Tuning Performance of 30 cal PCP

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ChrisS

Member
Jan 23, 2021
292
161
NV, United States
So, I built up this PCP rifle. Disco airtube with a performance valve by Magnum Air Power, a 24" TJ barrel and Cothran rear cocker are most of the distinguishable parts. Maxed out at 3000psi and the pre-tensioner all the way in, it makes about 860fps with a 45 grain pellet or 73fpe. Does that seem about right? What are you guys getting with your 30 caliber PCP's?

Thanks

Chris
 
Not regulated, fairly basic build. It seems to be dead accurate, at least in the 20 feet I have tested it in my garage...one hole. I throated the barrel out enough to be able to get smaller pistol slugs in as well. It will launch an 80 grain slug at something less than 700fps...also very accurately. Just seems to me it should make a bit more power. 

Thanks
 
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I contacted Magnum airpower and was informed that it would be at least a year before he will get any "big bore" valves in stock. I took a look at the valve I have and there is no way I'm gonna open it up to anything like .250", just not enough meat in there. 0.187" maybe, but there would be very little meat left between the port wall and the poppet seat.

I may just go the Cothran valve route. I have a 357 caliber that I built up from all Cothran parts and it does really well. I used his "middle" valve for that build, 0.25" transfer port I.D. His smaller valve is 0.180". But, it is also a force reduction valve, meaning it takes far less spring/hammer/whatever to get it to open. I bet that valve would do more than what I need here. I really like his parts as well, all 304 stainless and perfect fit.

In the meantime, this little rifle is doing well. I was shooting it tonight on 3000psi with the power adjuster about halfway out. Shooting 42-ish grain roundballs, it was making right at 870fps and one hole groups. Gotta love these Crosman/Benjamin builds...

Fun stuff-

Chris
 
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My Cothran 357 will do pretty much the same velocity with an 81 grain pellet; 900 to 1000fps on 3500psi. And it shoots roundballs really nice as well as pistol slugs. But, it is a 2 shot wonder and I'm waiting on a longer airtube for it now. I'm using a 26" TJ barrel and I want the tube to go right on up to the end of the barrel to maximize my air volume...hoping for one more shot ;-).

I'm also waiting on one of Don's Marauder valves for my .25 Marauder. That should be interesting as well, be nice to get a couple hundred more fps out of it. They are a nice rifle if not a bit heavy. Accurate and quiet. Well, relatively so, compared to my other PCP's, the Marauder just whispers.

Should have both of those items this next week...then the fun begins...again. Just too much fun these Crosman/Benjamin things. 
 
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WooHoo! The longer airtube on my 35 cal gave me not just an extra shot or two, but several more shots. I'm getting like 8 or 10 good shots now from a 3500psi charge where I was getting 2 good shots before. I'm just tickled. The tube actually extends beyond the end of my 26" barrel, so kind of odd looking, but volume is volume, I'll take it! 

-Chris
 
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I finally changed out the valve in this 30 cal to one of the Cothran ".250's". What a difference! I went from being able to get about 77lbft on pellets to right at 130lbft on slugs (100 lbft on pellets) that I can cast myself. Only around 7 good, strong shots from a charge of 3Kpsi down to perhaps 1Kpsi, I used to get a dozen or so with the Magnum valve. But that is a swap I'm more than willing to make. 

This Cothran stuff never ceases to amaze...4 guns now and counting.

Chris
 
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