Custom AirForce .224 slug barrel project advise

[luge007]

This message was originally intended for 'Dyotat100' (the recognized guru of AirForce stuff) but his PM box is perpetually full, so I will submit this to the forum.

Hi,
I realize this barrel idea has been done before, but I'd like to get your advice on selecting a twist rate for a.224 barrel blank to machine for my Airforce Escape.

 I was considering Green Mountain's 1:14 twist, BX22mag barrel blank for .224dia. 55gr.-ish slugs from a Lee Bator mold 225-55(that may be hollow pointed and end up lighter) that has a round nose and considerable bearing surface,  and a Lyman mold 2660415 gas check, that drops I think 53grains that has more of a tangent ogive with a tiny flat point.  The question is, will the 1:14 stabilize these projectiles and potentially provide good accuracy at the 850-1200fps I intend to drive them?  I'm also not opposed to milling off the mold to remove the rebated GC portion of the projectile if it is going to degrade accuracy (though I suspect it may improve accuracy at sub-sonic velocities).  

GM also has 1:6, 1:7, 1:8, 1:9, 1:12 twist rates in centerfire .224, but from what I have been reading, slower air projectiles like the slower twist rates.  I have read reports of a .22 short barrel with a 1:20 twist rate to be extremely accurate with custom sized slugs, but another source leads me to believe a 1:10 is a good place to start for the above mentioned projectiles.

Thank You in advance for your help,
Matt

[PikeP]

I'd personally go with anything between 10-14 twist (can go into my calc and under ammodb sheet put in your bullet data and it recommends a twist rate range for that bullet on the reticle page.)

[luge007]

Thanks for the response.  It's looking like I may end up making several barrels and seeing which one performs best.  I was HOPING to avoid wasting money on barrels that will not work well.  Perhaps my velocity goals were not realistic with a stock AF platform and such a heavy projectile, no idea but I'll give this post some time and see what turns up. 

Cheers,
Matt

[KnifeMaker]

Remember, even though the twist rates you list are for .244 projectiles, you are not shooting at centerfire velocities. You have to look at subsonic .22 velocities.


It all  comes down to rpm. I have found that the 1-2- works best for my length of slugs. The slug you are listing is longer, so a slightly faster twist would work. Which would put it into the 1 in 16 to one in 14 range.


Weight has Nothing To Do with it. Hp it and it still will want the near same twist. it is length. Not weight that dictates twist at a given velocity. 


Knife

[Sbak]

I built a .224 using a TJ's 1:14 twist. It shoots the Lee 224-55 bullet extremely well

https://www.midwayusa.com/product/1016832078

My mold drops them around 56grains

[UnderPressure]

Very interesting that NOE offers .224 in some very heavy weights (up to 100 grains):

https://noebulletmolds.com/site/product-category/224

However, I would not expect 900 FPS from the very heavy ones, but maybe a lower velocity could be interesting --> https://www.gatewaytoairguns.org/GTA/index.php?topic=174190.msg155965518#msg155965518

P.S. Here is the Kolbe twist for the 100 grain ---> http://www.geoffrey-kolbe.com/cgi-bin/barrel_twist.cgi?diameter=.224&length=1.0&nose=.389&meplat=.128&base_diameter=.224&angle=&boat_tail=&b_twist=&secant_radius=&unit_length=inches&temperature=59&humidity=0&local_pressure=29.92&pressure=29.92&altitude=0&density=11.4&custom_density= (Starts off a 1 in 7.25" at 500 FPS and progresses to 1in 7.6" at 1000 FPS)

SIDE NOTE: 1 in 7" twist will also work with Bob Sterne's proposed G7 drag profile 75 grain .224--> http://noebulletmolds.com/smf/index.php?topic=1128.0

[UnderPressure]

Duplicate Post.

[luge007]

Thank You all, so far I am learning a lot and beginning to get a grasp on this (I think).
'Knife' - Thanks for your input as always, I guess the 'weight' issue I was thinking about had to do with length from something I read a long time ago.  For a given bullet of 'conventional construction', a lighter bullet will need less of a twist rate, and a heavier bullet a tighter twist rate.  All of which directly relates to the 'length' of the projectile, everything else being equal. (see, you can teach an old dog a new trick but I am slow)

'Sbak'-  What sort of velocities were you getting with that 1:14 twist firing those 55 grain Lee bullets?  Was it an AF platform? If so, (or not) what modifications were done?

'UnderPressure'- Interesting input on the NEO projectile and twist rate, I was hoping to utilize the 50-55 grain molds I already have in my .224 project since I have pretty much gotten out of firing powder burners, hoping to re-purpose existing molds.  At some point I am hoping to MAKE custom molds, start to finish (the right way, utilizing my mill and or lathe) but a lot more learning needs to be done of the process.

