load inconsistency

[Iden]

Im in the process of building a load for my 338 lapua, and i have hit a snag. I found what I thought was a load of 84 gr h1000 shooting 300gr berger otm. The problem is the load will shoot a .5 inch 3 round group at 200, then after letting the barrel cool and test the load again it will shoot a 2.5 inch group at the same distance. The loads all have the same components, nothing is different. Have any of u guys/gals ever seen this happen? Does it mean the load is bad, or is it something else. Any input would be greatly appreciated.

 

[MudRunner2005]

Sounds like my experiences with H1000... Try another powder. I have found H1000 is not as consistent as people will tell you. The temp sensativity is also a joke, from my experiences.

 

[FearNoWind]

In chemistry, the general rule is that all chemical reactions occur faster as temperature increases. So every powder we use can be expected to be "temperature sensitive" to some extent; some more than others of course.
I recall reading a list of smokeless powder sensitivities at one time where over a hundred powders were ranked for sensitivity. H1000 was quite high on the list.

 

[Greyfox]

I'm not so sure that from the info provided that it can be concluded with certainty that the cause is the powder, or the temperature effect on it. What was the status of the barrel prior to the .5MOA group? I have seen similar effects from unstable bedding, and hot vs cold barrel dynamics. I personally haven't seen temperature variations when using H1000(and Retumbo) effect group size.

 

[Lefty7mmstw]

Im in the process of building a load for my 338 lapua, and i have hit a snag. I found what I thought was a load of 84 gr h1000 shooting 300gr berger otm. The problem is the load will shoot a .5 inch 3 round group at 200, then after letting the barrel cool and test the load again it will shoot a 2.5 inch group at the same distance. The loads all have the same components, nothing is different. Have any of u guys/gals ever seen this happen? Does it mean the load is bad, or is it something else. Any input would be greatly appreciated.

it is likely either a poor load tossing the occasional good group (even a crappy dart player will toss a ton or better now and again) or bedding as Greyfox has mentioned. If the load hasn't tossed multiple good groups it's likely the load needing work.

 

[Iden]

Thaanks to all for the replies. All the testing was done at or around 20 degrees. The rifle is fully floated and bedded. The powder is from the same lot. The barrel only has roughly 300 rounds through it.

 

[RockZ]

You may want to try retumbo.
I had much better results in my 338AI

 

[Bravo 4]

It could be your load but not the powder type. Are you sure your load is 84 grains of H1000 with a 300 grain bullet?
Sounds like a fairly low charge to me, should be closer to 90(maybe more) grains with that bullet.
H1000 has been all I used for the past 8 years in a very accurate .338 Edge and now in a buddy's EXTREMELY accurate Edge and my daughter's .243 Winchester.

Added: if the load is really 94 grains you may be pushing it too hard for your rifle and getting pressure spikes which can cause fliers and such.

 

[jlreff]

I found good results, with magnum and the sierra 300hpbt or barnes 280lrx. didn't have good results with h1000.

 

[barefooter56]

Iden,
You start out with a cold clean barrel and get the .5 group?

 

[Wyo7200]

Whats your load info and barrel length? I can look at it in QL and see if you are on an OBT node.

If you have this info- it will make QL more accurate:
Case capacity in h2o grains:
cartridge OAL:
barrel length and twist rate:
charge:
and if you have velocity chrono data for your powder:

 

[Snaketzu]

More consistent when the rifle is hot makes me think ignition problems. Are you using magnum primers?

 

[Hector Rodriguez]

Your problem may be to do with the harmonics of the barrel. Try changing the load incrementally until you hit the sweet spot.