I have a '56 Win. 52C which shoots extremely well with the factor barrel. Thinking that I might save the factory barrel for who ever buys this as some point I had a Benchmark 3-groove barrel installed. It shoots well but not quite as good as the factory bbl. My issue with the new bbl is velocity. After 1500-2000 rounds I am getting right at 1000fps from any and all standard velocity ammo. RWS R50, R100, SK Match, Norma Match (RWS made), plus a few more. The factory barrel achieves 1080 fps with the same loads. I can't really complain as it shoots well at 200 yds but wondering if I should lap the barrel a bit?
Low Velocity Barrel
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It has been known for many years that slower ammo (rimfire ammo) is less affected by the wind, so top shooters have always tried pistol ammo to see if there was a good batch that was accurate in their rifle.
It might sound counter-intuitive that slower ammo is less affected by the wind, but that is because the bullet drag goes as the square of the velocity (in the sub-sonic velocity region). So the higher the velocity, the greater the drag and so the more the wind will affect the bullet. It is possible to calculate an optimum muzzle velocity to minimise wind deflection and from memory it is about 980 ft/sec for 50 metres ranges.
It might sound counter-intuitive that slower ammo is less affected by the wind, but that is because the bullet drag goes as the square of the velocity (in the sub-sonic velocity region). So the higher the velocity, the greater the drag and so the more the wind will affect the bullet. It is possible to calculate an optimum muzzle velocity to minimise wind deflection and from memory it is about 980 ft/sec for 50 metres ranges.
1Merlin
Silver $$ Contributor
Geoffrey with all respect where did you get this information? Is this something you have read or from personal experience or...? I know I have seen postings from people that have experienced the best results from pistol ammunition but I have not seen anything definitive as to a slower speed being superior because of it being slower... (speaking of subsonic speeds)
Just curious.
Just curious.
1Merlin
Silver $$ Contributor
Thanks. Sorry if I gave the impression I felt the post was "fake news" or that I posted in a hostile tone or manner. Not my intention - just a question - nothing more.
orkan
Site $$ Sponsor
Didn't seem hostile at all to me. Seemed like a legitimate question, asked with respect.
The concept is true enough, however, I think as long as you're starting off subsonic... the differences between 1080fps and 980fps aren't going to show up on the target in most instances. The real argument for the effect shows up when you start off supersonic and drop subsonic during the flight path. With a 22lr, this can happen at very close distances and have very adverse effects. Those effects are largely blamed to trans-sonic destabilization, however, and not necessarily due to the enhanced wind drift early in flight.
Go to geoffrey-kolbe dot com, online ballistics, trajectory, and have a play yourself. Just choose the 22 RF projectile, put a muzzle velocity of 1080 ft/sec then click 'calculate table' and in the outputs you can see the wind drift for a 10 mph wind at various distances. Then go 'back' and do the same for a 980 ft/sec. muzzle velocity. The difference in wind drift is almost 20% at 50 metres (55 yards - pick that as a 'custom range') which is significant I think you will agree.
By playing around with muzzle velocities, you will see that 980 ft/sec is actually the optimum to minimise wind drift at 50 metres.
1Merlin
Silver $$ Contributor
Dr. GK I went to your website and so far I have not gotten past the awesome (yes I mean that) barrel vibrations program. Incredible stuff Sir.
Edit to add. I am now in my safe with my calipers and tape measuring and noting all my barrel dimensions..... Starting with my CZ 457 barrel to see if there is a reason that CZ went with 20.5 for the length....
Edit to add. I am now in my safe with my calipers and tape measuring and noting all my barrel dimensions..... Starting with my CZ 457 barrel to see if there is a reason that CZ went with 20.5 for the length....
Well, pistol ammo is made with that sort of velocity, but it is very difficult to make really accurate ammo at that sort of velocity. The chamber pressures are so low, and there is so little powder in the case, it is difficult to get the powder to ignite consistently at these low pressures.
orkan
Site $$ Sponsor
Plugging the numbers in your calculator at 1080fps and then 980fps for RWS R50 produced a 16% improvement. 2.0 moa vs 1.7 moa of drift in 10mph @ 50yds, respectively. So that's an reduction of .157" of wind drift at 50yds which you'd gain based on your calculator, if you were to achieve consistent ammo at that velocity.
Still, this kind of improvement is well under most shooters ability to read the wind, and would likely be masked on the target. The 16% improvement in 10mph constant condition is a significant enough improvement in flight path, but the difference between an 8mph wind and a 10mph wind would still produce a large enough variable to largely hide it. I think if the ballistic advantage were up towards 40% or greater, it would have a higher likelihood of positively impacting scores.
Still, this kind of improvement is well under most shooters ability to read the wind, and would likely be masked on the target. The 16% improvement in 10mph constant condition is a significant enough improvement in flight path, but the difference between an 8mph wind and a 10mph wind would still produce a large enough variable to largely hide it. I think if the ballistic advantage were up towards 40% or greater, it would have a higher likelihood of positively impacting scores.
I've had superb results with Aguila Pistol Match, which is even slower than some "subsonic" loads out there. I haven't chrono'd it, but I believe it's around 850fps.
doclu60
Silver $$ Contributor
I don't know what you shoot, but I know what I shoot in sanctioned competition. Your opinion is WAY off base. I would love to shoot against a bunch of guys in sanctioned RFBR that think leaving .157 on the table is not that important in drift or on target performance. Or, could be "masked" on their score.
orkan
Site $$ Sponsor
You misunderstand. You aren't gaining .157" drift. That's the difference in drift between 1080fps, and 980fps muzzle velocities. So how much is it going to show up in real conditions, when you're still holding 1.7 moa. The fact that you have to hold less does not immediately mean you gain that much closer to your POA in regard to where your shot is placed if you were shooting 980fps. Were this not true, then ONLY bullets with the highest BC's would win... and that's not what happens.
doclu60
Silver $$ Contributor
No sir, I DID not misunderstand. I understood completely. Also, your BC comments when shooting .22lr bullets is meaningless. Please tell me how different .22lr match ammo between brands is as to BC of the bullet? We aren't talking centerfire here.
I understood completely that we were talking about drift and you ARE gaining something, according to velocity, with a slower bullet in higher wind. The farther you have to hold off, the better the chance for error is. If you disagree with that, then you are the one that "misunderstands". I deal with very small decimal points of POI. If I don't, then shooting big time RFBR is a loosing proposition for me. Having to deal with a little more than an extra 1/8" in hold off, and the errors that can be made doing it, are very significant on an sanctioned RFBR target. Especially an ARA or PSL target where you have less reference points to use.
orkan
Site $$ Sponsor
You are only interested in shouting me down and attempting to get me to defend things I’m not saying. Good luck with all that.
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