Testing a new air rifle: Mike Morton explains how its done

Posted on 19/11/2020 by towens — No Comments ↓

Mike Morton explains how he checks a new air rifle to find how well it’s performing, and what ammo suits it best.

A shooting buddy recently asked me to run through the way we test the guns that land on our desks here at Airgun Shooter. My answer was simple: the same way we’d test our own guns or those we’re helping a friend to set up.

But what exactly do we do? I went on to explain to him the various steps we take, and thought it might be useful to do the same here.

The method I’ve illustrated represents one way to test a rifle, but it’s certainly not the only way. However, it is quite thorough, and it does offer the chance to see exactly what each rifle is capable of.

I’ve used a PCP to illustrate the process here, but the procedure for a springer or gas-ram is largely the same.

The naked gun

When I first got into shooting in the 1970s, it was very much a case of grab a gun, fit a scope — if you really must — and off you go.

Pellet selection was limited to what was on the counter, and that often meant swapping types every time you went back to the shop for a new tin, as it all depended on what the shop had in stock.

These days we’re a bit more informed, and we also have access to a wide range of scopes, mounts and pellets to help us build the perfect combo. But how do we know we’ve got it right? By testing!

Whether it’s a brand new rifle or one that you’ve bought second-hand, clean the barrel to ensure you’re starting from a known baseline

Before we can test a rifle, we need to assemble the necessary components
— these being the rifle itself, the scope and mounts, and any additional pieces of kit such as a moderator or bipod.

But before putting anything together, there are some basics I like to carry out straight away — the most important test being to make sure the gun is safe.

One gun I bought second-hand was delivered to me with the magazine still in the rifle — containing a few unfired pellets! I also like to familiarise myself with the controls and functions, and in the case of a PCP, find out what pressure it should be filled to.

PCPs can be safely dry-fired, and I like to take a few ‘shots’ to make sure the rifle is functioning as it should before going ahead and mounting a scope. When it is time to fit the optic, I try to match the scope to the rifle as much as possible.

For example, the Brocock Bantam I’m using here is being mated to the new Airmax Compact from Hawke, which is a scope that works very well with smaller rifles, bullpups and carbines.

Clean regime

When a rifle arrives, you don’t know what condition the bore is in. Some rifles will have been tested for accuracy and muzzle velocity by the factory, often accompanied by a target card and a chrono read-out, and will have a build-up of lead in the barrel.

Others may also have been tested, after which they may have been coated in grease or oil for shipping and storage. And if you’re buying second-hand, you have no idea of what’s been put through the bore, and how much lead or oil residue may have built up inside before it came to you.

Now it’s time to fit the scope — in this case, Mike’s using a new Hawke Airmax 30 SF Compact and Sportsmatch mounts

When it’s time to test your rifle, it’s good to do so from a known baseline — and that means a clean bore. You can carry out this process either before or after the scope has been mounted.

It won’t take long to re-lead the bore in any case, and most pellets work best when they are travelling down a barrel that’s been leaded with exactly the same lead alloy. This is done easily, just by shooting the same type of pellet.

More tips from Mike Morton

Adjust to taste

If your stock offers any adjustments, you can set the height and cast of the butt pad, as well as the height of the comb, to ensure perfect head and eye alignment with the scope.

You may want to fine-tune these adjustments once shooting has started, and you may also need to adjust them again if you wear thicker or thinner clothing than when you carried out your initial set-up, as this can sometimes affect optimal head and eye position.

Fill her up

PCPs can be filled to the recommended standard working pressure, which can vary from one gun to another, even between the same model. But an unregulated PCP will produce a power curve, which will usually be at its most erratic at both the start and end of the air fill.

If the stock allows, adjust the height and cast of the butt pad as well as the height of the comb to ensure perfect head and eye alignment

For this reason, I like to fill unregulated PCPs slightly below the recommended maximum, to give the gun a better chance of achieving optimal precision out of the gate.

Detailed testing to find that precision can be carried out later, when a good-performing pellet has been identified.

Weighty matters

Because a PCP can be dry-fired, it’s possible to test the trigger unit for first- and second-stage travel, then test for trigger-pull and adjust accordingly, but my own preference is to wait until the gun has been taken to the range and shot ‘for real’ before determining whether any adjustments should be made.

