Chrono numbers in semi-auto vs bolt?

[ToddM]

Question for those that have way more experience in this than me, but we know that in a semi-auto of similar barrel length that you won't get as high of velocity #'s with the same ammo as in a bolt gun.

However do you also expect to see significantly more spread and standard deviation?

So I've had a JP supermatch barreled upper (had two in fact) neither have ever impressed me with accuracy. To be fair to JP, if you dig deep in the manual, they state that these are not designed for max accuracy, but more for reliability (perhaps maybe "supermatch" is not the right name for them then). The accuracy issues seem to be just flyer related, it will stack 3-4 rounds and throw a couple badly, like 1" off at 50yds. I thought I've noticed shooting it that it seemed like perhaps the ignition wasn't great (weak cycling/sounding loads etc.) as the primer hits were not nearly as deep as my CZ or 10/22s. I know AR22's can be trigger picky, so I've tried 3-4 with no real difference, aside that a hiperfire would not even get ignition. Now that I have a garmin chrono for my centerfires I thought I'd do an experiment.

I took 4 different ammo choices: Tac 22, Eley Precision Benchrest, and 2 lots of SK Long Range. I ran 50 rounds of the same lot through both the JP and my CZ 457 with the chrono and compared #'s, same day, same range, same bipod/rear bag etc. I fully expected velocity out of the CZ to be higher, but the JP was also ~2x worse on spread and standard deviation as well. Tac 22 was by far the worst, some of the lowest velocities on those out of the JP were not even 900fps. The weak cycling from those very soft rounds also caused the next round to be a flyer (I can only assume because it changed the cycling speed). It got to the point where you could basically look at the chrono and call shots as good or flyers.

Ammo	JP AVE	CZ AVE	JP STD	CZ STD	JP Spread	CZ Spread
Tac 22 #4	986	1102	30.7	16.3	138	80.6
Eley BRP	995	1109	12.8	5.8	57	26.6
SK LR #6	1026	1110	13.8	7.1	50	21.7
SK LR #4	1044	1119	13.8	7.4	69	31.9

Lots of things jump out at me here, none of which are good for the JP and accuracy. First the average velocity across all four varied only 17fps for the CZ but almost 60fps for the JP. Both Standard Deviation velocity spread was basically 2x in the JP what the CZ was. Obviously this lot of Tac 22 is not good, and part of why I used it here was I know it's not consistent, but even so we can see the JP #'s are way worse than the CZ.

 

[ToddM]

Interestingly as an update to this increasing the recoil spring to the point that it would barely run with hot match ammo ~1050fps (in this platform) improved accuracy significantly and reduced the velocity variation with the same ammo, however it's still clearly suffering from consistent ignition, tried 3-4 triggers. Especially with some ammo, Eley seems pretty good, but something like CCI or Tac 22 has massive inconsistent velocities. Rim hits are also pretty weak.

 

[Emerson0311]

For background I’ve got a Duece/IBI, CZ 457 factory barrel that shoots Eley Match the same as the Duece, a 10/22 Ruger Competition, random crappier 22’s, and burned through 10+ cases of steadily more expensive ammo in pursuit of awesome. Semis never shoot as well. No one I am aware of stays with semis when the podium actually beckons. Lots of devoted fans, but rarely do they beat equally skilled bolt folks. Your data I find really interesting as a solid representation of the challenges inherent in a semi campaign towards excellence. I wish there was a way to stay semi, because my boy will need a solid bolt option sooner rather than later to replace the 10/22.

 

[ToddM]

Yeah I suspect the lack of any sort of locking bolt on the 22 semi's cost accuracy and consistency not to mention that there's really not a ton of market for super accurate 22's to start with and even less so for semi-autos when most of the PRS style game rules etc. for a long time (and a lot of places still) put semi-autos at a disadvantage. At least with centerfire AR's you have a bolt lockup. 22's probably don't have enough recoil impulse/gas to use a locking bolt design and if you don't have a locking bolt, you need mass and a strong recoil spring to help ensure ignition and more consistent pressures, which again not an option with 22 LR rounds, especially soft match rounds.

