Tuning Crosman DPMS SBR build

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I know this is an old post but I'm hoping you can help me out with a crosman r1 build. I'm going to do a full mod on the crosman r1 and I was hoping to find out which 2 stage hammer spring setup you used on it, as well as maybe a barrel setup maybe a couple inches longer than stock..I'm just curious so I can look into different options and what I can possibly do to it or will fabricate myself. Thanks.
 
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Converting an A4-P carbine to HPA. Basically, doing the same as I did on the DPMS SBR. I have most everything needed. Awaiting on drop block and female foster. I had the ASA adapter and used it, even though it is unlikely that I will mount the bottle to the gun. I will primarily use my tether bottle.

If you wanted to save some, you could try going with something like this: Coiled Tether and find a way to clamp coil to bottom of pistol grip.

I want to be able to go back to CO2 mags, if wanted, without changing springs, so no high powered mods for me.

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I am super impressed with your build!!!
If you could please elaborate on the following:

1.two stage hammer spring installation

2.where can you buy the two stage spring?

3.Are the other mods necessary to get reliable performance from the rifle?

4.is the accuracy positively or negatively affected from the pressure increase? 

I would really love to get my dpms over 600-700 fps! Of course I don’t want to break the gun in the process either. I am mechanically inclined but new to air guns. Any advice or information would be greatly appreciated! A current full parts list would be amazing.

Thank you for what you have already shared! 

 
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The mag that came with the A4-P leaked CO2 out of the hammer pin. Crosman sent out a replacement that works and didn't require sending back the defective one. Pictures and follow if I can get it fixed here: Mag Leak

The parts came today, so will start work on the conversion.

I did a volume check on the Ebay Dummy cart and it is about 1/4 of the volume of an empty 12g CO2 cart. I use an empty CO2 in the primary slot on the QR mag and the dummy in the secondary. There are probably some pressure fluctuations caused by the check valve. There is the internal one in the mag. I don't use one in the male nipple on the dummy cart, but do at the ASA adapter. All these check valves require a drop in pressure to open.




 
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I did initial pressure testing with the 9CI bottle that I had on the DPMS. There was a leak though. The female foster O-ring was significantly compromised. Even though I don't plan to run with the bottle on the handle, it balanced well with a full mag of BB's. Balance point is just behind the trigger blade. Running tethered, slightly muzzle heavy. 

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Running in tether mode, the nipple at the bottom of the pistol grip allows me to use one of my 2' pcp fill hoses. I just put a male nipple (no check valve) on the bleed.



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I put in a new -010 70D Urathane O-ring, and no other leaks. Seems to function just fine! :)

I don't post a complete list of parts, because some are not available, others hard to find, and they would all drive a change in the braided hose length. The information in this thread should be sufficient to select, fit, and get your gun running on hpa. If you are stuck on something, or just want an opinion, please post. I just don't have the high pressure/high velocity expierence that most seem to be interested in.


 
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Hey im sorta new to all of this. I have a dpms sbr and i was painting the lower receiver so I removed the trigger housing and so since there isn’t much online on how to properly remove it i was just taking out pins so when i put it back together the part that catches the hammer wont go up so the trigger doesn’t work properly anymore and i can’t figure out how to fix it.
 
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Hey im sorta new to all of this. I have a dpms sbr and i was painting the lower receiver so I removed the trigger housing and so since there isn’t much online on how to properly remove it i was just taking out pins so when i put it back together the part that catches the hammer wont go up so the trigger doesn’t work properly anymore and i can’t figure out how to fix it.
Click to expand...

I have not had the trigger apart, so can't offer much on that. :( Not sure the schematics will help you either, but I posted a link earlier in this thread.
 
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That’s a MasterChief design and a lot better to worthy of an Engineering Degree ! I’m doing the same thing to a bottom feed SBR.. my deal is I have ready cheap use of pressurized Nitro gen .. (HPA?) .. I want a way that is safe to do so.. Any ideas ? I’m also looking for the best ModSupp can with 14mm CCW threads that fit the factory barrel .. & one for a Beretta 93a.. Anybody got anything for sale out there ? I want to try my own baffles 

Thanks!

Wade @ text # 915-224-8366 

[email protected]

tge original cell number was incorrect ..Sorry 
 
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The linked to LDC does have internal baffles, but you can not open it to make your own. IMO, it is not worth having a quality LDC that can be dis-assembled and having it threaded M14 CCW. The mechanical noise overwelms the muzzle. Finding ways to "dampen" the mechanical without causing cycling issues, would provide bigger dividends. Then maybe a LDC.

Haven't used nitrogen, but should be OK if keeping to the same pressures. Don't see any advantage outside of no moisture.


 
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