Same EXACT load as last years load shoots like crap

[Shootin4fun]

I may have missed it, but I see no mention of velocity measurements / comparisons. If velocities are close/the same between the old loads and new ones, head scratching continues.
Was it mentioned that the same box of bullets are being used? Sometimes manufacturers change the profile. Berger certainly did on the 7mm 168s and I contacted them about it. Now I measure base to ogive of bullets and write it on the box to verify before loading from a new box.

 

[Shootin4fun]

Exactly! Why don't people read whole post before commenting?

Right, this is not rifle mechanics. Shooting old and new loads in the same session with old loads performing as expected rules this out, assuming careful shooting and adequate sample size.
This has something to do with the loads.

 

[Calvin45]

There's probably a very simple explanation that once figured out will seem so obvious it's embarrassing (in my experience)

Nonetheless, this being the LRH forum, I must put forth the LRH official answers.

Donuts
Carbon rings
Cold welding of bullets to cartridge necks.

For sure it's one of those

 

[Calvin45]

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.

For real though, this would be the first order of business for me

 

[MoaFlat]

Head scratcher all right.
1) I've found that the stock to action screws can change accuracy considerably…especially the front screw. With bedded actions we're talking upwards from 45inlbs to 65… get your torque wrench and make sure it's cinched down.
2) heavy copper fowling at front of barrel takes considerable elbow grease to get it out. Often accuracy restored.
3) mounting rail or ring mount loose . Took a nock?
4) try a different scope?
5) inspect your crown or re-crown it. Took a ding, worn by cleaning.
Cheers Joe

 

[Craig1978]

It could be a lot of different things. Barrel fouled, different brass or brass length. If your primers and/or powder were in a damp are too

 

[Hunterjones]

Other posters mention VELOCITY. Absolutely check good shooting loads versus bad shooting loads. If you have access to a chronograph, this is the easiest way to see if loads are indeed the same.
If the velocities are considerably different between good and bad loads, therein lies the problem. Then you can eliminate things one at a time that would have caused the issue…..

 

[Veteran]

Get the chronograph out and get some velocities to help diagnositics

 

[birddog 68]

Check your scale. Weigh powder charge old vs new. Check velocity old vs new. I know you say it's not mechanical but M77's are notorious for being finicky with the torque on the action screws.

 

[Lefty G-gear]

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?

Maybe you need to free-float the barrel.
That seems to help things a lot.

 

[Hunterjones]

Guys. READ THE WHOLE ORIGINAL POST.
The guy has some old ammo loaded that shoots well. He loaded some new ammo EXACTLY the same and the groups are 5 times bigger.
The gun shoots the old ammo FINE and the new ammo POORLY.
It is not a RIFLE ISSUE

 

[birddog 68]

I did. I mentioned the torque on the action screws LAST after other things I would check. M77's will shoot inconsistently without proper torque but wouldn't be my first thing to check.

 

[Bob Wright]

Velocity....
So maybe;
Your original loads were on the edge of a good accuracy node.
Your new loads are now out of that node by a lot.
If you don't have velocity data, start over on your load development just below your stated powder charge and work up with a chrograph and watch for velocity flats wide enough to start testing 3-5 shot groups.
Maybe your seating depth is widely varying (and make sure your using the correct comparitor Guage).
It certainly needs remeasuring of every component and velocity on the range.
You'll find it.

 

[orkan]

Exactly! Why don't people read whole post before commenting?

In my defense... His post was not exactly a wonderful specimen of the english language. It was pretty hard to follow.