Same EXACT load as last years load shoots like crap

[Les in Wyoming]

I am frustrated beyond expression. My 30-06 was a tack driver. Then it quit shooting well. Had it glass bedded, changed the load a bit, played with seating depth. Settled on an OK load which gets 1moa (it used to get 1/2 Moa). So I decided to load up all my empty cases and then test the load. First, I shot some of last September's load (this is now April). It shot well. So I loaded up several EXACTLY the same. Shooting 168 gr. Hornady BTHP over 59.3 grains of IMR 4350. (My old load was 59grains). This is a compressed load. The bullet seating depth, measuring cartridge base to ogive is exactly the same to .001. My cases are matched to within .004 of the same head stamp. This exact same load shoot 5" groups, all over the place. So, I shot 3 of my old loads. It shot a 1" group. So I went home, and very carefully loaded up more of the same EXACT load. It shot a crappy group. This does not follow the laws of physics and I cannot take this kind of weirdness lightly. BTW, each shot was put in the rifle individually and not in the mag, lest any chance of the seating depth being affected. Why is this happening?

 

[Joefrazell]

rifle details?

 

[orkan]

Barrel fouled up?

 

[dok7mm]

Different powder lot or primer change.

 

[ShtrRdy]

Are you using the same processed brass as you were using?
Same box of bullets and primers?
Has the powder bottle been tightly sealed since you loaded up last September load?

I've been chasing my tail on a 22-250 load. I don't have it totally figured out yet but one thing I learned is the last bit of powder in the bottle that has been used over the last year will give a higher velocity than a fresh, sealed, bottle with the same lot number. Like 80 fps for this 22-250.

 

[Les in Wyoming]

rifle details?

Ruger MK 2 (M77) 30-06.

 

[Les in Wyoming]

Barrel fouled up?

That would be a reasonable thing to check except the old (but same exact) load shoots a tight group from the same rifle and the same rest under the same conditions. The rifle was cleaned this winter and not shot since until now. All the normal things to check, such as action screws, fouling, hot barrel, etc are without relevance when last-year's load shoots ok between groups of the exact same recent load. In fact, I shot a good group from last-year's batch in a hot barrel.

 

[Korhil78]

I'd check your base and rings and make sure those are tight. Then put another scope on it and check that to rule both of those out.

 

[Les in Wyoming]

Different powder lot or primer change.

Same exact primer. Same powder charge. I believe it is even of the same exact can of powder. It is the only one I could find in my cabinet and it has been used. But even if it is of a different powder can, it could not make THAT radical of a difference. If it could, we could never duplicate a load.

 

[Korhil78]

Just read your previous post haha.

Was the brass from last year fireformed?

 

[Les in Wyoming]

I'd check your base and rings and make sure those are tight. Then put another scope on it and check that to rule both of those out.

That is something I could do, except it shoots the batch from last fall great. I can shoot a few 3-shot groups from those I load today and they are all wild. Then I shoot a 3-shot group from what I loaded last fall and it is a much tighter group. If it can shoot some well, it cannot be the scope.

 

[Les in Wyoming]

Just read your previous post haha.

Was the brass from last year fireformed?

Yes.

 

[Les in Wyoming]

There is only one crazy thing, which cannot be a realistic factor. The cartridges loaded last fall had time to sit and settle (though it is a compacted load). If ammo cannot be used until it settles 6 months, it is of no use. It has been in a climate-controlled place of same relative temperature. The outside temperature in September when I loaded the last batch was about the same temperature it is now in early April. IMR 4350 is not that temp sensitive anyway. I thought of trying to put newly loaded cartridges (which are in the same fire-formed cases as the loads of last year) upright in a cartridge case on an empty media tumbler. This would simulate ammo sitting in a truck during hunting season. But this is getting ridiculous. Compacted loads should not have to be jiggled to become accurate.

 

[Salmonhead]

Is the brass or different times being fired? Like 2x vs 5x brass? If so, might be time to anneal. I start to see squirrely groups and ES spreads when the brass needs to be annealed.
Other thoughts would be a different lot of powder, different primers possibly, or the lot of them, or different lot of bullets. I have the " same bullet" but some are older and some are newer and they measure differently. Sometimes up to .010". So if you are seating them the same, you could actually have a different relative jump to the lands.
Other thought is the throat might be going. The last barrel I burned up seemed to shoot well then not then decent, then trash all together.
Maybe test each lot of ammo with two consecutive three shot groups, so each lot of ammo gets 6 shots instead of three to hopefully rule out being lucky with the old lot.
Hope you get it figured out and share the details with us. Good luck. That's enough to drive a guy to golf.