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31 July, 2009

QB 57 Performance Review. Part 1 - Muzzle Velocity and Dieseling.

The QB57 is this interesting take down air rifle from China manufactured by the Shanghai Airgun Factory and sold by Archer Airguns.

I like the QB57 a lot - it’s a fun gun to shoot, unusual-looking and is quite hold-tolerant for a spring air rifle. And although I am the first to agree that the finish and appearance of the QB57 is not among the best, it really shoots well. But how well?

To answer that question, I’ve analysed the results of Archer Airguns “Gold Service” testing for a large number of QB57s and graphed the results for easier understanding. To my knowledge, this blog contains the first comprehensive performance analysis of “hard data” that has ever been published for the QB57. Here’s what I found...

Overall, the QB57 significantly improves on the manufacturer’s specifications and performs very well for an air rifle in this price range.

First things first. Please remember that “Gold Service” testing is performed with heavy, flat-nosed wadcutter pellets, so my results will clearly be slower than for the same gun shooting light, pointed pellets.

Also, I’m always testing new guns. Some of these are “dry” from the factory, while others have their innards liberally coated in oil. (Don’t ask me why, that’s just the way they are). This is important as all spring air rifles that have oil in the compression chamber will tend to “Diesel”. Some of this oil will actually combust due to the pressure of the compressed air in the chamber - the result is increased, but erratic muzzle velocity. We will see the effects of Dieseling clearly in some of the results here.

Let’s get to the results...

Muzzle velocity for the QB57 in .177 caliber is very close to the manufacturer’s claim of 650fps. “Gold Service” testing averages about 620fps - 95% of the manufacturer’s claims: it would probably equal the claimed muzzle velocity with light, pointed pellets.

This graph shows the distribution of muzzle velocities actually recorded on test. The higher velocities - above about 660fps are real and clearly the result of Dieseling.

QB57 muzzle velocity results in .22 caliber suggest that the manufacturers have under-specified this little gun with their claim of only 480fps. As you can see from the graph below, I have recorded muzzle velocities of 700fps on test with Dieseling guns. That’s around 15 ft/lbs of muzzle energy from this little gun. Wow!!!

I would suggest a more realistic muzzle velocity specification in .22 to be about 560fps, that’s 15% above the manufacturer’s claims. Now this is really unusual - an air rifle that actually gives a muzzle velocity greater than is advertised!

So how does Dieseling effect muzzle velocity consistency?

Well, consistency is expressed mathematically as “Standard Deviation”. Basically, a low standard deviation figure is good - it means that the shots are all of a similar muzzle velocity. A high number indicates considerable inconsistency and is, therefore, bad.

As we said, Dieseling effects all spring guns - not just the QB57. But the graph below clearly shows its impact.

“Dry” QB57s have a standard deviation of below about 10 fps in “Gold Service” testing. Compare this to an average for QB78s of around 5 fps. Not bad at all.

But it’s easy to see a sharp jump in the graph - suddenly standard deviations double and then triple very rapidly. This is Dieseling in action and it’s the guns with plenty of oil that do it.

Dieseling declines as the oil burns off - any spring air rifle will dry out with time. This leads to a conclusion that the average standard deviation for a “dry” QB57 is well below 10fps. Let’s say somewhere between 5 and 7 fps. This is very creditable for such a low cost spring air rifle.

But wait, there’s more... and it will be published in Part 2 of this review.


18 July, 2009

The Crosman 760 - a Review

Crosman claims that over 12 million of these little air rifles have been sold during an continuous production run starting in 1964 - that’s well over a quarter a million a year for 45 years - so they must be doing something right with their Crosman 160!

To find out, I did what most people do. I went to Wal-Mart and walked out with one under my arm for the princely sum of $29 plus tax. But then I decided to do what most people don’t : I gave the Crosman 760 an Archer Airguns “Gold Service” test to find out what performance it produces. I also tested it with four different types of pellets to see how pellet sensitive this 760 is.

Crosman claims a muzzle velocity of up to 600 fps with pellets for the 760. I’m here to tell you that my Crosman 760 achieves nothing close to that with lead pellets - it’s more like 500 fps. But using Crosman Silver Eagle lead-free wadcutters, my 760 did manage to average nearly 630 fps.

Amazingly, I’ve never shot a Crosman 760 before, but I here’s what I found...

The gun is overwhelmingly “plastic” to the touch - as most of the parts are made of this material. Personally I don’t like this, but it does make the 760 very light and easy to hold. It’s undoubtedly a big contributor to that sub-$30 price point, too.

Pumping was surprisingly hard and made a loud sound each time the forearm completes its stroke and hits the air tube. This actually seems louder than the sound of the 760 firing! I used 10 pumps for each shot, the maximum recommended by the manufacturer, to achieve the highest muzzle velocity.

I thought the trigger was fine. Mine pulled fairly evenly at about 3.5 pounds. And I had no jams in 50 shots (that’s 10 “warm up” rounds plus four test targets of 10 shots each). Not bad! The factory iron sights are also surprisingly good, although I used a red dot scope for the testing.

The 760 comes in a nice, brightly-printed box and the instructions are in Spanish and English. I can’t read Spanish, but the English instructions didn’t really seen ideal to me, I still needed a little experimentation to learn how to load the pellets into the clip and the clip into the 760, for example.

