UK Hatsan AT44-10 .177 with 12 FPE limit

[n00b]

This is a summary of the results from some tests I documented on the UK Chinese Airgun Forum (UKCAF). 

I have a couple of co2 rifles, however this is my first PCP. I'm enjoying the experience and my group size has reduced compared to the other guns I use - this gun is accurate up to the ranges I have tested it (up to 40 yards).

This is a UK 2017 model Hatsan AT44-10 in .177. It was purchased used, however an anti-tamper screw was still installed. As far as I am aware settings were UK stock - ensuring the power is below the 12 FPE legal limits here in the UK.

I read and was inspired by Bob's Hatsan AT44S-10 in .25 cal topic. I also read the following -

• Hatsan AT44 breakdown and tune - by UKCAF member walrus
• AT 44 Tuning - by UKCAF member spike589715

spike589715 webpage was of particular interest as he is also constrained by the UK 12 FPE power limit. I also planned to fit a regulator, something covered in spike's webpage.

The most difficult part of the working on the gun was removing the anti-tamper screw.

I note from the pictures of the AT44 here and elsewhere that Hatsan have developed the gun over the years. Mine already has a channel in the back of the stock and hole underneath that allows the hammer tension to be adjusted without removing the stock. The other main difference I can see is in the valve. The white delrin plug has been replaced by a black screw in part with 7 holes in it. I believe that this is similar to the one fitted on the BT65.

The valve stem appears to be the standard high power version. The guns power has been reduced in the UK version with the use of a small transfer port. I was unable to measure it myself, however believe that the TP diameter is 1.4mm (0.055" - approx. 1/16").

The testing methodology has evolved as I've been experimenting, which isn't particularly helpful. Pellets used in tests have changed as I ran out of the H&N Excite Hammer pellets used for initial tests. I didn't accurately record air cylinder pressure levels in some tests and also neglected to accurately record spring tension.


Pre-modifications

Pellets used - H&N Excite Hammer (7.87gr)

Results With the air cylinder filled to 200 BAR -

• Shot 01 - 680.3 FPS / 8.09 FPE
• Shot 10 - 711.5 FPS / 8.85 FPE
• Shot 20 - 748.0 FPS / 9.78 FPE
• Shot 30 - 762.4 FPS / 10.16 FPE
• Shot 40 - 758.6 FPS / 10.06 FPE
• Shot 50 - 753.1 FPS / 9.91 FPE
• Shot 60 - 743.1 FPS / 9.65 FPE
• Shot 70 - 735.2 FPS / 9.45 FPE
• Shot 80 - 714.0 FPS / 8.91 FPE

Shot string from approximately 200 - 110 BAR fill pressure. Shots 16 to 64 were between approximately 180 to 120 BAR.

Shots 1 - 80
Highest velocity = 764.2 FPS / 10.21 FPE
Lowest velocity = 680.3 FPS / 8.09 FPE
Average (mean) = 739.5 FPS / 9.56 FPE
Standard deviation = 21.9
Extreme spread = 83.9 FPS
Extreme spread % = 10.98%

Shots 16 - 64
Highest velocity = 764.2 FPS / 10.21 FPE
Lowest velocity = 739.6 FPS / 9.56 FPE
Average (mean) = 753.9 FPS / 9.94 FPE
Standard deviation = 6.5
Extreme spread = 24.6 FPS
Extreme spread % = 3.219%


Test 1

Modifications: Anti-tamper (AT) removed / deburr + polish / 3x radial ports in valve filled with JB Weld.

Hammer spring pre-tension was set close to maximum to get a reasonable initial FPS. Removal of the AT and spring guide resulted in difficulty adding enough pre-tension for my target of around 10-11 FPE.

The results showed no power curve - just a drop in FPS with each shot.

? the increased hammer spring pre-tension may have been enough to overcome the 200 BAR fill pressure when opening the valve. Before modifications, the hammer appeared to struggle initially until pressure in the air cylinder reduced to 180 BAR - resulting in the power curve in the pre-modification shot string before the AT was removed.

Pellets used - H&N Excite Hammer (7.87gr)

Results With the air cylinder filled to 200 BAR -

• Shot 01 - 779.7 FPS / 10.63 FPE
• Shot 10 - 750.4 FPS / 9.84 FPE
• Shot 20 - 725.1 FPS / 9.19 FPE
• Shot 30 - 692.4 FPS / 8.38 FPE
• Shot 40 - 660.0 FPS / 7.61 FPE

Shots 1 - 40
Highest velocity = 779.7 FPS / 10.63 FPE
Lowest velocity = 660 FPS / 7.61 FPE
Average (mean) = 729.1 FPS / 9.29 FPE
Standard deviation = 35.32
Extreme spread = 119.7 FPS
Extreme spread % = 15.35%


Test 2

Modifications: Transfer port opened out (from 1.4mm to 2.5mm) + previous mods (Anti-tamper (AT) removed / deburr + polish / 3x radial ports in valve filled with JB Weld).

