Author Topic: Any Interest in 6mm ? - Build Thread (Read 10462 times)

rsterne · « **on:** June 14, 2017, 04:34:43 PM »

I have had a few guys ask about the idea of making a 6mm PCP, and it has aroused my curiousity, so I did some research.... I knew that LW made barrels in various twists (8, 9, 10, & 14") but I had never seen one in TJ's list, so I contacted Mike and it turns out that he has a mandrel to make them with 0.237" lands and 0.243" grooves, with a 10" twist.... They can be made in 1/2" and 9/16" OD, and he has a 9/16" in stock.... Then I started looking around for moulds to cast bullets, and I found these....

The first one is a Lyman 225107, interpolated out to a larger diameter by NOE.... It says it weighs 46 gr., but they currently have no stock in the store....

The second one is a scaled down Lyman 257420, done at the request of Jack Bowman (Scandalous Airguns).... Aresenal have this mould available to order, listed at 60 gr....

The third one is listed as a 73 gr., and is also out of stock at NOE....

I scaled down my .257 cal 78 gr. BBT, and have sent the drawing to Al to add to the AirGun Discussion Section on the NOE Forum.... It looks like this....

All of these should work just fine in Mike's 10" twist barrel.... According to my "lofty goal" PCP spreadsheet, with a 24" barrel at 3000 psi, and bore-sized porting, it should be possible to hit about 139 FPE.... In reality, that means you could probably do that with a 28" barrel, with the gun tuned to the max.... It should put the mid 900's within reach with my 65 gr. BBT with a 24-28" barrel at 3000 psi.... In other words, without going to ridiculous barrel lengths or pressures, any of the above bullets should be usable.... with the 46 gr. only requiring maybe 2200 psi or so....

Anyways, I thought I would throw this idea out there for everyone to chew on.... If there is enough interest, I'm sure we could get Al to put the BBT in a Group Buy, and the others into Inventory Runs.... I already started a thread at NOE to express your interest in the 46 gr. in hopes of getting an Inventory Run started....

Bob

rsterne · « **Reply #1 on:** June 16, 2017, 04:51:02 PM »

I spent the day today drawing out a general arrangement of what I might build for a 6mm this winter.... Here is what I came up with so far.... I used my typical reversed tank block to keep the weight of the bottle centered.... and I may use a 1.25" OD x 0.095 wall 2024-T3 tube to keep the weight down....

I have already ordered a tank from AliExpress.... its a 500 cc Carbon Bottle rated at 300 bar.... the plan is to have an adjustable regulator built into the tank block, feeding a 150 cc plenum at about 200 bar.... I would like to use 3mm thick carbon fibre sleeve on the 14mm OD barrel, so the OD will be 20mm (over 3/4").... which should make it VERY stiff.... The plan is to use a PRod trigger group and an AR style stock in line with the main tube.... That will put the adjuster for the SSG inside the buffer tube.... A Cothran valve will handle the air delivery, with it's 0.257"ports perfect for the job.... If I can arrange it, I will get two 10" twist barrels, one in 6mm and the other in .257 cal., both 28" long.... The goal is to drive my 2.5 cal long BBTs at 950 fps, meaning about 130 FPE in 6mm and 156 FPE in .257....

Bob

Christopher · « **Reply #2 on:** June 16, 2017, 06:51:27 PM »

I like winter; hunting, no ticks, snow(gimme a break, I'm from Ky) and another air gun build from Bob. Sounds like a very interesting project. Looks like a good plan you have there.......especially the 6mm. Which bullet mold are you thinking about going with?

Chris

rsterne · « **Reply #3 on:** June 16, 2017, 07:58:28 PM »

For sure the 60 gr. Bowman, because it is available.... Hopefully I can convince Al to take the BBT to a Group Buy....

Bob

Alan · « **Reply #4 on:** June 17, 2017, 04:07:22 AM »

The you can add a 7 mm, and a .270, and.......

rsterne · « **Reply #5 on:** June 17, 2017, 08:11:16 AM »

I already have a 7mm....

.... realistically it's more power than I need.... but it was fun to build....

Bob

rsterne · « **Reply #6 on:** July 13, 2017, 02:17:14 PM »

I ordered a couple of 1M pieces of Carbon Fibre tubing from China through eBay.... Excellent service, less than 2 weeks to receive them.... I can't believe how stiff this tubing is....

It is 20mm OD and 14mm ID, so that means the wall thickness is nearly 1/8".... It is about the same stiffness as steel tubing at a fraction of the weight, and will make the barrel incredibly stiff.... I was talking to Mike at TJ's, and he thinks he can hammer the barrel down to 14mm to fit inside the tubing, I am sending him the 6" long piece in the photo as a sample....

Bob

Christopher · « **Reply #7 on:** July 13, 2017, 07:20:56 PM »

You plan on epoxying that cf sleeve to the barrel or use it to tension the barrel with it?

Chris

rsterne · « **Reply #8 on:** July 13, 2017, 08:09:28 PM »

It will be glued to the barrel with Loctite 638 (Green)....

Bob

rsterne · « **Reply #9 on:** August 15, 2017, 01:49:31 PM »

I got my barrels today from TJs.... Mike did a fantastic job of hammer-forging them to fit the sample piece of 14 mm ID Carbon Fibre Tubing I sent him.... Both the 6mm and .257 barrels I ordered are a perfect slide fit inside the CF sleeve.... They are both a 10" twist, and the blanks are 29" long....

I am slowly collecting the parts I need for this winter's projects, this was a big step along that path....

Bob

Dairyboy · « **Reply #10 on:** August 15, 2017, 02:03:50 PM »

Very nice!

rsterne · « **Reply #11 on:** August 23, 2017, 03:10:26 PM »

Here is the stock I ordered from DHGate, along with the buffer tube (Mil-Spec).... The fit is perfect, with about 3" adjustment in the LoP, and almost an inch of vertical adjustment for the comb height....

The stock / buffer tube assembly weighs just 1 lb. 5 oz.... and should look great with the PRod trigger group I plan on using on this build....

Bob

Christopher · « **Reply #12 on:** August 23, 2017, 06:22:38 PM »

Looking great Bob.....don't know how I did it but missed your post about the barrels. Looks like the chips are gathering for ya. You gonna keep the barrels the full 29"?

Chris

rsterne · « **Reply #13 on:** August 23, 2017, 09:40:32 PM »

Aiming for 28"..... not sure yet

Bob

rsterne · « **Reply #14 on:** September 18, 2017, 01:49:00 PM »

The mould for the 74 gr. FN, available as GC or PB, and also with a Lyman HP Pin, are now in the store at NOE.... along with the shortened version I requested....

http://noebulletmolds.com/NV/index.php?cPath=25

Bob

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