How much to back down?

Wookie316

Well-Known Member
Joined
Jul 13, 2009
Messages
145
Location
Border City (on the poor side}:-()
Well I made one last quick trip to the range to check my scope before I am gone hunting this weekend (Antelope).

I had decided that 75gr H870 & a 140gr Accubond @ 3206 FPS was a go. The last time I was to the range with that load I had no hard extraction or pressure signs & was shooting groups like I did today.

DSC_2643.jpg


The first shot was the hardest extraction I've had in a long time. It came out after but took a good pull to get it. The other 4 were sticky, but not bad if extracted immediately .

The case just above the belt measured 1 1/2 thousandths larger than another load I had today. It was 76.5gr US869 & a 140gr Accubond. I was getting an average of 3103 FPS with that load but no where near the accuracy of the H870 today. The Chrony failed to read when I shot the H870 group today :(

Temperature & conditions were about the same both days of testing. The only thing that has changed between the 2 days is this is a new bag of brass (Win cases again). I did notice that neck tension was more on this lot than the last. It is by no means tight, but it is more snug when seating.

My big question is how much to back down without affecting accuracy? I don't want a tight extraction in the field on an animal. I also know the sweet spot is going to be between 74 -75 gr as the groups didn't really tighten up until I hit 74gr the last time with H870.

Not sure what to do, no time to hit the range again & don't want a failure in the field.

Suggestions?
 

flyin lizard

Well-Known Member
Joined
Jan 27, 2008
Messages
361
Location
Millbrook ,NY.
Did you save any of the targets that you shot when you worked up the load? If so check the p o i on the ones slightly less then your 75 grain load, that should give you a good idea.

If not then drop 2 or 3 tenths and I think you should still be in the ballpark. I say a couple tenths because when working up my 300wsm I stepped up in 3/10th increments and could watch the groups go up the targets about 1/2 to 3/4 inch at a time. Just a thought..
 

Wookie316

Well-Known Member
Joined
Jul 13, 2009
Messages
145
Location
Border City (on the poor side}:-()
Her is a good one for you. I was able to sneak away to do one last check before I head out for Antelope tomorrow AM (Early). I had some tight extractions @ 75g H870 & a 140gr Accubond. This is a load I tested ok not much more than a week ago & it rocked right around 3206 FPS. Yesterday the Chrony failed to read while I was getting hard extractions, so I don't have a clue what the speed was?

Fretting a stuck case on an animal last night I decided to drop down to 74gr H870 with a 140gr & sneak away to the range quickly to check all was in order. I also loaded my last 130gr Accubonds @ 75gr H870 as my back up.

Well either my Chrony is reading over a 100 FPS higher now, or I picked up 100 FPS from somwhere ?

Here were my speeds

140gr.

3304 FPS - 3371 FPS - 3324 FPS

130gr

3420 FPS - 3421 FPS (These were the 2 touching on the left group) - 3457 FPS

DSC_2644.jpg


I had no tight extractions. Now according to the measurement above the belt, case expansion was as follows:

New case .509

After firing .514

I check a few once fired cases with loads I know that were lower charges. They measured in the .513 -.5135 range.

So am I really shooting over 3300 FPS with a 140gr or is my chrony out to lunch? I think I'm starting to really like this rifle :)

_JAY5151.jpg
 

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