Donation

All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

Barrel twist rates

(1/5) > >>

grandadg:
First question for me is what rate of twist is recommended for a 7.62 barrel shooting lead slugs (bullets) My mold is for a 155grain spitzer (Lee mold) and should I use a slightly harder than pure lead alloy. I plan on making the grooves on the shallow side to enable softer lead alloys to grip and fill the grooves without having to force them too hard into the breech. But my concern is that if I go too fast on the twist rate the softer bullets will simply strip themselves on the way out of the barrel. I'll be doing 12 grooves I have heard 7" twist is what I need BUT that sounds awfully fast for what is essentially going to be a slow speed projectile. I do know that Lothar Walther .30 barrels are only 16 -1  and the .25 is 17.7 - 1 But then again these barrels are made primarily for shooting lighter weights so would I be better off by altering my bullet mould to a lighter flat point casting pure lead??
Thanks in advance for any replies.
Graham.

nielsenammo:
1:7 is way too fast for .308.  If you want to shoot heavy bullets like 155 grain 1:14 should be good for you and you can shoot lighter down around 100 grains or so.  This twist is already proven in the .308 air rifles.  If you only want to shoot heavies you can maybe go 1:12 but I would not recommend faster than that.  If you want to shoot lighter around 100 grains mostly, I would use 1:16 or 1:18.

The LW barrels your are referring to are pellet barrels as well and not made for slugs in mind.

rsterne:
What are your plans regarding pressure, barrel length, and what velocity do you wish to achieve with your 155 gr. bullets?.... Those questions need to be answered before thinking about twist rate....

Bob

grandadg:
Thanks very much for the info Nick 16 - 1 sound about right  to me  I thought 7 - 1 was a tad on the speedy side.

Bob
I have 24" barrels (they all come in at that from the Chinese suppliers ) Pressure wise I will be keeping to around 2000 psi with a possible maximum of 2500 psi. I have actually got two barrels one is 7.62mm the other is 6.5mm I shall be playing about with porting and dwell times on the valves. I was also thinking of making the hammers adjustable so I can fine tune the strike. plus the pre tension of the spring will be adjustable too. I have just been out in the shed today (despite the freezing cold weather) and made two heavy hammers for my Condor Copy in .25 and my little Gunpower  Stealth in .22 with the 12" barrel both Brass and Delrin hammers As the OEM ones are sad to say the least, with the Stealth hammer being so light that the additional weight was as long as the hammer!!! So I simply made a longer hammer with a tad more weight. This gun is to stay at the sub 12fpe level so I can shoot it at the local airgun range where FAC powered guns are strictly banned. I am very interested in the concept of a .410 sized air shotgun and wondered if they are powerful enough for killing rats out to say 15 -20 yards ?

nielsenammo:
different build for sure, how fast is your bullet expected travel?  Why such a heavy bullet for 12 fpe?

Navigation

[0] Message Index

[#] Next page