Tuning a Texan to a Projectile

[Metnav1]

I decided to tune my Texan to 147gr round balls... I'd been obtaining very good accuracy shooting them at 900fps, at about 2400-1800 psi... So I adjusted the valve inwards until I was shooting them at 1100fps... My 50 yard groups went to 4" from the one hole groups at 900fps... I adjusted to 1050fps still at 3000psi, and still had the 4" groups... I adjusted the valve for 900fps at 2400psi and had one hole groups again?

So my question: Is the extra power and recoil causing the group spread, or the extra air speed of 1100fps causing instability?

My Ruger Mark 4 .22LR, gets straight bulls at 10m, however my Glock 19 9mm gets 4" groups, and I always figured it was the Glock recoil causing the bigger groups?

Any ideas?

[MJP]

Harmonics, you are just at the accuracy node at 900fps, little more or little less and it goes south.
What comes to the pistols, you may flinch with the 9mm because the recoil and the groups get big. But a red dot on the gun and it will reveal many things, from trigger pull to post hold.
Marko

[Gut2Fish]

Harmonics of a Texan's thin barrel is a good answer. Barrel stiffening with unilateral polycarbon tube or adding weights can reduce the effect.

Another problem is anything approaching the speed of sound (1126 ft/sec or so) is effected to a degree. Passing through the barrier is a large disruption but the barrier still effects trajectory as you approach it. You shouldn't shoot anything over 1000 ft/sec or under 1300 ft/sec, avoid the barrier by a good margin. Faster than sound has the double whammy of dropping back into disruption as the slug slows in flight. With air power 850-950 ft/sec seems to be best accuracy. You could probably tune up the round ball to 950 without losing grouping.

[pepegraves]

I'll be watching this thread closely

[Extreme]

    RJ Porter has his shooting 3/4" and 5/8" groups at 75yds with a simple tune and his ammo. RJ has his shooting under 900fps at the moment, but has been experimenting with different ammo, getting over 920fps. This man knows his stuff when it comes to Airguns. The Texan is his speciality, he tunes around his own ammo which makes your gun even more accurate.

   Best of luck Texan owners.

[stevrom828]

    RJ Porter has his shooting 3/4" and 5/8" groups at 75yds with a simple tune and his ammo. RJ has his shooting under 900fps at the moment, but has been experimenting with different ammo, getting over 920fps. This man knows his stuff when it comes to Airguns. The Texan is his speciality, he tunes around his own ammo which makes your gun even more accurate.

   Best of luck Texan owners.

Does RJ tune Texans by having them sent to him??

[Extreme]

    Yes sir, if you send him the gun he can tune her to your needs. He makes the ammo that is working extremely good with this barrel. Basically keeping her stock, just a few tweaks and his ammo are producing these groups and energy levels.
  RJ Porter
(843) 356-3777
Accurate Big Bore Airgun Ammo