AusVarmint

To members,

Just to help me fill out my air rifle knowledge, does anybody know the twist rates of the common air rifle calibre's? Are they the same as firearm calibre's?

I am thinking of the following -
.177;
.20;
.22; and
.25.

I was wondering if air rifle twist rates were slower than the same calibres in firearms because of their much shorter pellets compared to bullets (which are not projectiles incidentally, because projectiles are bullets or pellets which are moving - just to be a bit pernickerty.)

Hi afaik they are 1in 16 same as .22lr. I'm led to believe this was a carry over from when peoples like bsa were making .22lr. Some recent experimentation here in the uk has given results that indicate it might not be quite the optimium at 12ftlb.

What !!??? All of them???

Dennis La Varenne wrote:To members,

Just to help me fill out my air rifle knowledge, does anybody know the twist rates of the common air rifle calibre's? Are they the same as firearm calibre's?

I am thinking of the following -
.177;
.20;
.22; and
.25.

I was wondering if air rifle twist rates were slower than the same calibres in firearms because of their much shorter pellets compared to bullets (which are not projectiles incidentally, because projectiles are bullets or pellets which are moving - just to be a bit pernickerty.)

Dennis, 1:16 to 1:18 inch is the general going rate regardless of calibre (there have been a few exceptions) .. I doubt it is the ideal especially for longer and extreme range shooting. .. Best regards, Harry.

Thank you to both Yrrah and Stillair1.

I must say I am amazed that all four calibre's can operate so well with such a narrow range of twist rates.

Best regards,

The Steyr LG110 FT .177 cal match rifle has a 1:15.5 twist rate. It is one of the most successful Field Target models available.

Characteristics I have noted with a JSB EXACT 8.44 gr pellet are that it tends to be dependant on the density of the air out to 30 yards on whether it spirals slightly, .....and then drag stability makes the pellet very stable thereafter. Of course the higher the Density Altitude (less dense air) the more suitable the twist rate becomes, and the pellet is very very stable at all distances.

It could in fact do with a slightly slower twist rate than 1:15.5 at sea level IMHO. Get up around 1500-2000 ft above sea level on a warm day and its like shooting a lazer.

Its not so much that the pellet is short, but that its oblique/dome nose creates a CP before the CG, causing instability. Less dense air reduces significantly the tendency to helix/spiral and therefore the twist rate is pretty inconsequential really.

Looking for answers about pellets, one should consult the ballistics principles of black powder era researchers, rather than the modern bullet ballistics principles.


GS

Thank you GS.

I think you are onto something in regard to the blackpowder business. The old Minie balls would have similar flight characteristics when you think about it, even though they are not waisted. The VERY forward CG would be much closer to the CP and would approximate that of air rifle pellets, especially the blunter varieties.

The standard twist rates would be best in Oz most probably because we don't have too many bumpy areas where air pressure is as low as you can get it over there. 2000 ft above sea lever is VERY high over here.

Regards,

Dennis La Varenne wrote:Thank you GS.

I think you are onto something in regard to the blackpowder business. The old Minie balls would have similar flight characteristics when you think about it, even though they are not waisted. The VERY forward CG would be much closer to the CP and would approximate that of air rifle pellets, especially the blunter varieties.

The standard twist rates would be best in Oz most probably because we don't have too many bumpy areas where air pressure is as low as you can get it over there. 2000 ft above sea lever is VERY high over here.

Regards,

Yes I have pondered Yrrah's practical experiments over the years and feel a lot of his groundbreaking observations lead back to that conclusion. Air Rifle diabolo pellets are basically still in the Black Powder era.......crossed with blowgun darts and Badminton shuttlecocks.

I'm positive that his demonstration of diabolo pellets displacing in the opposite direction to cylindrical pellets under the effect of a 90 degree crosswind relates back to that.

I did some of my own tests (undocumented, as a true amateur would) with changing the drag profile of a batch of pellets, and found there is far more to be gained from attention to the pellet friction surfaces than rifling pitch. The gain is not in pellet speed, but in stability/accuracy. Of course the initial speed does not degrade as fast either.......

Without coming out and making a definitive statement, I'd mention only that a pellet with an entire shiny surface will perform no better than a dull oxidized one. It is only when you alter the area of CP, and leave the area subject to tail drag un-altered that one sees changes in the flight profile and stability. I'd make the case that pellet makers recently marketing harder alloy pellets which are significantly shinier on their entire surface have not "got it" yet. JSB will still dominate in the accuracy stakes for a while yet, as those who pay due care and attention to what they feed their air rifles can pick and choose, and ultimately make their own alterations as they see fit.

Short story,.....my opinion is rifling pitch/twist rate could be a red herring as far as air rifles are concerned. Concentrate on your ammo quality/consistency......as Yrrah has ably demonstrated over the years it pays dividends.

cheers
GS