Jam Depth Test .223 CZ 527 Varmint Tactical

[Andr01d]

This is my first forum post, used to capture my results of varied OAL, specifically jamming into the lands, using 1 thousandth neck tension (Wilson dies, bald eagle arbor press), lapua brass trimmed to 1.750 w Sinclair micrometer trimmer (best money I ever spent!) , rem 7-1/2 primer, Berger 70 grain VLD target bullets, CFE 223 24.7 grains( this is well below seeing any pressure signs and runs at +-2800fps). Max oal measured with Hornady oal tool and Berger bullet is 1.881. So far best performance I have seen is at 1.887 but I have not gone any deeper than that ( getting .4MOA as best , averaging .6 MOA AT 425 yards). Looking to test deeper jam and see MOA difference, pressure signs, velocity change etc. Using Chrony Master to measure velocity, rcbs chargemaster to throw powder, have not checked runout but using Wilson dies.

 

[SporterII]

Me, I would load 1.891, 1.871, 1.866, and 1.860.
Measuring each length to ojive.
.010 IN, .010 OFF, .015 OFF, .020 OFF.
CFE speeds sound decent in your rifle.
.001 neck, that's all?

 

[jbell]

I don't think 0.001" NK tension is too bad. I have found 0.0015" gives me the best results with MANY different rifles. I also have found up over 0.004" can cause poor accuracy at times load dependent.

 

[Andr01d]

Right on SporterII, I just made up a few rounds to confirm excessive pressure signs do or don't happen as I push the OAL further into the lands. Just last week end I have tried 5 round groups with varied OAL( .003 spacing) AWAY from the lands down to 1.853. Found one sweet spot in there at 1.878, but it seems to be a very narrow sweet spot. Groups opened up the further out I went. So now I am looking for a fat sweet spot jammed in the lands. Hopefully I can confirm that jammin does not end up with me wearing my gun on my face and then get a batch of 5 round groups loaded for the weekend.

 

[SporterII]

Sounds like you need to be at .010 in. No less.
Bell, I seem to have settled at .002 to .0025. Just fell that way and is working well. I would be afraid for durability sake at less. Cease fire on a loaded round, I am not rattled with re chambering it , no break in my rhythm. Just me.

 

[Andr01d]

Jbell, I found that 1-2 thou neck tension is what keeps my SD down low teens, 3-4 thou is real bad SD ,paper agrees with chrony at 425. Did a test with dummy rounds to see if one thou would be enough grip to stuff it deep in the lands, it is not, pushes bullet back to 1.905 which gives me .024 jam. Anybody know how deep is too deep into the lands if there are no pressure signs?

 

[SporterII]

Clean your rifle.
Foul it.
Load .010 jammed, .002 neck.
Shoot two five round groups, two different days.
If it works, drink a beer when you get home.

 

[wadcutter]

Andr01d,
If they are being pushed back into the case and settling at a constant 1.905" Then I would that that as being your "full contact" point with the lands. A lot of benchrest shooters use this method and get great accuracy.

 

[Andr01d]

Good point, would not want to extract the loaded round as it would most likely leave the bullet behind and a mess in the chamber. I will most likely try the 1 thou just to test accuracy and my curiosity. But 2 thou sounds like the do all neck tension to me, we'll see how she shoots.

 

[jbell]

Oh that is one thing I should of pointed out. I don't ever shoot in the jam if I can help it, I have always been able to find a load off the jam. I just don't like the idea of it. When I was shooting BR I was playing around with slip fit bullets and had some luck with that...

 

[Andr01d]

Varied Jam Length Results:

Lapua Brass, neck sized to .249, giving .001 neck tension. Loaded 8 rounds with Rem 7 1/2 primer, 24.7 Grains of CFE223, Berger 70 Grain VLD's. Varied jam depth as follows ( this was just a prelim test for pressure signs and to see velocity before loading 5 round groups shot at 425 yds )

Seating Depth / Velocity
1.887 / 2694
1.891 / 2698
1.895 / 2687
1.899 / 2648
1.903 / 2658
(1.905 max jamb with .001 NK Tension)
1.907 / 2691
1.911 / 2671
1.915 / 2706

No pressure signs at all on any of these rounds. Ready to load 5 round groups and shoot at 425 for a real accuracy test

Considering this is varied jam depth, looking pretty tight and promising!
Target Results at 200 yards,

 

[Andr01d]

Range results using 5 round groups, .001 neck tension, CBTO 1.904(found this to be max slip fit ). Outstanding reduction in group size, .51, .57, .39, .35 MOA, looking very consistennt.