"Any Interest in 6mm? - Build Thread"

[rsterne]

I swapped the 6 mm upper onto the unregulated gun tonight and filled it to its MSWP of 4200 psi.... I set the SSG to just a whisker of gap and fired one shot to settle things, topped it up and fired two shots with the 73.4 gr. bullets.... 1028 & 1029 fps (173 FPE).... Then I did something I have just been dying to try ever since I came up with the idea of building a 6mm.... I loaded up a 1.8 gr. Airsoft BB, topped it up to 4200 psi and took a bead through the Chrony.... 2093 fps.... repeated it.... 2097 fps.... once more.... 2087 fps.... That gives a three shot average of 2092 fps (17.5 FPE) with a basic PCP, just shooting very light ammo.... No special equipment, just a standard SS style valve, porting that turns through 180 deg., and a rifled 29" barrel that is a poor fit on the BB.... it will actually roll out the muzzle if you hold it pointing downwards.... Running air at room temperature (the pressure in the 300 cc reservoir dropped ~ 250 psi each shot), not Helium.... Lloyd still holds the record at 2162 fps.... but he better be looking over his shoulder....

Bob

[wesb2007]

That must have been fun! [emoji5]

Sent from my LG-H812 using Tapatalk

[FRANK]

And to say not to long ago they told us the max for airguns was 1600fps that physics calculation made it that.

[rsterne]

Fun & LOUD !!!

There was about 70 gr. of HPA in the barrel for those shots.... nearly as much as the lead bullet.... and nearly 40 times the weight of the plastic BB....

Bob

[rsterne]

Although I plan on running the .257 barrel on the unregulated gun, while I had the upper removed to try the 6 mm on it, I thought I would try the .257 upper on the regulated lower.... It had a slight leak in the transfer port area, but I did my testing anyways.... Here are the results for the 73.5 gr. Lyman 257420 at 2800 psi....



At 5% below the maximum velocity I was at 894 fps (130 FPE) at 8 turns of gap on the SSG, and the efficiency was 1.17 FPE/CI.... While that is similar to what I was getting on my .257 Hayabusa, it was a little below the 1.28 FPE/CI I got on the previous testing, which I attribute to the leak.... I was either losing a bit of velocity (likely), using more air (unlikely), or both.... but no question it would affect the FPE/CI either way.... If I was going to set this gun up as a regulated .257 I would likely bump up the setpoint pressure to 2900-3000 psi, although that may not be necessary with the 66 gr. HP version I have of this bullet, it might well shoot better at this pressure....

This pretty much completes the basic testing of these two guns.... I am extremely pleased with the results for both power and efficiency.... The plan is to put the 6 mm upper back on the 2800 psi regulated gun and run the .257 barrel on the unregulated version, and tethered it at 3800, but tune it for a few shots off tether.... All I hope now is that the snow disappears before the Motel gets too busy so that I have a chance to see how they shoot....

Bob