Need help troubleshooting 300 RUM pressure issue.

[Erik Kiser]

My 338 Edge developed a carbon ring that had pressures sky high for no apparent reason. Even to the point of blowing a primer with a reasonable load. A borescope would tell you a lot

 

[bigngreen]

I think I would attack that thing with some abrasive cleaner from the throat to about 6-8 inches, I've cleaned up with just solvent and every thing was squeaky clean on the patches but the bore scope reveled carbon fowling in the first section of the bore, I hit it with some abrasive cleaner and broke the glazing and hit it with carbon solvent and the patches come out like caked coal dust.

 

[MontanaRifleman]

Mark,

I had two different custom 300 RUM barrels do the exact same thing. Both started doing it early in their life and one did it less than 70 rounds. It seemed like every time I pulled the trigger the velocity went up and the bolt got stickier. I kept backing off charges and velocities still went up. I fought and fought with it for a couple hundred rounds and it settled in to a point but never stopped settling down completely. After a certain point, instead of dropping charges every few rounds, I only had to drop them every 50 rounds or so. When it was all said and done, the only powder I could get to work in one was H50BMG under the 178 amax and 180 accubond. In the other I was down to 80 grains of H1000 under the 178 amax or 92 grains of H50BMG under the 208 amax. All were reduced velocities but still showed signs of fairly high pressure.

Shortly after it started happening on my second barrel, Mike Rock told me it was from severe throat erosion and severe heat checking. He said those will actually increase friction on the bullet dramatically and that is where my high pressure was coming from. A trip to the smith and look through the borescope confirmed his statements. It was bad. Really bad.

It can happen VERY fast in a barrel chambered in 300 RUM. Especially if you run top end loads. In my experience, top end loads in 300 rums even without pressure signs initially, kill barrels and fast.

I know thats not what you were hoping to hear and I hope I'm wrong but that's most likely the problem.

Factory barrels can sometimes hold up better IMHO. They're often hammer forged and subsequently very durable and so rough they can actually improve before going downhill. With a top end fine custom barrel, they have ONLY one way to go. That is downhill. You can't typically improve a good custom bore. They're their best for only one shot. That's their first. They start going downhill after that. The hotter the caliber and the harder you run them, the faster they decline. It's not at all uncommon for the 7mm RUM and 300 RUM customs to go south short of 100 rounds. I get PMs occasionally about how fast one went south. I used to preach my feelings on this matter a lot and caught a lot of flame for it here. Guys not wanting to catch flame would pm me and say yup! You were right!

In this case I truly HOPE I am wrong.

M

EDIT: I almost forgot, make sure there is no carbon ring present either. I'm just guessing here but it doesn't sound like you have enough rounds down it to be a carbon ring but a carbon ring will generate a lot of extra pressure and if not corrected quickly, can kill your barrel as well.

I really doubt this is the case Michael. During break-in I ran 25 mild rounds, 90 gr of RL33 and the 230's. Velocity was about 2700. I cleaned after each for the first fifteen than shot two 5 shot accuracy test groups before sending it to be nitrided and cleaned after the first five. I let the barrel cool between shots dutirng the test groups. I babied it because I want it in good shape for nitriding. During the load development I shot 3 strings amounting to 25 rounds. only 3 of those rounds were stout enough to produce a heavy bolt lift and most were below max. It was a cold breezy day and 1-2 min between shots while I read chronys and recorded data. The Barrel never even got warm.

I hope it's just a carbon ring but that is doubtful as well as I had only 25 rounds through it since nitriding and it got a good cleaning when I got home.

Today I'm going to polish out the chamber, neck and throat with some Iosso paste and give it another cleaning. Load up some rounds and head out to the range. Single digit temps today.

Thanks everyone for the help so far. Any other ideas welcomed.

 

[MontanaRifleman]

I think I would attack that thing with some abrasive cleaner from the throat to about 6-8 inches, I've cleaned up with just solvent and every thing was squeaky clean on the patches but the bore scope reveled carbon fowling in the first section of the bore, I hit it with some abrasive cleaner and broke the glazing and hit it with carbon solvent and the patches come out like caked coal dust.

