How to DIY tune a HW77K spring airgun: Part 4
Tuning Weihrauch air rifles is one task that most guys skip over and if they endeavour to “tune” their springer, they seldom follow a recognised series of steps that need to be followed to the letter ( if you want the best from your gun that is). It is not a “five-minute” process and in fact, can result in pulling down a gun many times to get it right. One HW77K that comes to mind, took me 14 rebuilds and adjustments to reduce the group from 48mm at 30 metres down to 8mm at 30 metres. In fact, throughout the competitive life of a spring air rifle, it needs constant adjustment and resetting to get the optimum performance from it.
What I am putting forward here is how I do it and there are others who are tuning Weihrauch air rifles that do it differently than myself, with each of us getting there in the end with the results we want (most of the time that is…). Tuning Weihrauch air rifles does not stop at fitting a Vortek or V-Mach kit. That is but one of the first steps and I will assume that you now have a kit in your Weihrauch HW77, HW77K or HW97K and wish to complete the tuning cycle. Tuning a HW97K will be exactly the same procedure.
Air rifles Australia wide are usually FAC classed and this tends to reduce their accuracy to a degree when put against a 12Fpe air rifles that they use in the UK.
Test Fire your air rifle
If you have fitted the kit and assembled the rifle then you will need to check that it functions correctly. So take extra care loading the gun and placing your digits in the loading port, should the trigger let go, it will hurt I reckon. You need to test the bear trap works while holding the loading arm down (do NOT let go of it…) and then you need to test the safety while pointing the air rifle at a backstop capable of trapping a pellet.
Fast forward here. Let us assume that the assembly went well, the bear trap works, you haven’t lost any fingers and the safety works well. Now set up a target at no more than 20 metres as we are but testing the rifle, not competing yet.
At this point, I usually put through 20 or so shots using H&N Baracudas and pepper the target. The reason I put through 20 shots is that the grouping tends to change after a few shots as the rifle seal beds in and the spring develops a ‘set’ etc. 20 shots will give you a good idea of how it groups and feels and will allow you to re-zero the scope.
Then with a new target, I put 10 shots into it recording the speeds, energies, extreme spread and standard deviation. This gives you a benchmark to start tuning. If you do not have a chronograph and you can’t borrow one, then rely on your grouping and follow along.
Tuning Weihrauch air rifles: Pellet Selection Testing
Know this, the perfect pellet does not exist that suits every air rifle, period. You would have a better chance of finding Keyser Söze than the perfect pellet, so don’t bother looking.
At this point I get out a good cross-section of pellets, sometimes as many as 15 or more types, to put through the air rifle to find a suitable match for the gun. You need to understand that every air rifle is different and each gun has its own “DNA” for want of a term, so now you need to find which pellet type performs the best.
Next put in 10 shots per target without changing your point of aim (POA) so that you can compare the trajectory of each pellet in your gun. Shooting only 3 pellets into a target does not give you the grouping, but 10 pellets do give you a good idea of where it’s at.
I generally narrow it down to between 6 and 10 pellet types, finally selecting the one with the tightest group. Which pellet this is, only testing will decide.
Tip #1. When aiming at the target I zero in on the circle in the centre of the 5 in a 6-circle target or the centre of the 9 in a 10-circle target – see image below. Aim small and miss small, aim large and miss greatly. I set the scope so that the pellets hit the bull (hopefully) below my POA. If you aim at the bull, it is fairly large, and you need to judge the centre which is harder to do that placing the reticle on a small circle. Then if you do hit the bull, the resultant damage to the bull with multiple shots makes judging the centre more difficult. You can always move the Point of Impact around the target with your scope settings.
When you have found a pellet that is grouping well, then you can move onto getting it to group even better.
Your selected pellet type
At this point, I will use the H&N Baracuda Hunter as the “best” pellet in this exercise. This pellet supposedly weighs in at 18.21 grains for a .22 calibre pellet. However, if you weigh a bunch of these pellets using a digital jewellery scale that can measure down to .01 grains, you will find that these pellets can weigh anything from 18.10 to 18.30 and in-between.
To start the selection process so you can drill down and find the best weight for this pellet, you need to first inspect each pellet, yup, each individual pellet. Skip this process and you may as well fast forward to the end of this article.
Empty a few of tins of H&N Baracuda Hunter (in this example only) onto a soft towelling material and carefully pick up each pellet and inspect it for dents around the nose and more importantly, around the skirt. The pellet skirts are thinner and more prone to being deformed through rough handling and transport.
Place in one pile all the ‘good’ pellets and put the failed ones away from this process. Once I have around 200+ ‘good’ pellets I then wash them, 50 at a time, in a plastic jar with a sponge base so that the pellets do not get crushed. I use acetone and a 1” paint brush and gently brush the pellets around the bottom for half a minute or so. I then empty them into a plastic sieve and wash them under hot water, finally drying them in soft towelling.
