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Old 08-15-2017, 06:10 PM   #1 (permalink)
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Line SI Bushmaster velocity woes- will this gun shoot 300fps on HPA?

Wondering if there's enough meat there to streamline my bottomline setup. I'd really like to get the hose to run parallel to the gun and I've got parts to plug the ASA adapter.

Side-tapped Nelson ASAs just don't seem to be in ready supply these days.



Last edited by The Inflicted; 08-27-2017 at 10:48 PM.
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Old 08-15-2017, 06:17 PM   #2 (permalink)
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I just looked at mine and you probably have just enough space to do it.
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Old 08-15-2017, 08:04 PM   #3 (permalink)
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I actually drew up a CAD model of a Bushmaster valve, pre-90s, with a side tap. There was plenty of space in the flat on the side. The trick is ensuring you don't hit the screw hole running top to bottom.

I did the same on a 007 valve that I couldn't get the broken piece pin out of. Had a guy weld the pin shut and side tapped.
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Old 08-19-2017, 12:56 AM   #4 (permalink)
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Going straight out the back and looping down to the asa is very comfortable and less clunky you may like it even if at first it seems like it may be going back too much towards your face. It was great on my lapcos and is ambidextrous unlike your current setup.
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Old 08-19-2017, 02:38 AM   #5 (permalink)
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I actually prefer a forward loop on my nelson based guns. It's ambidextrous (though I totally suck with my left hand so I never bother), and you don't feel like you're going to bump into the hose with your mask.

On my Hammer I simply put two 90 degree elbows in a row, a 90 street elbow, then a 90 macro but a second street elbow can work as well. The hose then goes forward and down just behind the pump arm and a bit in front of the trigger.

One potential issue with using two street elbows and a braided hose is that the hose might be too close to the body. In that case you may need to add a short male/female adapter (basically a very short extension) between the elbows, or like I did with one setup, replace one of the 90 degree elbows with two 45 degree ones.
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Old 08-19-2017, 02:43 AM   #6 (permalink)
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Yeah, forward like a mag. I struggled with this a lot with my lapcos but the very simple loop straight out the back ended up satisfying aethetic and ergonomic requirements on the gun. but a mag style loop is better when you've got a valve setup that way.
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Old 08-20-2017, 01:13 AM   #7 (permalink)
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Well I wanted to avoid using macroline on this gun, but both of you are right- the forward loop is just the best option.
Fortunately, the field owner had a hugely-oversized piece of macroline to give me.

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Old 08-27-2017, 10:48 PM   #8 (permalink)
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So I'm having a devil of a time to get this gun to chrono anywhere near 280fps. The best I can manage is about 210. Any real increase in mainspring tension is leading to major problems with the valve popping under cocking, if not freeflowing uncontrollably. Shimming the valvespring didn't seem to fix anything.

I've owned about 30 odd Nelson-valved pumps over the years, mostly Trracers, Phantoms, and SL-68IIs, and I've never had this much trouble getting one to shoot at speed. Then again, I've never owned an SI.

I feel like the lightweight aluminum hammer might be part of the problem. Why would they use such a lightweight part here? Are replacement stainless hammers that interact correctly with the bolt available? For that matter, are my guts normal, stock bushmaster parts? The powertube is marked with a number four, for what it's worth.



I'm using nail polish detents right now but the paint I'm using is quite small- probably in the neighborhood of .674. Will this gun even be usable until I freak bore the barrel?
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Old 08-27-2017, 11:11 PM   #9 (permalink)
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I hate to be the bearer of bad news in telling you that you will most likely need to get your barrel freak bored. I tried multiple hammer and valve spring combinations and, no combination could get me there with the factory barrels. Back before folks knew it was possible to freak bore a Bushmaster barrel (I think I was the first to ask about that here) I had Palmers build me a custom barrel for mine and that got me where I needed to be (I'm currently using a medium hammer spring and, a light valve spring).
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Old 08-27-2017, 11:14 PM   #10 (permalink)
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Good to know, I suppose.
So does the ultra-lightweight hammer on these things just give them an extremely narrow band of adjustment to work with? Since the mainspring is having to do all the work without the benefit of momentum?

Again, I've gotten a LOT of cheaper, albeit newer Nelson clones to work with tiny paint, but never had problems like these.
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