Doing it as we type. Just loaded another workup string starting @ 96 gr.

 

[Michael Eichele]

Doing it as we type. Just loaded another workup string starting @ 96 gr.

Mark,

Please keep us posted as to your results and your progress.

I normally don't hope to be wrong for pride's sake, but this is a case where I hope I'm wrong.

 

[MontanaRifleman]

OK, so here is the latest... good news and not so good news.

Gave the RUM a good BTE cleaning and IOSSO scrubbing and loaded up some rounds. Got to the range with the 3 rifles and started with the 300 RUM. I started with the workup string i did last week, starting with 96 gr and worked up to 102. Data listied below. It went well and after 6 shots, the last being 102 gr, It appeared I was almost back to "normal". there was no pressure signs with 102 charge and velocity was very close, but just a little higher than the first go around last week.

Today's velocity readings were generally higher. Temp was colder... 7 vs 23

RL33/230 Hybrids

....Last Week..Today
96...2937......2988
97...2963......3037
98...2962......3025
99...3037......3056
100..3105.....no reading
101..3121.....3174
102..3162.....3186 - no pressure sings
103..3192.....---- slight bolt lift @ 103/3192

Then I shot a short RL17/GSC 177 string

....Last Week..Today
88...3424.....-----
89...3429.....3385 (possibly a bad reading)
90...3479.....3538 no pressure signs
91...------......3599 blown primer

Hmmmm... form no pressure signs @ 90 to spike in pressure and velocity @ 91

Note: I have noticed that RL17 tends to spike very rapidly in large overbore cases. I only used it the the 300 RUM because GSC bullets tend to be lower pressure bore riding type bullets and it was in a nitrided barrel which is also "supposed" to reduce pressure.

After the RL117/GSC 177 string, I shot another 102/230 Hybrid load because I was sensing a gradual increasing rate of pressure. Sure enough, velocity was 3217, but there was no apparent sign of excess pressure.

Then I ran a Retumbo/180 C21 CEB string

....Last Week..Today
96...-----.......3371
97...3376.....3415
98...3401.....3445
99...3472.....3494 today's showed no pressure signs
100..3506....3533 last weeks load resulted in a slight blot lift, today's load blew a primer
101..3530....----- last weeks load blew a primer

The trend developing here is higher pressure and velocities with same charge. I decided to shoot one more 102/230 Hybrid load to confirm my suspicion,that the more rounds I sent throught the barrel, the more pressure it was generating. Third round of 102 RL33/230 Hybrid resulted in a velocity of 3550 and a blown primer.

Something is going on inside the camber and/or bore.

More interesting data form the other 2 rifles in the next post.

 

[MontanaRifleman]

I also continued load development with the other 2 rifles, 6-284 and 6.5 WSM.

Results from the 6.5 WSM... the load was 74 gr of RL33 and 140 VLD's. Last weeks single round velocity was 3346

First 5

3373
3373
3369
3373
3376

The next 3

3387
3401
3441

As you can see, the first 5 were about as good as it gets for ES, then, pressure and velocity begin to increase.

6-284, 64 gr RL33, 105 Hybrids, without typing it all out, they were all over the place from 3503 to 3579... not sure what that's all about but it was an extremely compressed load with powder filling the case literally to the top of the neck. Last weeks 64 gr single round velocity was 3476

64 RL33/100 CEB's

3573
3576
3599
3589
3623

There seems to be a clear trend of both higher velocities than last weeks workups and increasing velocities and pressures as rounds are fired.

I do not think it's the powder because it's happening with Retumbo and RL17 as well.

The biggest common denominator is the nitrided barrels. When I got them back, I scrubbed them for a while to remove a dark brownish residue. I never got all of it out, but I read if i got most of it out and fired a couple rounds and cleaned after that it would be good to go. Now I am wondering if this is the problem. I had called H&M last week to find out more about this residue and they said it was a ferrous oxide which is what the black finish was. They did not seem to be too concerned about it and said it contributed to the corrosion resistance of the black nitride treatment.