Unless the trigger on a review rifle has been set wildly too light or too heavy for its intended purpose, I’ll usually leave it alone so I can give a fair report on how it feels out of the box.

Zero hour

I carry out an initial zero of the rifle at 10 or 15 yards, depending on where I’m carrying out the test and the suitable backstops that are available. I sometimes get asked why I don’t just skip the short-range zero and crack on at my chosen zero, which is usually 30 yards.

With the scope and moderator fitted and the rifle adjusted for fit, it’s ready to be taken to the range to be zeroed

Any difference between your point of aim and your point of impact will increase with distance, so I find it easier to zero the scope at short range, then fine-tune back at my normal zero distance.

But if your range conditions allow, and your targets are big enough to let you see where the pellets are striking, you could do the zeroing session at your chosen distance.

Velocity Rapture

A chronograph, or at least access to one, is essential for every airgun shooter, as it is our legal responsibility to ensure we are shooting air rifles with a muzzle energy of no more than 12 foot pounds, unless we are shooting the rifle on a Firearm Certificate.

But a chrono offers the shooter so much more than the confirmation of a rifle’s legality, as it can also be used to measure how consistently it shoots. In order to get accurate results, it’s important to use pellets of exactly the same weight, otherwise a variance in muzzle velocity can be down to inconsistencies in the ammo rather than with the gun itself.

If you’re shooting an unregulated PCP and haven’t yet worked out the optimal spot, it’s best to slightly underfill the rifle

Some chronos are clever enough to calculate and display muzzle energy themselves, sometimes requiring a phone app or PC/laptop cable to display the data.

If your chrono doesn’t do this, you can work out muzzle energy for yourself by taking the weight of the pellet in grains and multiplying it by the square of the velocity, then dividing the result by 450,240.

This sounds more complicated than it really is, so for a pellet weighing 8.4 grains and a muzzle velocity of 780 feet per second, the calculation would be 8.4 x 780 x 780 = 5,110,560.

Now divide this number by 450,240 and you get the muzzle energy figure, in this case 11.35 foot pounds. Recording muzzle velocity in feet per second, noting the spread over a set number of shots and working out the average velocity will not only let you calculate muzzle energy, it will let you compare your initial findings with any future results you record — provided you use the same pellet.

After a few hundred shots have been fired, velocity may increase or decrease slightly, so check to make sure it’s still legal, but it should also become more consistent as the rifle beds in, regardless of whether it’s a PCP, a springer or a gas-ram, so I like to chrono a rifle at least twice over this test period.

Great expectations

Testing a favourite pellet in a different rifle is a bit like following a favourite football team. You know they’re a good team that are capable of getting some great results, and expect them to keep on winning. The reality is a bit different, however.

While we all want our guns and pellets to perform well, some will perform better than others. The real test is to find out which pellet will maximise a gun’s potential, whether it’s a hunter, plinker or target rig.

Let battle commence

In order to get the most accurate results, the rifle should be shot in as perfect conditions as possible, and that means shooting indoors in still air, from either the prone position or a bench.

It’s not always possible to get the range time to carry out tests indoors, and when that’s the case, which can be quite often, I will have to shoot outdoors instead, but choosing as windless a day as possible.

Heavy-duty shooting bags are a very stable way to support the rifle when you’re carrying out any testing

While I like shooting prone, shooting off a bench is preferable. It’s extremely stable, much more comfortable, and lets you load magazines and take note of your results more easily. If a rifle is capable of fitting a bipod up front, I will sometimes shoot it this way, but a sturdy bench bag can offer more stability.

If you have the option, I suggest you try both and choose the one that you feel most comfortable with. If I’m shooting a springer, I’ll rest my leading hand on a bench bag, then rest the rifle on the palm of that hand.

In general, no matter how tempting it may be, resting a springer directly on a bag just won’t work, because the rifle will not be able to recoil in exactly the same way each time, and so point of impact will therefore be inconsistent.

There are some rare exceptions, such as the Diana Model 56, a sidelever-operated springer that minimises felt recoil due to an integrated sled system, and doesn’t seem to mind being shot off a bag.

