Today, Doug Wall explores how the hammer affects PCP performance. It’s the final part of his Barra 1100z tuning series. In this post, he replaces the hammer from the Gen 1 gun with that from the Gen 2 model and finds a significant improvement.
In fact, Doug’s work shows up to a 52% increase in regulated shot count and up to 50% increase in total Muzzle Energy for those regulated shots. WOW!!!
Compared to other tuning methods, changing the hammer has generally received less interest. Doug’s work shows that the hammer affects PCP performance. It’s much more than many of us have thought. Read on to find out…
How The Hammer Affects PCP Performance – Planning
In the last installment, I tested the regulated Barra 1100Z, and one of the conclusions was that a concern could be wasting air, due to hammer bounce. In my discussions with Barra, they suggested that the 1100Z, Gen. 2 hammer might be a good addition for my testing. I was told that with the Gen. 2 hammer installed, I might get some “impressive” shot strings.
When I change the hammer I will also add a 0.20-Inch spacer between the valve and the gauge block, to support the force of the pressure difference between the regulated and unregulated sides of the gauge block.
The Gen 1 hammer weighs 78.77 grams. The Gen 2 hammer is a different design than the Gen 1 hammer, and weighs 63.23 grams. The “general wisdom” is that lighter hammers can give better efficiency, and going back to the old QB78 days, the “wisdom” was that having flats or grooves on the hammer would give less air resistance when it was flying forward (I can’t prove this).
To do this job, I’ll have to do a pretty extensive disassembly, somewhat similar to the regulator installation.
As always, with safety as the first concern, I will degas the gun before working on it.
The next step is to remove the safety lever and stock (see the part 2 article).
Next, slide the barrel band over the end of the pressure tube (it can stay on the barrel).
Remove the upper receiver, by removing the screw inside the “chamber” and the one at the rear of the receiver.
Remove the trigger assembly by unscrewing the two screws holding it on.
At this point, the back end cap of the receiver tube is loose, and if you’re just changing the hammer, you can remove the cocking pin on the hammer, remove the Gen 1 hammer, replace it with the Gen 2 hammer, put the cocking pin in the Gen 2 hammer, and reassemble.
In this case, since I’m adding the spacer between the valve and gauge block, I have to take everything out of the receiver/pressure tube, and reassemble it with the 0.20-Inch spacer.
This is all described in my BARRA 1100Z Part 4 article, and in the Barra Youtube video on the regulator installation, “How to Install a Regulator on the Barra 1100Z PCP”
Briefly:
Remove the end fill plug from the tube. It might be stubborn, and need some tools to do it.
Pull out the regulator using an appropriately threaded tool (1/4-Inchx28).
Remove the gauge, valve screws, and stock lug screw, and carefully push out the gauge block, valve, and the spacer behind the valve.
Carefully reassemble everything, including the 0.20” spacer between the valve and gauge block, using silicone grease on all O-rings, keeping everything in the correct orientation, and taking care not to nick any O-rings.
After reassembly, and leak testing, it’s time to do some shooting!
Since this hammer may behave differently than the original, a few shots at different hammer spring settings were in order, to get a baseline for testing. It appears that the 4, 5, and 6 turns in will work for comparison testing between the two hammers.
For a better look at the performance with the Gen 2 hammer installed, I’ll do shot strings at 4 turns in, 5 turns in, and 6 turns in. All starting with a 3000 PSI fill, and going out below the 1900 PSI regulated pressure.
How The Hammer Affects PCP Performance – Four Turns In
Here are the velocity curve for the Gen 2 hammer at four turns in.
This takes me out to about 57 regulated shots. This is a considerable improvement over the 38 regulated shots with the Gen 1 hammer! Graph below…
The total energy is 973.75 Ft/Lbs for the Gen 2 hammer, compared to 648.96 Ft/Lbs for the Gen 1 hammer. This is a 50% increase!
| Gen 1 Hammer | Gen 2 Hammer | |
|---|---|---|
| Regulated Shot Count | 38 | 57 |
| Average Muzzle Energy Per Shot | 17.10 Ft/Lbs | 17.08 Ft/Lbs |
| Total Muzzle Energy For Regulated Shots | 648.96 Ft/Lbs | 973.75 Ft/Lbs |
| Energy Increase With Gen 2 Hammer | 50% | |
| Shot Count Increase With Gen 2 Hammer | 50% |
How The Hammer Affects PCP Performance – Five Turns In
The velocity curve at five turns in gives a similar improvement. Here’s the Gen 2 hammer.
Now for the Gen 1 hammer in the same gun…
I’m seeing about 47 regulated shots with the Gen 2 hammer, compared to about 32 shots with the Gen 1 hammer. The total energy is 821.30 Ft/Lbs for the Gen 2 hammer, compared to 650.49 Ft/Lbs for the Gen 1 hammer, for a 26% increase.
| Gen 1 Hammer | Gen 2 Hammer | |
|---|---|---|
| Regulated Shot Count | 31 | 47 |
| Average Muzzle Energy Per Shot | 16.93 Ft/Lbs | 17.47 Ft/Lbs |
| Total Muzzle Energy For Regulated Shots | 650.49 Ft/Lbs | 821.30 Ft/Lbs |
| Energy Increase With Gen 2 Hammer | 26% | |
| Shot Count Increase With Gen 2 Hammer | 52% |
How The Hammer Affects PCP Performance – Six Turns In
At six turns in, we see a similar story. Here’s the Gen 2 hammer performance.
This was with the Gen 1 hammer.
At 6 turns in, I’m seeing about 41 regulated shots with the Gen 2 hammer, compared to 27 regulated shots with the Gen 1 hammer. The total energy is 706.70 Ft/Lbs for the Gen 2 hammer, compared to 565.53 Ft/Lbs for the Gen 1 hammer, for a 25% increase.
| Gen 1 Hammer | Gen 2 Hammer | |
|---|---|---|
| Regulated Shot Count | 27 | 41 |
| Average Muzzle Energy Per Shot | 16.53 Ft/Lbs | 17.24 Ft/Lbs |
| Total Muzzle Energy For Regulated Shots | 565.53 ft/Lbs | 706.70 Ft/Lbs |
| Energy Increase With Gen 2 Hammer | 25% | |
| Shot Count Increase With Gen 2 Hammer | 52% |
How The Hammer Affects PCP Performance – Accuracy
Velocity Shot Curves for 6 turns in Gen 1 and Gen 2
As a side note, the accuracy with the 6 turns setting seemed to be exceptional, and I might sacrifice a few shots per fill if this proves to hold true.
How The Hammer Affects PCP Performance – Conclusion
The Barra 1100Z Gen 2 hammer seems to offer a significant performance increase in the 1100Z Gen 1 rifle. For those of you inclined to do the airgunsmithing involved, I would encourage you to make this upgrade.
It may well be that the hammer affects PCP performance in similar ways in other airguns…
This concludes Doug Wall’s series on tuning the Barra 1100z air rifle. Doug has made some outstanding improvements to the performance of his air rifle, plus he has described every step very clearly.
Thanks Doug!!!
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Barra 1100z Air Rifle
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