by Tom Gaylord
Writing as B.B. Pelletier

El Gamo XP-68
The El Gamo XP-68.

Part 1

A history of airguns

This report covers:

  • Preparing to shoot
  • Petroleum oil or silicone?
  • Velocity determines which oil you need
  • Velocity
  • Deep-seating
  • JSB Exact RS
  • H&N Baracuda Match 5.51mm head
  • RWS Meisterkugeln
  • Trigger pull
  • Cocking effort
  • Evaluation so far

I said I would return to this report after I repaired the plastic clamshell halves of the buttstock. That job is now finished. I was able to epoxy the pieces of the broken post that receives the stock screw together and, although it wasn’t completely straight, it was straight enough for me to drill a new pilot hole for the wood screw that holds the two halves together. The butt is now complete, so today I will test the velocity.

Preparing to shoot

In preparation to shoot I oiled the piston seal with a lot of silicone chamber oil and let the rifle stand on its butt for a day. If it has a leather piston seal, and I am almost certain it does, the oil will be absorbed and make the leather pliable again. That should give the highest velocity.

Petroleum oil or silicone?

Before I get to the velocity test, I have some words about oiling the piston seals of older air rifles. First, the age of the airgun usually determines whether the piston seal is leather or synthetic — but not always. I would say that most spring-piston guns from the 1950s and earlier have leather seals, but one exception to that is the Hakim military trainer that Anschütz built for the Egyptians in 1954/55. Anschütz was also making the same action into a sporting rifle for sale in Germany at the time, and I have to believe that one used the same black synthetic parachute seal that was in the military trainer. It’s too expensive and confusing to do otherwise.

Why do I tell you this? Because leather piston seals need more oil to keep them pliant. Synthetic seals will operate on far less oil, because they always hold their shape. If you know you have a leather seal, you know it needs a lot of oil. But which type — petroleum or synthetic?

Velocity determines which oil you need

It isn’t the seal material, it’s the velocity the rifle generates that determines the type of oil that should be used. That’s because when the velocity gets up over a certain level, the heat generated by the compression is very high. You want an oil that will not burn easily, so there is no explosion.

The velocity thresholds are caliber-specific. Once the velocity of a .177 spring-piston rifle gets up over 800 f.p.s. it’s time to oil the seal with silicone regardless of what it is made of. But usually it would be synthetic, because that level of velocity only came about in the late 1970s, when synthetic seals came into popular use. For .22 caliber the threshold is around 700 f.p.s., and so on. Nothing is exact or precise, these are just general guidelines.

Given that information, it is a sure bet this El Gamo can use petroleum-based oil on the piston seal with no worries. Not that silicone won’t work, because it works fine. But it costs more and isn’t really needed.

To generalize, spring piston airguns made in the 1950s and earlier are lubricated with petroleum-based oil. Those made after that time may use silicone, unless you know for certain that the velocity is very low. Then petroleum oil works best, because it is cheapest. This air rifle I am testing is low velocity for sure, so petroleum oil will work. I used silicone, however, because the applicator needle was easier to get inside the air transfer port.

Velocity

Now let’s see what the velocity is. I will start with a lightweight lead pellet that is widely used to determine the velocity of airguns, because it often shoots the fastest. Of the practical lead pellets you might use — the .22-caliber RWS Hobby is one of the best. In .22 caliber Hobbys weigh 11.9 grains, nominally.

Hobbys averaged 454 f.p.s. from the rifle, which tells me the powerplant is in fine condition and doesn’t require attention. Shooting is smooth and crisp, without much vibration. The spread ranged from a low of 447 f.p.s. to a high of 461 f.p.s., which is a total of 14 f.p.s. That’s pretty good for an older spring-piston gun and a leather seal.

Deep-seating

I did try deep-seating the pellets with a pellet seater, but it didn’t seem to make any difference. So I seated most of them flush with the breech.

JSB Exact RS

Next to be tested was the JSB Exact dome. At 13.43 grains these are a little heavier than Hobbys, so we expect they will go slower, but not that much. They averaged 437 f.p.s. in the 68-XP and ranged from a low of 433 f.p.s. to a high of 443 f.p.s. That’s just 10 f.p.s., which is very consistent. And I must observe that the powerplant was the calmest with this pellet. This will be one to try for accuracy.

H&N Baracuda Match 5.51mm head

Next I tried the H&N Baracuda Match with a 5.51mm head. The first shot was loud and the gun vibrated a lot. When I saw that the velocity was only 170 f.p.s. I resolved to try one more shot and if it wasn’t better, to give up. Shot two went out at 192 f.p.s. and I was finished. This pellet is just too heavy for this powerplant.

RWS Meisterkugeln

The last pellet I tried was the RWS Meisterkugeln wadcutter. At 14 grains it’s about the heaviest pellet I think I will try, though it might be fun to try a Superdome in the accuracy test. I got a bimodal (two differing averages) distribution with this pellet, depending on how it was loaded. Seated flush the Meisterkugeln averaged 370 f.p.s. with a low of 362 f.p.s. and a high of 377 f.p.s. Seated deep this pellet averaged 400 f.p.s., with a low of 394 f.p.s. and a high of 408 f.p.s.

I noticed when I seated the Meisters there was a lot of resistance entering the bore. If I test this pellet for accuracy it needs to be seated deep.

Trigger pull

The 68-XP has a heavy two-stage trigger pull. It breaks at 7 lbs. 7 oz. at present. The shape of the pistol grip enables me to pull it without affecting the hold on target, so it won’t affect accuracy, but I may try to lighten it a bit. We learned from the other 68-XP that the trigger does respond to adjusting.

Cocking effort

This rifle cocks with just 13 lbs. of effort. That makes it one of the lightest-cocking air rifles I have ever tested! There is an anti-beartrap mechanism that prevents the gun from firing, once cocked, until the breech is closed, so you have to fire it when you cock it. The detent is light enough to not need the muzzle to be slapped to open the barrel, which is quite pleasant.

Evaluation so far

This surprise buy in a pawn shop is turning out to be a very nice air rifle. Now that the butt is fixed and I know the power is where it needs to be, all that remains is to see how accurate it is.