P90 DMR, yes its a sin against nature

[the_monkey]

So, a little project. I have a spare tm p90 as you do,now I have a wonderful red dot version that is 350fps i n the button and 18 to 20bps .
So my plan with the second tm p90 is to create a dmr of a nice stable 420 fps. I have a rough task list, but need some advice on making sure its just right. I'm doing it because its a project, why the hell not.

So far I have done all the normal cleaning and shinning mods for the gear box. I'm assuming thestandard tm gear set and tm1000 motor will suffice to pull back the spring.

Speaking of springs, I'm assuming a madbull m120 will be about right for 420fps.

Barrel wise, I am considering a black python or similar 6.03 of 300mm length (stock is 247mm but I want to extend through the silencer a little bit)

Hop up, I'm considering an aftermarket metal hop unit but I am unsure if its necessary.

Cylinder, this I find confusing. The stock tm version is ported, is there any benefit to a non ported cylinder?

Any other advice would be useful, thanks

The monkey

[dannyeprice23]

Barrel - prommy every day
Hop - promethius neo hop unit, best I've ever come across. Use one in my DMR with an sp120 and prommy barrel and it's hitting 80m with ease!

[jagillham]

Re: p90 dmr, yes its a sin against nature

Neo unit is M4 only....?!

Does anybody do a aftermarket P90 type one even? Have you thought how you will lock it to semi only?

[the_monkey]

Re: p90 dmr, yes its a sin against nature

Jag, that's easy. P90 has two trigger contacts, if I remove the copper plate from the full auto contact then it won't fire anything but semi, if I need to resolve a gear box lock up, I can open the access panel where the spent cases would come put from the real steel, lift the cutoff lever and pull the trigger.

[sj_asc]

Re: p90 dmr, yes its a sin against nature

As said, the P90 Semi lock is an easy mod, much like it is with the AUG.
Prowin do a CNC'd chamber for the P90 if you're interested, but to be honest the stock one is fantastic and stable enough for M120 use, the best thing it could benefit from is a tougher chamber spring.
The stock Cylinder in Marui P90's (except the HS) is 3/4 ported, which is sufficient for .25g bbs and the 247mm .08mm barrel. It would also work with the 300mm inner barrel, you would probably see slightly higher FPS with 0.20g's, however there would be losses if you used heavier weights in comparison to the stock length. A 4/5 port cylinder would give you the additional usable volume which is essential for retaining fps with heavier bb's and is the most efficient method of energy transfer.
It's not simply base measurement of FPS achieved with .20g bbs that will deliver the best range, in a DMR build ideally you want to be looking at weights nearer .30g, and a setup optimized for .2's but firing .3's will not be able to match one optimized for .3's fps in the first place.

[the_monkey]

Re: p90 dmr, yes its a sin against nature

Thanks sniperjesus, so your recconendation is a new cylinder. Do you have one in mind?

As for the advice about the prowin chamber, thank you very much. I shall stick with stock.

[dannyeprice23]

Neo unit is M4 only....?!

Does anybody do a aftermarket P90 type one even? Have you thought how you will lock it to semi only?

Ahh. Didn't even think of that ha.!

[the_monkey]

Re: P90 DMR, yes its a sin against nature

So a little update, I have stripped and cleaned the gear box and come up with a list of requirements. These are
Optimised for .28 to .3 gram bbs.
Reasonabley quiet
Reliable
Fps of 420 fps. ( keep it legal at all sites that allow dmr)

, no major issues there. I am however seeking some advice, the piston is stripping, so I am looking for a new one. Is like advice if that's ok, do I just buy a stock tm piston or an aftermarket.
My plan is also to get a cylinder with no porting hopefully increasing the useable volume and combining with a tightbore will mean I can have a lesser spring thus saving wear and tear.

Secondly will the stock gear set and eg 1000 motor be sufficient to pull a 420 fps spring (eg madbull m110

[sj_asc]

Re: P90 DMR, yes its a sin against nature

Did you decide on an inner barrel length?
Stock ratio gears are sufficient enough for pulling an M110 with the EG1000. Madbull M110's have always been pretty much dead on 400 fps w/.20g for me and i've never had any issues with the stock ratios and Marui EG1000
However Stock Marui gears, the Sector gear in particular is very soft and won't hold a great lifespan, but it really depends on how much you intend on firing and the paired battery output.
What piston do you currently have in there?

[the_monkey]

Re: P90 DMR, yes its a sin against nature

I have an existing 6.03 247mm barrel, I may stick with that. I'm hoping heavier bbs will mean an unported cylinder can be used, I could extend to 300mm and extend through the silencer a little.

My existing piston is a stock tm, the white one with the piston head forming part of the piston, I don't think its removable. It is plastic toothed apart from the 1st tooth I think. I don't have it with me.

[B.E.N.]

Re: P90 DMR, yes its a sin against nature

Lots of sites that allow semi-auto rifles only run up to 400fps.

[sj_asc]

Re: P90 DMR, yes its a sin against nature

Sounds good,
Marui Pistons are good stuff, unlike most pistons out there, they are consistent and have a reasonably predictable lifespan.

With both barrels still only being quite short, and using weights around .28/.3g it would be better to switch the cylinders from 3/4 to 4/5. 4/5's are typically paired with M4 length (363mm inner barrels) and are fine there. With 247mm and 300mm they would have the additional volume to gain better muzzle energy efficiency with weights around .3g, however if you have too much volume (1/1 + said weight and barrel lengths) the energy is wasted as the BB is far less likely to get close to it's terminal velocity before it leaves the barrel. The excessive volume will deliver a much louder muzzle report - all that noise = wasted energy.

And the Stock marui piston set is detachable, you can either carefully but tightly grab the piston head and then unscrew it from the piston body, or if the thread lock has gone you can bore out the small hole on the face of the piston head and it will reveal a Phillips screw which you simply take out, that will release the base that it screws into and with it the main spring.

[the_monkey]

Re: P90 DMR, yes its a sin against nature

Excellent news, really helpful sniper Jesus. Parts ordered and I will let yoy know my results soon.

[laurence]

Re: P90 DMR, yes its a sin against nature

Just like to point out a few things, id reccommend getting some new gears, just as the TM ones arent designed to run on that high a spring, you should be okay for a while but they wont last as long as they could. Second, i end up saying this on all the DMR threads but the key to a DMR is CONSISTENCY. Theres no use just whacking a big spring and longer barrel in it if your shots are going all over the place. You want the least deviance shot-shot so this means The best air-seal you can get and then a reduction in vibration. Vibration in the barrel is actually a big player in accuracy, one of the first things people do in upgrading their VSR's if theyre serious about it is buy some barrel spacers. Consequently, if your planning on having the barrel extend through the silencer, you want to have something supporting through the silencer. Dont bother getting the metal hop, you will literally see no difference and the TM one works just fine.
Parts i would reccommend for this build:
-New gears, something cheap but strong like Element or JG
-Barrel, something a little more rigid than a Madbull one, again to reduce vibration so maybe a Deepfire one
-Bearing spring guide, this will reduce spring twist and so smoother and more consistent compression
-Air-nozzle with o-ring, this will complete your air seal and ensure no air's escaping around there.
-Metal bushings if you dont have any yet, its just a durability thing

I personally think that a p90 is an excellent choice for a DMR as it has a V6 gearbox which is very solid, bullpup so the gun need'nt be too long and its very manouverable. Also the P90 has a very good and consistent Hop, and remember, its ALL about consistency.

Hope this helps

[Clone1B]

Re: P90 DMR, yes its a sin against nature

Make sure you turn it into the PS90, then it'll look like a proper legit DMR!