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Temperature Sensitivity
Discussion regarding the reloading of ammunition and tuning of loads for accuracy
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slimjim
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PostPosted: Wed Jul 22, 2015 7:28 pm    Post subject: Temperature Sensitivity 2 Reply with quote

Observations:

- AA2200 with CCI 450 Primers under 110 BTHPs showed the same sensitivity as in the prior test (consistency is good)

- 1200R was the most temperature sensitive of the 6.8mm powders as was the case in prior testing. No instability during this test session but I'm still cautious about this powder.

- The 110 BTHP fired from the 20" ARP SS were all identically loaded with 28.6 grains of powder, Hornady brass (multi-fired), CCI 450 Primers, and 2.295" COAL with mild crimp. This shows the relative energy potential of each powder. H322 has superior temperature sensitivity but does not have the energy potential of the other two powders.

- Interesting that H322 actually had a slightly higher average velocity at 25F than at 98F. Hmmm, more testing required. I plan on using this powder more with the 6.8mm comparing it to AA2200 which has more energy potential but more temperature sensitive. H322 appears to be running lower pressures per charge so will use SSA or S&B brass which have at least a grain more case capacity than the Hornady brass.

- Standard primers improved temperature sensitivity with 150gr Federal RN bullets in the 6.8mm. I continue to achieve better accuracy and more consistent results with standard primers and this heavy-for-caliber bullet. This is a special load developed for using the 6.8mm as a major caliber in carbine action matches.

- Group size and POI changed occurred more with powders that were more temperature sensitive and was evident even at 100 yards. An example in shown with the 6.8mm target of 150gr RN impacts. The bullets joined by the purple line are from the cold test series. The same loads at the hot temperature were shot to the same POA. The 3-shot CFE group had some load development. IMR 4166 and 8208 XBR had no load development, were chosen to fill the case, and be at least a 0.5 grain below max chamber pressure. Still, the IMR and XBR groupings showed a consistent mean point of impact for both Hot and Cold conditions.

- During cold testing, one Hornady brass cracked around the shoulder which had 8+ reloads on it and two annealing cycles. I did not keep track of how many firings since the last annealing. This is the first 6.8 case I've lost that was not due to a loose primer pocket. There may be a higher risk of case failure during cold conditions with work hardened brass.



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Last edited by slimjim on Fri Jul 24, 2015 5:04 am; edited 8 times in total
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Elvis
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PostPosted: Wed Jul 22, 2015 10:22 pm    Post subject: Re: Temperature Sensitivity Reply with quote

cfe looks fairly consistant...that a very dead deer.

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Aloysius
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PostPosted: Thu Jul 23, 2015 12:08 am    Post subject: Re: Temperature Sensitivity Reply with quote

Elvis wrote:
cfe looks fairly consistant...that a very dead deer.

Sure, but when you only want to remove ticks, you will still miss a few...


Smile


Slim, doesn't this temperature sensitivity also depend on the maximum pressure? I would expect so because it's told that burning rates changes according this initial pressure. (I mean comparing burning rates of the same powders will give different lists when using them as shotshellpowders compared to using the same powders in handguns)
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dhc4ever
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PostPosted: Thu Jul 23, 2015 2:37 am    Post subject: Re: Temperature Sensitivity Reply with quote

The beer in Belgium is good, yes?

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slimjim
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PostPosted: Thu Jul 23, 2015 4:16 am    Post subject: Re: Temperature Sensitivity Reply with quote

Elvis wrote:
cfe looks fairly consistant...that a very dead deer.

Elvis, You can see that the mean point of impact is 3/4" higher for the hot rounds because of the velocity change caused by temperature.

You would love this 150gr round nose bullet. Its asleep by 50 yards and the group size is the same at 200 as it is at 50 yards. I developed this load for shooting the 6.8mm as a major caliber to compete with the .308s. Its done so well, I will be using this for deer hunting when I'm still hunting through dense woods.

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Elvis
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PostPosted: Thu Jul 23, 2015 11:05 pm    Post subject: Re: Temperature Sensitivity Reply with quote

sounds great, have a 150grn partition sitting here infront of me that did a good job with a piss poor shot placement, the hind must have been playing twister or something when Nathan squeezed trigger as it went through left rear leg just above hock, then un zipped about 6" of gut flap from teats to navel before boring through lungs and coming to rest beside front leg on the skin. small fragment of tip lead 3" away from the rear of projectile, she was very sick when I neck shot her with .223 less than a minute later and wouldnt have got much further. that was at about 200 yards. lad has a wee bit to learn still,,,on brighter note the venni tastes plurry AWESOME.

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Vince
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PostPosted: Fri Jul 24, 2015 2:18 am    Post subject: Re: Temperature Sensitivity Reply with quote

Elvis wrote:
...on brighter note the venni tastes plurry AWESOME

Well mate, young Nathan did 'tenderise' the meat for ya, didn't he... Laughing Laughing Laughing

Did the gut bust and taint the meat mate? Hopefully not. Can't really blame the young fella if the beastie moved just as he fired the shot...just the luck of the draw unfortunately.

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Elvis
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PostPosted: Fri Jul 24, 2015 10:36 pm    Post subject: Re: Temperature Sensitivity Reply with quote

bust the gut?????? no I did that carrying it in two halves up the hill to wagon...my gut that is...mind you its big enough at moment and can do with some busting...as for meat tainting, no show, it was out n gone pretty darn quick and only the eye fillets could touch it any way. hung it for a couple of days on garage then boned it out and sat on bath in cool room for another few.

