Pellet weight question / accuracy?

[echo1974]

Hello all, with help of the forum(s) i have just bought some scales (on balance ct 250, @ £36) and they are very good. I weighed about have of a tin of jsb exact 4.53, 8.44gn, and the results where as follows: 190ish @ 8.4 to 8.5 (i.e a mix of say 8.40/8.41/8.42/8.43/8.44 & so on up to 8.50) and about 20x 8.30 to 8.39, - 20x 8.50 to 8.59, - 10 x 8.60 to 8.69, and a couple of 8.2's. Anyway my question is, what deviation in grain weight terms, would affect the accuracy of a decent regulated rifle? By this i mean, randomly loading one of the lightest pellets from the tin 8.2/3gn and then the heaviest @ 8.6+gn? thanks m

[Archer50]

I've done some experiments and found that, as a rule of thumb, using JSB Exact 4.52's in my Steyr, each 0.02 gn variation changes velocity by about 1 fps. According to Chairgun, this would give a change of POI of around 0.01 inch at 45 yards, assuming you are shooting around 775 fps.

So by my estimation, the maximum effect on POI of the weight variation in your tin would be about 0.2 inch at 60 yards - a bit more than a pellet diameter.


Alan

[ballisticboy]

The problem is not so much the pellet weight difference but what other changes in the pellet the weight difference may indicate. Pellet weight itself has very little effect in the position of the impact point even at 50 yards, though in certain circumstances the difference may be enough to be significant.
Some years ago I modelled the effect of a change in pellet weight, all other factors being kept constant for both a springer and a PCP. The effect for a PCP is much less than it is for the springer due to the basic properties of the different types of rifle. At 50 yards range a change from 8.3 grains to 8.5 grains produced a change in impact point of less than 0.1 inches. The size of the change is linear with the change in weight. This took into account the change in muzzle velocity as well as the change in flight. For a springer the equivalent figure was around twice as big due to the changes in muzzle energy with weight change. These figures are very small but remember they represent the pure weight change effect only. Other small changes which may go with the weight change (such as start pressure, head size, centre of gravity position etc.) can produce larger figures. The variations in weight will not affect accuracy but they may effect group size.
It is because of the relative size of the effects of other changes in pellet characteristics compared to the weight effect that it is not possible to experimentally see the pure weight effect as no two pellets, even of the same weight, are ever identical.

[bozzer]

Shoot them and let us know. Before you shoot them ... measure the head sizes and see how many measure 4.53.

[lensman57]

Shoot them and let us know. Before you shoot them ... measure the head sizes and see how many measure 4.53.

If my experience is anything to go by the answer will be a very few indeed if any.

A.G

[angrybear]

Hello all, with help of the forum(s) i have just bought some scales (on balance ct 250, @ £36) and they are very good. I weighed about have of a tin of jsb exact 4.53, 8.44gn, and the results where as follows: 190ish @ 8.4 to 8.5 (i.e a mix of say 8.40/8.41/8.42/8.43/8.44 & so on up to 8.50) and about 20x 8.30 to 8.39, - 20x 8.50 to 8.59, - 10 x 8.60 to 8.69, and a couple of 8.2's. Anyway my question is, what deviation in grain weight terms, would affect the accuracy of a decent regulated rifle? By this i mean, randomly loading one of the lightest pellets from the tin 8.2/3gn and then the heaviest @ 8.6+gn? thanks m

I'd be very surprised if 0.5gn or under made any noticeable difference to POI above what you would expect from normal human error.

[echo1974]

Interesting replys, by the sound of it there is not much in it up 50yards? but im thinking that if the pellet weights are the very close, and the guns reg chrono's well, then its down to me if im off, unless ive missed something else? pellet lube maybe? I think ive got the accuracy bug and its bad! thanks all.

[PhatMan]

echo1974,

A year or so back I did some tests at forty-five (45) yards in a warehouse using my TX200, and JSB Express (notionally 4.52): the JSB Express was the TX's favourite pellet.

I shot fifteen (15) x ten (10) shot groups with the pellets sorted by i) weight, ii) head size, and iii) head size & weight.

Statistically, there were no differences in the group position on the target or the average group size between (i), (ii), and (iii), and no difference in the standard deviation of the group size within (i), (ii), and (iii).

Now, I would caution against drawing a globally applicable conclusion about this - this was a one (1) off test, by me, on that day, with a limited sample size, etc., etc.

But for me, I no longer bother sorting pellets - I just use them out of the tin; this saves me a lot of work, and again for me, I haven't noticed any downsides to doing this.

However, YMMV.

Have fun & a good weekend

Best regards

Russ

[echo1974]

I must admit it is a hassle to do, sitting there and weighing 500 pellets - makes you wonder why they call them exact's ? i think its only worth doing for long range precision target shooting, not general plinking.