AR-15 Barrel Question

ultramagmed

ultramagmed

JKM
Hi Guys,


I've been away for awhile, I hope you all are well but, I'm starting a new project I don't have much experience with so here it goes. I have a 1:14 twist 22-250 take off barrel I would like to cut down and use on an AR, the barrel is 26" long and I think I can get it to finish out at 22-24". So my question is with the slower twist, where would be the best place to locate the gas port hole (longitudinally)? I have an AR barrel here and the gas port is roughly 8.25 measured from the face of the barrel extension, will that work? I took some rough measurement of a buddy's AR with a 24" barrel and came up with appx. 12.875, would this be better, or is the slower twist going to cause me problems with cycling? And lastly, what is the preferred gas port diameter? As always any and all comments are welcome.

Thanks in advance,
Med.
 
Last edited:
the twist rate wont affect cycling, but it will severely limit the bullets that will be able to be fired accurately from a .223/5.56.
 
Thanks Lefty,

Do you happen to know why the gas ports are differently placed between these two barrels? My initial thought was the difference in barrel length between the one I have (16 1/2") compared to the 24" of my buddy's gun (both 1:9 twist) and the gas ports being placed 4.625" different longitudinally that the pressures at the gas port would be different and potentially cause cycling problems. This a learning project for me and I'll take all the info I can get, I just want to try something a little different. Also, I knew I was giving up bullet selection, if this one works, I will try another one with a tighter twist. Just playing with a barrel I got laying around in the shop.

Thanks for the reply,
Med.
 
Last edited:
It will probably not stabilize a bullet heavier that 50 to 55 grains based on my experience with prarie dog guns. They need a 7 to 9 twist for 69 grain and heavier and a 12 twist for 40 to 55 grain. Some folks get by with a 14 in the 22-250. Remington is offering a 14 twist in the 22-250 now. I always use a 12 twist - always, however I always shoot 50 to 55 grain bullets. My 12 twist will not accurately shoot a 62 or heavier bullet.

Some folks may disagree, however this is my real world experience over the last 15 or so years.

Good luck.
KG
 
KG,

Thanks for the reply, I live in Utah, and prairie dogs are the prime target for me. I was planning on shooting 50 gr. VMAX's or 52gr. AMAX's for a little added velocity. I just want to try my luck at something different than a bolt gun. I'm a bit of a beginner and want to learn some more about these "black guns".

Thanks again,
Med.
 
ok...for the record...nothing new i have posted many times...my ar15 BENCHREST rifle is chambered in a min spec 223 win with a short thorat. the bbl is a hart 1/14 twist that is 26" and just over 1" in dia at the muzzle. i shoot 52/53 gr match bullets at 3500 to 3600 fps. it shoots just under 0.2 my gas port is 2" out from stock 20" rifle config. hart to find premade tubes. easiest is to use two to make one with a silbrazed lap joint from larger material.
so your big issue is a reamer with a short throat...most stock reamers are designed for heavy not light bullets.
you can go with a std config and an adjustable gas port in the tube or block....much easier to deal with.
just do a search online.
mike in co
 
Mike,

Sorry, I didn't even think about doing a search. I am rather naive to AR configurations, I'm sorry, but can you either tell me how far down the barrel you drill the gas port from either the face of the barrel extension and/or the barrel face? Or, if you know the distance down the tube for the 20" AR barrel configuration, that'll get me started. If you know of a link, or the name of a thread I can search I'll see what I can find that way too. I don't mean to dredge up something that has been beaten to death.

Thanks for the post,
Med.
 
i'm out of town for the weekend but will try when i get back
mike in co
 
ultramagmed said:
Hi Guys,


I've been away for awhile, I hope you all are well but, I'm starting a new project I don't have much experience with so here it goes. I have a 1:14 twist 22-250 take off barrel I would like to cut down and use on an AR, the barrel is 26" long and I think I can get it to finish out at 22-24". So my question is with the slower twist, where would be the best place to locate the gas port hole (longitudinally)? I have an AR barrel here and the gas port is roughly 8.25 measured from the face of the barrel extension, will that work? I took some rough measurement of a buddy's AR with a 24" barrel and came up with appx. 12.875, would this be better, or is the slower twist going to cause me problems with cycling? And lastly, what is the preferred gas port diameter? As always any and all comments are welcome.

Thanks in advance,
Med.
Click to expand...

Hi Med,

I believe there are three lengths of gas tubes that are generally available. Carbine, medium length and rifle. Plus there are pig tails. The rifle length tube is generally used on the longer barrels.

First I would make sure the barrel is of sufficient diameter to accept a gas block at the appropriate length. I believe you mentioned going with a longish barrel, so I would go with a rifle length gas tube, and an adjustable gas block.

The first procedure to be done is screwing on and headspacing the barrel extension. All extensions are different. The threads on them are not indexed, so you have to have the extension in hand to set the headspace. If you screw up the extension by lets say polishing the feed ramps too much, you have to get another extension and sometimes redo the entire works. (Don’t ask how I know this).

Make sure the extension is the correct one for the upper frame. M4 ramps versus the M2 ramps. The M2 ramps can be massaged to fit though. The last ones I ordered were listed as barrel extensions and didn’t specify what ramps they were. They were M4.

With the extension mounted you can place the barrel in the upper and using the gas tube and block, figure out where the gas block is going on the barrel. Then you can figure out the location of the gas port and drill it. Gas port sizes are dependent on barrel length and diameter. But with the adjustable gas block, it is possible to go larger (with the port) and use the gas block to regulate. IIRC the port size for rifle length tubes is around .093. Check that.

