.30cal big bore PCP build
My mission is to build a light weight short .30cal big bore PCP from scratch suitable for taking deer and pigs with cast projectiles.
I have 3 different barrels to test with a range of twist rates and bore diameters for the range of .308 cast projectiles which are in themselves tunable in weight and balance with an adjustable depth hollow point.
Ive got my money on the 1-14″ twist .307.5 match barrel for the 105gr cast projectiles but also have a 1-18″ twist for 80gr -120gr projectiles and a 1-10.5″ twist shallow cut microgroove for up to 160gr projectiles.
This is the bullet I have chosen, it is a 115gr Lyman bullet
The mould has been modified into a hollow point that now casts a 95-110gr HP pure lead bullet depending on hollow point depths.
My goal is to get about 170-180ftlbs from this rifle so although making a bullet for a barrel before the rifle is even built may seem a little backwards but it was a big part of the R&D process for this project and I needed to be very sure there was a bullet that would suit my needs and will be stable at a lower than intended velocity range in one or more of my barrels. I pushed a sized one through the microgroove bore to get a feel of the bore friction and check out the rifling groove cuts in the bullet.. the weight and balance can be fine tuned by altering the hollow point depth and diameter at a later date if needed.
For the action I cut a piece of 1-1/4″ 6061 T6-51 alloy to length and skimmed one side down on the mill to 1″ to form the start of the receiver.
Then I marked the barrel/bolt centre, fitted up my 4 jaw chuck and drilled the pilot hole with a long series 8mm drill bit..
Followed by the 1/2″ barrel clearance size drill and a 10mm bore for the bolt.
I then cut the loading port for the feed tray and the 45 degree chamfers to pretty it up..
A little more milling and the basic shaping is done.. It will get a raius to mate up with the cylinder, transfer port and then the bolt and cocking pin cut outs on the underside..
A few more components to the list.. the rear plug is yet to be bored out and threaded for an external power adjuster/spring guide and the bolt still needs the probe, O ring groove and handle to be made.
The 1-14″ twist match barrel has been pre fitted and is ready for the transfer port to be drilled.
I have decided to use a modified German made Gecardo trigger because Im too lazy to make one from scratch.. 🙄
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Looks promising Wingman, Beautiful job. Any idea what your next creation will bring us?
LarryW 
Smoke em if ya got em!
Here’s the results of it first 100m field test.. I tested two bullets, my 105gr HP and a 85gr HP
I shot prone of my rest and there was a strong gusty wind up the gully I was shooting through so I expected a little
horizontal patterning, I’m a little over waiting for the weather to clear so I can test this build so pushed on..
After getting the scope zeroed at 100 yards I shot the following 5 shot group with the lighter 85gr HPs
I then topped it up to 3000psi again and shot these 10 shots consecutively of that fill… the wind had really picked up at this point ::)
So although a windy and rainy day I have the confidence I can get 5 shots inside an inch at 100 meters on a still fine day
with both these bullets… I will try again when the weather settles. ::)
This was the first 5 shots I put on paper at 100m the other day when sighting and tuning..
Genius Wingman :ugeekn: should start his own production of air rifles 😀
Those would be really EXCLUSIVE and HANDMADE pieces of work of art that only very few of us could dream of 🙁 .
While the price tag, the waiting list for fine exclusive air rifles like Beaumont, Drummen Sinner, etc is very long ….
Weight was something I was thinking of throughout this build as it is a deer rifle which means it will be carried through the hills for hours on end. I just weighed it and it is 3.5kg with the scope (7.7lbs).. much lighter than all me other bullpups. 😀
Its showing some very good groups at 100 yards too.. shot several groups around 1.5″ today with the 105gr HP but they should get even better once my .308 bullet sizing die turns up and I can size this lead a little smaller for this tight match barrel..
I finished it all off yesterday by attaching the new trigger linkage and polishing all the parts ready for anodizing.
That’s a great looking build, you have a talent. I also like the table with drawers it’s sitting on.
Not that I have any expierience, but I would sure be proud of owning that.
Its quite loud yes.. about the same as a 9mm handgun round.. ear protection is definitely required for range work. I’m undecided on whether to blue the barrel and and bolt etc or leave them polished but the air cylinder and receiver will be anodized flat black.
