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COL, and brass capacity. Important Considerations.

 
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  #15  
Old 05-02-2009, 07:06 PM
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Re: COL, and brass capacity. Important Considerations.

Thanks for the response AJ, I respect and appreciate your expertise.

There sure are a lot of opinions on this subejct. The article was interesting, btu I dont measure case head expansion to determine excessive pressure. I figure all it gives is a very relative idea of pressure and cant actually and precisely measure excessive pressure.

I also realize that there are variables in the visual signs as you have mentioned, so I guess my perspective is... that if my brass is not being damaged and my bolt lifts reasonably well and there appears to be no potential damage to the rifle, then "all is well". I think chrony velocity can be another backup tool, but I have persoanally experienced on a couple of occasions where I got a very stiff bolt with extractor marks and very flat primers that showed a lower chrony velocity than the 1/2 gr lower increment fired just before that showed no extractor marks or stiff bolt, etc.

There seems to be a lot of voodoo and black magic in this game, but in my experience, if one is attentive to detail, one can get a good feel for what is going on.

I still think there are too many variables in looking at velocity, not the least of which is the difference from one chrony to another, and not to mention the differenc from one rifle to another shooting the same load.

I can understand your view and I sure dont discount your experience and knowledge which is greater than mine.

Thanks again for all the interesting info and your contribution. I will keep it in the grey matter data base

Mark
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  #16  
Old 05-02-2009, 08:33 PM
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Re: COL, and brass capacity. Important Considerations.

Thanks Mark,

The way I look at interior ballistics is pretty simple. As long as the bullet isn't against the lands, I don't see how higher pressure can't lead to higher velocity. Conversely, as long as the bullet isn't jammed; higher pressure should lead to higher velocity and be a great measure of pressure.

Even if the bullet is against the lands, it would seem that higher pressure should lead to higher velocity. As long as you don't try to compare one load that has a jump and another that doesn't, it seems like it should work (same powder burn rate of course).

I don't shoot bullets that are jammed into the lands. As long as my loads are around the same velocity as expected, I'm pretty sure that they are safe. I don't have to read the tea leaves on the case head.

Might be a simple minded perspective, but it's how I think about it.

AJ
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  #17  
Old 05-02-2009, 09:36 PM
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Re: COL, and brass capacity. Important Considerations.

I would agree that higher preasure should lead to higher velocity. But who knows what the issues were that led to the lower reading. It cold have been any number of things. Like I said earlier, sometimes it seems like black magic.

I went back and checked my notes after making my previous post from memory and this is what I found...


SAKO M85 300 WSM
HAT (Henson Aluminum Tipped), 180, Mic depth, 3.6, OAL 3.117, (~.050 off the lands) OAL (lands) ~ 3.167
H4350,
63 - 2833
63.5 - 2866
64 - 2873
64.5 - 2986 (?) maybe 2906? Or 2896?
65 - 2916
65.5 - 2953
66 - 2953, 2935, 2951, (2946) stiff bolt

and...

TTSX, 168, Mic depth, 2.5, OAL 2.930, Lands OAL, ~ 3.070 (~ .140 off lands)
H4350
63.5 - 2930, 2956
64 - 3004, 2968
64.5 - 2956, 2972
65 - 3011, 3034
65.5 - 3034, 3029, 3014, 3011 One extractor mark
66 - 3001, 3006 No signs of excessive pressure
for group accuracy
65.5 - 2999, 2987, 3039, (3008)
66 - 3054, 3021, 3069, (3048) Stiff bolt


In the case of the HATs, two of the rounds fired with 66 grs of H4350 were of less velocity than the one round fired at 65.5 grs and the third was the same.

In the case of the TTSX's, only one of the three rounds fired at 66 grs was less velocity than the one of the three rounds fired at 65.5 grs.

Maybe the chrony was off? Who knows? Some of these groups were fired in low light conditions.

Maybe my view is simplitic, but if it looks and feels like pressure, then back off. If it looks and feels comfortable, then OK.

Cheers,

Mark
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  #18  
Old 05-02-2009, 10:08 PM
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Re: COL, and brass capacity. Important Considerations.

Quote:
Originally Posted by BigUglyMan View Post
That could well explain why a guy I work with hasn't blown his 300 RUM up in his face by stuffing 100.5 gr of Retumbo behind a 180 TSX. Still, he doubts that the ejector marks in the brass are a real danger sign. He says it makes it easier for him to tell how many loadings his brass has been through...