Jim
 
Last edited by a moderator:
I'd suggest getting the gas tube first for the length of barrel that you are wanting to use and then locate the port based on the gas tube that you have. As to the barrel extension, on the few AR's that I've done, I used the extension that Bat Machine makes and sells through Brownell's. When I drilled the gas port, I took a lead core for making bullets and swaged it with an arbor press to where it would fit like a slug in the bore. Oiled it and tapped it to where I wanted it with a cleaning rod and then drilled the hole into the lead core. Then pushed the core out the end of the barrel. On Josh's rifle we drilled the hole with an .081" drill bit and wound up having to go back in and drill it larger to get the bolt to cycle correctly. Adjustable gas blocks will let you adjust the gas flow down from whatever size hole that you have drilled, but you can't increase the flow of a hole that's too small.
 
Last edited:
Thanks for all the replies, I really appreciate them!!

I have the upper, gas block, barrel extension & gas tube but, the latter of the four is for a short length 16" barrel (i.e. 9.75 carbine length gas tube). I guess my question is; will this same configuration work with a 1:14
twist 24" barrel that is 7.5-8 inches longer (as opposed to a 16.5" long 1:9 twist), or should I move to the rifle length gas tube? I realize this may be a hard question to answer, so any replies are welcome!! This is a purely an experimental and learning project. I'd rather ruin this p.o.s. barrel sitting on my shelf before I move to a custom barrel, if I jack this barrel up, I'm not out anything!! My main focus is to try and avoid any cycling problems if at all possible, but I also know I may be asking too much working with what I have.

Thanks again,
Med.
 
Last edited:
I have chambered a couple of AR barrels for a friend, one, oddly enough, in 221 fireball. I put the gas port hole where the originol holw was in the barrel that came with the originol top.

They all function just fine. The only thing he did on the 221 221 Fireball was play with the system back in the stock to get it to come back far enough to grab the next case........jackie
 
Thanks Jackie,

Maybe I should quit asking so many questions and just go for it, I really don't have anything to lose. I really do thank you all for sharing your knowledge, you guys are great!!

Thanks,
Med.
 
for a 22-24" AR barrel you definitely want to go with the rifle length gas tube. Otherwise there is just too much barrel after the gas port and you will get too much gas and experience hard recoil. Start small on the gas port, about .080 and work your way up. You should get perfect function between .085-.093 and a rifle length gas tube. As stated earlier, fit the barrel extension, chamber for correct headspace and then mark the barrel for the block. If you assemble the gas block and tube, the tube should extend past the extension right at 1" (+/- .010").
 
how about.....pistol, carbine and rifle.....
mike in co
pdhntr said:
Hi Med,

I believe there are three lengths of gas tubes that are generally available. Carbine, medium length and rifle. Jim
Click to expand...
 
on a 20" bbl, from the forward face of the chamber end of the bbl past the threads( where the bbl extention contacts the bbl) to the aft shoulder of the gas block dia is 12.150. the port is 0.310 forward of that shoulder. in some competition guns that port is .099....start medium and work up or start big and use an adjustable gas block/tube.
mike in co
ps i measured three new ar15 223/5.56 bbl extentions i have in stock...all measured 1.119..so i would guess they are speced at 1.120....time warped by wilburs software update..
 
Last edited by a moderator:
mike in co said:
how about.....pistol, carbine and rifle.....
mike in co
Click to expand...

I was referring to the three most common lengths you see when trying to find them from a vendor.

To my knowledge (which if you ask anyone, is suspect) there are four straight tubes that are commonly used.

Pistol.......4.5"
Carbine.........7.5"
Mid..............9.5"
Rifle..............13"

Lengths are approximate and from memory but I think that is right.

There is also a pig tail and a straight with a gas regulator.

Jim
 
ultramagmed said:
Hi Guys,


I've been away for awhile, I hope you all are well but, I'm starting a new project I don't have much experience with so here it goes. I have a 1:14 twist 22-250 take off barrel I would like to cut down and use on an AR, the barrel is 26" long and I think I can get it to finish out at 22-24". So my question is with the slower twist, where would be the best place to locate the gas port hole (longitudinally)? I have an AR barrel here and the gas port is roughly 8.25 measured from the face of the barrel extension, will that work? I took some rough measurement of a buddy's AR with a 24" barrel and came up with appx. 12.875, would this be better, or is the slower twist going to cause me problems with cycling? And lastly, what is the preferred gas port diameter? As always any and all comments are welcome.

Thanks in advance,
Med.
Click to expand...

mid length and rifle length gas tubes reduce the felt recoil because they have less gas available to cycle the bolt. any feeding / ejection issues are usually caused by an improper relationship between the buffer weight, buffer spring and load being shot. there are several variations available to get an AR cycling properly, based on the load you are feeding it.

a 16 inch barrel should be driving a 55g bullet at least 2800 fps to cycle properly with a stock buffer / spring.

remember also that gas blocks come in 3 general diameters for the 3 major barrel types, so you may need to turn a portion of the barrel down to permit the gas block to fit.

i would think this is a very ambitious project given the nature of the feed ramps for the AR. you definitely want at least a 1:9 twist. while you can cycle 55 grain bullets with a 1:12, they are a rarity (the twist rate) today on your garden variety AR.
 
like i said,,,i shoot 52's from a 14 twist..it shoots fine. no need for a 1/9.......
50-52 should be fine in a 14...sierra sent me 45's to try when they found out i had a 14 twist.
the ramps should be no problem...std bbl extention or some grinding with m4 ramps....
thread and install the bbl extention, then chamber...its a pain to keep it all clean to check headspace. then do your gas port.
mike in co
AMMASHOOTA said:
i would think this is a very ambitious project given the nature of the feed ramps for the AR. you definitely want at least a 1:9 twist. while you can cycle 55 grain bullets with a 1:12, they are a rarity (the twist rate) today on your garden variety AR.
Click to expand...
 
You must log in or register to reply here.
Back
Top