RogerW Posted January 15, 2020 Report Share Posted January 15, 2020 What are the advantages vs disadvantages of the two different length gas systems. My thoughts would be an earlier, less pressure gas pulse with the mid length and a higher pressure gas pulse with the rifle length. Would you need an adjustable gas block with the rifle length tube? Does the mid length offer a longer cycle time over the rifle length? Quote Link to comment Share on other sites More sharing options...
DNP Posted January 15, 2020 Report Share Posted January 15, 2020 (edited) There is more to it than just the length of the gas tube. In fact, it probably has the least to do with it. The real factors are the dwell time and the size of the gas port opening in the barrel. The longer the bullet is in the barrel past the port, the more pressure you have coming down the tube. The bigger the gas port opening, the more pressure you have coming down the tube. The others who use them might. E able to share more about the benefits of an adjustable block, but most AR’s shouldn’t need one if all else is in check. Gas and recoil-wise. Edited January 15, 2020 by DNP Quote Link to comment Share on other sites More sharing options...
Armed Eye Doc Posted January 15, 2020 Report Share Posted January 15, 2020 (edited) As DNP said, the amount of gas going to cycle the bolt carrier is dependent on much more than where the gas port is located. Not knowing your level of firearm knowledge, this thread has a couple of videos that give detailed explanations how these firearms work and may help to understand the different parts of his post easier. Welcome to the forum. It looks like you joined a while back but just posted now. Head to the introduction section and tell us about yourself. https://forum.308ar.com/forum/22-introductions/ Edited January 15, 2020 by Armed Eye Doc Quote Link to comment Share on other sites More sharing options...
washguy Posted January 16, 2020 Report Share Posted January 16, 2020 All my rifles use mid length...do have carbine length too in old school rifles.....one because the barrels are 16's and 18's......never had a problemo with a middie gas system....and the middie gas length keeps the gas block under the hand guard where it belongs...which I like.....the felt recoil can always be dealt with in other ways Wash Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 16, 2020 Report Share Posted January 16, 2020 (edited) 5 hours ago, RogerW said: What are the advantages vs disadvantages of the two different length gas systems. My thoughts would be an earlier, less pressure gas pulse with the mid length and a higher pressure gas pulse with the rifle length. Would you need an adjustable gas block with the rifle length tube? Does the mid length offer a longer cycle time over the rifle length? This would be directly opposite of what really happens. 4 hours ago, DNP said: There is more to it than just the length of the gas tube. In fact, it probably has the least to do with it. The real factors are the dwell time and the size of the gas port opening in the barrel. The longer the bullet is in the barrel past the port, the more pressure you have coming down the tube. The bigger the gas port opening, the more pressure you have coming down the tube. The others who use them might. E able to share more about the benefits of an adjustable block, but most AR’s shouldn’t need one if all else is in check. Gas and recoil-wise. DNP is on it. Dwell time. The longer your dwell time, the harder the recoil, and the more punishment on the cyclic components. Think about a gun with an 18" barrel, midlength gas or rifle length gas. Or carbine gas. The distance from the gas port location, to the end of the barrel, is "dwell time." That's the total amount of time that the barrel is feeding gas pressure to the bolt carrier, and it's also the amount of time that the barrel starts feeding gas pressure to the bolt carrier. You start the unlocking process too early, and you have BIG problems on your hands, as far as function goes. So, the closer the gas port is to the chamber, on a given barrel length, the sooner is tries to start unlocking the bolt, and the longer it provides "propulsion" to the bolt carrier. 18" rifle gas is gonna be the "softest" shooting. Moreso than 18" midlength gas. 18" carbine gas is gonna be a handful, it's gonna beat the shiit out of components, and beat your shoulder up. Now, think about trying out something with 18" pistol gas system - that's gonna SUCK to shoot, and you'll be breaking internal reciprocating parts in short order. The closer to the end of the barrel that the gas port is located - the larger gas port you need, to function the rifle. Recoil systems play heavily into this - the gas system and recoil system are independent of each other, i.e., you have carbine gas, doesn't mean you have to run carbine recoil systems. They're not tied together - but they MUST be balanced, and WORK together... Edited January 16, 2020 by 98Z5V Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 17, 2020 Author Report Share Posted January 17, 2020 Thanks guys. I have a very different understanding of how the gas system actually functions. Thanks to you I can make a better decision on gas tube length on my upcoming build. I want to build a 308 hog thumper. 18” barrel in an Aero Precision upper. 80% lower. No decision on the stock yet. Aero M5 Atlas S1 hand Guard. No decision on the muzzle device. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 17, 2020 Report Share Posted January 17, 2020 16 minutes ago, RogerW said: Thanks guys. I have a very different understanding of how the gas system actually functions. Thanks to you I can make a better decision on gas tube length on my upcoming build. I want to build a 308 hog thumper. 18” barrel in an Aero Precision upper. 80% lower. No decision on the stock yet. Aero M5 Atlas S1 hand Guard. No decision on the muzzle device. Do you reload ammunition? Are you a reloader? Quote Link to comment Share on other sites More sharing options...