Tip#2. Check that the sponge, plastic jar and paint brush can withstand Acetone by using a small amount as a trial.
Tip#3. Some guys use washing detergent instead of Acetone that works well too. Safer by a long shot but it needs closer inspection to see that no remaining manufacturing compound still remains on the pellets.
The idea of washing the pellets is to remove any factory added preservatives, anti-oxidants or lubrication necessary for the manufacturing process. I have seen some pellets with visible amounts of a “wax-like” compound in and around the skirts.
Once you have washed and dried your pellets you then need to weigh them on your digital weighing scale. I usually end up with up to 5 piles of pellets of different weights, that is +/- .02 grains.
Further Pellet Selection
In the next step, you need to arm yourself with pen and notebook and set up ready to test each individual pellet pile. Start with either the heaviest or lightest and fire 10 shots noting the speeds and groups obtained. Then work your way through the individual piles of pre-weighed pellets and you should find that a particular weight works best, giving you the best group.
Now do NOT expect to get marksmanship results doing this as it is only one brick in the tuning wall and there are more bricks to lay, so to speak.
I then record the best, next best and third group by pellet weight. Following this, I lube some of these pellets with Dry Lube sprayed onto a fine sponge and I lightly rub them around to cover them. Do not drown the pellets with dry lube but let the sponge transfer sufficient lube to do the trick. Only do 10 pellets of each of the three best-performing weights.
I then shoot 10 shots using one group and record the results. Then fire 5 un-lubed pellets through the gun before shooting the next 10 best performing pellets. Repeat this until you have fired all 30 lubed pellets followed in-between each group with 5 un-lubed pellets. You should see a difference in grouping at this stage and if you don’t, then repeat the process using a different lube like a varying viscosity of silicone.
You can actually buy pellet lube, with 2 customers of mine in Brisbane, Tony and Allan, swearing by it. Below are 2 sets of images before and after with lube on the pellets much like I have done above but using a branded pellet lube called Napier Pellet Lube. There are others and a Google search will identify them but getting them here in Australia is another issue. You need to follow through if you are into improving accuracy in an air rifle that does not perform.
Target Images Courtesy of Allan Ruffolo, Brisbane, Qld.
The next step
OK, so if you have followed this process up to this point, you should have increased the accuracy of your air rifle by some small margin. Now if you want to go further and tighten the group some more, you need to alter your pellet speed.
This can be done by first stripping the air rifle and adding some shims to the spring and then firing 3 groups of your best-performing pellets with the best performing lube (or no lube as the case may be). If the groups tighten, then add another couple of shims and so on. If the groups do not tighten or in fact get larger, then you need to remove any default shims that are in place and reshoot the gun. When you run out of shims you will need to shorten the spring bit by bit or replace it with a softer spring. This is where a lot of air rifle accuracy problems start and end.
I have had to take off 1½ coils on one gun I tuned to bring the groups down to a competitive level, so you can now see that guns, springs, barrels and pellets etc., all vary considerably. The reduction in spring pressure obviously reduces the pellet speed, but more importantly, it reduces the recoil too, hence the addition of spring guides in tuning kits. There are exceptions to this, as in all spring gun tuning. I have cut off 2 coils on a spring and the pellet speed increased! The accuracy also increased, why? Most likely the spring was too long to begin with and was spiralling when under compression. Reduce the spring length and you reduce spiralling under pressure, hence you increase the efficiency and spring rate.
You need to record the weather temperature and humidity if you want to get really serious here as humidity and temperature play a big part in pellet performance. Now I can just hear the ‘naysayers’ rumbling in the background. Well do this if you do not believe me:
- Record your best consistent grouping along with the ambient temperature and humidity.
- Then on another day when it is either hotter or colder shoot the group again with the same pellets. Point made.
We have found that when you sort your pellets into 5 groups after weighing them and final testing, that you get different results according to the climate. In fact, I have noted with one springer, on a cold day it performed better with a different pellet altogether. So, do not be surprised if you find your results kind of ‘fluid’ and forever changing, hence the need to document your tuning to make sense of it all so you can stay in front.
In another article, I will cover resizing pellets and give examples of temp/humidity changes to grouping results as this article is getting a bit long at this point.
Tuning Weihrauch air rifles summary
Before you race off and start tuning your air rifle, you need to be able to demonstrate to yourself that you are at least a fairly competent shooter. If you can’t hit a barn while standing inside one or your shooting is erratic at best, then no amount of tuning is going to help. Your air rifle should have a good quality scope on it like a Hawke Airmax or one of the up and coming MTC scopes, as these sights handle springers well. Those of you who are into tuning Weihrauch air rifles, you need to have a benchmark of what you are capable of doing target wise, PRIOR to embarking on an air rifle tuning exercise.
Author: Ian McIntosh, Gunroom