AEA HP varmint upgradabilty?

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I changed the springs in the trigger assembly on my AEA HP Carbine, the trigger was much lighter, but I immediately started getting a couple of double shots shooting each magazine. I put the original springs back in and it went back to normal semi-auto function. I think the lighter trigger springs would work in the Varmint model as it doesn't have to capture the hammer like the Carbine does in semi-auto.
 
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So my .25cal Varmint is here and I'm loving it so far!
It shoots JSB 25.39gr pellets hole-on-hole at 35 yards, moving around 920fps. That setting on the power wheel is a little over 1/3 up the scale, and it's very repeatable if I want to go back to it from another tune. The shot-to-shot velocity is remarkably consistent over at least 4 magazines of shooting.

The issue I'm seeing now, and I'm hoping someone else has a thought on it... When I'm tuning for slugs, I turn the power wheel all the way up. What happens is that the velocity starts pretty low (840), and the slugs don't group very well. But then after about 1 magazine, the velocity creeps up to about 880 and up to a little over 900, and the slugs will group to right on top of each other, actually sub-MOA.

This is with H&N 36gr and ZAN 37gr. Has anyone else seen this with their rifle? Every lower power setting on the dial shoots a very even shot string, but at max power it takes about 10 shots to get to a workable velocity.

My workaround for this so far has been to only fill to about 3400 PSI, or about the pressure when the shots start pushing past 880. If I do that, the velocity is good and the accuracy is like a laser beam. But obviously that means I'm sacrificing a certain percentage of my shot count. Is there something else I can do to counter this and still be able to fill my bottle to 3600? This only happens at the max power setting, and it would be great if I didn't have to sacrifice shot count for power and accuracy.


Varmint 1.jpg
 
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The problem is that your hammer is not striking hard enough to open the valve fully at high pressure and you’re seeing that with the heavier slugs.

Your solution of filling to lower pressure is a good one. An easy alternative would be to add some spacers to increase the amount of preload on your hammer spring. Another possibility is increasing the weight of the hammer but that is probably not as simple.
 
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This seems to be the norm for these guns. 3600 is just a bit too hard to crack/dwell the valve. Most have found what you have, 3400 down for the sweet spot. It’s kinda nature of the beast when running unregulated.

Different springs and hammer weights can change this but I’m not of the opinion the gains are worth it. Sounds like yours is performing quite well.

Thanks for the update on your new shooter there!

Dave
 
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sb327 said:
This seems to be the norm for these guns. 3600 is just a bit too hard to crack/dwell the valve. Most have found what you have, 3400 down for the sweet spot. It’s kinda nature of the beast when running unregulated.

Different springs and hammer weights can change this but I’m not of the opinion the gains are worth it. Sounds like yours is performing quite well.

Thanks for the update on your new shooter there!

Dave
Click to expand...
Mr P was posting as I was, lol
 
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Thanks everyone for the insight. I think I'll probably just fill to 3400 when I shoot slugs, since that's predictable, and I wouldn't need to make any changes to the gun. I can fill all the way to 3600 to shoot 25.4 pellets and the velocity is even from the first shot.

But out of curiosity... If I were to preload the hammer spring a bit in order to even out the shot string at max power- would that be likely to ruin my consistency for my pellet tune? I'd hate to sacrifice one for the other.
 
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Sicumj said:
I have two AEA's, one a HP Backpacker and a Terminator…Polishing and lighter springs will lower it some but the sear and hammer catch is where the biggest gain can be had. I lower the sear catch .015 - .020 and polish the hammer catch that changed the Terminator from 6.5 lb to 4 lb. I go gradual on shorting the sear until I get what I want. Go slow and use moly grease on the contact surfaces . Shoot it at least 50 times before you work on the sear again. The moly generally will lower another 1/2 lb as it burnishes in.
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Firewalker said:

Sicumj, That's what I did on my HP Carbine, worked very well. :)​

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@Sicumj and @Firewalker Moly grease on the contact surfaces of the hammer and sear? Why do that after you’ve polished the surfaces? How much are y’all applying?
 
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Ezana4CE said:
@Sicumj and @Firewalker Moly grease on the contact surfaces of the hammer and sear? Why do that after you’ve polished the surfaces? How much are y’all applying?
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2 reasons: 1.) Rust. With polishing after stoning, there is no prevention to water related oxidization on the bare metal and moly coats the surface. 2.) Lubrication. Polished metal feels slippery but it's not. Infact, the friction will build over time as metal against metal galls and pulls up new edges. Burnishing is a myth on hardened steel, you may like the feel but I prefer no felt friction.
 
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@Firewalker This is news to me. I’ve never polished a sear or hammer. I have, however, put moly a hammer and sear of another gun. The result was slippage. Upon cocking it, the gun would try to fire. Fortunately I could feel that the hammer wasn’t catching the sear and didn’t release the cocking handle. From then on I thought and was told that applying moly paste to the hammer and sear surfaces was a bad idea. How much do you apply when doing what you and @Sicumj described?
 
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Ezana4CE said:
@Firewalker This is news to me. I’ve never polished a sear or hammer. I have, however, put moly a hammer and sear of another gun. The result was slippage. Upon cocking it, the gun would try to fire. Fortunately I could feel that the hammer wasn’t catching the sear and didn’t release the cocking handle. From then on I thought and was told that applying moly paste to the hammer and sear surfaces was a bad idea. How much do you apply when doing what you and @Sicumj described?
Click to expand...

That would be a defective trigger group. I have been smithing PB's since the late 80's and AG's have similar triggers and sears. All metal needs to have some kind of lubricant so that you don't wear the contact surfaces down to the point where there is a slip-fire.

Adding a LOT of lube can interfere with the trigger reset (oblong hole in the trigger and/or sear) where a stiff grease or globs of Molly keep it from resetting correctly.

I use a toothpick and apply a pinhead on the contact surfaces and rub it into exposed metal.
 
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@Firewalker Ok. That makes more sense. In ignorance I’d over-applied molly paste. The trigger assembly is fine. I just went back in and cleaned the contact points off with q-tips I believe. Gun’s been operating good ever since. Also after that episode I bought a little hobby paintbrush set to use to apply molly in order to have better control of the amount I’m applying. Thanks for the response.
 
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Ezana4CE said:
@Firewalker Ok. That makes more sense. In ignorance I’d over-applied molly paste. The trigger assembly is fine. I just went back in and cleaned the contact points off with q-tips I believe. Gun’s been operating good ever since. Also after that episode I bought a little hobby paintbrush set to use to apply molly in order to have better control of the amount I’m applying. Thanks for the response.
Click to expand...

Now, man you are golden! Let the gun speak to you and listen to what she says. That trigger should a soft caress!
 
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customcutter said:
I don't know if there is a regulator available for these guns or not. The Carbine has the same issue. It's so bad that the bolt won't cycle properly until pressure gets back down to 3400PSI. You have to manually cock the gun each shot if overfilled. A regulator would be great.
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There seems to be a regulator from HUMA that works, with the exception of the HP MAX.

www.huma-air.com

AEA HP SS Tuning Regulator by Huma-Air

Huma-Air high power pressure regulator for tuning your AEA HP SS, for maximum performance
www.huma-air.com www.huma-air.com
 
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fe7565 said:
There seems to be a regulator from HUMA that works, with the exception of the HP MAX.

www.huma-air.com

AEA HP SS Tuning Regulator by Huma-Air

Huma-Air high power pressure regulator for tuning your AEA HP SS, for maximum performance
www.huma-air.com www.huma-air.com
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Thanks, but I don't think that will work on the bottle guns. The HP-SS models have air cylinders.
 
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