GAS SYSTEM length on an ar15

[dpaqu]

having said that' just built a super dooper lightweight rig with a pencil barrel , 20'' incher with rifle gas n' M4 stock' also with tubbs spring n' H2 buffer. in a word = AWSOME.

Wow! I've been thinking about building something very similar but its hard to make an AR15 lighter than a Keltec Su16. Very cool.

klcarroll- you must shoot an awful lot. I've been trying to wear out my bushmaster, 2,000 rounds and counting and that takes some real doing. I wonder if you couldn’t buy some 50bmg pull down powder and get what you’re looking for. It's cheap, lowers velocity, and might be a little less loud. I’ve never tried it so I could be way of base here.

[mike in co]

Im just giving you a hard time Mike, no insult intended. I find carbine length works for alot of different variations as long as you use an adjustable block or tube, or get the right port size.
What caliber do you have in mind? Or is it just an "in general" type question?

i knew you were....

in my list under 16" is both 223 and 7.62x39.....

i sold the 16 223 already...will get another, but was wondering about the ak/ar.....

shorter gas port distance, higher pressuer....good /not good ???
is it beating up the rifle.....
there are adjustable gas port tubes....and different springs
inquiring minds want to know
mike

ok ran some numbers...anyone think they are off say so i will rerun

16" ar based 7.62x39...123 at 2350fps port pressure at 6" is aprox 18kpsi
20" ar in 5.56x45 with a 55 at 3160fps port pressure at 11.5" is 17.5kpsi
16" ar in 5.56x45 with a 55 at 3160 port pressure at 6" is 30kpsi....nearly twice that of a 20" gun....
is this beating up the gun ?

[madsenshooter]

Wow! I've been thinking about building something very similar but its hard to make an AR15 lighter than a Keltec Su16. Very cool.

klcarroll- you must shoot an awful lot. I've been trying to wear out my bushmaster, 2,000 rounds and counting and that takes some real doing. I wonder if you couldn’t buy some 50bmg pull down powder and get what you’re looking for. It's cheap, lowers velocity, and might be a little less loud. I’ve never tried it so I could be way of base here.

Just for the fun of it, I'll be trying a caseful of WC860 behind the Eagan. I'm guesstimating it'll get up around 2000fps. I also found I had some 245498 boolits that BadgerEd gave me, they go about 102gr unchecked or lubed. The fast twist of the Obermeyer should like the longer boolit better than the Eagan, and the point design should feed better. I'm going to have to do some polishing on the M4 feedramps before trying to feed either of the cast boolits. Here's a picture of my new pogo stick. My sizing die should be here tmrw and I'll get some loading done.

[BD]

Mike,

I'd be prepared to tear the head off a case or two opening the bolt with 30,000 psi in the chamber. There's an awful lot of older cartridges out there that sealed the chamber just fine at that pressure level. I'm not saying you shouldn't try it, just that you might want to take a case extractor with you to the range.

I had a good evening at the range today. I finally accepted reality and admitted that my 55 year old eyeballs aren't cutting it past 100 yards, so I spent the morning flat topping my old Bushmaster DCM. The first 3 shot group out of the new receiver was on paper and under 1/2 moa @ 100 with a Nikon Monarch 4-16 mounted. And, it stayed under 1/2" with the BUIS @ 100. But the real good news was staying under 1/2 moa @ 300 yards with the Nikon That's something I've not been able to do with iron sights in years.

I'm thinking the old A2 NM upper and front sight might need to become a light weight 16" gun. Maybe a 16" gun with the rifle sight radius.

BD

[mike in co]

bd,
i think rifle sight radius on a short bbl'd ar is a good thing. i think one draw back of the ak is it's poor sights( i like the sks over the ak for a heavier bbl and longer fight radius).

i'm guessing that the 16 rifles have a heavier spring ?


but maybe case slows it down some.....anyone ??

mike in co

[82nd airborne]

Mike, I dont remember the brand but Ill look for it; there is a company that makes a very high quality peep that goes on the rear of the dust cover, which lengthens the sight radius of the AK much better, now if it only had a thumb safety!
I havent got to read this whole thread and I dont want to muddle things by being repetitive, so Ill keep my opinions to a minimum untill I get a chance to read the whole thing.
Too large of a port will damage the rifle over time, and for a rifle intended for combat, I think an oversized port is good, but it needs to have a heavier buffer and spring to increase reliability, while minimizing wear and tear.
I keep a list of port sizes we do on all of our wildcat AR's so that I have a something to go off of when a new project comes up.
We are hoping to start on a .358 AK here shortly, once we get our group buy for castboolit AR's underway. Ill post the best port size for that when we get it figured out.

[madsenshooter]

Got some loaded with the Eagan boolit, and a caseful of WC860. 10/20 had significant runout. I bought those Hornady dies with the funky thing hanging down that gives the case zero support. I knew better, quit using one in 30-06 a long time ago. So I have another seating die coming from CH4D. Maybe I'll get this thing to the range some day.

[82nd airborne]

Not before the 24th though...bummer.

[BD]

I like the rifle length sight radius as it works with my shooting glasses. I wear polycarbonate bifocals with the the distance prescription in the top of the left lens and the mid range, (arms length), prescription in the top of the right lens and close range in the small bottom lenses on both sides. The front post on a standard AR carbine is never really in focus. I had these made primarily for handgun shooting, but they also keep the front post on most rifles sharp.

BD

[madsenshooter]

Not before the 24th though...bummer.

Nope, didn't make it, it's either cough up the $200 annual fee, or go to the public range which is about twice the distance away. I'll probably cough up the $200 and make it back selling stuff on ebay. I've got a lot of old scopes and mounts. I wouldn't mind making an article for Handloader out of the experiment.

[82nd airborne]

That would be interesting, I wouldnt mind reading it. Did you get all your dies you needed in yet?

[madsenshooter]

Nope, waiting on a seater from CH4D, Dave asked for a drawing of the boolit, which I just happened to have, so he can make a seater plug to fit. He'll give me the die at standard price though. Good guy, his shop is not far from where my grandma used to live. I'll not buy anymore of those Hornady dies, I'm sure lots of people use them, but they don't work for me. Maybe next week I'll get something together and in the meantime, I'm sizing and lubing.