So how did my 760 shoot? Well, the test targets are below. I simply followed the standard Archer Airguns “Gold Service” test procedure four times with different pellets. Each test was fired with 10 pellets. And each time I called a “flyer” with one pellet that was way out of the main group. You’ll see this below. All the tests were shot using my trusty Leapers red/green dot sight.

First off, the standard Crosman wadcutters. Available everywhere, these shot at an average muzzle velocity of just over 480 fps, giving a muzzle energy of a little over 4 ft/lbs. Don’t hunt any bird or animal with this gun, there’s not enough power for a humane kill in my opinion. Accuracy was OK-ish. Not bad for a sub-$30 gun with an un-rifled barrel.

Next, I tested Crosman Silver Eagle wadcutter pellets. As in every gun I’ve shot these through, the muzzle velocity was excellent - 25% better than with lead pellets. The bad news? That muzzle velocity comes with even less muzzle energy (because of the light weight of the pellets) and abysmal accuracy. I can’t hit the proverbial barn door with these pellets in any air rifle.

Third was the turn of the Chinese “The Peak” pellets that we sell. These produced better accuracy and muzzle energy than the Crosman lead wadcutters, probably because they use a softer lead and have a wider “skirt”. These probably sealed better in the barrel and allowed less air to leak past the pellet than the Crosman wadcutters. They gave the highest muzzle energy at nearly 5 ft/lbs, together with fairly reasonable accuracy.

Finally I tested Crosman Premier Light pellets. These domed pellets are relatively expensive, but wow, what great accuracy! Suddenly the 760 was producing excellent accuracy, vastly better than I expected for this little air rifle. Just look at this test target!

So, the little 760 finally found a pellet it liked, and how!

Overall, I feel that you can’t complain about the Crosman 760 for $29.00. But somewhere around $70 buys a far, far, far better air rifle, such as the QB78 or QB36-1. These guns are all metal and wood and will last a lifetime, they’re more accurate and significantly more powerful, yet still easy to shoot - and they don’t need all that noisy pumping...


09 July, 2009

QB18 or QB20?

This air rifle is an experimental model produced by the Shanghai Airgun Factory and shown at the 2009 SHOT Show. It carries the designation QB18, serial number Y802557, but actually was at the show representing the QB20 model. The difference between the QB18 and the QB20 is really just the stock. The QB18 has a wood stock, the QB20 stock is synthetic.

What makes this particular air rifle unique is that the stock is printed with a prototype camoflage pattern - the QB20 shown in the Shanghai catalogue has a black synthetic stock. It's a "one of a kind", at least so far. Do I like it? Well, let's say I'm not keen on the cammo pattern...

I test fired the gun for this blog - certainly the first time it had been fired. There was no dieseling, but the muzzle velocity for three shots averaged 605fps with heavy (8.6g) "Peak" wadcutters, which matches the factory spec of 600fps well - this is a .177 model. Accuracy was commendable too, with my first three three shots making a tight cloverleaf at 10 yards over open sights. And this in spite of an incredibly heavy trigger pull of around 9lbs! This is not typical for the QB18, in my experience.

Overall, a sweet little gun. Light weight (5lbs 12 oz), easy to cock and shoot - with good accuracy. Maybe the factory thought it would never be shot, or they would certainly have done something about the trigger pull.

Will we ever see this model in production? Your guess may be as good as mine...


02 July, 2009

New Single Shot JRA Breech for QB78 Family Air Rifles

Many of you will have heard of “JRA”, Jay Joyner’s venture into making custom airgun parts. Jay’s first product was the QB78 family rotary indexing magazine system (which you can find in our store).

Jay’s next move is to manufacture replacement breeches for the QB78 family. This post covers the single shot JRA breech - in fact of a prototype that Jay sent me for review. Archer Airguns will be selling these breeches very soon - once we receive stock available from production.

The main benefit is the increased height and clearance provided by this breech compared to the factory breech. The rise is 4.5mm greater than for the factory breech. This allows much greater clearance for 9oz tanks used on a QB79 or AR2079A, or for use with custom shrouded barrels. The breech also provides a precision mounting base for scope rings and accepts the factory rear peep sights, too.

My first thought was “wow this is heavy!” The JRA breech weighs 21 ounces - that’s 14.6 oz (yes, nearly a pound) - heavier than the stock factory breech. It’s precision CNC-milled from solid steel and is supplied with replacement hammer and cocking pins, breech locking screw and barrel setscrews. This is clearly a high quality product. It functioned faultlessly.

This single shot breech works with standard factory barrels and bolts in either .177 cal. or .22 cal. from any QB78 family model. Installation is very simple - almost exactly the same as for fitting a factory breech. A material difference is that barrels are a tighter fit than most factory breeches and they are retained with two setscrews instead of one. This provides a very solid fixing for the barrel in the breech, useful as factory front bands can no longer be used with this breech due to the increased rise.

You can see a comparison of the JRA and factory breeches in the photograph below.

Archer Airguns will be offering the JRA single shot breech as a parts kit, or we will install it on new QB79 family air rifles ordered from us if you wish.


About This Blog

This blog shares information, ideas and knowledge about air rifles. It compliments the information Stephen publishes on the Archer Airguns website, on YouTube and the Chinese Airgun Forum.

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