Looking forward to more info coming in, despite this topic having more or less been gone over before.
M

[rsterne]

I know that the 47 gr. Arsenal works in a 14" twist TJ's barrel, but I have not tried anything heavier.... I also have a 9" twist TJ's but no accuracy testing yet.... I have bullets as heavy as 61 gr. to try in that, I can shoot those at 960 fps....

Bob

[Sbak]

Ive never worked with the air force rifles, but from what ive seen they should be plenty capable of maxing out the .224 platform. I used a prototype xisico senty, cause im cheap. Although, i really enjoyed this gun i would not suggest it for a high energy build. It is limited in hammer energy by design. I have it maxed out in hammer weight and travel and it is still pretty hard to cock.

I was able to get a little over 900 fps maxed out @ 3000 psi with the 56 gr lee. .22 porting minus .10 probe (.203 equivalent). From 3000 psi to 2500 gave a tune of 850-870-850 for i think 6 shots on 240cc of air. It has since been detuned for 20 shots @ 65FPE with the NOE WFN

The .224 is a very underappreciated caliber, mine shoots pretty much everything fantastically

[PikeP]

Ive never worked with the air force rifles, but from what ive seen they should be plenty capable of maxing out the .224 platform. I used a prototype xisico senty, cause im cheap. Although, i really enjoyed this gun i would not suggest it for a high energy build. It is limited in hammer energy by design. I have it maxed out in hammer weight and travel and it is still pretty hard to cock.

I was able to get a little over 900 fps maxed out @ 3000 psi with the 56 gr lee. .22 porting minus .10 probe (.203 equivalent). From 3000 psi to 2500 gave a tune of 850-870-850 for i think 6 shots on 240cc of air. It has since been detuned for 20 shots @ 65FPE with the NOE WFN

The .224 is a very underappreciated caliber, mine shoots pretty much everything fantastically

Nice...two things I would consider, bush the valve stem bore to 2.5~ mm, run a 2.5mm valve stem. That will help significantly with a bullet shooters, from there you just need to find the right valve spring and hammer spring preload to help 'tame' the closure of the valve to around 97% of peak...and of course a peek poppet. Nice build btw.

[Sbak]

Ive never worked with the air force rifles, but from what ive seen they should be plenty capable of maxing out the .224 platform. I used a prototype xisico senty, cause im cheap. Although, i really enjoyed this gun i would not suggest it for a high energy build. It is limited in hammer energy by design. I have it maxed out in hammer weight and travel and it is still pretty hard to cock.

I was able to get a little over 900 fps maxed out @ 3000 psi with the 56 gr lee. .22 porting minus .10 probe (.203 equivalent). From 3000 psi to 2500 gave a tune of 850-870-850 for i think 6 shots on 240cc of air. It has since been detuned for 20 shots @ 65FPE with the NOE WFN

The .224 is a very underappreciated caliber, mine shoots pretty much everything fantastically

Nice...two things I would consider, bush the valve stem bore to 2.5~ mm, run a 2.5mm valve stem. That will help significantly with a bullet shooters, from there you just need to find the right valve spring and hammer spring preload to help 'tame' the closure of the valve to around 97% of peak...and of course a peek poppet. Nice build btw.

Appreciate it, i should have added, 24in barrel, peek poppet, flat wire spring ssg, and i did experiment with valve springs. My experience has only been with "QB" stiffness springs and less, but the valve spring has zero effect on shot curve. YMMV

[PikeP]

Ive never worked with the air force rifles, but from what ive seen they should be plenty capable of maxing out the .224 platform. I used a prototype xisico senty, cause im cheap. Although, i really enjoyed this gun i would not suggest it for a high energy build. It is limited in hammer energy by design. I have it maxed out in hammer weight and travel and it is still pretty hard to cock.

I was able to get a little over 900 fps maxed out @ 3000 psi with the 56 gr lee. .22 porting minus .10 probe (.203 equivalent). From 3000 psi to 2500 gave a tune of 850-870-850 for i think 6 shots on 240cc of air. It has since been detuned for 20 shots @ 65FPE with the NOE WFN

The .224 is a very underappreciated caliber, mine shoots pretty much everything fantastically

Nice...two things I would consider, bush the valve stem bore to 2.5~ mm, run a 2.5mm valve stem. That will help significantly with a bullet shooters, from there you just need to find the right valve spring and hammer spring preload to help 'tame' the closure of the valve to around 97% of peak...and of course a peek poppet. Nice build btw.