Pellets used - H&N Excite Hammer (7.87gr)

I took two shots and quickly dissembled the gun. FPS = 1111 (21.58 FPE)


Test 3

Modifications: Previous mods (Transfer port opened out (from 1.4mm to 2.5mm) / Anti-tamper (AT) removed / deburr + polish / 3x radial ports in valve filled with JB Weld).

Pellets used - H&N Excite Hammer (7.87gr)

Results With the air cylinder filled to 200 BAR -

• Shot 01 - 689 FPS / 8.30 FPE
• Shot 10 - 704 FPS / 8.66 FPE
• Shot 20 - 735 FPS / 9.44 FPE
• Shot 30 - 745 FPS / 9.70 FPE
• Shot 40 - 763 FPS / 10.18 FPE
• Shot 50 - 779 FPS/ 10.61 FPE
• Shot 60 - 817 FPS / 11.67 FPE
• Shot 70 - 858 FPS / 12.87 FPE
• Shot 80 - 898 FPS / 14.10 FPE
• Shot 90 - 933 FPS / 15.22 FPE
• Shot 100 - 939 FPS / 15.41 FPE
• Shot 110 - 948 FPS /   15.71 FPE
• Shot 120 - 925 FPS / 14.96 FPE
• Shot 130 - 892 FPS / 13.91 FPE
• Shot 140 - 849 FPS / 12.60 FPE

Shot pressures:  Shot 20 = 190 BAR / shot 40 = 180 BAR / shot 60 = 160 BAR / shot 80 = 140 BAR / shot 100 = 120 BAR / shot 120 = 100 BAR / shot 140 = 75 BAR

Hammer spring adjuster at approximately 6 full turns in (low pre-tension - maximum is 7-8 turns in). Fill pressure = 200 BAR.

Based on a visual check of the pressure gauge in the air cylinder, peak power was achieved at somewhere between approximately 120 to 100 BAR.

Shots 1 - 100
Highest velocity = 945 FPS / 15.61 FPE
Lowest velocity = 687 FPS / 8.25 FPE
Average (mean) = 805.05 FPS / 11.33 FPE
Standard deviation = 79.20
Extreme spread = 258 FPS
Extreme spread % = 27.3%

Shots 78 - 129
Highest velocity = 950 FPS / 15.78 FPE
Lowest velocity = 895 FPS / 14.0 FPE
Average (mean) = 927.35 FPS / 15.03 FPE
Standard deviation = 16.96
Extreme spread = 55 FPS
Extreme spread % = 5.79%


Test 4

Regulator fitted - pressure set to 90 BAR.

Modifications: Previous mods (Transfer port opened out (from 1.4mm to 2.5mm) / Anti-tamper (AT) removed / deburr + polish / 3x radial ports in valve filled with JB Weld).

Pellets used - RWS Superfield (8.3gr)

Results With the air cylinder filled to 200 BAR -

• Shot 01 - 768 FPS / 10.87 FPE
• Shot 10 - 770 FPS / 10.93 FPE
• Shot 20 - 760 FPS / 10.65 FPE
• Shot 30 - 770 FPS / 10.93 FPE
• Shot 40 - 764 FPS / 10.76 FPE
• Shot 50 - 766.1 FPS / 10.82 FPE
• Shot 60 - 766.1 FPS / 10.82 FPE
• Shot 70 - 770 FPS / 10.93 FPE
• Shot 80 - 770 FPS / 10.93 FPE
• Shot 90 - 759.6 FPS / 10.64 FPE
• Shot 100 - 756.8 FPS / 10.56 FPE
• Shot 110 - 764.2 FPS / 10.77 FPE
• Shot 120 - 774.8 FPS / 11.07 FPE
• Shot 130 - 774.8 FPS / 11.07 FPE
• Shot 140 - 759.6 FPS / 10.64 FPE

Shot pressures:  Shot 20 = 175 BAR / shot 40 = 160 BAR / shot 60 = 140 BAR / shot 80 = 120 BAR / shot 100 = 100 BAR / shot 120 = 80 BAR / shot 140 = 60 BAR

The hammer spring adjuster was turned most of the way in to keep FPE under 12. This resulted in no pre-tension on the hammer / spring - it was able to move slightly in the receiver before being cocked.

