Tuning R1 underpowered? SOLVED!!

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Lewis

Lewis

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May 2, 2015
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Eureka, California, United States
I am rebuilding an R1 for a friend. The stock spring was weak and bent. It was only shooting at about 6 FPE!

I installed a shiny new Vortek 12 FPE kit and... 7FPE!

The Vortek spring is shorter than the stock spring but still a bit stiffer to cock. I have installed a new piston seal and breech seal and both have been checked for a good seal.

I installed a much too long spring from a 97 just to see. It had a lot of preload and was much harder to cock, and.....8.6FPE! 

I have tuned many springers (including several R1's as recently as my own just a week ago) and this is a new problem to me for sure? 

I checked the tube for roundness and it is not the problem. The action is an older San Rafael model but is in generally good condition.

What could I be missing?




 
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First thing, what caliber? 

The .22s are famous for loose barrel bores. Hard to make good power if the air is getting around the pellet. How does it feel at the shot? Is it bouncy and sluggish, or slammy and harsh? 

I had a San Rafael era HW80 and the receiver tube had deep chatter marks inside, and the tube was badly bellmouthed just as JohnnyPiston said to check for. Also try and be sure that the fork plug isn't leaking at the brazed joint. Older 35s were famous for this, and I've seen it before on other models. My San Rafael era Weihrauchs have been the most troublesome with fit and tolerances of any I've ever owned. 

Also, you can lose a lot of power with a really heavy spring and a thin deep lipped parachute seal in a good tube. The difference between seals in the same gun with the same spring was between 12fpe for one, vs 18fpe for the other. This may not be as relevant for a soft tune at 12fpe, but something to keep in mind.

The transfer port should be right at 2.9-3mm factory. 

The fact that it was so slow with the factory setup is concerning. They have heavy wire springs, and they generally don't fatigue to that point. Now if the seal was obliterated that's a different story. 

Good luck, and keep us posted.
 
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Make sure the piston sleeve is properly oriented..
07EBA1E2-3CA7-4B9E-9991-09E5731E3718.1625833168.jpeg


The opening is away from the cocking arm..
 
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It sounds like the low power may be due to a couple things, most likely the receiver ID opening up towards the bottom and the barrel opening up past the breech block. The latter can be checked by pushing a pellet through.

I'd try a factory seal/parachute seal.
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This ^^^^^

1. Double check the breech seal for leaks with tissue paper. 

2. Piston seal diameter can make a huge difference in velocity. Your new piston seal may be too tight. You should be able to push the assembled piston and seal into the tube fairly easily with one finger. Try a different seal or resize the one you have.

3. Too much lube/tar used during assembly. Less is best. 

4. Pellet diameter too small. Don't use cheap pellets.

5. Your chronograph is fried. LOL
 
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Click to expand...

First thing, what caliber? 

The .22s are famous for loose barrel bores. Hard to make good power if the air is getting around the pellet. How does it feel at the shot? Is it bouncy and sluggish, or slammy and harsh? 

I had a San Rafael era HW80 and the receiver tube had deep chatter marks inside, and the tube was badly bellmouthed just as JohnnyPiston said to check for. Also try and be sure that the fork plug isn't leaking at the brazed joint. Older 35s were famous for this, and I've seen it before on other models. My San Rafael era Weihrauchs have been the most troublesome with fit and tolerances of any I've ever owned. 

Also, you can lose a lot of power with a really heavy spring and a thin deep lipped parachute seal in a good tube. The difference between seals in the same gun with the same spring was between 12fpe for one, vs 18fpe for the other. This may not be as relevant for a soft tune at 12fpe, but something to keep in mind.

The transfer port should be right at 2.9-3mm factory. 

The fact that it was so slow with the factory setup is concerning. They have heavy wire springs, and they generally don't fatigue to that point. Now if the seal was obliterated that's a different story. 

Good luck, and keep us posted.
Click to expand...

These are solid points. +1
 
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SOLVED!

And the winners are...

THUMPER and WADCUTTER!

Thumper - Also, you can lose a lot of power with a really heavy spring and a thin deep lipped parachute seal in a good tube. The difference between seals in the same gun with the same spring was between 12fpe for one, vs 18fpe for the other. This may not be as relevant for a soft tune at 12fpe, but something to keep in mind. 

Wadcutter - 2. Piston seal diameter can make a huge difference in velocity. Your new piston seal may be too tight. You should be able to push the assembled piston and seal into the tube fairly easily with one finger. Try a different seal or resize the one you have.

Resized the piston seal and all is perfect in the world.

First 10 shots with JSB 8.44

Avg 789 for 11.7 FPE PERFECT. 

I still had to use a different spring and guide from the 12 FPE Vortek kit. The outer Delrin guide does not fit into the piston. I ended up taking apart a more current hw90 just to see what could be going on. Same results also the spring is only good for about 7 FPE and is very light. I believe it must have been mislabeled and probably for an HW 35 or another very low-power rifle.
 
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How tight of seal are we talking about Lewis? It must have been way to tight to drop velocities that much.
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That is the surprising part. It felt snug but not unlike many others I have used in the past. I removed a small amount of material by placing the piston in a chuck and using 400 wet/dry paper. I kept doing this as velocities improved until there was no change then finished with 800 wet/dry. Another well-regarded tuner told me he has all but stopped using parachute-style seals for this reason. He said that he will typically remove about 1/2 of the depth of the parachute seal so that it doesn't flare out under pressure as much. I did not try this method but it does make sense. Proof that I'm never too old to learn.

For what it's worth, I measured the compression tube for roundness and consistency. I swapped barrels with another R-1 to make sure it was not a loose bore issue and both pressure and vacuum tested to make sure it was not the breech seal. Just so others know I tried and/or tested all the possibilities mentioned. 

I am very grateful for all your help and suggestions. I apologize if I left anyone out. The process of elimination yielded a positive result.
 
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I guess a snugger seal would be more of a problem with a weaker mainspring than a full power spring.
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Not sure which would create the bigger issue. It seems to be the stronger the spring the greater the loss from a parachute seal since the faster you try to push it the more it expands against the walls. This seemed to be the case since the power of the spring made very little difference in velocity. I tried very weak springs that were super easy to cock all the way to springs with a lot of pre-load that were very difficult to cock. less than 100 fps difference no matter what I tried until I started removing material from the seal. I'm going to try one of the newer Vortek Vac seals that is impregnated with moly and has no parachute groove. I'll post back here after that test when I get it.
 
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