Appreciate it, i should have added, 24in barrel, peek poppet, flat wire spring ssg, and i did experiment with valve springs. My experience has only been with "QB" stiffness springs and less, but the valve spring has zero effect on shot curve. YMMV

You certain you're tuned a little below peak and not over-driving the valve? Other than that, you seem pretty well off. Curious what hammer weight you're running? (sorry for minor threadjack, its semi on topic with discussion of another .224 )

[UnderPressure]

Ive never worked with the air force rifles, but from what ive seen they should be plenty capable of maxing out the .224 platform. I used a prototype xisico senty, cause im cheap. Although, i really enjoyed this gun i would not suggest it for a high energy build. It is limited in hammer energy by design. I have it maxed out in hammer weight and travel and it is still pretty hard to cock.

I was able to get a little over 900 fps maxed out @ 3000 psi with the 56 gr lee. .22 porting minus .10 probe (.203 equivalent). From 3000 psi to 2500 gave a tune of 850-870-850 for i think 6 shots on 240cc of air. It has since been detuned for 20 shots @ 65FPE with the NOE WFN

The .224 is a very underappreciated caliber, mine shoots pretty much everything fantastically

Impressive!

Do you have a build thread on this?

P.S. How easy is it to load the .580" length LEE 225-55 into the Sentry?

[Prouzy]

I had a TJ 1:14 .224 made for a QB78.  While I was waiting for that and the NOE 39gr mold, I bought the Lee 55gr to practice.  I sized them down to .220 and tested them for speed in a AF with 24in .22 barrel, over 950fps.  That is an unmodified AF "Escape" set up in .25 with the barrel switched out, so you will have no problem getting velocities in that platform.  I think we have all had good luck with NOE 225 39 FN in TJ 1:14.  I had not seen that the 55gr (Ive never tried, my little QB cant push them) shoots.  Thats pretty cool, great pill in that caliber. 

I too was looking into GM barrels for AF but the smith I was discussing with wouldnt do the work on the RX blanks to get from 1.20"OD down to the breech dia for the AF.  But those BX should make it a little easier.  I must say though, Ive had 7 barrels from TJs on various platforms in .224, .257, .300, .308, and .457 and none of them have disappointed.

[Sbak]

The Lee barely fits in the breach, I have to load them in at an angle. Off the top of my head I think my hammer weight was around 50gr. I do know I was a little low in the dwell department and driving the hammer pretty hard to shoot the Lee's. I tried all the modern .225 molds available from NOE, arsenal, and Lee. They all shot great, the Lee is just a little to heavy for my guns hammer energy. The NOE 39gr Lyman copy is a good little round and easy to get up to speed. I took some long range Aberts (tassle eared) tree squirrels way up in the ponderosa's last winter with them. I think they are slightly overspun as you will get occasional fliers at longer ranges, but hole in hole at 75yrds and under.

No, I didn't do a build thread. I would suggest you read up on Bob's .224/.172 build it was the one that inspired mine.

[Ribbonstone]

HAve mentioned this before.....I'd not be too hung up on barrel diameter for a rebarrel.   Way easier to make new bushings than to lathe the barrel full length thinner.

Are limits...but the AF frame is pretty darn large on the inside.

[Prouzy]

HAve mentioned this before.....I'd not be too hung up on barrel diameter for a rebarrel.   Way easier to make new bushings than to lathe the barrel full length thinner.

Are limits...but the AF frame is pretty darn large on the inside.

Its sure been done, but that little breech end may be intimidating for some I guess. 

[KnifeMaker]

Remember, even though the twist rates you list are for .244 projectiles, you are not shooting at centerfire velocities. You have to look at subsonic .22 velocities.


It all  comes down to rpm. I have found that the 1-20 works best for my length of slugs. The slug you are listing is longer, so a slightly faster twist would work. Which would put it into the 1 in 16 to one in 14 range.


Weight has Nothing To Do with it. Hp it and it still will want the near same twist. it is length. Not weight that dictates twist at a given velocity. 


Knife

[luge007]

Under Pressure, where did you come up with the 'print' for the Lee projectile?  It does not look like the Lee "Bator" projectiles dropped by my mold (though mine is about 20 yr old).  My Lee mold drops what can be described as cylindrical projectiles with a 'dome' nose and a few lube grooves.  I'll post pics if I get a chance. 

My guess is the longer bearing surface may require a faster twist rate than my RCBS projectile?  Stability comes from the twist rate, or the gyroscopic stability from the RPM which is driven by the FPS as projectile leaves the barrel at, correct?  So the "length" of a projectile and velocity determine the twist rate required BUT is the "length" what touches the barrel or the TOTAL length of the projectile?

Almost coming into focus here........

M