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Barrel Swap Question  


OBM
 OBM
(@obm)
Joined: 1 year ago
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Topic starter  

I am considering converting a .22 pcp rifle into .177 for field target. 

Has anybody swapped barrels from .22 to.177 in a PCP?  I’d like to know what kind of energy I can e expect  with just a straight swap with the same barrel length. 

 

The rifle in question is doing 35fpe in.22. 

Tank you. 


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Franky
(@hn21grains)
Joined: 3 years ago
Posts: 8
 
Posted by: @obm

I am considering converting a .22 pcp rifle into .177 for field target. 

Has anybody swapped barrels from .22 to.177 in a PCP?  I’d like to know what kind of energy I can e expect  with just a straight swap with the same barrel length. 

 

The rifle in question is doing 35fpe in.22. 

Tank you. 

20flb is Max for FT 925fps w/10.5 CPH's in .177/4,5mm.....Franky


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Doug Wall
(@doug-wall)
Joined: 3 years ago
Posts: 166
 

That won't work for FT. You might get slightly less FPE with .177, but you'll still probably get over 30 FPE. You would also have to change out the bolt, and probably the valve. to get the power down. As was mentioned, 20 FPE max for FT.


Jim Bentley thanked
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Jim Bentley
(@jim-bentley)
Joined: 3 years ago
Posts: 253
 
Posted by: @doug-wall

That won't work for FT. You might get slightly less FPE with .177, but you'll still probably get over 30 FPE. You would also have to change out the bolt, and probably the valve. to get the power down. As was mentioned, 20 FPE max for FT.

I agree.


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OBM
 OBM
(@obm)
Joined: 1 year ago
Posts: 5
Topic starter  

Thank you guys. I can turn the power down to 20fp later. I was just concerned about my start point. I wasn’t sure if the power loss would be so much I would struggle to get to 20fpe.


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nervoustrigger
(@nervoustrigger)
Joined: 3 years ago
Posts: 251
 

No you won’t get anything close to 30fpe after the caliber change.  It is quite likely in fact to be close to the 20fpe FT limit before any further adjustments are made.  

The reason being a .177 pellet has a substantially smaller surface area on which the air pressure is acting to accelerate it. 


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OBM
 OBM
(@obm)
Joined: 1 year ago
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Topic starter  

You’re probably right. I just remembered that once I noticed a .177 valve stem was twice as long as a .22.  That complicates things. 
I was hoping someone who had done it would chime in. 


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Hector J Medina G
(@hector-j-medina-g)
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Posted by: @obm

I am considering converting a .22 pcp rifle into .177 for field target. 

Has anybody swapped barrels from .22 to.177 in a PCP?  I’d like to know what kind of energy I can e expect  with just a straight swap with the same barrel length. 

 

The rifle in question is doing 35fpe in.22. 

Tank you. 

WHICH rifle are you talking about?

There are constant energy rifles, constant velocity rifles, efficiently valved and inefficiently valved.

There is as much difference in PCP architecture as in the stocks.

It ALL depends on the rifle itself and how it is built.

 

What barrels are we talking about?

There are good and bad, long and short, efficient and inefficient barrels.

 

Too vague a question to provide ANY answer. Sorry, please elaborate with details.

 

 

HM


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OBM
 OBM
(@obm)
Joined: 1 year ago
Posts: 5
Topic starter  

Thank you for the response. The question was intentionally vague. I can always tune a gun to make it work in .177 but I’m not looking to get into a huge project. 

I wanted to know what would happen when only a .22 barrel is swapped with a.177 barrel, same brand, same length. Leaving all the other variables out. 

My reasoning was -If the.177 barrel crippled the power of the rifle, then it would take a lot of work to get it sorted. I wouldn’t pursue such a project. 


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ribbonstone
(@ribbonstone)
Joined: 3 years ago
Posts: 371
 

For what it’s worth, ended up with a few airguns that could “top swap” between .177 and .22, and an AirForce that basically just swaps barrels. (Top-swap would be a complete barreled breech).

 

Some things didn’t up perfectly “even” in a top-swap...no two parts are truly perfectly the same, so there could be some little differences here and there.

 

Pretty well adjusted as a .22, tried them as .177’s.

 

Best .177 lost 12% energy, worst lost 27%….as you can guess, the, the more powerful it started as a .22 the more energy it lost going to .177 and they got to be pretty gas hogish.

