by Asa
www.pellet-perfect.com In the previous post we saw evidence that many pellet brands show a considerable variation in pellet weights from their published weight.
The big question still remains: What variation in the weight of a pellet causes a noticeable difference in its POI (point of impact) at the ranges that it will be commonly used?
The variation that we are interested in is the elevation of the POI and not so much the lateral variation.
The ranges that are going to show the significant variations, if any, are the longest that sub 12ftlb rifles are generally used at ie: 45yds to 55yds.
Of course the veracity of any data gathered from this test is dependent on whether the pellets used are ones which the test gun “likes” – by that I mean that whatever the quality control in manufacture and design of the pellet it may not produce consistent results out of all guns - it has been the experience of many shooters that even the same make and model of gun does not favour the same pellet.
The rifle used for the testing is an unmodified HW100 .177 with a Deben 4-12x44 AO scope. Not really enough magnification to see what’s going on at 55yds but hopefully with a bench rest the results will be consistent enough.
This HW100 achieves good results with JSB Exact 4.52mm so that is the pellet selected for the tests.
These tests were done outside using a Buffalo River Bench Rest.
(The target is called “holdover”, designed by Mike Chapman)
(The target is called “holdover”, designed by Mike Chapman)
The horizontal marker lines on the target are 1/4"inch apart.
5 shot groups were used.
Starting out using the 1/10th grain groups of pellet weights as in the weight tests (see previous post). For the JSB EXACT these ranged from 8.20gr to 8.70gr. I shot groups at 45, 50 and 55yds. However, the groups at 50 and 55yds were disappointing but showed enough of a variation to keep me interested and so I decided to narrow the weight ranges further and have the groups more distinct in weight. So the new weight groups were (in grains):
8.24 to 8.29
8.30 to 8.35
8.40 to 8.45
8.50 to 8.55
8.60 to 8.65
I then shot groups at the same ranges again.
Here are the results:
At a glance, the elevation of the POI clearly varies according to the weight, as we would expect, but the question remains: is the variation shown here “significant”. That of course depends on what you want to do…
The total range of elevation for all the pellet weights tested, ie: as if pellets were taken straight from the tin, considering that each horizontal marker on the target is a ¼ inch/ 6mm, is as follows:
45yds = 1 in / 25mm
50yds = 1 ½ in / 38mm
55yds = 1 ¾ in / 44mm
Against the average size of the groups achieved after weighing and grouping by weight, ie: as if the zero were adjusted according to the exact weight of each pellet:
45yds = 3/5th in / 15mm
50yds = 4/5th in / 21mm
55yds = 4/5th in / 20mm
What these figures seem to indicate is that at up to 45yds, a group straight from the tin is very acceptable, so fine for HFT and hunting up to this range. But as soon as the range exceeds 45yds the groups we can expect direct from the tin are far less convincing and suggest that for consistent grouping from 45 to 55yds in this case weighing pellets is advisable.
Final Conclusions:
Although this could be viewed simply as a test of JSB EXACT and not representing a general rule that can be applied to all pellets, if your chosen pellet does show a weight variation of over about 3.5% (see previous post) and if you want to get the most out of your gun at longer ranges then weighing pellets is going to help you achieve it.
copywright Asa Goldschmied
www.pellet-perfect.com
copywright Asa Goldschmied
www.pellet-perfect.com