Initial ladder/OCW for N135 & Barnes

[BringBackThe80s]

Despite the heat, I spent 8 hours at the range to get 60 shots (two OCW/ladder tests) through my Tikka T3x in 308 Winchester. Barrel cooling adds so much time, I need to make the most of my next loads/tests so there's still time to practice at distance before archery seasons suspends handloading for a couple months. So I would welcome feedback on where and how you would drill down on a recipe with for each bullet.

Equipment: Tikka T3x Lite, started the day with 537 shots through the (thin/light) factory barrel. Burris Signature 3-15x40 scope, tube-mounted level, vertical grip, Victor check rest/riser, Backstop recoil pad; right at 8 lbs with full magazine and sling. Shooting off of heavy front bag and rear rabbit-ear bag on cement bench covered with a blanket. Chronograph is kaput, but hope to replace it before my next range trip.

Conditions: Tests shot at 100 yds over 2-3 hours each. Public range, so frequent interruptions and helping folks with questions or difficulties. Sunny, 68F at 7am arrival, ~90F at 3pm departure. Negligible wind.

First Test (labeled "Load 50A"): 175 Barnes LRX seated long (30 thousands off the lands) at 2.8725" COL/2.250" BTO. Norma cases (2 previous firings) trimmed to 2.007" with 58.12gn water capacity. CCI Br-2 primer. Pic of target attached. Also a pic of where I charted each group's average POI. 3-shot groups with VV N135:

1. 39.8 gn, 1.38"
2. 40.2 gn, 0.95"
3. 40.6 gn, 1.90"
4. 41.0 gn, 1.22"
5. 41.4 gn, 0.92"
6. 41.8 gn, 0.63"
7. 42.2 gn, 2.02"
8. 42.6 gn, 1.58"
9. 43.0 gn, 0.19"

I don't think the tiny group at 43.0gn is a purely random fluke. In the previous range trip I ran a pressure screen with the same 0.3" intervals but shooting from 36.6 up to 43.3 gn. The last five shots/steps spanned a full grain of powder but all went into one ragged hole/cluster. (However, at 43.3 gn, a step below my simulation's predicted max, I thought the bolt might have felt slightly sticky so I did not want to push any further and backed it down a step for Saturdays test.

Technique: For all of the first test and most of second, I shot free recoil, thumb resting on right side of pistol grip, no contact between left hand and rifle. Works great for the 243 and okay for lighter bullets in the 308. But I felt like some of the high "flyers" coincided with shots where I saw faster and higher muzzle flip. I probably need some coaching on consistent posture to keep muzzle rise consistent. But until then, I think I will use a bipod (to add forward weight) and a left hand putting downward pressure on the wrist/forward comb.

Family is calling I'll add 130TTSX test results later.

What would you shoot next with this combo? Any other thoughts or suggestions?

 

[RegionRat]

An OCW test is shot to determine if the centroid of a group is shifting or steady. It is all about the X-Y location of the group centers (centroids). It isn't about the group dimensions, (although it is never a good sign to see large groups in one of these tests either).

The idea is you find a window of charges where that centroid shift is steady, and then go back and re-test that window. Some folks run an Audette Ladder at distance to then verify their OCW results, and then start to investigate their seating depth.

Not all guns will have an obvious response to these tests. Most light carry guns are very recoil sensitive and don't do well with free recoil.

It is a little difficult to read your results and I'm not sure if the first target and the second one are of the same recipe and steps? If those targets represent an OCW, there are large centroid shifts between steps.

I only see step 3 and 4 being steady. If the results amount to that 3 and 4 step being the only steady spot, I would try again with a bench hold on the gun instead of a free recoil. What has me worried about your hold, is how large the jumps of some of the other steps are showing.

It may be I am not reading your results correctly, or it may be that the free recoil bit you. Good Luck and in for the range reports.