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The first sign of excessive pressure is...

 
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  #22  
Old 05-31-2009, 03:18 PM
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Re: The first sign of excessive pressure is...

Youre welcome.

I was fortunate enough to have pulled my hair out with a smaller caliber that didnt eat my barrel up while I was trying to figure out what the he!! was going on.

I have actually done side by side comparisions for accuracy AND point of impact using two loads that I trust implicitly using the exact same powder but a different bullet type of the same or similar weight and two loads of the same bullet yet different powder. The results were very suprising.

For example, with my old 308 barrel, I had a 155 AMAX load of 42.5 grains of BENCHMARK and a 150 ACCUBOND load using the exact same charge weight and powder. Both loads from a clean barrel and fouled with one shot would shoot a very concistent 1/2 MOA. The POI was a bit different for each one. When I fouled with one or the other, it didnt matter which one I started with and shot a few more, then switched to the other bullet, the accuracy suffered quite a bit for a few shots then sometimes settled down. Whether or not it settled down depended on which bullet I started with. If I started with the AMAX, the ACCUBONDS would suck for a while and then settle in but if I started with the ACCUBONDS and switched to the AMAX, the AMAX never would settle in to normal levels. It is however way worse when you change powders. I have done ladder tests with one powder then switched to another using the same bullet and NOT cleaning only to come up with a "good" load, go home scrub her out, load more, go back to the range and never be able to duplicate the results without shooting 10 rounds of the load with the other powder.

I have read in magazines years ago that it didnt matter what you fouled with, just foul with 2 or three rounds of whatever and go hunting. I have never heard such bad advice as this. This is also why it took me a while to figure it out as I had bad info in my head.
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Quote:
Originally Posted by Broz View Post
Please just answer one very simple question. Why would anyone shooting long range load a low BC , low SD 168 gr offering in a 300 win???????

My answer to this is. The only reason is to make the 7 RM look good. There is no other reason.

Jeff.
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  #23  
Old 06-01-2009, 10:29 PM
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Re: The first sign of excessive pressure is...

OK guys, once again I am not near the experienced handloader that many in this forum are. But I have to ask some questions about using velocity as your primary indicator of pressure.

1) How do you know how accurate your chrony velocities are?

2) If you are going to go by "published" data/velocites then what affect does using different primers, brass and/or seating depth have on the velocity?

3) How different is the chanber, throat and bore of your rifle compared to the manufacturer's test rifle? Chamber, throat and bore dimensions can affect pressure which can and often are different from rifle to rifle.

4) Different rifles will shoot the exact same ammo out of the same box or handload batch at different velocities.

5) What about the case where two members here have reported getting 100-150 less fps while being at or over the "book" max in grains?

6) Not all data matches. If you visit the Nosler and Hodgdon sites and check the data for 300 RUM/200 gr AB using IMR 7828, you will find a huge difference in their data.

Hodgdon max -82.0gr/2857 fps
Nosler max - 87.5 gr/3102 fps

Now that is a huge difference. The Hodgdom max is lower than the Nosler starting load. Which is right?

Also, if you check the Hodgdon site for the 300 RUM/Retumbo/200 AB you will see that they list 95.5 gr as max with a velocity of 3048, and I have read numerous posts in here with members getting 3200 or more with that load.

Finally, there are many cartridge/bullet/powder combinations for which there is no data - how do you determine max for those combinations?

IMO, if you are going to go by the "book" data then you need to go by ALL of it. Same primers, same brass, same brass dimenssions, same barrel chambering, same seating depth (COAL), etc. Once you change any of that you throw your book off because it all has an effect on pressure and velocity and then you start guesssing.

Not trying to pick a fight here with anyone, but I just dont see how any of these factors can be ignored. IMHO, the chrony can be a valuble tool but to say that it is the final or primary word on pressure I believe is a stretch.

OK, I stand braced

-MR

Last edited by MontanaRifleman; 06-02-2009 at 02:09 PM.
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  #24  
Old 06-01-2009, 11:07 PM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by MontanaRifleman View Post
OK guys, once again I amnot near the experienced handloader that many in this forum are. But I have to ask some questions about using velocity as your primary indicator of pressure.

1) How do you know how accurate your chrony velocities are?

