Kral Arms Going up from 25 to 357

[Dr. Kralenstein]

Little update. Ordered a complete breech for an NP03. Going to bore the barrel cavity out to fit the 357 barrel and port the action up to match the barrel.

I have an extra valve for my jumbo drop block that is stock port. I will port match that and then be able to use my 300 BAR bottle off the jumbo to test this thing out. Will be going to a local shop I know that has tons of spring assortments. Going to get something pretty stout to get the air moving.

One thing I did notice, the barrel rifling is very shallow and spaced far between grooves. Maybe im just used to seeing smaller bores lol.

I'm hoping it'lbe accurate. If this works out, I will source a drop block and make a stock to fit the NP03 trigger location and bottle. I do believe a big horn drop block will fit into the action, I think the only difference in breech blocks is the rear is larger for the longer hammer.

 

[Rvaughn]

Sounds like a good plan. Looking forward to your results…

I noticed the complete breech blocks on Canada shooting supply just the other day.. Is that where you picked up the NP03 block?

 

[Dr. Kralenstein]

Sounds like a good plan. Looking forward to your results…

I noticed the complete breech blocks on Canada shooting supply just the other day.. Is that where you picked up the NP03 block?

Yep. They have that Rambo one too lol. It's a pump like a shot gun. I may pick one up for chits and grins.

It's cool they have so many parts available, but the prices seem like they're on clearance. Makes me worry they're the last of the parts for that series of puncher guns. I think Kral may have discontinued the NP and mega platforms, possibly the breaker as well.

 

[Rvaughn]

Agreed, the prices for those spares sure do make it tempting to start some sort of build with.. hopefully they aren’t discontinuing the puncher line though

 

[Dr. Kralenstein]

Got the NP03 breech block today. Drilled the barrel bore out to 13mm and had to turn a section of the barrel down to slip in the breech. Had to cut off the threaded boss for the shroud as well, to get the barrel deep enough.

Everything together, running stock port, it shot an 82 grain at 491 fps. Once I port the breech and valve out to 1/4", I should get into the 700s I hope.

 

[Dr. Kralenstein]

Since my jumbo bottle is ported to 3/16", and that's the largest I can go without blowing through the power adjuster walls and needing to remove it and put set screws in the sides of the breech, I decided just to drill it out to 3/16" for now and see what it gets me.

596 fps! So I gained over 100 fps from going up about a 16th of an inch!

 

[Dr. Kralenstein]

Well I said F it, and drilled out the action to 1/4" right through the transfer port adjuster. So far its holding and not blowing out the side of the gun.

I bored the valve exhaust to 1/4", replaced the valve spring with a much lighter one, and filled to 250 bar(capable of 300). Here's the results.

Overall, I'm satisfied. Needs a moderator BAAAAAD! Shakes the whole house when I fire it lol. Got my ears on, so thats good.

I will be ordering some different hammer springs to try, but im sure I'm getting close to max. Considering the bighorn gets around 750-800 fps with similar weight pellets, I think this is a good velocity, since the BH has a bigger hammer and valve system.

 

[Rvaughn]

Nice!
Looks like you need to try some 68 grain hybrids and you should be able to push em 750 or so plus the higher BC will retain more energy, good work though.
I’m working on machining my bighorn .35 barrel to fit my Raptor, I’ll post results once I get it all together.
So far I’ve gotten the breech end machined to fit by way of my “backwoods lathe” and removed the choke which shortened the barrel to 21 inches overall.
I’m waiting on my local gunsmith to put a new crown on the barrel and also to receive the .35 cal bolt from Matt @ JSAR
I believe I can order a challenger .35 cal mag and that will fit my raptor from what I’ve read on GTA.
I’m hoping to push a minimum of 120fpe with the 21” barrel and original ports which if memory serves correctly they are around .30ish
Should be a fun gun if I can make it shoot straight

 

[Dr. Kralenstein]

Nice!
Looks like you need to try some 68 grain hybrids and you should be able to push em 750 or so plus the higher BC will retain more energy, good work though.
I’m working on machining my bighorn .35 barrel to fit my Raptor, I’ll post results once I get it all together.
So far I’ve gotten the breech end machined to fit by way of my “backwoods lathe” and removed the choke which shortened the barrel to 21 inches overall.
I’m waiting on my local gunsmith to put a new crown on the barrel and also to receive the .35 cal bolt from Matt @ JSAR
I believe I can order a challenger .35 cal mag and that will fit my raptor from what I’ve read on GTA.
I’m hoping to push a minimum of 120fpe with the 21” barrel and original ports which if memory serves correctly they are around .30ish
Should be a fun gun if I can make it shoot straight

That's awesome! I have the same lathe lol. Vise, 1/2" drill, and a steady hand. Drill press helps too, but for turning things down a few 1/10ths, it works no problem.