Ammo and targets

If you’ve been shooting for a while, you’ll probably have a stash of pellets that you can try in your new gun, otherwise you may have to start from scratch.

Advice from friends, forums and our pellet tests in Airgun Shooter can point you in the right direction, but what shoots well in one gun may not in another, so you may need to shoot several types of pellet before you find ‘the one’.

Assemble a selection of pellets — you may have your own favourites, but the only real way to find out what works best is by testing

I like to use the same type of targets for rifle testing as I do for my pellet tests — a Birchwood Casey Target Spot. These are available in a variety of sizes, but I like the 1” type for accuracy testing. I lay out 10 Target Spots and shoot five pellets at each target, shooting a total of 50 pellets of each type.

Interpreting the results

With a pellet that’s known to be a good performer in a particular barrel, I’ll expect to see a wide cluster slowly getting tighter with each subsequent group, as the barrel leads up to its optimal level when it’s been shot from a clean bore.

But with a rifle that’s never been tested before, the results you actually get may be quite different. The pellets shot at the first target shown here didn’t deliver the expected results.

I shot top to bottom, left to right, and the groups started off quite well before getting worse, then steadily better, then worse again. I suspect the head size and bore are only marginally mismatched, but nevertheless it’s enough of a mismatch to reject these particular pellets in this particular gun.

Whichever pellet you choose the begin the test with, the rifle will still need to be zeroed, starting at a close-range target

When switching to the next pellet to try, I cleaned the barrel again. It might not have been that dirty after just 50 pellets, but it’s all about starting the next test from the same baseline — a clean bore. Keep an eye on your air too if it’s an unregulated PCP.

It’s a fairer test to shoot from the same starting pressure each time. It means more time spent on top-ups, but it also ensures more consistency when testing.

Now it’s time to shoot again, and the pellets shot at the second target delivered some impressive results, with an already reasonable five-shot group shot from a clean bore becoming nice and tight after just 15 shots.

Be prepared to make massive turret adjustments to alter your point of aim and shift point of impact at a target 10 or 15 yards away

I’m showing just two targets here to illustrate a point. In reality I’ve shot guns that have turned in superb results with the very first pellet I tried, while I nearly gave up on another gun after experimenting with 10 different pellets, only to find it was a real tack-driver when I tried the eleventh.

So the moral is to keep trying until you’ve got the results you’re looking for.

How many shots?

One of the most frequently asked questions concerns how many shots a PCP will deliver. There are two fairly easy ways to find out, but both potentially involve a lot of shooting, and both of them require you to start from the same fill pressure.

The first involves using the chrono and recording the muzzle velocity of each and every shot. You’ll typically see a pattern forming where the shots are within a few feet per second of each other.

50 pellets of the same type were shot from a clean barrel to first lead the bore and then to determine their performance

Job done! Going from a clean bore to a one-hole group at 30 yards in just 15 shots marks this pellet as a stellar performer

When muzzle velocity fluctuates outside of this pattern, you know you’ve gone beyond any reliable shot count. The second method is more accurate — and is certainly more fun, although it’s more mentally draining — and that’s to shoot a series of groups.

Just keep going until group size starts opening up, then you’ll have found the limit. Both these methods can be used to find the sweet spot too, with the groups maybe not being so tight at the start of the test, shrinking as you shoot over the flat part of the power curve, then opening up again as fill pressure gets too low.

What next?

I haven’t touched on how to calculate holdover or holdunder points, because these are skills the shooter needs to learn to get the most out of their combo, and are not a function of how well a gun shoots.

But with the testing done, it’s time to get out in real-world shooting situations and start testing yourself, not just your gun – and that’s going to be a welcome break after some intensive range-work.

It’s important to clean the barrel when switching pellet types to establish a known baseline for the next test

Several hundred pellets and weeks of shooting later, you’ll not only know how well a rifle performs, but know how well it works for you. And wherever you take your rifle, whether it’s in the hunting field or in competition, remember the main reason we shoot — to have fun.

Rifle testing, like any other type of shooting, demands a high level of concentration. But once you know you can take a successful shot, it’s a case of grins all the way — every day.