Chronies are a guide and NOT the final authority. They may or may not be accurate but in most cases they are very close.

2) If you are going to go by "published" data/velocites then what affect does using different primers, brass and/or seating depth have on the velocity?

All these things have a large effect. Even more is different "lots" of powder can cause HUGE differences. This is why we follow the "start low" and work up rule.

3) How different is the chanber, throat and bore of your rifle compared to the manufacturer's test rifle? Chamber, throat and bore dimensions can affect pressure which can and often are different from rifle to rifle.

You are spot on here. Again, this is where the rule "start low" and work up applies.

4) Different rifles will shoot the exact same ammo out of the same box or handload batch at different velocities.

Spot on again.

4) What about the case where two members here have reported getting 100-150 less fps while being at or over the "book" max in grains?

This is simple. It is usually a number of things. Chamber specs, bore specs, powder lots, seating depth, primer choice and lot, case capacity, freebore and more. Another case of start low and work up.

5) Not all data matches. If you visit the Nosler and Hodgdon sites and check the data for 300 RUM/200 gr AB using IMR 7828, you will find a huge difference in their data.

Hodgdon max -82.0gr/2857 fps
Nosler max - 87.5 gr/3102 fps

Now that is a huge difference. The Hodgdom max is lower than the Nosler starting load. Which is right?

Both are right. That is, with each set of indavidual components used, and a given companies "conservative" factor.

Also, if you check the Hodgdon site for the 300 RUM/Retumbo/200 AB you will see that they list 95.5 gr as max with a velocity of 3048, and I have read numerous posts in here with members getting 3200 or more with that load.

Finally, there are many cartridge/bullet/powder combinations for which there is no data - how do you determine max for those combinations?

Start low, work up. When the bolt gets sticky and there are ejector marks and craters on the primer, this is IMHO just over max. Once you back off a bit, this is the "max load".



IMO, if you are going to go by the "book" data then you need to go by ALL of it. Same primers, same brass, same brass dimenssions, same barrel chambering, same seating depth (COAL), etc. Once you change any of that you throw your book off because it all has an effect on pressure and velocity and then you start guesssing.

Not trying to pick a fight here with anyone, but I just dont see how any of these factors can be ignored. IMHO, the chrony can be a valuble tool but to say that it is the final or primary word on pressure I believe is a stretch.

Exactly. Even though I use a chrony as a guide, I still dont rely on it for the end result. For example the other day I was developing loads with a new powder and the 178 AMAX. The velocities were so high and the recoil so light I though I had accidentaly loaded 155 AMAX's. This is a case where max loads far exceeded "book" max. However, with totally easy bolt lift, normal primers and NO ejector marks, the velocity isnt a real issue. It wasnt until later that I learned that the powder I was using was made for higher than normal velocities.

OK, I stand braced

-MR


No need to stand braced. You are right on the money.






.
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Quote:
Originally Posted by Broz View Post
Please just answer one very simple question. Why would anyone shooting long range load a low BC , low SD 168 gr offering in a 300 win???????

My answer to this is. The only reason is to make the 7 RM look good. There is no other reason.

Jeff.

Last edited by Michael Eichele; 06-01-2009 at 11:10 PM.
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  #25  
Old 06-02-2009, 10:31 AM
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Re: The first sign of excessive pressure is...

when we weigh charges we test our weights against check weights. When we measure distance, we test our measurements against feeler gauges and jo blocks.

My question: Is there a way to test a chrony against a known standard other than "reported velocities" and guesswork? Sure would be nice to fire a range of actual velocites over a chrony and plot the difference of actual and recorded velocity. Maybe this is overkill?
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  #26  
Old 06-02-2009, 11:10 AM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by nheninge View Post
when we weigh charges we test our weights against check weights. When we measure distance, we test our measurements against feeler gauges and jo blocks.

My question: Is there a way to test a chrony against a known standard other than "reported velocities" and guesswork? Sure would be nice to fire a range of actual velocites over a chrony and plot the difference of actual and recorded velocity. Maybe this is overkill?