I'm really considering getting a table top lathe just for making end caps and threads for shrouds. Bushings and stuff like that are expensive to buy or have machined, and buying off the shelf is almost non existent nowadays. Also limits what sizes you can run of tube for shrouds and whatnot.

Let us know how your beast build turns out!

 

[Rvaughn]

That's awesome! I have the same lathe lol. Vise, 1/2" drill, and a steady hand. Drill press helps too, but for turning things down a few 1/10ths, it works no problem.

I'm really considering getting a table top lathe just for making end caps and threads for shrouds. Bushings and stuff like that are expensive to buy or have machined, and buying off the shelf is almost non existent nowadays. Also limits what sizes you can run of tube for shrouds and whatnot.

Let us know how your beast build turns out!

Yes sir… my makeshift lathe is slightly different but there are many different ways to skin a cat as they say lol
A little ingenuity and determination can go a long ways!
I’d love to get real lathe one day also, but right now I need build a new shop first due to a tree falling through my old one.. but even that task will have to come second to many others. Let’s just say I never get bored on the farm from a lack of things to do.
I did receive my bolt from JSAR, still waiting to hear back from the gunsmith about my barrel..
If my mini raptor doesn’t put down the power I’m after due to the limited plenum volume I may try running it unregulated with pass thru type device in place of the reg. I’m sure it’ll have no issues pushing whatever I feed it in that config!
But Ideally I’d rather keep it regulated if I can.

I’ll update once I get mine together, Looking forward to hearing about your progress as well!

 

[Dr. Kralenstein]

I ordered some custom sized baffles for a 30mm carbon tube I have coming. Basically they're just up sized Mrod style baffles. Made a big vent air stripper the other night too. Hopefully this will quiet the bark enough to shoot in the backyard and basement without ear pro.

I also ordered a bighorn drop block from Canada. The shop says it will fit the NP03 action. Once that shows up, I can start making the stock. Already have a rough idea on that as well. Bought some different pellets to try. Jsb diabolos, polymags, and hades. Hopefully one of these will group well. The snowpeak pellets I got for chrony testing are very stiff to load and have alot of bent skirts.

 

[Rvaughn]

I like your idea with the baffles.. I much prefer a shroud over a scew-on mod.
Where did you order them from?
also very good news with the bighorn drop block , that outa flow much better!

From what i noticed with my barrel the lead or transition point into the rifling was very rough/sharp and is gonna need some attention for certain.
This may be the same issue causing your rough loading and bent skirts..

 

[Dr. Kralenstein]

@Rvaughn

To be honest, I haven't even looked at the leade. Rifling is pretty shallow in my barrel, how's yours?

I'm in for a wait on the shroud tube. Only vendor I could readily find that had 30mm ID carbon tube in 1000mm length was in China. Waiting on some EPDM rubber backed conical 30mm washers too. Going to put one at the back of the shroud facing forward to help dampen that blast against the rear support bushing.

I made my air stripper slip on tight to that lower section of the barrel where they dropped the OD down to 14mm by the threads. I didn't like the idea of that thin threaded area hanging a heavy moderator off it. This way my air stripper will be set screwed around the perimeter of the barrel, and then supporting the shroud, with an expansion area in front of the stripper top hat, and then a few of these monster baffles.

When I get them in I will let you know how they look and perform. Baffles are shipped, and will just be a waiting game til everything shows up. Also picked up a 500cc 300 BAR bottle for it. Hopefully I break 100 fpe when said and done.


Here's a link to the sellers store. You can message them with dimensions you want, and they can't print it.

10x Baffles for Umarex Origin / Avenger For .177, .22 or .25 CAL - 3D printed | eBay

This listing is for a set of 10 3D Printed baffles for the Umarex Origin / Air Venturi Avenger and are 23mmx23mmx23mm We can also make these in custom sizes! If you need a different size send us a message and we can create them for you. The Umarex origin only uses 4 baffles... We are including 6...

www.ebay.com

 

[Bassett]

Hello I have a puncher and was thinking about doing this, was wondering if you thought there was anything else you could do to get closer to 900 fps?

 

[bearair]

Nice work. It is quite amazing that type of power.

