked well. Something else is going on here and still not sure what it is. But at least it looks like I'll be able to work with it.

 

[MontanaRifleman]

Well now, that ain't half bad. 100yds I'm guessing? Step that bad boy out to 300 . 1x brass or new?


t

Well Tyler, I wish I could say that was my 300 yd group but you guessed right... 100

I can live with it, but I'm going to fool around with 97 gr and see what happens.

It is abused 2-3 fired RP brass that I annealed about 2 firings ago.

Yeah, I'll step it out if I get a calm day around here. They are few and far between in this country this time of year.

 

[Outlaw6.0]

....
Yeah, I'll step it out if I get a calm day around here. They are few and far between in this country this time of year.

You're preachin' to the choir brother.... i'm already tired of it.


t

 

[MontanaRifleman]

Well now, that ain't half bad. 100yds I'm guessing? Step that bad boy out to 300 . 1x brass or new?


t

Here ya go... had a nice day yesterday and shot these groups. I actually shot the 326 yd group first thinking I was on the 212 yd target The 427 yd group was the third group... put a smile on my face This is with the 96 gr load.

No more pressure "issues", other than the charge weights are low for the pressure/velocities I am seeing. Based on the results of my initial pressure testing and others results, I believe I am about 4 gr lower on average than what I would consider as "normal" pressure range for charge weight.

Fooled around with the 97 grain load on Sat and accuracy was about .5 - .7 MOA from @ 212, 326 and 427 yds and felt I was flirting with high pressure. So I backed it back down to 96 with good results.

 

[IdahoRedneck]

Im getting ready to play with the 230 in my ultra......factory sendero barrel..........how long is your barrel im sure I missed it, where would you start with retumbo.........I may have a line on some re 33 but for now all I have is retumbo and H1000, what kind of velocity could I expect................sorry for the quick hijack buddy but youve been playin around with this combo quite a bit and couldnt think of anyone better to ask

 

[varmintH8R]

Here ya go... had a nice day yesterday and shot these groups. I actually shot the 326 yd group first thinking I was on the 212 yd target The 427 yd group was the third group... put a smile on my face This is with the 96 gr load.

No more pressure "issues", other than the charge weights are low for the pressure/velocities I am seeing. Based on the results of my initial pressure testing and others results, I believe I am about 4 gr lower on average than what I would consider as "normal" pressure range for charge weight.

Fooled around with the 97 grain load on Sat and accuracy was about .5 - .7 MOA from @ 212, 326 and 427 yds and felt I was flirting with high pressure. So I backed it back down to 96 with good results.

That 427 group is something! You're more honest than me, I would have wrote the data in REALLY BIG HANDWRITING. . Not that you need to make it look any smaller anyway!

I'm glad you got it shooting, if at lower charge weights than you would expect. Have a final hypothesis on what caused this on 3 different rifles?

Brandon

 

[MontanaRifleman]

Im getting ready to play with the 230 in my ultra......factory sendero barrel..........how long is your barrel im sure I missed it, where would you start with retumbo.........I may have a line on some re 33 but for now all I have is retumbo and H1000, what kind of velocity could I expect................sorry for the quick hijack buddy but youve been playin around with this combo quite a bit and couldnt think of anyone better to ask

Dan, I haven't tried Retumbo with the 230's because I believe that 33 is the go to powder for the heavies in the 300 RUM. That said, I have read some members using about 89 gr of Retumbo with the 230's. Try the google search, you'll find some threads on it.

I'm shooting a 27" tube.

 

[MontanaRifleman]

I'm glad you got it shooting, if at lower charge weights than you would expect. Have a final hypothesis on what caused this on 3 different rifles?

Brandon

Brandon, Not really sure what the deal is. In the other two rifles, charges are closer to what I would consider normal range, maybe 1-2% lower whereas the RUM is about 4% lower.