Finding the load in a troubling rifle...

[TNBillyEarl]

Hypothetically, of course... Let's say you had an accurate rifle and you cut 1 inch off the bbl. And then let's say that rifle no longer consistently grouped any of the loads it used to. Any of them. Can any of the previous data help you sort out where you are or give direction? Must you just start load development from scratch? Is there any shortcut to this?

-B

 

[bdbrown66]

Hypothetically, of course...accuracy is all about barrel harmonics. If you change the physical characteristics of the barrel, the harmonics will definitely be affected. No telling how much.

 

[noslerpartition]

Ask the slow Mo guys if they can see if your barrel is shortly before, or after the apex of the oscillation.
Then think about what to do about that.

Or start again
Sorry - I like their content and they might be convinced to try. But I think a new ladder would be easier.

 

[TackDriver284]

Once barrels are cut shorter, harmonics changes, I would run a new ladder to max velocity under a chronograph and back off a grain from max pressure to set your max velocity, see if you see any nodes. Make some 3 round charges, in .2 grain increments for small calibers, .3 for medium calibers and .4 for large calibers within the nodes you may see on your ladder, and see what the paper tells you. I normally start midway from minimum and max and work my way up to max. If barrels are cut too short and twist is slow, then there will be some issues on stabilization of bullets depending on weight. Below was my work up last week with the 6.5 Creed.



Last night I prepped 4 groups of 3 rounds, 41.4, 41.7, 42.0 and 42.2 grains of H4350 lit with a Fed 210M. .090" off the lands as per my old notes. Recorded speeds on a P35, overcast sky.
1.) 2738, 2749, 2740 ( one was a fouler after cleaning )
2.) 2760, 2735, 2744
3.) 2772, 2769, 2768
4.) 2785, 2785, 2786

 

[TXbaldhunter]

Other things that could give you problems,if the barrel was cut off,could be a crown issue.Another thing could be the stock.I assume the stock was removed.If so make sure the action is not binding,bolts properly torqued,poor bedding,barrel touching the barrel channel of the stock,just to name a few things that can also cause sudden accuracy issues.If scope was removed,loose mounts will cause issues too.

 

[remingtonman_25_06]

Yes, you would need to redo load development since the harmonics changed. I'd echo exactly what TD284 stated.

 

[Divernhunter]

could be a problem with the crown on the barrel and not the loads.

 

[michsteve]

could be a problem with the crown on the barrel and not the loads.

Doesn't need much to ruin accuracy.