bubbas4570 Posted January 17, 2020 Report Share Posted January 17, 2020 (edited) FWIW, my 16" 308AR had the rifle length gas tube, and functioned very well....bad handloads not withstanding. The recoil was less than my Ruger bolt actions, and it shot better than I could. I wish I could give you port measurements, but it sold to a good friend as soon as I mentioned something about thinking of selling. It ran and shot that good. Edited January 17, 2020 by bubbas4570 Fukn spell checker Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 18, 2020 Author Report Share Posted January 18, 2020 98z5v, yes I reload. I have a Dillon 550b progressive press. ROG Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 18, 2020 Report Share Posted January 18, 2020 (edited) 17 minutes ago, RogerW said: 98z5v, yes I reload. I have a Dillon 550b progressive press. ROG Excellent information!!! If you just need one to bust hogs, think about .338 Federal. All you're doing is necking up .308Win cases. I'm loading up 225gr Hornady SSTs in mine, and they shoot great. Distance wise, are you hunting the hogs from a long way off, running hogs (like farm eradication, where you set up at different places, and have to move to get on them), or are you in a fixed static position, and wait for them to come in? .338 Fed will get you to 300 yards, easy,very minor holds/corrections. Edited January 18, 2020 by 98Z5V Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 18, 2020 Author Report Share Posted January 18, 2020 (edited) I will be doing a hunt through an outfitter. I am looking at one in Texas and one in Missouri. I would love to do a farm eradication No long range shots I would want the shot to be 150 yds or less. ROG Edited January 18, 2020 by RogerW Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 18, 2020 Author Report Share Posted January 18, 2020 I am setup to reload 6.5 Creedmoor, .308 and 30-“06. I have rifles chambered in both calibers and 6.5 Creedmoor. My 308 and 30-“06 are bolt guns. The 6.5 Creed is an AR-10 build. ROG Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 18, 2020 Report Share Posted January 18, 2020 2 hours ago, RogerW said: I am setup to reload 6.5 Creedmoor, .308 and 30-“06. I have rifles chambered in both calibers and 6.5 Creedmoor. My 308 and 30-“06 are bolt guns. The 6.5 Creed is an AR-10 build. ROG If you're shooting 150 yards or less, I'd go with something that's easier to carry - cut that barrel length down, and make a 16" gun. If you think that you'll be shooting the same .308 Win handload through this, as you do through the bolt gun - just make it a .308 Win AR. If you anticipate a completely separate handload for the Hog AR, than the .308 bolt gun - might as well make that thing a .338 Fed, pick up a set of .338 Fed dies, and neck some .308 Win brass up to .338. It'll be a far more efficient hog gun that way. Wilson Combat has the .338 Fed barrels, and they are very accurate. Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 18, 2020 Author Report Share Posted January 18, 2020 Nothing wrong with having a bolt load and a AR load. I do kinda like the idea of maybe trying out 338 fed. Looks like I could get 2600fps with a 200gr bullet which should put a wallop on a pig or deer ROG Quote Link to comment Share on other sites More sharing options...
