Jerry Reisdorff
New member
For 25 meter benchrest .177 cal — has anyone done testing to determine what barrel length has Best accuracy ?What twist for 13g pellets?Jerry
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Barrel length question
- Thread starter Jerry Reisdorff
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Boomer_Mikey
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Standard twist
Here are some notes I have gathered about airgun barrels from various sources on the net including comments from Dan Brown and Lothar Walther.
Airgun Barrel Twist Rate & Specifications
Dan Brown: ”I've never found any published info on airgun twist rates. I suspect it is not as important as with powder burners due to the self stabilizing pellet. Here are some rates that I've measured and read. LW barrels and BSA have a 1:18" twist rate, HW are about 1:15". My (FX) .22 smooth twist has a 1:156" rate, yes that is 13 feet. The Benchmark barrels cut for airguns have a 1:17" rate. I believe that Whiscombe's had a slow rate of around 1:30". Benjamin marauder 1:16", .22 cal. Hope that helps.”
One of the key factors, Whiscombe says, is barrel twist rate. At 40 yards, it really doesn’t matter what twist rate you use. But remember that air rifle diabolo pellets are drag stabilized. With a conventional twist barrel, the pellets come out of the barrel spinning furiously. At 50 yards and beyond, the pellet rapidly sheds forward velocity, but it continues to spin very fast. If the pellets were perfectly balanced, it wouldn’t matter but when you have less-than-perfectly balanced pellets as the pellet loses forward velocity, there is less drag stabilization and eventually the spinning and unbalance of the pellet causes it to yaw, decreasing accuracy. And this is particularly noticeable with guns that shoot close to or faster than 1,000 feet per second.
Airgun barrels with a very slow twist rate of one twist per meter have a marked improvement in accuracy at 75 yards. With a slow twist barrel, it’s possible to shoot sub-one-inch groups at that range, he says."
Lothar Walther (Factory Specifications)
Diameter Length Grooves Land Groove Twist Dia. Dia. Rate
.177" Airgun with choke .630 23.8 12 .176 .182 17.7
.22" Airgun with choke .630 23.8 12 .215 .221 17.7
.25" Airgun with choke .630 23.8 10 .248 .254 17.7
7.62mm (.30") airgun (no choke) .670 28.0 6 .298 .306 16
9mm (.35") airgun (no choke) .710 28.0 6 .349 .355 16
Twist Rate for FWB P70 and 700 is 1:12”
I personally have tried 3 barrels with slower twist rates and lesser chokes and found that they haven't delivered any advantage over industry standard twist rates/chokes at 25 yards/meters. Most of the shooters I know are using Lothar Walther full length barrels in the R.A.W. and Thomas rifles. 12 groove for LV and Polygon for HV. My R.A.W. BM500 MKII came with a shorter 12 groove LW barrel to save weight, my other 2 LV rifles have ~24" barrels and all of them are equally capable. both of my HV rifles have regular polygon LW barrel and my open rifle has a slow twist polygon that I'm going to replace with a standard twist polygon. Several of us have tried custom barrels and went back to standard LW barrels as the results were disappointing.
Boomer
For 25 meter benchrest .177 cal — has anyone done testing to determine what barrel length has Best accuracy ?What twist for 13g pellets?Jerry
Here are some notes I have gathered about airgun barrels from various sources on the net including comments from Dan Brown and Lothar Walther.
Airgun Barrel Twist Rate & Specifications
Dan Brown: ”I've never found any published info on airgun twist rates. I suspect it is not as important as with powder burners due to the self stabilizing pellet. Here are some rates that I've measured and read. LW barrels and BSA have a 1:18" twist rate, HW are about 1:15". My (FX) .22 smooth twist has a 1:156" rate, yes that is 13 feet. The Benchmark barrels cut for airguns have a 1:17" rate. I believe that Whiscombe's had a slow rate of around 1:30". Benjamin marauder 1:16", .22 cal. Hope that helps.”
One of the key factors, Whiscombe says, is barrel twist rate. At 40 yards, it really doesn’t matter what twist rate you use. But remember that air rifle diabolo pellets are drag stabilized. With a conventional twist barrel, the pellets come out of the barrel spinning furiously. At 50 yards and beyond, the pellet rapidly sheds forward velocity, but it continues to spin very fast. If the pellets were perfectly balanced, it wouldn’t matter but when you have less-than-perfectly balanced pellets as the pellet loses forward velocity, there is less drag stabilization and eventually the spinning and unbalance of the pellet causes it to yaw, decreasing accuracy. And this is particularly noticeable with guns that shoot close to or faster than 1,000 feet per second.
Airgun barrels with a very slow twist rate of one twist per meter have a marked improvement in accuracy at 75 yards. With a slow twist barrel, it’s possible to shoot sub-one-inch groups at that range, he says."
Lothar Walther (Factory Specifications)
Diameter Length Grooves Land Groove Twist Dia. Dia. Rate
.177" Airgun with choke .630 23.8 12 .176 .182 17.7
.22" Airgun with choke .630 23.8 12 .215 .221 17.7
.25" Airgun with choke .630 23.8 10 .248 .254 17.7
7.62mm (.30") airgun (no choke) .670 28.0 6 .298 .306 16
9mm (.35") airgun (no choke) .710 28.0 6 .349 .355 16
Twist Rate for FWB P70 and 700 is 1:12”
I personally have tried 3 barrels with slower twist rates and lesser chokes and found that they haven't delivered any advantage over industry standard twist rates/chokes at 25 yards/meters. Most of the shooters I know are using Lothar Walther full length barrels in the R.A.W. and Thomas rifles. 12 groove for LV and Polygon for HV. My R.A.W. BM500 MKII came with a shorter 12 groove LW barrel to save weight, my other 2 LV rifles have ~24" barrels and all of them are equally capable. both of my HV rifles have regular polygon LW barrel and my open rifle has a slow twist polygon that I'm going to replace with a standard twist polygon. Several of us have tried custom barrels and went back to standard LW barrels as the results were disappointing.
Boomer
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