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Elvis
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PostPosted: Sat Jul 25, 2015 1:22 am    Post subject: Re: Temperature Sensitivity Reply with quote

Did I mention it was tender????



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slimjim
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PostPosted: Mon Aug 10, 2015 4:44 am    Post subject: Re: Temperature Sensitivity Reply with quote

Speaking of getting meat on the table, I'm getting ready for my Elk Hunt in December. I decided I should try to do my load development during the 100+ degree Texas Summer at colder ammo temperatures since I'm using AA2200 in my 6.8 and IMR4350 in my .270 Win, both show sensitivity to temperature change. I want to be confident of my loads for the temperature I'll be hunting in. I didn't want to drag frozen meat out of the freezer so used ice and got the powder temp down as low 36F. It turned out to be fairly easy to accomplish and temperatures stayed fairly constant if I kept the ammo on the ice. I would place ammo in a plastic shell holder or magazine inside a bubble-wrap bag and lay it on top of the ice at the bottom of the cooler with the powder temp gauge on top. This way the ammo is not in direct contact with the ice or get wet. I would pick up the bag, slide the shell holder out to expose 1 round at a time and single feed. With the .270, I can only shoot two at a time before barrel heat impacts POI so just slip back into the cooler while the barrel cools. Using gloves handling the rounds helps to preserve temperature and insulate the round from body heat. If you don't want to single feed your AR, magazines just go from the ice directly into the mag well. I try to take about 5 seconds or less between rounds. It worked out well and I now have increased confidence in my 110 TSX 6.8 load for deer and 129 LRX .270 load for elk. Still working on the 100 ABs.



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slimjim
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PostPosted: Mon Aug 10, 2015 4:45 am    Post subject: Re: Temperature Sensitivity Reply with quote

Crunched the numbers on yesterday's range session. The temperature sensitivity of AA2200 was evident. I'm still working load development with H322 but velocity change was negligible with a drop of temperature to 45F. In colder temperatures, it appears that the performance difference between AA2200 and H322 will not be that significant. Just a start. Will update with more data after the next range session. Please note: these loads are longer than mag-length COALs with more powder than a 6.8mm case normally will hold. The temperature sensitivity is still applicable.



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"To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt

"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein


Last edited by slimjim on Mon Aug 10, 2015 6:26 am; edited 1 time in total
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slimjim
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PostPosted: Mon Aug 10, 2015 4:48 am    Post subject: Re: Temperature Sensitivity Reply with quote

Here is the load for the 6.8mm. I continue to be amazed at how much adjusting seating depth affect group size. What's interesting is, if I saw the group size of the 2.375" COAL, I would have likely abandoned that charge weight. With the 10-mph variable wind at 200 yards, I was pleased with the lateral spread of the bullet impacts of the 2.415" COAL. For the next load development, I may try a charge weight under max pressure and vary COAL to see if positive results can be obtained. The stick-ons are 1-, 2-, and 3-inch circles.



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slimjim
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PostPosted: Mon Aug 10, 2015 4:59 am    Post subject: Re: Temperature Sensitivity Reply with quote

Elvis, you'll like this load for the .270 Win. It's with the Barnes 129 LRX Rem brass and IMR 4350 which has shown less temperature sensitivity with mag primers. I did drop the charge down 0.5 grains to 55.5. COAL was 3.320". This is a keeper. Powder temp was 36F. That is a 1-inch stick-on at 200 yards.



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"To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt

"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein


Last edited by slimjim on Wed Sep 02, 2015 5:10 pm; edited 1 time in total
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Elvis
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PostPosted: Wed Aug 12, 2015 12:58 am    Post subject: Re: Temperature Sensitivity Reply with quote

looks good slim, from all Im reading the ADI stick powders EG AR2213sc are much more temperature stable than a ball powder.
will use up projectiles Ive got then maybe go to 130grn /150grn??? partitions as I dont fire that many rounds so cost not a biggy. I cant see myself doing the 100-200rounds to get a fine tuned load for the old girl, a 1 ---1 1/2" load will do it for me as barrel stretching just isnt my thing.

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slimjim
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PostPosted: Wed Aug 12, 2015 1:45 am    Post subject: Re: Temperature Sensitivity Reply with quote

Elvis wrote:
I cant see myself doing the 100-200rounds to get a fine tuned load for the old girl, a 1 ---1 1/2" load will do it for me.

I agree. I gave up using 5-shot groups for load development several years ago. I learned that I only needed 2 shots to determine if a load was bad, e.g., if the second shot fired isn't a cozy cousin with the first one, that load isn't going to meet my expectations for accuracy. With typical load development, I was pulling too many rounds. Now, I do an initial powder charge vs velocity ladder in 0.5 grain increments to determine performance and pressure limits while looking for 3 consecutive shots that group close together. I then use a 3-shot group with the middle charge to confirm accuracy. It doesn't work all the time but more often then not I have a good hunting load in 10 to 15 rounds. You have to know how your rifle shoots and that it is capable of 1 moa groups or better or you end up chasing your tail.

In the situation above, I was switching to magnum primers to reduce temperature sensitivity and was checking if COAL adjustment would help. Because of the switch to magnum primers, I tried the first group at a 0.5 lower charge than my prior load. So I lucked into this and will happily pull the other loads I didn't shoot because this one was so good.

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