308 OCW can someone explain this?

[D_Lamz]

This past weekend I did an OCW test on my stick (700 SPS tactical 20in in an AICS; HDMR, Timney 517, MRAD brake)
did a starting of 43.8gr and went up in increments of .2gr up to 45gr using Varget loaded with 175 SMK at an OAL of ~2.845in with Hornady brass.
The first set of shots were looking great at around 44.6gr and 44.8gr. Then I fired another set after a short cool down and they looked horrible........ (in the picture it shows 2 holes since 44.6gr had a light primer strike and 44.8gr had no primer LOL)
Was this due to the barrel heating up, shooter fatigue, etc? Shots were taken in the prone with TAB rear bag. Should I use the first set of shots as my reference? Please help and THANKS!

First set

Second set

Rifle

 

[CK_32]

I think your supposed to let the barrel cool after every shot being the temp from the 1st to the last shot will be way different and alter results. I think like you got.

At leat that's what I got from the instructions. Shoot one, let cool.. Shoot again, let cool . And so on

 

[AZ.noob]

CK makes a good point. Also, OCW is most effective when done "round robbin". See Dan Newberry's website, great information. I read it through several times to make certain I had a firm grasp on his process.

 

[AZ.noob]

And BTW, bitchin rig

 

[Pinecone]

What caliber?

And yes, OCW should be shot round robin, that is the lowest charge, fire one round, then the next lowest, etc, up to the highest charge. Then repeat. This evens out the affects of heating and fouling.

And I waited 2 minutes between each shot for cooling.

 

[shoot4fun]

You may not have followed the OCW protocol but the top set of targets coincide with what I have found to be true. 44.7 Varget, FGMM primer, Lapua brass and 175 SMK has been a great load in almost every 308 I have ever fired it thru.

 

[HobbyShooter]

I think that you had a light primer strike that didn't go off may hint at inconsistent ignition between rounds. Maybe the primers aren't seated deep enough preloading the anvil, maybe they're not seated all at the same depth, or it could be they're too hard for your firing pin.

From what you have so far, I think 44.0 or 45.0 may be your best bet.

 

[D_Lamz]

Opps looks like I should have read the procedures! I'll redo this again this weekend and post results. Thanks guys!

ps: 2 minutes between shots?! That's an eternity LOL

 

[bh-ltr]

Hopefully you get better results once shot round robin. I didn't wait that long between shots when I did it but did give it some time to cool. Another thing that might help but takes longer was that I did 5 rounds at each charge weight. I've got a 20" LTR and in doing the same testing I found 44.5 to be my load. 44.3 and 44.5 actually both would have worked quite well but I chose 44.5 to get the addtl velocity for longer shots. I was using Lapua brass FGMM primers and a 2.800 OAL.

 

[rduckwor]

Shoot it round robin and wait a predetermined period of time between each string. Get up, walk around, get some water and let the barrel cool a bit. There's no rush to get this finished.

I'm betting you are going to find a node between 44.6-44.8 simply based upon your first set of targets. seat your primers well.

Good luck.

 

[oldfatguy]

Opps looks like I should have read the procedures! I'll redo this again this weekend and post results. Thanks guys!

ps: 2 minutes between shots?! That's an eternity LOL

Takes less time to do it right then to do it over.

OFG

 

[D_Lamz]

Here are the results of doing it correctly while waiting 2 minutes between shots. What do you guys think? Probably 44.8 - 45? Also, I have no idea what happened during that 7 shot string.

 

[oldfatguy]

Looks like a pretty broad node from 44.2 to 44.8. Pick a charge weight (44.4 or 44.6 would be in the middle) and work on seating depth.

OFG

 

[D_Lamz]

So I should pick a charge of like 44.4gr and load with different seating depths and then shoot for groups?

 

[81sfo]

Put a Thunderbeast on the end, it will tighten the groups to one hole !

 

[oldfatguy]

So I should pick a charge of like 44.4gr and load with different seating depths and then shoot for groups?

Yup, that is the next step.

OFG