That's the max load listed on the can for a 180g Speer SPBT, so he may not be too hot, depending on his rifle and a number of other variables.
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  #19  
Old 05-03-2009, 08:01 AM
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Re: COL, and brass capacity. Important Considerations.

Quote:
In the case of the HATs, two of the rounds fired with 66 grs of H4350 were of less velocity than the one round fired at 65.5 grs and the third was the same.

In the case of the TTSX's, only one of the three rounds fired at 66 grs was less velocity than the one of the three rounds fired at 65.5 grs.
Montana I just had a similar experience with my 06, 168grain Nosler BT and RL17. At 59 Grains I chronyd 3001, 3010, 3020. At 59.5 I chronyd 2991, and 2997. I never had any pressure signs but I decided based on the velocities not try any higher loads. I think often times the pressure signs will not show themselves until you are 70,000 PSI plus. And depending on the chamber maybe higher. I use both methods, if I get sticky bolt lift I stop, if I get velocities that dont seem realistic I stop even if the cases seem fine. I am not as expert as many on here just my two cents that are probably worth one cent.
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  #20  
Old 05-03-2009, 09:05 AM
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Re: COL, and brass capacity. Important Considerations.

Quote:
Originally Posted by 3006savage View Post
Montana I just had a similar experience with my 06, 168grain Nosler BT and RL17. At 59 Grains I chronyd 3001, 3010, 3020. At 59.5 I chronyd 2991, and 2997. I never had any pressure signs but I decided based on the velocities not try any higher loads. I think often times the pressure signs will not show themselves until you are 70,000 PSI plus. And depending on the chamber maybe higher. I use both methods, if I get sticky bolt lift I stop, if I get velocities that dont seem realistic I stop even if the cases seem fine. I am not as expert as many on here just my two cents that are probably worth one cent.
One of the major points of the paper I posted, is that different pieces of brass behave differently for the same load. You can be running high pressures and many of the brass won't show signs. Other lower loads will show brass signs, this is the jist of the paper I posted.

AJ
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  #21  
Old 05-03-2009, 09:46 AM
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Re: COL, and brass capacity. Important Considerations.

One of the better reads I've ran across regarding pressure signs has been "Any Shot You Want" by Art Alphin with A-Square.

He makes reference to the classic pressure signs usually being indicative of actually being way overpressure..75-80K+ PSI.

He makes the case for it with all three of the aforementioned indicators, primer indications, bolt lift, and ejector marks.

One of the more enlightening arguments made is regarding stiff bolt lift. It's points to the history/origin of the stiff bolt being a safe indicator of overpressure loads was in an era 30-40 years ago when manufacturing methods and precision machining capability wasn't as prevalent, and arguably not the levels seen today...even in factory rifles.

If you contemplate the precision involved in the chambers of the custom rifles today, by some of the gunsmiths/machines today, he makes the argument that relying on a slightly out of round/egg shaped chamber and the difficulty in extracting brass from that chamber might lead one to exceed safe pressures.

Of course if you have brass that has flowed into the ejector on the bolt face, and your shearing that off, and that's causing stiff bolt lift...you're way overpressure....he was speaking to the precision involved in chambering concentric chambers in most production and all of today's customs rifles.

The book makes some other enlightening remarks regarding ejector marks and primers as well...using the result of in house pressure barrels/copper crushers and pressure measuring equipment.

If you’re looking for another book to add to your reloading library, that one might be worth a read....especially if your one that likes to "push" things:(

About the velocities being inconsistent with powder charges above....it's been my experience that are usually several "steps" regarding velocities as the powder charge is slowly increased. Example.....given a powder/bullet/primer/seating depth combination, I've observed avg velocity increase for a given powder charge, (ex for .7 grains 50 fps), and then with one powder charge increase suddenly the velocities tend to level out and the ES goes haywire.

That's been an indicator for me that I'm either passing through a "step" in the powder charge ladder, or I'm near/at/over my max load.

I've also seen contaminated chamber walls (due to my own incompetence i.e. lubricant or cleaner on chamber wall) allow for a moderator ejector mark well below the max load.

Good discussion, and thanks for sharing.
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