Author Topic: high pressure signs (Read 1139 times)

gdolby · « **on:** February 11, 2004, 07:14:15 PM »

good day, my question revolves around a load I have developed for my 7 mm. I have used CCI primers, 63.5 grains/ IMR 4831 and 150 GR Nosler partitions for 2 years. When I shot last time I had pressure signs where I used to didnt. The only thing that changed was the lot # on my powder could that make that big of difference? thank you and enjoy reading all the forums and replies....B

KN · « **Reply #1 on:** February 11, 2004, 08:04:06 PM »

If your up near max it could make a difference. What about temperature? A real hot day will cause preasure to rise. KN

HL · « **Reply #2 on:** February 12, 2004, 01:54:17 AM »

When ever you change components, always work your load back up to where you had it. Each lot has a slightly different burn rate, not much, but enough to cause problems when near max. as stated above.

gdolby · « **Reply #3 on:** February 12, 2004, 08:00:23 AM »

thank you for your interest and time. Im new to reloading so I have a lot to learn. both KN and HL made the reference of being close to max . Max is 65 grains and Im at 63.5. Am I really that close? Far as temperature goes I worked this load in 98 to a 103 degree weather in the mo of aug and july. My problems have shown up in 50 degree and below
Thank you both and I want to thank everybody on this forum because I have finally found a use for this computer

ricciardelli · « **Reply #4 on:** February 12, 2004, 10:31:33 AM »

Different lot numbers can vary up to +/- 5%.

Thomas Krupinski · « **Reply #5 on:** February 12, 2004, 12:22:00 PM »

Quote from: gdolby

Max is 65 grains and Im at 63.5. Am I really that close?

Don't hold the published data as gospel, only as suggestions. Different lots of powder, primers and different case and capacities will make a difference.

Besides your most accurate loads, what you are really striving for anyway are usually not nearly at maximum.

T/C nimrod · « **Reply #6 on:** February 13, 2004, 03:26:03 AM »

What pressure signs are you noticing that you didn't before? As was mentioned above, powder lots (or any component lot differences for that matter) will change your operating charateristics - Hence the statement you've seen everywhere "Reduce by 10% when changing components".
Remember, as Thomas K. pointed out, every gun is different - what is max load in yours may not be in the next fellows rig.

Are you loading to the same oal(col) as before?

How fast are you shooting in the cooler temps. compared to the warmer temps.? If your chamber temperature is higher due to faster shooting (less time between shots), that may be affecting what you are seeing.

Just out of sheer curiousity - did you see a lower point of impact during your 50 degree ambient shooting, or did it impact higher then when it was in the 90 degree ambient?

gdolby · « **Reply #7 on:** February 13, 2004, 06:37:30 AM »

good day sir. The pressure signs I'm noticing are mainly w/ my primer-ridge around firing pin depression /bolt face marks and a minimal degree of flowing. I am keeping my same AOL. My firing cadence was the same/chamber one-fire-eject -chamber. Funny that you mention it but i did see POI change. Lower Thank you for your time sir. P.S...Thank you also Mr Krupinski. you all have a good day

BruceP · « **Reply #8 on:** February 13, 2004, 04:14:25 PM »

The only thing I might add is how many loadings does the brass have on it and have you measured the length of the brass. If you have either fired it enough for it to lengthen or stretched it during resizing. (It can be done if the inside of the neck is not lubricated) Then you might need to trim the cases. If they are to long for your chamber then they won't release the bullet properly and will increase pressures.
BruceP

ButlerFord45 · « **Reply #9 on:** February 14, 2004, 03:11:59 AM »

From the information avaiable it is starting to sound like BruceP has hit the nail on the head. Would you measure one of your stressed case lengths?
You didn't mention which 7mm, but the load sounds like a 7mm Rem Mag so that's where I peeked in my Nosler manual(an old manual kept for reference) and your load is in the middle of the range for this powder and bullet. I looked in my new sierra manual and their max for imr-4831 and 150 grain bullet is 61.9 grains. While some may say something about this being apples and oranges, I contend the they are both still fruit. Hopefully manufacturers have made improvements in the quality of their products in the last few years which could account for some increase, so I guess my next question would be: How old is your loading manual?

gdolby · « **Reply #10 on:** February 15, 2004, 07:57:53 PM »

good day sir. I have 4 firings on these cases. from the first firing I have kept them trimmed. I have also lubed and chamfered between each loading. thank you for your time. shoot straight. B

gdolby · « **Reply #11 on:** February 15, 2004, 08:02:40 PM »

good day sir. I measured the 3 that cracked and the most was right at a thousandth over. the other 2 were at half(roughly). the manual im going by is noslers 5th edition. Which to my understanding is their most recent. Thank you for your time. shoot straight. B

Iowegan · « **Reply #12 on:** February 16, 2004, 01:34:43 PM »

Your rate of fire has a giant effect on pressure. First, all powder burns faster when the temperature increases. A faster burn rate will increase chamber pressure. The outside temperature is not nearly as important as the chamber temperature. The brass cases conduct heat very well and transfer that heat to the powder. As your chamber and barrel heat up, there can be as much as 100 degree difference from unfired to fired. Try placing your hand on the barrel if you are a non-believer. Second, as the barrel heats up, it expands in all directions. The bore diameter will shrink a little on a hot barrel causing pressure to increase. Last is the chamber. Again, heat will shrink the internal dimensions a little and will increase chamber pressure.

