Should i carry on tuning my gun? 34grain @ 915fps & 30grain @ 984fps

[tiny_cabbages]

Hi

So i'm still waiting for my slug liner to arrive, and i've been tuning and messing around with my fx crown.

I've got them firing JSB mk2 34grain at 915fps, and NSA 29.5grain slugs at 984fps, fx hybirds 26grain at 984 fps as well.

I can't test the accuracy at the moment, as i'm waiting for the liner. The slugs are really wild with the standard stx liner i have right now.

My reg pressure is 140 right now, so i've still got a bunch a room to mess around, may install a new reg to push it 160-170 bar. So the question should I, should i try and push the 34 grains up to 1000 fps? as i'm hoping to get this gun to fire slugs accuractly at 150-200yards. Does it need 1000fps?

 

[Ghostranger169]

tiny_cabbages,

If you're looking for better accuracy at over 100 yards and/or in windy conditions, then stop trying to tune pellets and wait for slugs. 

Btw, the AMP regulator in your gun is good up to about 170 bar, so reg isn't the problem. Problem is, the gun doesn't have the ability to make the hammer hit the valve hard enough to open it sufficiently at higher reg pressures. Try looking at JoeCool's older post about hammer, hammer spring, and transfer port upgrades/modifications he made to MK1 Crown to be able to shoot heavier ammo faster.

The distances you are trying to shoot will be a big stretch for the Crown MK1(or even the MK2). A better tool for the job would be the Impact.

Good luck

 

[biohazardman]

I would guess by the projectile weights you are talking about the .25 caliber. I shoot a modified Impact-X with the 700mm slug A liner @ near 130 bar and have dropped the velocity down to 940-960fps to save air and gain accuracy. The gun is MOA at 100 yards at velocities from 740 to 960fps with most of the NSA .250 slugs, the VK 34gr and the JSB Heavy MKII pellets do near as well. The gun is good to over 200 yards with this tune and I plink off paint cans at that distance.

You really don't need near 1000fps to shoot slugs. You do need the right barrel though. The slug A or Superior Heavy will shoot lots of slugs MOA and the regular Superior will shoot a few the same. The regular old style ST and the STX barrels don't do so well with slugs from what I have seen. Nor are they designed to do so.

 

[tiny_cabbages]

Yea i'm just getting the gun ready, cos well i got nothing better to do. It takes like a month for the liner to arrive because of customs etc.

So given i can fire the 29.5 grains at 984fps, do you think i need to tune it even more, e.g. upgrading the hammer/spring? Should i prep the gun to be able to fire 34grains at over 1000fps?

Regarding the impact would be better, So i'm new to air rifling, so this isn't meant to be a argument etc. Just trying to understand a bit more.

So my thinking is, given the liner are the same, if i can get the crown to shoot at the same ft/lbs / fps, why would the impact be more accurate? Is it because it has a better reg / some other parts that allows it to be more consistent?

 

[Ghostranger169]

No worries. Simply put, the Impact has the ability to shoot heavier ammo at higher power(better/beefier valving, bigger plenum, specialized pin probes to seat slugs, etc...). In order to shoot longer distances and resist wind drift, you need to shoot ammo that has a high ballistic coefficient(bc). Most slugs have WAAY higher bc than pellets. That is what enables them to still maintain accuracy at long distances. A slug need to be stabilized gyroscopically(spinning) as opposed to "shape" stabilization of the pellet skirt. The twist rate of the liner imparts this spin. High bc ammo is usually harder to propel, so it takes more power.

A Crown is a fine gun(I have 2 of them), but it does have it's limitations. That's why you don't see youtube vids of shooting Crowns at 200yards, mostly Impacts. 

 

[tiny_cabbages]

Thanks @biohazardman, yea ive got a 700mm .25 barrel.

So i was watching this https://www.youtube.com/watch?v=xhhl2GtGFks so based on that i've only ordered the superior liner, you think its worth it to get the superior heavy as well?

Also i was thinking of trying the 33.5 / 36.2 grain, i think at my current tune, they'll be coming out at around 915fps, do you think that'll be ok?

 

[tiny_cabbages]

Ah i see, yea i notice one of the thing that can't be upgraded on the crown is the power plenum. With this plus other limitation, am i just chasing a unicon in try to get the crown to shoot accuratly at 200 yards?

I thought that maybe if i can tune/upgrade certain parts of the crown to up its ft/lbs i would be able to get similar results of the impact at long range.

 

[Ghostranger169]

tiny_cabbages,

I don't want to discourage you at all! Don't take what anyone says to be gospel until you've tried it yourself. Everyone has their own idea of what accuracy is also. 

Just understand, that you MAY be asking more than the gun is capable of delivering. From my experience of trying, I could not get an unmodified Crown MK1 to shoot any type of ammo to be able consistently to hit a 6" target at 150 yards unless it was dead calm(and the stars lined up). Others may may done it tho.

 

[Long_Gun_Dallas]

I've seen a number of guys shoot these. Hunting small game at 150-200+ yards in 30 caliber with pellets. Massive drag disadvantage. And under 900fps muzzle velocity. With pretty much factory guns. So, it's not a question of whether it can be done. It's a question of how good is your tune, and what does your gun like to shoot.

Is your crown a mkii? I feel like it must be. If so, you already have decent plenum volume. And you honestly have enough speed already.

The new FX liners do seem to like being shot fairly fast thru. So, just see what your results are, and adjust accordingly. 
I settled with a 500mm barrel on my Crown because I tend to hunt just under 100 yards. Mine does not have the larger plenum, and shoots slugs (in .22 caliber) PLENTY fast.

 

[srtmat]

My “Gen 1” Continuum shot 34gr at 900-905 max from factory w/700mm. I found that the factory hammer is only good up to 155 bar. (Take my FX gauge reading for what it’s worth)

If you plan on going the Huma route and take pressure up to 160-170 you may need a new hammer weight.

With a little porting on my transfer port and probe I was able to get 34gr up to 965fps. Porting is a great power adder without the need to crank up the reg pressure.

I looked back at your other post to see what your setup is. Looks like your running a 700mm barrel on a Gen 1 Crown.? Just be aware FX did upgrade the Crown block w/4 screws to hold the 700mm more securely. I have no idea if it really matters that much.

I look forward to watching your progress I’ve been so busy experimenting and tuning my 380mm I haven’t shot the 700mm in months. 

 

[tiny_cabbages]

Uea, its a crown mk1, with a 700mm barrel.

I think i've maxed out my gun, I've already got swapped out the transfer port and probe. The best consistent fps i've got is 925fps for the 34grain JSB and 1014fps for the NSA 29.5slugs both at 155bar (same as what you're seeing i guess), however with the 25grains, i got them up to 1047fps with 160bar. Yea, i think I'll have to change the reg, and hammer to get anymore out of it as wwell, but I think i'll leave it at that. Anymore and i'll have re-charge the gun too much.

Accuracy looks pretty good at lvl 5 and 4 (892fps and 840fps) red dot is 1/2 inch. Bare in mind this is outdoor with wind and i'm firing these prone with a tripod, not a benchrest.

With the 34 Grain JSB mk2