147mm barrel to 350fps

[Liamcella96]

Hello, I have managed to get my hands on a great VFC m4 which is a smiling size to an mp5 so I plan to use it more as an smg but also if I want to field it in woodland games that would be great.

 

The barrel I have to use is a 147mm 6.03 bore.

 

Can anybody help in what will help me achieve 350fps? Any tips etc.

 

What cylinder do you recommend? Should I go for a full cylinder or a 1/2. Etc 

 

Thanks

[Colin Allen]

A full cylinder will lead to over voluming; in theory, a 1/2 cylinder would be the best match.

If you are in the UK, do not try to achieve 350fps (I assume you mean when using a 0.20g BB); given the variability of site chronos, there is a decent chance your new toy will end up going back in its bag.

Running between 0.97-1.05J on your preferred BB weight with a good hop unit (ZCI?) and a Maple Leaf Macaron with an AK2M4 red nub will give you all the range you need.

[Liamcella96]

Hi mate. Thanks for reply. I have a zci hop & Macaron rubber with an omega nub. Would you just recommend to go up a spring strength.

 

I forgot to mention I'm currently at 290fps. I'm just looking to boost to the 340ish mark. 

 

Uk based yes and on 0.2gs

[Colin Allen]

1 minute ago, Liamcella96 said:

Hi mate. Thanks for reply. I have a zci hop & Macaron rubber with an omega nub. Would you just recommend to go up a spring strength.

 

I forgot to mention I'm currently at 290fps. I'm just looking to boost to the 340ish mark. 

 

Uk based yes and on 0.2gs

Before you start bunging a heavier spring in, have you checked that the airseals (piston head, cylinder head, air tube to nozzle, nozzle to rubber) are all good?

If they are, a somewhat stronger spring would be a good idea.

[Fatboy40]

@Liamcella96 With an inner barrel of that sort of length look at what people are doing with the G&G Firehawk. Stock this has a 120mm inner barrel, so to get any power from it as stock it also runs an M130 spring (it's the combination of the short inner barrel, strong spring and amplifier on the end that makes it so loud with a loud crack when firing).

 

I've done a lot of work on my son's, which has now become his backup rifle, and with such a short barrel you'll only get genuine power increases with first the spring and then improving your air seal (however getting good improvements on your air seal costs money).

 

Considering all the different inner barrels I've tried with the Firehawk I'd say that you'll want to buy both an M130 and M120 spring from https://www.ak2m4.co.uk/ to hit 1.14J (the M130 will take you very close to the limit, potentially even a little over). Also pulling such a strong spring you may want to consider, money permitting and what's already in the rifle, a full metal rack on the piston and a high torque motor.

[Rogerborg]

1 hour ago, Fatboy40 said:

getting good improvements on your air seal costs money

 

Stretch the piston o-rings (or replace with 19mm x 2.5mm nitrile rings), drill some extra ports into the head, bit of silicone grease, and use rubber o-rings rather than a spring to tension the hop against the gearbox.  I've seen 1.3J (oops!) out of a 229mm barrel using an M100 spring and stock CYMA air-seal components.

[Fatboy40]

11 minutes ago, Rogerborg said:

... use rubber o-rings rather than a spring to tension the hop against the gearbox.

 

That's one thing that's been on my list to try, not so much regarding air seal but vibration reduction / consistent inner barrel placement (to improve accuracy / consistency between shots).

 

Do you do this yourself / any tips on it?

[The_Lord_Poncho]

1 hour ago, Fatboy40 said:

 

That's one thing that's been on my list to try, not so much regarding air seal but vibration reduction / consistent inner barrel placement (to improve accuracy / consistency between shots).

 

Do you do this yourself / any tips on it?

I have on my SR25 - think i used three O-rings on the inner barrel sandwiched between the hop unit and the end of the outer barrel in the end, but very much trial and error. Just added/removed until i seemed to get good feeding. I hadn't thought about the accuracy benefits to be honest - no idea if it has made an improvement to my SR25, but i did it as i had swapped out the stock hop unit and didn't have a suitable spring to pop there.

[Liamcella96]

2 hours ago, Rogerborg said:

and use rubber o-rings rather than a spring to tension the hop against the gearbox.  

You just place some o rings over the barrel until the maximum pressure is applied that still let's you put the receivers back together?

 

Not heard of this before I will give it a go. 

[Rogerborg]

1 hour ago, Liamcella96 said:

You just place some o rings over the barrel until the maximum pressure is applied that still let's you put the receivers back together?

 

Yes, that's it. The little tensioner spring on top of hop units is pretty wimpy: you can replace it with o-rings, or slide a beefier spring over the barrel.

[Colin Allen]

1 hour ago, Liamcella96 said:

You just place some o rings over the barrel until the maximum pressure is applied that still let's you put the receivers back together?

 

Not heard of this before I will give it a go. 

It works.  I have done it on a couple of builds.

6 hours ago, Fatboy40 said:

@Liamcella96 With an inner barrel of that sort of length look at what people are doing with the G&G Firehawk. Stock this has a 120mm inner barrel, so to get any power from it as stock it also runs an M130 spring (it's the combination of the short inner barrel, strong spring and amplifier on the end that makes it so loud with a loud crack when firing).

 

I've done a lot of work on my son's, which has now become his backup rifle, and with such a short barrel you'll only get genuine power increases with first the spring and then improving your air seal (however getting good improvements on your air seal costs money).

 

Considering all the different inner barrels I've tried with the Firehawk I'd say that you'll want to buy both an M130 and M120 spring from https://www.ak2m4.co.uk/ to hit 1.14J (the M130 will take you very close to the limit, potentially even a little over). Also pulling such a strong spring you may want to consider, money permitting and what's already in the rifle, a full metal rack on the piston and a high torque motor.

I run a 125mm inner barrel M4 with an M105 spring, getting 1.02J.

 

Sorting out airseals is cheap; better O rings, maybe a better fitting cylinder head and an O ring nozzle.  Good airseals also help deliver more consistent power.

[Liamcella96]

Amazing thanks everyone. I've taken it apart today and the internals seem shot. Plastic piston a little stripped. Nozzle not the best. I will replace the internals and let you know how it goes. Thanks

[Colin Allen]

23 minutes ago, Liamcella96 said:

Amazing thanks everyone. I've taken it apart today and the internals seem shot. Plastic piston a little stripped. Nozzle not the best. I will replace the internals and let you know how it goes. Thanks

One of the advantages of a plastic toothed piston is that it can "settle in" when the AoE is not quite correct; this results in it looking a "little stripped".

Another advantage is that only the piston dies if PME or one of a few other nasty things happens.