Velocity of modded 1377 or 1322 with 24" barrel @ 10 pumps?

[NickB79]

I'm thinking of modding a refurbished 1377 into a carbine.  So far, I'm looking at adding a synthetic stock, 24" barrel, Mellon FT piston and valve with the cutting and porting done, flow-through bolt, and steel breach.

I'm still not sure if I want to go with a .177 or .22 barrel, and was wondering what kind of velocity could be expected with either of these at 10 pumps?  Are there any other parts I should add to boost velocity?

[Bentong]

From what you listed on top, you should see 707.1 fps with 7.9 CPL with 10 pumps & 828.7 fps with 20 pumps with same pellets. That's what I get on mine and do 10 pumps on nutters using .177 predators to 18yrds. I added Mellon power adjuster to dump all air on 15+ pumps. I can put a stiffer hammer spring but it makes cocking harder and hard in the internals.

[reddheadnla]

I won't be far behind ya! I just ordered mi9ne today. I can't wait till it gets here!! Let us know what kind of goodies that you can find for it.

[NickB79]

Anyone know what a .22 cal barrel and bolt would do?  700 fps with 7.9gr pellets seems a bit lower than I was hoping for energy-wise.

[rsterne]

Porting a valve is a waste of time in .177 and you are as likely to lose performance as gain it.... unless you are over the 850ish fps mark.... In .22 cal, however, the porting will definitely help.... With a 14.5" barrel and similar mods to yours I was getting ~550ish in 10 pumps and 650ish at 18 pumps (where it started retaining air) with 14.3 gr.... You will gain roughly 10% with a 24" barrel over those figures....

The only way to increase velocity is by more pumping.... Since retaining air becomes the problem, then you will need a Disco hammer spring and an RVA.... You can gain another 100 fps or so, but you'll be up around 30 pumps.... and that gets OLD really fast....

Bob

[1377x]

.22 24" barrel flat top set up 14.3gr cphp 10 pumps 650fps