The AirGun Guild

General Category => PCP, C02, and Helium Powered Airguns => Topic started by: ShakySarge on December 11, 2018, 06:58:32 AM

Title: Converting Original Run B-Rod .25 to .30 Cal?
Post by: ShakySarge on December 11, 2018, 06:58:32 AM
A few years back I got one of the original bottled marauders from a good friend of mine in .25. I have had no issues with it and it has been a superb shooter getting about 60FPE for almost 40 shots with the King Heavy MKIIs. Well, Another buddy is looking at doing a group buy on some .30 cal barrels and this drew my attention. I have wanted a .30 cal for a while now and this may be the ticket. Then again, I am torn with parting with the current setup for the .25s even though I have a full tubed Gen I in .25 that is still a dream to shoot.

We believe that we can modify the 2263 valve to give up to about 70FPE but that really isn't a huge increase from what it's doing now. For those of you that have already done the .30 cal conversion, what would you suggest? The current bottle is a 500cc plus 50cc of tube for about 550cc of air on board. What I would like is some serious power, but not so much that I can't get off more than 20 shots or so. Is this even feasible???

Any input on valves, spring setup etc.. would be greatly appreciated!!!
Title: Re: Converting Original Run B-Rod .25 to .30 Cal?
Post by: rsterne on December 11, 2018, 08:10:03 AM
I suggest you read through this thread....

If you just change the barrel, and don't increase the size of the valve throat, you should be able to use your existing hammer setup, and the FPE will go up just because of the caliber increase.... putting you over 70 FPE just because of the bigger pellet base area for the HPA to push on.... You probably can't hog out the existing valve big enough for a "proper" .30 cal setup, and if you did, with a conventional valve, the cocking force would be quite high.... I would look at using either a Cothran Powerhouse valve, or a JSAR Max-Flo SS Valve.... They both have 1/4" exhaust porting, and are capable of delivering 100 FPE in .30 cal, depending on the regulator setpoint you use.... and either valve is super easy to cock.... You will have to drill out the receiver and change the transfer port with either valve....

One thing you might consider doing is annealing the bolt and drilling and tapping the cocking lug hole out to 10-32.... That pin is the only thing holding the bolt closed, and by increasing to .30 cal you are increasing the load on it by over 40%.... If you run 2000 psi instead of the 3000 it was designed for in .25 cal, that pretty much is a wash.... but if you are considering running unregulated, or should the regulator fail, the larger caliber is increasing the stress on that critical part.... The bigger pin is probably not necessary on a regulated .30 cal, but would be on an unregulated .30, or on the regulated .35 cal which I just built.... I replaced it on my .30 cal build as well, because I wanted to play with it unregulated.... With an Cothran at 3000 psi, I was getting about 145 FPE with 68 gr. BBTs....  :o

Title: Re: Converting Original Run B-Rod .25 to .30 Cal?
Post by: ShakySarge on December 11, 2018, 09:31:35 AM
Awesome information Bob! Thanks so much. I figured that the bolt pin would need to be enlarged for the increased pressure exposure. This definitely helps me on my quest.