 

 

 


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Hector J Medina G
(@hector-j-medina-g)
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Posted by: @obm

Thank you for the response. The question was intentionally vague. I can always tune a gun to make it work in .177 but I’m not looking to get into a huge project. 

I wanted to know what would happen when only a .22 barrel is swapped with a.177 barrel, same brand, same length. Leaving all the other variables out. 

My reasoning was -If the.177 barrel crippled the power of the rifle, then it would take a lot of work to get it sorted. I wouldn’t pursue such a project. 

OK

So, IF we are TRULY talking of a "Ceteris Paribus" (all things remaining equal)  situation, then the ONLY difference is the barrel's expansion ratio.

And then the Muzzle Energy would be the relation between the inverse of the square of the calibers (because barrels are the same length), in this case:

1/[(0.22 X 0.22) / (0.177 X 0.177)]=1/(0.04840/0.03133)=1/1.54489=0.64729

Meaning that you would LOOSE ABOUT 35% of the muzzle energy when going from 0.22" to 0.177"

From your OP, the 35 ft-lbs would potentially become 22.65.

But again, this is a HIGHLY HYPOTHETICAL situation.

Just think that to reach this ME with any "normal" 0.177" pellet, it would have to weigh upwards of 11½ grains to still retain some stability, and that would imply that the flow rates in the plumbing can go up at corresponding pace.

HTH

 

 

 

 

HM


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nervoustrigger
(@nervoustrigger)
Joined: 3 years ago
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Incidentally, Ribbonstone’s example ties nicely into Hector’s point about some valves exhibiting different behavior.  

I don’t own any Airforce guns so I wasn’t aware of this difference until recently so it seems like an interesting example to discuss here.  Compared to a conventional valve, it acts more like a constant velocity valve.  That is, the longer the pellet is in the barrel, the greater the valve dwell.  Shooting heavy pellets or slugs, that has the effect of overcoming the substantial velocity drop you might otherwise expect.   Not completely, just contrasted with a conventional valve.   Naturally, that means it uses more air per shot with heavy projectiles than it does with lighter ones.  

With a conventional valve, dwell is influenced comparatively little by the projectile’s weight.  Air use (shot count) is about the same whether you’re using heavy pellets or light ones, and the FPE increase for heavier pellets will not be as great at the same state of tune (say, adjusted for efficient air use with medium-weight projectiles).


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ribbonstone
(@ribbonstone)
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Got to thinking about it...what could I be sure was a “one shot air dump”….which would be as equal as I could arrange.

 

So thought of SSP. No doubt about what volume or pressure they ran on….no doubt they dumped it all in one go….spit that air though the same passageways....just the bore size/pellet weight changes.

 

Pretty much the most uniform tune I could think off...nothing was going to change the air pressure/air volume.

 

Still had the barrel quality, fit of the pellet as variables….but it ended up a lot closer to 15-18% difference.

 

Still have that diminishing returns thing...the faster you go, the harder it is to go even faster.

 

Even trying to “even up” the weight (JSB is good about that...can find the same weight pellets in .177, 5mm, and .22) the energy change still worked out to be area.


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nervoustrigger
(@nervoustrigger)
Joined: 3 years ago
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That’s a good point of comparison, a single stroke pneumatic. The example given sounds like a pretty good design, having a sort of in-between energy difference. Meaning they’d invariably use one valve design and hopefully design it with a compromise volume that makes it equally well suited to either caliber. For example if they instead optimized it for .22, the valve volume would need to be somewhat larger to compensate for the larger volume of the .22 barrel it is tasked with pressurizing to accelerate the projectile. In so doing, that means the poor guy who bought the .177 is clack, clack, clacking away in vain to charge a volume that does him no good. All it does is work him harder, with the reward being nothing but a louder report.

My best guess is it’s this good compromise design and the common porting that holds the energy difference to 15% or so.

The best example I could think of from my own experience was a bottled QB producing 36fpe in .22 and 24fpe in .177. Each with a barrel port approximately 75% of the caliber, and each with heavy pellets weighing roughly 2x the de-facto (Crosman) weight...28.5gr and 15gr. 36fpe versus 24fpe is a difference of 33% which works out pretty closely to Hector’s calculated figure.


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