I worked up a very accurate load for my 22-250 using an IMR 4831 powder. I did as recommended and waited a good 5 minutes between shots as I was shooting test groups. There were no signs of overpressure. Later, I took the gun out prairiedoggin' and got into some hot and heavy shooting. I noticed my cases were getting harder to extract and the primer dents were puffed and flowed to where they looked like they had never been fired. Obvious pressure issue. When I got home, I was able to replicate the problem. I changed powder to Varget and tried again. This time the pressure stayed under control. My velocities increased over 200 fps with the IMR and only 40 fps with the Varget after 5 rapid fire shots. Also, 36 gr of Varget with a 55 gr Ballistic tip was just as accurate as the IMR loads.

Varget was designed as an extreme powder (meaning temperature extremes). Pressure does rise with heat but only a fraction as much as IMR 4831. I've never tried it in extreme cold weather but Hodgdon says it performs better and ignites more uniform than most other powders at sub-zero temps. I have tried my loads at 10 degrees and they were about 30 fps slower than at 70 degrees.

The moral of the story is: If you are going to be shooting rapid fire, leave your ammo in direct sun, or other temperature extremes, go with a powder that is rated extreme.

gdolby · « **Reply #13 on:** February 22, 2004, 10:34:40 AM »

thank you for your interest and time. good day and shoot straight

hogship · « **Reply #14 on:** March 07, 2004, 06:36:44 AM »

Quote from: Iowegan

Second, as the barrel heats up, it expands in all directions. The bore diameter will shrink a little on a hot barrel causing pressure to increase. Last is the chamber. Again, heat will shrink the internal dimensions a little and will increase chamber pressure.

Iowegan.....

I'm having some trouble understanding how the bore diameter will get smaller when the barrel gets larger, due to heat expansion. It sure seems like it should be the other way around, but I've been known to be wrong about things before......!

I wonder if you'd shed a little more light on the concept.

hogship

hogship · « **Reply #15 on:** March 09, 2004, 12:58:39 AM »

Answering my own question.....

In theory, a 1/4x1x12 piece of steel will expand on the top, as well as on the bottom. If you took the same piece of stock and bent it into a tube, it would expand in the inside, as well as the outside.

I think I understand, now.

Never really gave that one any consideration before!

hoghsip

Iowegan · « **Reply #16 on:** March 09, 2004, 09:07:55 AM »

Hogship, You figured it out perfect. Most shooters think the bore will get bigger when it expands. As you stated, it doesn't. Depending on the thickness of the barrel (and chamber), the bore can easily shrink .001". That doesn't sound like much but if the ammo is loaded near max, it might be enough for over pressure conditions.

Most shooters don't have a ballistics lab handy to prove this but they might have a chronograph available. As chamber pressure increases, velocity will increase (assuming same load). Compare a "cold barrel" reading to a reading after 5 shots have been fired in 1 minute. The velocity will go up considerably with the hot barrel.

gdolby · « **Reply #17 on:** March 10, 2004, 05:39:38 PM »

good day sir, glad to see my question is still causing discussion. what your saying makes sense and no doubt is true. But the round that got me to paying attention to my brass was the first one of the day. I cracked 2 more and went home and started pulling bullets and weighing powder. Out of the 3 the very first was the most damaged. but that could have been due to to having been stuck in the chamber and being forced out w/ a cleaning rod. thank you and enjoying the comments you all have a goodun B

PaulS · « **Reply #18 on:** March 11, 2004, 06:31:46 PM »

Ok there is some bad information being passed around.

If you heat a steel cylinder the bore gets bigger - the expanding metal grows in circumfrance and does NOT compress inward. If you are performing an interferance fit (slug and cylinder) you cool the slug and heat the cylinder - slide them together and let the temperature equalize. When it does the two pieces become one. The inside diameter of the bore of the rifle will increase in diameter with heat, lowering pressure. On the other hand the same heat will transfer to the load when chambered and cause an increase in pressure. The warm powder will likely produce more pressure that the barrel lowers it causing a net increase in pressure. The new lot of powder could affect the pressure more than either with close to maximum loads.

PaulS

hogship · « **Reply #19 on:** March 11, 2004, 07:30:01 PM »

PaulS....

As stated previously, I've never really considered this before....so I don't really care what the truth it.....I'm doing nothing more than exploring possibilities. Paul, from the start, I would have been on the same page as you, but now I'm not so sure.

PaulS said: "If you heat a steel cylinder the bore gets bigger....."

In the spirit of discussion, not debate, I understand and agree with your thinking on this, when considering a cylinder......but, we are not discussing a cylinder. We are discussing a tube.