This is tough. I had 2 chrony's and I thought one of them was reading too high. So I spent a lot of time trying to figure out how to verify correctness. I thought about dropping something from the top of a building through the chronograph. I could calculate the speed and see if the chrono read correctly. I decided the speed would be too slow to verify within 1% or so.

After shooting all my rifles through the new chronograph and getting readings that are completely 100% within my expectations, I started trusting my new chrono. I also shot some 22LR through the chrono and they matched what I was expecting (looked for velocity figures for the ammo on the internet).

I also verified that my drops fit my Exbal estimates when using the velocities from my new chrono.

If you figure out a good way to verify your chrono, please share your idea.

AJ
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  #27  
Old 06-02-2009, 04:32 PM
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Re: The first sign of excessive pressure is...

Michael, I agree with you completely. My questions were mostly rhetorical. Yup, always start low and work up. Question in this thread is work up to what? Work up to predetermined velocities or work up to touchy-feely signs like bolt lift and brass stress signs?

There is really no way to determine pressures without the proper equipment, so we all have our differnt techniques. I am like you... when I start to see and feel the signs I back off a little and consider that as my "max" working load.

Recently I worked up some loads in my 300 WSM with RL17 and 168 TTSX's, 180 E-Tips and 210 Bergers. There was absolutley no data (that I could find) for this combination. I got some data from an article using other 165 and 180 bullets, so I proceded to load and fire incrementaly and consrvatively until I "saw and felt" signs. The results were very surprising to me with the TTSX's and E-Tips. I loaded the E-Tips to 68 gr and that is where I first started seeing pressure signs which is what I was expecting. My velociteis were good, about 3100 which was a little higher than I expected. I first started to see pressure signs at 66 gr with the TTSX's which surprised me. A slight stiff bolt. I fired a couple at 66.5 and the bolt was a little more stiff. I decided to try one at 66 (which maybe I shouldn't have) and the bolt was very stiff with some primer cratering. That night I went back and loaded some more E-Tips at 67.5 and 68. I loaded 5 at 67.5 gr at 2.95 COAL (max mag legnth) and 5 at 3.12 COAL (about .050 off the lands) I also loaded 5 at 68 gr at 3.12 oal because I want tot conduct a little experiment to see if seating the bullet farther out would decrease pressure by increasing case space. I fired the 67.5 loads and was completely surprised to see an almost 100 fps increas from the evening before. The ones seated deeper had an average velocity of 3193 which was about 7 fps faster than the ones seated farther out. I fired just two at 68 gr. They did seem to feel like a little less pressure then the one fired the night befrore but still a slight stiff bolt.

Anyway the E-Tips which had a greater bearing surface and which were heavier allowed more powder and got higher velocities than the TTSX's. Go figure?

Interestingly, the 210 Bergers maxed at 65.5 (same as the 168 TTSX's) with a velocity of 2935. However, the Bergers shot with 66 gr of powder only showed slightly crateres primers but no stiff bolt. Very interesting.

Sorry for wandering

-MR
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  #28  
Old 06-02-2009, 05:23 PM
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Re: The first sign of excessive pressure is...

Quote:
Originally Posted by AJ Peacock View Post
After shooting all my rifles through the new chronograph and getting readings that are completely 100% within my expectations, I started trusting my new chrono. I also shot some 22LR through the chrono and they matched what I was expecting (looked for velocity figures for the ammo on the internet).

I also verify the chrony w/a certain 22 LR cartridge in one certain 22 Rifle. I also use the XD-9. The XD w/winchester cartridges (have a stash for this purpose)

I use cheap chrony models and change often, until I learned to put a piece of glass in front of the LCD screen. (Too many people pushing too much stick powder down the bore. Then it fails while I'm shooting through it)

I also verified that my drops fit my Exbal estimates when using the velocities from my new chrono.

This is a must and actually can make the chrono unnecessary. I use the chrono for a feel good thing when the velocities are high, but use actual drops to "calibrate" the chrony and software.

I mostly use the chrono for ES from which SD can be calculated.

Validating the drop chart is the final verification.

If you figure out a good way to verify your chrono, please share your idea.

AJ
As far as a chrony being a must, I some times wonder. There is one fella around here, at least, that can dial from 100 to 1500+ yards and put the group on the bull and I doubt he has ever shot his 7mm AM over a chrono.
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