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7mm AM WC872 and temp sensitivity?

 
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Old 02-12-2014, 06:05 PM
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7mm AM WC872 and temp sensitivity?

To save some time and barrel life sending rounds down range, does anybody have any data that they'd like to share on how temp affects this powder?

Here's why, and my observations.

Shooting 180g Bergers, 45F 770' elevation MV 3350 fps. for load development and sight in at home. Everything is great. loading 108.0 grains WC872

Went to Colorado for a cow elk hunt in December. Since elevation was a wee bit different, I ran rounds to verify drops. Started at the 300 yd zero, adjusted that zero for the different elevation then ran it all the way out to 1334 yds. Very happy with the way it performed. 39F ambient, 6600 ft elevation, less than 1 moa wind adjustment for all shots. Made a drop chart for every 100 yds.

Nothing the first day of the hunt, 2nd day we stayed inside because it was snowing and blowing. Ended up with 24" of snow in less than 24 hrs.

The next morning it was -17F at the lodge. We went down the hill, and to make a long story short ran into the cows at 5,000ft elevation. Temp at that time was -8F. Dead calm, at the most 2-3 mph winds. Shot twice at 500 yds, aiming for a heart shot. Nothing. At the 2nd shot, the group came towards us and went into a canyon. When they popped up they were very close to 600 yds out. Dialed up, sent one. Nothing. WTF???

Again, they came towards us, dropping into a canyon for a while. We moved up, and finally saw the group again, this time at 700 yds. My spotter told me what to dial according to the drop chart and then said "wait a minute. Dial in 2 more moa". I did, held for a high shoulder shot and when the trigger broke the cow folded where she stood. The bullet went exactly where the crosshair said it should go. In retrospect, the only thing that I think was happening was the bullet was going under their belly, impacting on the other side of the herd. They heard the impact of the bullet hitting the ground on the opposite side of the herd, not the muzzle noise, and came towards us instead of going away.

Running the numbers in exbal here at the range yesterday in -10F to +10F it was a bear. 24+" of snow on the ground, flat terrain. Couldn't get a spotter and it was VERY hard to spot for myself. Could only shoot at 600 yds and 1,000 yds. Couldn't hit a 36" gong at 1,000 yds. Hit the 10" gong at 600 yds 2x out of 4 shots, could see that one of the missed shots was barely to the left (misread the wind). No bullet impact shown in the snow for the 4th shot. I was leaving the barrel cool for 20 minutes between shots.

Thoughts and advice??
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Old 02-12-2014, 08:31 PM
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Re: 7mm AM WC872 and temp sensitivity?

From the data Kirby posted for the 175 SMK, you are at the bottom end of the load for a 180 and WC 872

Kirby said velocities were very inconsistent at 107 grains for he 175 gr SMK at 75 degrees F and his altitude.

I would surmise that the 180 Berger being much softer and compressible bullet than the SMK and you being way way colder just started getting very poor burning of the powder and never got up to pressure.

I never got WC872 to shot well in mine. It was just really dirty which I suppose was that I didn't get to the right load range myself
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Old 02-12-2014, 08:55 PM
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Re: 7mm AM WC872 and temp sensitivity?

BB, I'm not married to WC872. What powder should I try? I have shot the 175g SMK, and 109/110 was max load depending on whether it was above or below 75F out. 109 in 80F was hitting 3495 fps. 110 was 3550 fps, any more powder and I was seeing a shiny spot on the head. Maybe the 16# that I bought was a fast lot?

BUT, after around 200 rounds down the tube, the 175g SMK's were vaporizing at 40-50 yds. @ 3490 fps Accuracy wasn't there at slower speeds, that's why I went to the 180 Bergers. I have some 200g WIldcat bullets, but haven't been able to figure out an accurate load with them yet.
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Old 02-12-2014, 09:24 PM
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Re: 7mm AM WC872 and temp sensitivity?

I use 103-104 grains of US 869 with the Canadian 200 gr Wildcats. It gives me under 0.5 MOA always. Clean the barrel every 15-20 rounds.

Kirby was recommending Retumbo with the lighter bullets IIRC the last time I saw him post a load.
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Old 02-13-2014, 08:29 AM
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Re: 7mm AM WC872 and temp sensitivity?

Thanks Bob. I have WC689 but they are the USA Wildcats. I was a little bit too late and Richard already sold.
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Old 02-13-2014, 08:51 AM
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Re: 7mm AM WC872 and temp sensitivity?

The USA Wildcats that I tested gave me pressure signs at 103 grains so be careful working up to there.

Are the Wildcats now being made again?
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Old 02-13-2014, 10:32 AM
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Re: 7mm AM WC872 and temp sensitivity?

BB, I have no idea. Mine are from the first batch or 2 that were made by the new owners.

I've got them bearing surface sorted by .001" into lots. I weighed some and they are 1-2 g light.
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