Now, I don't know if that is what is causing my increased pressures, but it's a big maybe. Maybe I need to scrub a little more?

 

[Michael Eichele]

Mark,

I wouldn't do anything more until you borescope them. Period. I might give them a 'normal' cleaning first so you can see the details of the bore.

I'd hold off on the 'scrubbing' till after you look. You can make matters worse by scrubbing with abrasives too much and it doesn't take much to be too much. Take it from a guy who has ruined the best of many barrels in record time.

How many rounds do you have through the 300?

 

[MontanaRifleman]

Mark,

I wouldn't do anything more until you borescope them. Period. I might give them a 'normal' cleaning first so you can see the details of the bore.

I'd hold off on the 'scrubbing' till after you look. You can make matters worse by scrubbing with abrasives too much and it doesn't take much to be too much. Take it from a guy who has ruined the best of many barrels in record time.

How many rounds do you have through the 300?

Michael, I agree, I will not clean them at all until they are scoped. I want to see them, or have them looked at in their current condition.

I'm not too concerned about scrubbing them with mild abrasives. The surface steel is close to 75 Rockwell hardness and is almost bullet proof. I'll talk to H&M more about it and get their opinion.

 

[Michael Eichele]

Michael, I agree, I will not clean them at all until they are scoped. I want to see them, or have them looked at in their current condition.

I'm not too concerned about scrubbing them with mild abrasives. The surface steel is close to 75 Rockwell hardness and is almost bullet proof. I'll talk to H&M more about it and get their opinion.

What do you consider a 'mild' abrasive?

 

[MontanaRifleman]

What do you consider a 'mild' abrasive?

Montana Xtreme Copper Cream.... IOSSO....?

 

[bigngreen]

There was a specific cleaning routine and break in that someone had who ran quite a few nitrided barrels and if I remember right is was pretty involved but I don't know if I can find it again.

Blowing primers is not cool, especially when you consider the chamberings your shooting.

What did you do with the barrel prior to nitriding, did you break it in at all, did the smith lap the throat or just send it in as cut?

 

[Michael Eichele]

Montana Xtreme Copper Cream.... IOSSO....?

I've never used IOSSO so I won't comment. I've used a ton of JB and a little bit if Copper Cream. I have noticed Copper Cream if used too much acts like JB in 'polishing' the bore. I've been using it a little bit in a new bartlein barrel and have noticed the slight 'polished' streaks on the very edge of a couple of the lands developing. I'm done with the break in and much of the development is done so I'm done using any abrasives for a few hundred rounds now.

These cleaners take little effort to polish the surface of the bores and once you get the ball rolling, they polish even easier. 75RC or not. These really are a double edge sword. You need them for the worst carbon buildups but they polish the surface which causes copper fouling. Whatever the barrel maker does to get the finish to the right texture gets quickly destroyed. Basically, too much (a little) is like taking a frosted peice of glass and turning into a mirror.

I've in just a handful if cleanings taken barrels that showed virtually no copper fouling and turned them into serious copper magnets with abrasives.

Use sparingly.

 

[MontanaRifleman]

There was a specific cleaning routine and break in that someone had who ran quite a few nitrided barrels and if I remember right is was pretty involved but I don't know if I can find it again.

Blowing primers is not cool, especially when you consider the chamberings your shooting.

What did you do with the barrel prior to nitriding, did you break it in at all, did the smith lap the throat or just send it in as cut?

Outlaw sent me a copy of a cleaning routine which I modified a little... used PB Blaster instead of soapy water, then finished with IOSSO, probably a total of 5 scrubbings of PB Blaster and IOSSO with about a dozen wet patches between.

Yeah, blowing primers is not cool. In each case it came after no pressure signs, but I usually had the feeling I was on the edge.

I broke in each barrel, one shot and clean and followed with a couple of accuracy check groups, with light loads. the last couple of cleanings on each barrel, I used Montana Xtreme Copper Cream to scrub and polish a little and make sure I was getting all the carbon out. H&M also has a process to make sure the bores are clean.