As Iowegan said, "the barrel will expand in all directions". With a cylinder the metal cannot expand toward the center without compressing metal at the center, but with a tube the story is entirely different.... Since a tube is hollow there is room to "expand" toward the center, since there is nothing there.

Besides that, the heat source is generated in the interior surface of the tube and transfers from that point outward. Generating the heat at the center represents an impossibility, when considering a cylinder. Because of that, with a tube, heat cannot cause the metal to expand on the cooler exterior surface of the tube at the same rate as the interior surface without compressing metal in a reverse fashion (compared to what happens with the cylinder).....at least until the temperature stabilizes between the inside and outside surfaces of the tube. At that point the tendency for the bore to expand could be circumvented by the opposite tendency for the bore to contract.....the only way to know for sure is to conduct a scientific experiment in a controlled environnment, where the bore size is measured in concordance with the effects of heat generated in the same way that a bullet passing throught the barrel does.

At this point, I tend to agree with Iowegan, but without research conducted, which imitates the exact set of circumstances that would be needed for conclusive evidence......all is speculation.

For that research to happen, you'd need an actual barrel, shooting actual bullets, generating friction heat on the interior surface of the barrel......and a method of measuring the bore diameter whithout the heat, itself, effecting the instrument of measurment transfer....ie: "slugging the barrel". It would have to be a true reading taken directly on the bore diameter, not a lead ball which would, in turn, be effected by the heat on itself.

hogship

Badnews Bob · « **Reply #20 on:** March 11, 2004, 09:30:48 PM »

Hey fellers Paul s is right metal cylinders always expand out, They can't shrink the circle it would push against itself. Thats why you can stand on a tube and not crush it. And think about this... when you change the ring gear on alot of flywheels and such you heat the ring gear up and it will fall right off the flywheel you the let things cool down set the new ring gear on the flywheel and heat the gear up and it falls right into place on the flywheel. When it cools you can't remove the ring, all that holds it on the flywheel is the constriction from shrinking. I've done this alot and know it to be true. Good day. :wink:

hogship · « **Reply #21 on:** March 12, 2004, 01:11:07 AM »

Hmmmmm.......

On the surface, that sounds reasonable, too, Badnews Bob.....

There could be some differences in comparing the two because of the point source of the heat caused by friction, and overall heating of the entire object in an oven. A barrel heats from the interrior outward, and the flywheel ring would be heated over the entire surface equally. If you heated a barrel in an oven, I'd have to agree, but there are differences to consider here regarding the source of the heat.....

"Besides that, the heat source is generated in the interior surface of the tube and transfers from that point outward. Generating the heat at the center represents an impossibility, when considering a cylinder. Because of that, with a tube, heat cannot cause the metal to expand on the cooler exterior surface of the tube at the same rate as the interior surface without compressing metal in a reverse fashion (compared to what happens with the cylinder).....at least until the temperature stabilizes between the inside and outside surfaces of the tube. At that point the tendency for the bore to expand could be circumvented by the opposite tendency for the bore to contract.....the only way to know for sure is to conduct a scientific experiment in a controlled environnment, where the bore size is measured in concordance with the effects of heat generated in the same way that a bullet passing throught the barrel does.
"

Like I said before, I am only speculating. It doesn't make any difference to me......what is, is! My reloading efforts don't revolve around knowing the answer to this one. I'd still be able to find my way around town if I thought the world was flat, too!

Got any input on that, Iowegan? Where did you get your information on the bore shrinking in the first place?

hogship

HL · « **Reply #22 on:** March 12, 2004, 02:14:41 AM »

What Paul stated is correct. One way to see this is with stress and pressure diagrams for various metal configurations, ie cylinders, bars, tubes etc.

If a barrel expanded inward, a barrel would collapse when overheated, but that does not happen. When a barrel is continued to be fired after being heated too much, the groups of bullets become erratic due to the bore enlarging and not stabilizing the bullets as it did with normal operating temps.

hogship · « **Reply #23 on:** March 12, 2004, 09:17:26 AM »

Let's try this from another angle....

Suppose you had a piece of 8"x8" steel 1" thick.

If you take a "rosebud" tip and heated one side of the steel plate squarely in the middle, would the metal expand toward the source of the heat......or, would it expand toward the unheated side of the plate?

Well, the answer is that it would expand toward the source of the heat, since it cannot do so against the other side of the plate which has not yet been influenced by the heat.

This is the issue that a few of you are not considering, or addressing......the point source of the heat, and unequal heating of the inner and outer surfaces of the barrel.

I'm sure both HL's and BN Bob's examples are the results of heating objects in an oven, where all sides of the test samples are heated equally on all sides. When a barrel heats up, the source of the heat begins, and is sustained, from ONLY one source point......the inside of the barrel.

I don't know this to be fact, but I am assuming that, at some point, the outward expansion will overcome any initial contraction of the bore, but only after inside and outside temperatures are roughly equal to one another.

Still, I'd like to hear from Iowegan and his source for this information.

hogship