 

[Dr. Kralenstein]

Hello I have a puncher and was thinking about doing this, was wondering if you thought there was anything else you could do to get closer to 900 fps?

Well after I get the bighorn drop block installed and running the 300 BAR bottle, I will let you know where I end up. The BH block has a larger passage bore and can also be ported out a bit more.

I also have some bigger hammer springs coming that I will try. I'm hoping for at least 750 fps with 82 grain, but I'll take more.

Currently I am under 600 bucks with all parts, including a full functional shroud, upgraded bottle, and the wood for the stock. I'm just going to glue a few 1x8 Whitewood boards together that I found with some nice grain. Will router and carve to what I want, then hopefully find a stain that works well with that wood.

 

[Bassett]

I'm looking to push a 170 grn around 900fps. Thank you , I'm curious to see how fast you can get it but I think I'll not go down this rabbit hole . Going to be shooting big bore silhouette this year and need something for power at 200 meters , enough to knock down a 45lbs steel turkey at 150 meters. I would like to knock down the 65 lbs ram at 200 m but u just have to hit it for score.
Good luck

 

[Dr. Kralenstein]

I'm looking to push a 170 grn around 900fps. Thank you , I'm curious to see how fast you can get it but I think I'll not go down this rabbit hole . Going to be shooting big bore silhouette this year and need something for power at 200 meters , enough to knock down a 45lbs steel turkey at 150 meters. I would like to knock down the 65 lbs ram at 200 m but u just have to hit it for score.
Good luck

Without getting a longer barrel and a different hammer, I'd think your goal is way out of this guns league. I think Troy Hammer only got the Bighorn up to around 220 fpe with a 28" barrel and his own valve he built.

I don't know of any off the shelf pcp in 357 that does over 300 fpe like you're looking for. Maybe AEA does? You could try contacting a member here named the Bearded gunsmith, he is currently designing/building some big bores that are putting out some serious power. I think he has his 30 cal doing over 300 fpe.

 

[Rvaughn]

Quick update… I received my barrel back from the gunsmith the other day with a nice 11 degree crown in place of the rough cut where I removed the choke, Now sitting at about 21” of barrel from the original 23”

Took a bit longer than I had anticipated with gunsmith but hey, he’s a busy man I guess.

Quickly assembled the Raptor mini with its new .35 probe and Bighorn barrel.
Didn’t mess with any reg pressure
(2100 psi) or hammer adjustments.
Just left the time same as it was as a 50fpe .25 cal.

1st shots where with 68grn hybrids
All Hovered around 815 ish fps for 99 FPE!
Not bad imo

Next I went the opposite end of the spectrum and jumped to my Bulldogs preferred ammo, NSA 142 grain slugs.
Which ended up flying out around 565fps
For 101FPE…
Bulldog pushes these out around 830-850 if I remember correctly, definitely needs some more oomph for these rounds!

Also Gotta do some adjusting to see what kind of power can be had in its current regulated configuration when I get a chance.
If that doesn’t get me where I want to be I’ll have to try it with a reg that I removed all the guts to make it unregulated.
That’s when it oughta really shine!

Another side note is I haven’t scoped it yet to see what it likes or how this barrel performs. Fingers crossed it does well…

 

[Dr. Kralenstein]

Quick update… I received my barrel back from the gunsmith the other day with a nice 11 degree crown in place of the rough cut where I removed the choke, Now sitting at about 21” of barrel from the original 23”

Took a bit longer than I had anticipated with gunsmith but hey, he’s a busy man I guess.

Quickly assembled the Raptor mini with its new .35 probe and Bighorn barrel.
Didn’t mess with any reg pressure
(2100 psi) or hammer adjustments.
Just left the time same as it was as a 50fpe .25 cal.

1st shots where with 68grn hybrids
All Hovered around 815 ish fps for 99 FPE!
Not bad imo

Next I went the opposite end of the spectrum and jumped to my Bulldogs preferred ammo, NSA 142 grain slugs.
Which ended up flying out around 565fps
For 101FPE…
Bulldog pushes these out around 830-850 if I remember correctly, definitely needs some more oomph for these rounds!

Also Gotta do some adjusting to see what kind of power can be had in its current regulated configuration when I get a chance.
If that doesn’t get me where I want to be I’ll have to try it with a reg that I removed all the guts to make it unregulated.
That’s when it oughta really shine!

Another side note is I haven’t scoped it yet to see what it likes or how this barrel performs. Fingers crossed it does well…

Hopefully you can get that thing up to 150 fpe or so. 21" isn't a bad length, but most of these big bores are 28" or so to get that higher power.