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Topic: 6.5x47 POI Shift (Read 81 times) previous topic - next topic

6.5x47 POI Shift

Been doing load development for a new 6.5x47 barrel using H4350 and Varget.  Narrowed down a load for both each powder--.4 gr different charge and .003 jump difference, with virtually same velocity.  Loaded 20 rounds of each to for groups today (didn't take Labradar, big mistake).  I shot groups of 5, alternated H4350, Varget.  Thru the load development, the POI for both powders were identical on target.  All development was with Lapua brass, CCI 450's & 140 ELDm's.

For today, I had 12 H4350's hold overs (3X fired brass) from previous outing.  Loaded 8 NEW brass.  Loaded 20 Vargets in NEW lapua brass. When I got to the 3rd round, the first two shots were with the 3X fired brass & went a tad high.  Next three were new brass and landed about 1 MOA low.  My first thought was how in the hell did I do that.  As I was waiting for barrel to cool, I realized the split in the brass.  The next round of new H4350 landed in same MOA low.  Varget's POI did not shift (rules out stupid shooter error).

During all the load development with both powders, I did not experience that magnitude of POI shift--I did zero the scope when I settled on the two loads.  This was also the first time I shot brass with different loading cycles.  I'm estimating that the virgin brass (shoulder about .004 to .005 shorter than the 3X fired brass) was stretching and reducing velocity.  The Labradar would've verified If I'd only taken it with me. 

Any ideas on the shift other than the stretch in brass?  Thanks for your input!

Jeff


Re: 6.5x47 POI Shift

Reply #1
Jeff chances are your new brass had more neck tension than your 3x fired brass.. new lapua brass seems to me like has alot of neck tension..
Grant

Re: 6.5x47 POI Shift

Reply #2
I think you both are right.
Dave

 

Re: 6.5x47 POI Shift

Reply #3
Jeff chances are your new brass had more neck tension than your 3x fired brass.. new lapua brass seems to me like has alot of neck tension..

If the 3x fired brass was not annealed between reloadings, I would sure agree with this thought.

Re: 6.5x47 POI Shift

Reply #4
Repeat the test next time if you have more new brass.  The combination of 4350 and new brass might just show up significantly  different than the others on the chrono. 
Like others said the fireforming and neck tension differences combined with the difference in burn rates & pressure "build up" might account for just one type of powder/brass combo showing significantly different results (poi).
 There is always a chance that velocity won't be much different either.....then time to scratch your head. 🤔
11X Grandfather
Part time Savagesmith

Re: 6.5x47 POI Shift

Reply #5
Repeat the test next time if you have more new brass.  The combination of 4350 and new brass might just show up significantly  different than the others on the chrono. 
Like others said the fireforming and neck tension differences combined with the difference in burn rates & pressure "build up" might account for just one type of powder/brass combo showing significantly different results (poi).
 There is always a chance that velocity won't be much different either.....then time to scratch your head. 🤔

The 3X fired brass was not annealed.  However, I did run the new brass thru my sizing die and mandrel prior to loading.  My thought process was I was maintaining the same neck tension.  I suspect the initial fire forming came into play, including the spring rate of new brass necks.

I have plenty of 3X fired brass, new brass, and now 1X fired brass.  I will run the test with all three to compare.  I think I will add new brass and 3X fired to the Varget load to see if the same shift in POI occurs as an indicator if pressure or burn rate is the between the powders is the culprit.

Thanks for the responses

Jeff

Re: 6.5x47 POI Shift

Reply #6
Jeff your new brass came sized.. so even though you ran it through your sizer its not the same as brass that has been blowin out when fired and resized.. chances are your new brass still had more nect tension (bullet grip).. least thats been my experience..
Grant