Shots 1 - 100
Highest velocity = 773.8 FPS / 11.04 FPE
Lowest velocity = 748.5 FPS / 10.33 FPE
Average (mean) = 765.41 FPS / 10.80 FPE
Standard deviation = 4.202
Extreme spread = 25.3 FPS
Extreme spread % = 3.27%

Shots 1 - 140
Highest velocity = 776.8 FPS / 11.12 FPE
Lowest velocity = 748.5 FPS / 10.33 FPE
Average (mean) = 766.205 FPS / 10.82 FPE
Standard deviation = 4.92
Extreme spread = 28.3
Extreme spread % = 3.643%


Test 5

Regulator fitted - pressure set to 90 BAR.

Modifications: Spring replaced (see below) + previous mods (Transfer port opened out (from 1.4mm to 2.5mm) / Anti-tamper (AT) removed / deburr + polish / 3x radial ports in valve filled with JB Weld).

Pellets used - H&N Excite Econ II (7.4gr)

Spring replaced with 8mm OD x 57mm length x 1mm gauge spring. Using a longer and weaker spring resulted in being able to put some pre-tension on the spring whilst still keeping the gun under 12 FPE - stopping the hammer from being able to move around in the receiver.

Initial test with the new spring and hammer adjuster fully in using 8.3gr pellets -
Fully in = 671 FPS average.
3/4 turn out = 734 FPS average
1 1/4 turns out = 758 PFS average
1 1/2 turns out = 769 FPS average

Partial refil of air - same spring tension gave 810 FPS with H&N Excite Econ II pellets

Refilled to 200 BAR and a full shot string was completed with the H&N Excite Econ II pellets.

Results With the air cylinder filled to 200 BAR -

• Shot 01 - 812.4 FPS / 10.85 FPE
• Shot 10 - 809.2 FPS / 10.76 FPE
• Shot 20 - 796.7 FPS / 10.43 FPE
• Shot 30 - 805.0 FPS / 10.65 FPE
• Shot 40 - 804.0 FPS / 10.62 FPE
• Shot 50 - 804.0 FPS / 10.62 FPE
• Shot 60 - 806.0 FPS / 10.68 FPE
• Shot 70 - 796.7 FPS / 10.43 FPE
• Shot 80 - 795.7 FPS / 10.41 FPE
• Shot 90 - 809.2 FPS / 10.76 FPE
• Shot 100 - 812.4 FPS / 10.85 FPE
• Shot 110 - 804.0 FPS / 10.62 FPE
• Shot 120 - 818.8 FPS / 11.02 FPE
• Shot 130 - 806.0 FPS / 10.68 FPE
• Shot 140 - 776.7 FPS / 9.92 FPE

Shot pressures:  Shot 20 = 180 BAR / shot 40 = 160 BAR / shot 60 = 140 BAR / shot 80 = 120 BAR / shot 100 = 100 BAR / shot 120 = 85 BAR / shot 140 = 70 BAR

Shots 1 - 100
Highest velocity = 815.6 FPS / 10.93 FPE
Lowest velocity = 795.7 FPS / 10.41 FPE
Average (mean) = 803.24 FPS / 10.60 FPE
Standard deviation = 4.21
Extreme spread = 19.9 FPS
Extreme spread % = 2.44%

Shots 1 - 140
Highest velocity = 818.8 FPS / 11.02 FPE
Lowest velocity = 776.7 FPS / 9.92 FPE
Average (mean) = 804.04 FPS / 10.63 FPE
Standard deviation = 6.64
Extreme spread = 44.3 FPS
Extreme spread % = 5.41%
_______________________________

If/when I have permission I will attach the excel spreadsheet I have used to record the full shot strings for the tests completed so far.

The most recent test with the weaker hammer spring (Test 5 above) gave very good results from shots 1 to 120. There was a noticable drop in FPS from shot 137 onwards, which messed up the results for the full shot string when shots 1 to 140 were included. I will likely keep my shot count to 120 when at the range. 

I used the H&N Excite Econ II pellets for test 5 because I had run out of the Excite Hammer used for most of the previous tests and did not want to waste my remaining RWS Superfield pellets. Shooting with the same spring tension and switching pellets for JSB Heavy increased my FPE to around 11.5. I will be using these pellets for shooting as they group well and suit my gun.

I noticed a pattern in tests 4 and 5 - both of which were completed with the Lane Lancet v9 regulator installed and set to 90 BAR. When the pressure in the air cylinder dropped to close to (and possibly below) the regulator pressure there seemed to be a slight spike in FPS/power. This can be observed in the attached spreadsheet - refer to shots 115 to 125 in both tests.

My stirrup pump has now failed and further tests and shooting is on hold until I get a replacement or fix the pump.

n00b