The finished bullpup looks great. Must be deafening to shoot though. Are you going to leave it polished or get it anodized?
Finally got it fully assembled and in the stock with the forward scope mounts set up, Ive just got to do a small job on the trigger linkage tomorrow and its ready for tuning and hope to get some groups on paper.
I have backed the power off to a maximum of 915fps to help flatten the string a little more too so I’ll also run a few more strings over the chrony..
:8:
Wingman my brother, you are a FUXING genious!!! I hope you do some videos when testing this monster?
Now make a Lelya clone, so we can get Hoot into some long Pants!!!
Regards
LarryW 🙄
If so, you should have put the cocking handle on the left side and made a linkage so that the cocking handle is forward near the trigger like on the Vulcan. Assuming you’re right handed, when it’s shouldered in the field you can cock it after a shot then load a pellet and push it forward and be ready to go (using your left hand so that you’re always holding the AG by the pistol grip at all times). On a bench rest, use the bolt.
I think a forward cocking handle or lever is great for a multishot bullpup. The AG can always be cheek welded and your eyes on the scope never leaving the target for a quick follow up shot. Even with the Bobcat design right now, you can do the same but for me, I would prefer my dominate hand always on the grip supporting the weight of the gun and near the trigger. I’ve never handled a Bobcat but I can see a few added seconds needed after moving your hand from the grip to cocking the lever, finding the grip again and getting comfortable on the trigger before the follow up shot. The design of the Colibri and Vulcan with forward bolt in my opinion has great ergonomics (even though the Colibri is semi-auto). A forward lever cocking handle would be the best of both world in keeping the side profile of the AG clean looking. Can you imagine a R3M with a forward lever? That would be close to amazing in the field.
No,there is only one cocking handle, it is the new one on the side. The top bolt action just opens the breech to load a cast bullet (not pellet) and then seals and locks solid as the pressures generated when firing a bigbore airgun would destroy and std sized bolt action. I moved the cocking mechanism away from under the bolt to a stand alone handle as there was too much cocking pressure on the bolt. I am right handed so where it is located keeps it clear of my face and also lets me use my right hand to cock it.. it takes quite some effort to cock, there is one big bad ass hammer spring in there.. The biggest problem with the “cock off bolt” arrangement was the hight of the action (necessary for original barrel shroud design clearance) with the the cap screws connecting too far above the hammers centre line creating side loading which makes the hammer want to dig its nose into the slot cut outs at the top and bottom of the cylinder.. the new direct cocking handle is very easy and smooth to operate just not as aesthetically pleasing in my opinion.
It was usable with the bolt cocking set up but I could see receiver bore and hammer bore wear being an issue with time and use.
In hindsight the action could be cut lower to reduce the barrel hight to the cylinder as I dont think Ill bother with a shroud type suppressor with this build. The muzzle break reduces the recoil and muzzle flip at least 50% and the noise is manageable without the need for ear protection.
I will just change my design slightly for my next builds to get a more direct hammer contact point and cut smaller slots in the hammer section of the cylinder. Like most prototypes there are things that can be improved on and loads of trial and error design work..
In fact after setting up the trigger, I found that that lower slot didnt even have to be cut at all.. the drop away sear could have worked through two 8mm holes in the cylinder.. live and learn.. like I said.. nothing ever goes to plan in my workshop ::) MkII will be better 😉
A forward cocking mechanism has its benefits on a plinker but is just added weight and really no point on this build. This is not a back yard plinker or squirrel hunter that would benefit from a multishot breach and a way of cycling it faster from the front side or where ever, It is a short, light weight precision big bore that shoot cast bullets to 200+ lbs that I intend to use on deer. Think of it as a single shot with 9 back up shots if shit hits the fan.. If you get to fire one shot off when your out after deer then you have had a good day..
So wait, you have two ways to cock it? Via bolt or cocking handle? Both methods moves the probe?
If so, you should have put the cocking handle on the left side and made a linkage so that the cocking handle is forward near the trigger like on the Vulcan. Assuming you’re right handed, when it’s shouldered in the field you can cock it after a shot then load a pellet and push it forward and be ready to go (using your left hand so that you’re always holding the AG by the pistol grip at all times). On a bench rest, use the bolt.
