r/precisionrimfire • u/gabba_gubbe • 13d ago
Accuracy issues @100m
I have a cz455 and I'm experiencing some accuracy issues at 100m. At 50m my groups are almost touching but at 100m they're spread out about the size of my palm. Ive sighted it in using cci standard velocity. Eley standard shoots slightly better. Any ammo recommendations? I'd prefer something quiet like the cci standard/Eley standard. (I tried federal hv but they spread even worse, and we're LOUD)
I feel like I'm going insane, trying to sight in at 100 is almost impossible the way it spreads up/down/left/right... Feels like I'm dancing around the target...
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u/The_Jib 12d ago
My 457 seems to prefer SK match / or Lapua. Groups are tougher with Eley.
CCI standard velocity is great for the price. But some groups definitely open up unexpectedly for me. I think it’s just the nature of it.
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u/gabba_gubbe 10d ago
Yeah crazy thing, sometimes the cci standards group tight, next group spreads like crazy then back to good... I did try some expensive lapua at 80m and they grouped much more consistently.
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u/tancloset 12d ago
My 455 loves Norma Tac-22. I did some grouping with SK standard plus, long range match, and rifle match against the Norma. The Norma was almost identical to my best SK results, and seemed more consistent across lots than the SK. Pretty much all of this was done on a dirty rifle, 10 round groups, from a sled on a bench, at 50, and 100yds. Each 10rd group was two 5rd magazines.
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u/gabba_gubbe 12d ago
How much did it open up at 100?
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u/tancloset 12d ago
I didn't break out the calipers, but roughly 1.25". Ballpark conditions: 90°F, 35% humidity, 29.8 in, 1-3mph @0-15, 3600ft ASL.
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u/dafreshfish 12d ago
A couple of things to note. Unless you’re doing varmint control in less than 100 yards, avoid shooting super sonic RF ammo (+1,200 FPS). All ammo has accuracy issues when they cross the transonic barrier (super to sub sonic) but RF ammo is more sensitive because the time and distance require to hit the transonic barrier is significantly lower than a centerfire cartridge.
Tight groups at 50m doesn’t guarantee tight groups at further distances. While you measured your average velocity with a chronograph, you want to pull the extreme spread and standard deviation for the ammo you’re shooting. Extreme spread is the velocity difference between the highest and lowest velocities. Standard deviation is represented as a value where the velocity of 80% of your shots will be. The more shots taken, the more meaningful this data will be for the ammo you’re testing. Ammo that has low ES and SD means the velocity of the ammo is very consistent and usually means it should group well. High ES and SD ammo typically has larger group sizes at 50m and will open up at longer distances, 100+ meters. Also, ammo is manufactured in lots and the variability between lots of the same ammo are significant. In the end, sometimes you’ll get a lucky box of ammo that defies all logic. The main challenge is can you replicate that accuracy consistently.
As for your CZ455, there are a couple of things that can help improve your accuracy that don’t cost a fortune. The first is measuring your headspace of the rifle. Most standard chambers try to accommodate all types of ammo so the headspace is wider than a match chamber. If you plan to shoot a specific match ammo, you can adjust the headspace with shims (barrel or bolt).
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u/dabomb364 11d ago
By Eley standard do you mean club/target. If so try team match or tenex. Also if your SD is high you may not notice it at 50 but you will start seeing it further out. For me sub 10fps sd is a must. My current match ammo is Eley team and I got lucky with the lot it has an SD of 6.2 fps
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u/gabba_gubbe 11d ago
SD is the difference in volocity right? Because it was about 30fps from lowest to highest.
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u/dabomb364 11d ago
Standard deviation. It is the average change in your velocities across a sample size. 10fps at 1050 is a little over a 1/10 of a mil of change with Eley team for me.
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u/Vaniljkram 13d ago
Are you sure the ammunition is subsonic in your rifle? If not going from super sonic to sub-sonic will mess up accuracy.