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Old 08-15-2013, 12:01 PM   #1 (permalink)
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Adjusting velocity on Sterling STP

I purchased a Sterling STP from a user on this site a while back, and I'm just now working on getting it ready to play. I took it out and it shot beautifully, but a bit hot at 314 fps. I went to adjust the velocity according to the directions I've seen online and guess what? No hole in the pump handle to adjust the velocity. I did see that some models had to adjust the velocity by changing the main spring. Is that the case here? Is there another way I can do this, like adding a regulator somehow? I will try to include a pic of the model I have. Thanks for your help!



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Old 08-15-2013, 01:12 PM   #2 (permalink)
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When you're shooting hot, is it with Co2 or HPA? I've noticed Co2 shoots hotter than HPA.
To adjust the velocity by the springs you need to put either a "lighter" Hammer spring in or a "stronger" Valve spring in. I would suggest the first, it's just a lot easier, remove the front thumb screw pull the pump handle out a little, swap springs re-install the pump handle and thumb screw. If you want to put a regulator on I suggest using a Palmers Female Stabilizer, I mounted one on one of my Proline Sterling's and have had great success. If I need to drop the velocity I just turn the adjustment with a 3/16 allen key and get it all to be good. You'll see in the picture I just ran a macro-line fitting into the back of my "Donkey Body" you could just put one into the adapter on the back of your gun.



I hope this helps
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Old 08-15-2013, 01:18 PM   #3 (permalink)
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A few options:
1. Cut the spring and use shims for adjustment
2. Put an adjustable reg on it somewhere
3. Try to find an adjustable bolt
4. Drill the bolt out for an adjustable choke(have a machinist do this)


There's not a simple adjustment like on the new STP's but there's still some options.
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Old 08-15-2013, 01:20 PM   #4 (permalink)
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A skilled airsmith should be able to add the relevant parts for the velocity adjuster. I had one added to an old sterling bronze that I picked up and it works well.
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Old 08-16-2013, 11:40 AM   #5 (permalink)
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New problem

I was able to get in and cut the spring down a bit. Now my velocity is mostly under 300 but all over the place. I'm thinking I should have stretched the spring out after cutting it, could that make a difference? The only other thing I did was lube the internals. Maybe it's the 2 year old paint I'm using...
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Old 08-16-2013, 12:07 PM   #6 (permalink)
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Quote:
Originally Posted by Crimson Wolf - AWP View Post
I was able to get in and cut the spring down a bit. Now my velocity is mostly under 300 but all over the place. I'm thinking I should have stretched the spring out after cutting it, could that make a difference? The only other thing I did was lube the internals. Maybe it's the 2 year old paint I'm using...
One thing I've noticed when chronoing ANY gun is a good paint to bore match is essential if you want to have the +/- 5 fps. Old paint most likely has flat spots and isn't that round so that would be an issue I would address. Until you can get a good paint to bore match it's going to be tough to get a consistent FPS reading.
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Old 08-16-2013, 07:48 PM   #7 (permalink)
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Cutting/stretching springs is a no-no. Stretched springs return to their normal length after a few cycles. Cut springs, don't have the "finished end" and can cause kinking and damage to the hammer/pick-up assembly.
Do this only in case of emergency.

Try a large hardware store for springs.

Sterling factory barrels are very good, their "lead" allows "Wedgits" to be swaged into them nicely.

If this beauty was mine, I'd send it, along with the barrels to Palmer's.

I'd have:

The valve job done.
Wedgits swaged into all your barrels.
A detent installed in the body.
And if you still have the plastic frame/body spacer plate, I'd get Palmer's aluminum spacer.
While you're at it, I'd get a Stabilizer to adjust your velocity.

You have a nice gun. A little more investment of cash would make this your all-time favorite.

I did all these things to my ancient first generation Sterling, and she's a real heartbreaker.

I had this all done to my ancient Sterling, and she's a heartbreaker.
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Old 08-16-2013, 08:05 PM   #8 (permalink)
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Thanks for all the advice guys. I normally would put the time and money into this right away, but I have a game tomorrow so I resorted to cutting the spring. I have several springs, hopefully one will work for me. If I can get the money together I will work on the wedgits and stabilizer at least.

I also noticed this marker seems very loud compared to my Nightkast. Kind of a burping sound and much louder. Don't know if that's normal or a sign of a valve issue.

Thanks again for all your help. Looking forward to trying this baby out!
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Old 08-16-2013, 08:12 PM   #9 (permalink)
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That's just a tuning issue, although sterlings do have a particular bark.
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Old 08-21-2013, 11:29 AM   #10 (permalink)
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OK, so I took it out to the field for about 8 games, and I really like the way it shoots. The velocity was still all over the place, fluctuating from 250's to 280's with mid-grade field paint. The thing is so loud compared to my pump Nightkast, but that's OK as long as it's not a symptom of a problem.

I'm also wondering, did I buy an old STP or did someone sell me a Bronze and call it an STP. Most of what I've seen lists the bronze as non-milled body, right feed, and not externally adjustable. Did I get rooked?

Either way, I hope to get this to PPS for some wedgits and valve job at least. Any recommendations you guys could give on tuning this to make it a little quieter?
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