I think a forward cocking handle or lever is great for a multishot bullpup. The AG can always be cheek welded and your eyes on the scope never leaving the target for a quick follow up shot. Even with the Bobcat design right now, you can do the same but for me, I would prefer my dominate hand always on the grip supporting the weight of the gun and near the trigger. I’ve never handled a Bobcat but I can see a few added seconds needed after moving your hand from the grip to cocking the lever, finding the grip again and getting comfortable on the trigger before the follow up shot. The design of the Colibri and Vulcan with forward bolt in my opinion has great ergonomics (even though the Colibri is semi-auto). A forward lever cocking handle would be the best of both world in keeping the side profile of the AG clean looking. Can you imagine a R3M with a forward lever? That would be close to amazing in the field.
looks beautiful and powerful, just don’t forget ear-plug. 🙂
A little more progress in the last few days..
Regretfully I cut another slot in the side of the cylinder to add a stand alone cocking handle, not really my preference but it is much better in terms of smooth operation. it cocks with very little effort now and the cocking handle has added weight to the hammer which may eliminate the need for an internal tuning weight. I have left it quite long but will cut it down a little once I shoot a few strings.
I also spent a little time polishing the machining marks out of the various parts, eventually after all testing is done the external alloy parts will be bead blasted and anodized flat black.
I cut the bolt probe to length and fitted two 007 O rings (cool size huh) to it, it seals just inside the breach against the receiver itself ant the other sits just outside the transfer port in the barrel. I am a fan of at least two O rings in this position as there’s nothing worse than a breech leak on a bullpup.. loud and uncomfortable is the best case scenario and a permanently flared nostril and an eyelid turned inside out is the beginning of something quite dangerous..
I have shortened the bolts stroke to just allow a bullet in the loading tray by a second safety cap screw in the bolts shaft and added a sprung ball bearing with a detent in the bolt shank to positively lock it up in the closed position. It all runs very smooth now.
The 26″.308 match barrel started its life on a .308 win target rifle and after the .308 Win chamber section was removed it showed signs of a section of throat erosion which is common and it had a an inch or so or wear at the muzzle end too probably from excessive cleaning from that end.
I have trimmed both ends back to remove the bad sections and have ended up with 21″ of good strong shiny rifling to work with.. I have added a muzzle break to keep the aesthetics looking right because it ended up an inch and a half shorter than I’d hoped but”accuracy first” 😀
Thanks to my gunsmith friend for the loan of a piloted .308 tapered throat ream I have the cast bullets slipping in with perfect resistance and a nice gradual taper from the lands to the groove without any angled shoulder to gather lead.
This match barrel is tight, it slugs at .3072″ so I will be sizing my bullets to .308″ not .309″ like I had intended for a .308 bore. Ill be very keen to see these on paper..
Nearly finished.. I still have to modify the scope riser mounts for this barrel and set up the trigger linkage..
It is VERY light and will be a pleasure to carry, it is 30″ over all length.
I test fired a few shots out of the stock and all is well.. no leaks and the breech seals perfectly.
I filled it to 3000psi and fired its first string over the chrony without any hammer weights fitted..
105gr cast HP bullet 3000psi: FPS = 921, 929, 916, 896, 881, 840, 829. 1700ish psi end pressure, not bad.. I need to fill my dive bottles to try a full 3500psi fill which should show the top of the curve rising slightly and 10-13 usable shots. I will aim to peak the thread at 900fps so will drop the hammer spring tension slightly too.
Realistically this build will be usd a 50-100 yard deer gun so 3 high power even shots is plenty but I will tune the flattest consistent string out of interest. 200ftlbs in a bullpup certainly puts a smile on my face! 😀
Just for shits and giggles I put a 44gr .30 cal JSB pellet over the chrono..3000psi fill got 1176fps and it sounded like a .223rem letting rip! These pellets are too small for this bore and the twist is too fast but it was entertaining..
Great progress.
Good to hear you did all the necessary calculations on this build. Just asking to be shure;)
Keep up the great work!
Cheers,
Marc
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What distance do you plan to hunt for deer using this new bullpup? Just curious what’s the max distance you would take a shot given it’s 200 FPE? Probably has a nice kick and the sound it makes would scare everything in the forest.