If you read some of stories of old timers messing with 10/22's shooing in 100yard warehouses those guys were buying a dozen barrels from Lilja etc. reselling the 9 that didn't shoot well enough, and cutting down barrels 1/8" at a time to find the best harmonics for their loads, machining their own bolts/firing pins etc. Those rigs are rumored to have shot scary good groups, almost unbelievable for 10/22s but basically no one today is doing that.

 

[Godsent2018]

Yes. Semi autos often run slower and show larger SD and more flyers than bolts.

 

[obx22]

Question for those that have way more experience in this than me, but we know that in a semi-auto of similar barrel length that you won't get as high of velocity #'s with the same ammo as in a bolt gun.

However do you also expect to see significantly more spread and standard deviation?

So I've had a JP supermatch barreled upper (had two in fact) neither have ever impressed me with accuracy. To be fair to JP, if you dig deep in the manual, they state that these are not designed for max accuracy, but more for reliability (perhaps maybe "supermatch" is not the right name for them then). The accuracy issues seem to be just flyer related, it will stack 3-4 rounds and throw a couple badly, like 1" off at 50yds. I thought I've noticed shooting it that it seemed like perhaps the ignition wasn't great (weak cycling/sounding loads etc.) as the primer hits were not nearly as deep as my CZ or 10/22s. I know AR22's can be trigger picky, so I've tried 3-4 with no real difference, aside that a hiperfire would not even get ignition. Now that I have a garmin chrono for my centerfires I thought I'd do an experiment.

I took 4 different ammo choices: Tac 22, Eley Precision Benchrest, and 2 lots of SK Long Range. I ran 50 rounds of the same lot through both the JP and my CZ 457 with the chrono and compared #'s, same day, same range, same bipod/rear bag etc. I fully expected velocity out of the CZ to be higher, but the JP was also ~2x worse on spread and standard deviation as well. Tac 22 was by far the worst, some of the lowest velocities on those out of the JP were not even 900fps. The weak cycling from those very soft rounds also caused the next round to be a flyer (I can only assume because it changed the cycling speed). It got to the point where you could basically look at the chrono and call shots as good or flyers.

Ammo	JP AVE	CZ AVE	JP STD	CZ STD	JP Spread	CZ Spread
Tac 22 #4	986	1102	30.7	16.3	138	80.6
Eley BRP	995	1109	12.8	5.8	57	26.6
SK LR #6	1026	1110	13.8	7.1	50	21.7
SK LR #4	1044	1119	13.8	7.4	69	31.9

Lots of things jump out at me here, none of which are good for the JP and accuracy. First the average velocity across all four varied only 17fps for the CZ but almost 60fps for the JP. Both Standard Deviation velocity spread was basically 2x in the JP what the CZ was. Obviously this lot of Tac 22 is not good, and part of why I used it here was I know it's not consistent, but even so we can see the JP #'s are way worse than the CZ.

Interesting thoughts.
I was purely shooting for accuracy and not paying much attention to velocity on my most recent build, so I’ll have to test and get back to you.
My current match AR build uses a Sako Finnfire heavy barrel. I had two unmodified and tested many rounds to determine if one was better than the other in accuracy.
Ultimately flipped a coin, then had the tenon modified to fit the barrel adapter for my Tac-Sol. The smith botched the job and I ended up loosing several thousandths off the chamber end and had to go with a modified Bentz chamber to allow feeding.
Excuses aside I have a rifle that feeds and ejects reliably, and has proven it needs a better driver in our matches
I’ll try and run you a chrony test of the AR against the factory Finnfire head-to-head.
These barrels are 16.5T and 23” long, I’ll be testing with Eley 42gr Contact subsonic semiauto.