Tuning Dealing with hammer bounce

[MrP]

I believe I am getting a fair to large amount of hammer bounce on my Hp max 357 based on the sound and occasional heavy recoil as excess air is released. 


I am able to change the spring preload and can also add weights to the hammer using a hex nut or washers. 


Any thoughts on what to change first? 

 

[Long_Gun_Dallas]

Bounce usually occurs when the hammer has nowhere to go. At full spring de-compression, the hammer is pushed against the valve stem. Multiple ways to deal with this. Create a contained hammer spring assembly that holds the spring partially compressed inside the gun and prevents it from fully de-compressing so the hammer can bounce off of the valve stem. Bstaley mod, use orings in front of the hammer to dampen the inertia possibly halting a rebound. Get a stiffer, shorter hammer spring. Or remove some coils from your existing one. You may lose some power with a shorter spring, though. I have a number of guns that just use shorter springs, sometimes stiffer, sometimes not. Some gun designs do this in the first place. Others use a slingshot hammer that is a multi-piece hammer where the hammer floats loosely in a cage that the spring rests on, and thus has room to back off of the valve stem. 

 

[MrP]

Ok, thanks for that information. 


i put two small o rings in front of the hammer. That decreased the strike to the point that the valve barely opened. I then added a hex nut behind the hammer - adds about 5g and adds a bit of preload to the spring as well. This was a nice crisp shot with none of the extra recoil or noise. 


i will test with a chronograph later but I suspect having at least one o ring in there is the way to go.


i know there is a thread on how to find a short stiff spring to replace the longer stock springs and have a projectile hammer but not sure how to find it or how to order the right part. I’ll figure it out eventually.

 

[Long_Gun_Dallas]

No problem. Sounds like progress!

I just take the springs out and measure them. Last one I did fit in the rear of the hammer, and it had a recess in the rear of the tube it sat in. I got a 12mm OD (same as original) and 1.2mm wire thickness spring (original was 1mm) that was 90mm long. (I needed something like 85mm) So, you order them by wire thickness and spring OD which would have been determined by the smallest recess the spring goes into, I think being the hammer on this gun. Being slightly over 12mm, the spring guide in the rear of the hammer was something like 9.7mm, so you figure 12mm minus 1.2mm+1.2mm puts me at 9.8mm just barely clearing the guide. I think mine was a 1.2mm wire with 10mm ID. Any larger than 1.2mm would not fit in the gun. Also you'll want to look at photos and make sure it is a darker color wich should indicate heat treating (Stiffer spring). I can't ever find anything I'm looking for stateside, so usually wind up on ali express or ebay.

 

[MrP]

Ok great. O rings can’t work where i put them it is obvious now. I have mainly messed with airforce guns and the hammer strikes a flat smooth surface but this is hitting a pin and chewing up the rings. I was trying some random compression springs (none of which were long enough) and what I saw agreed with the diameter limit you estimated. 


Time to search for springs…

 

[Ezana4CE]

Ok great. O rings can’t work where i put them it is obvious now. I have mainly messed with airforce guns and the hammer strikes a flat smooth surface but this is hitting a pin and chewing up the rings. I was trying some random compression springs (none of which were long enough) and what I saw agreed with the diameter limit you estimated. 


Time to search for springs…

@MrP I came across a couple of spring threads recently. Here are a couple that have information and links to source springs. 

https://www.airgunnation.com/topic/where-is-the-best-place-to-order-replacement-hammer-springs/

https://www.airgunnation.com/topic/need-source-for-springs/

 

[SpiralGroove]

I believe I am getting a fair to large amount of hammer bounce on my Hp max 357 based on the sound and occasional heavy recoil as excess air is released. 


I am able to change the spring preload and can also add weights to the hammer using a hex nut or washers. 


Any thoughts on what to change first?

Hey MrP,

Investigate how you could make or have someone make a SSG for your gun. Spring Stop Guides (SSG) are 100% effective in eliminating hammer bounce .... which is wasting air, lowering shot count and increasing your gun's report.



Here is a pic of a SSG for one of my RAW HM1000xLRT's :

 

[MrP]

So the spring can be compressed but only expands to the limit set by the screw? That’s a nice looking device. I think I understand the principal I wonder if I could put something like that together if I make a trip to Ace Hardware…

The only thing that made any difference yesterday was backing off the hammer spring a little bit. This is a replacement for my first Hp max that had no bounce at all but leaked all over the place. I wonder why this would have so much bounce if it’s basically the same gun?

 

[Brent]

It may have been built on a hang over Monday.

 

[MrP]

It may have been built on a hang over Monday.

It must have been - screws were scuffed up, the valve seat wasn’t set correctly, the check valve to the tank was off, and the magazines were too loose against the breech and it could not be fixed by threading it in more which worked on some other guns. The new one has none of these issues. The only thing I am wrestling with is hammer bounce and efficiency.


Would changing the valve return spring have any effect on hammer bounce

 

[Long_Gun_Dallas]

Hmmm my reason is that a stiffer return would cause the hammer to rebound harder against its spring creating more of a double strike? Theoretically 

 

[MrP]

Right now I have a shorter stiffer spring (some random spring from ace that probably won’t hold up long term).


It was a little too short so I added a hex nut behind the hammer which adds weight and eats up some of the slack.

it shoots well like this and is wasting less air, less hammer bounce, but with a somewhat softer strike and a first/strongest shot at about 130 fpe with 96 gr pellet ( as opposed to 145 fpe with these slugs and stock setup)

next, I think I will add a second nut and back the spring retainer off a bit, and see how that works. Three free-bouncing weights instead of a single weight might dampen the bouncing. 

 

[Long_Gun_Dallas]

Hm yeah, that might have an effect. I still feel. You'd need to make some slack behind the hammer or find a way to really slow the hammer down 

 

[MrP]

I just got a better shot string with a nice tight “snap” for a report (with ldc on end). There was a bit of hammer bounce at shot number two - highlighted on the pic attached - but nothing like what it was doing before. The other shots had no audible sign of bounce

I left the original spring and dropped a single hex nut over the spring guide (between the spring and the hammer). I then backed the retainer nut/stock out just a bit less than the thickness of the nut so spring preload is just about the same. I was hoping that the extra weight that is free to move independently of the hammer itself would maybe dampen the hammer oscillation more quickly.