Cliff R Posted January 18, 2020 Report Share Posted January 18, 2020 Not meant to get you off-track but for hunting anything on this Continent out to 250 yards difficult to beat the 450 Bushmaster. 250 grain bullet at 2200fps, DEADLY accurate right out of the box with factory Hornady ammunition. I have an early Bushmaster upper, chrome lined, extremely light and every 100 yard group I've ever shot thru it puts ALL of the bullets literally in the same hole if the shooter does their part. I've seen nothing out of the box to rival it using factory ammo. Even with all the stops pulled out to lighten things up you'll be pushing 10 pounds with these larger platforms. Not trying to talk you into or out of anything, just be aware than the larger 308-AR based guns are considerably heavier. My 308-AR crosses the scale at 10 pounds with a lighter profile 14.7" barrel, A-2 stock and smaller 2-7 Leupold scope on it. I haven't weighed the 450 Bushmaster but it's a LOT lighter and more manageable.........Cliff Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 19, 2020 Author Report Share Posted January 19, 2020 I went looking for 338 Federal and did not find what I was looking for. The Wilson barrel was nice but very pricey. I made a sound fiscal decision and ordered a Ballistic Advantage barrel for 1/2 the cost. I have not used a BA barrel before so I am on an adventure. I have read some good things about BA merchandise. If it shoots minute of pig I will be happy. ROG Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 19, 2020 Author Report Share Posted January 19, 2020 Thanks for the feedback Cliff. I am well aware of how much an AR10 can weigh. I have a6.5 Creedmoor with an 18 inch barrel. That guy is a beast. I will be shooting from sticks or tripod so I am not that concerned about the weight. My primary rifle for deer is an AR15 in 6.8SPC. That round is deadly on Whitetail at the typical shot distance I encounter. what is the recoil pulse like with 450 Bush? I have not had the opportunity to shoot that round so it is a complete mystery to me. ROG Quote Link to comment Share on other sites More sharing options...
washguy Posted January 19, 2020 Report Share Posted January 19, 2020 10 minutes ago, RogerW said: y primary rifle for deer is an AR15 in 6.8SPC. That round is deadly on Whitetail at the typical shot distance I encounter. Hi Rog Yep the 6.8 is an awesome round....ive got a few of them....what cartridge does your 6.8 like the best? Wash Quote Link to comment Share on other sites More sharing options...
Cliff R Posted January 20, 2020 Report Share Posted January 20, 2020 (edited) 13 hours ago, RogerW said: what is the recoil pulse like with 450 Bush? I have not had the opportunity to shoot that round so it is a complete mystery to me. I barely notice it in a hunting scenario. It "thumps" a bit bench resting it especially in the summer with just a t-shirt on, but not nearly as much as folks regurgitate about it on the Forum's. If you want to get whacked shoot one of my Marlin 45/70's with a full case of Reloader 7 pushing a 300 grain bullet at 2400FPS. I make sure to remove my hat and glasses before I touch one of those off, because they are going to be on the ground anyhow!......LOL.....Cliff Edited January 20, 2020 by Cliff R Quote Link to comment Share on other sites More sharing options...
washguy Posted January 20, 2020 Report Share Posted January 20, 2020 My thinkin is if ya cant stand the lil thump then put more padding in your bra Wash Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 22, 2020 Author Report Share Posted January 22, 2020 On 1/19/2020 at 11:52 AM, washguy said: Hi Rog Yep the 6.8 is an awesome round....ive got a few of them....what cartridge does your 6.8 like the best? Wash I use the Hornady 120 gr SST. It is DRT for the kills I have with the gun. ROG Quote Link to comment Share on other sites More sharing options...
RogerW Posted January 22, 2020 Author Report Share Posted January 22, 2020 Never shot a 45-70. I would like to that’s for sure. I just need to find some body that would let me try it. Biggest I have shot is a 8mm German Mauser. That rifle was a thumper. ROG Quote Link to comment Share on other sites More sharing options...
Cliff R Posted January 22, 2020 Report Share Posted January 22, 2020 The 45/70 has great potential in the right weapon. The problem with factory loads is that many older guns chambered for it will not take the heavy pounding of higher pressure "high performance" hand loads. I've been exploiting the 45/70 round sine the early 1980's and have not found a better propellant for it that Reloader 7. Depending on bullet weight (I prefer 300 grain bullets as they are easier on the shooter and flatter trajectory) 50 to 60 grains of Reloader 7 will have bullet performance knocking on the door of the 458 Win mag. The increased velocity also step things up for long range shots. I wouldn't hesitate to take a shot on an Elk at 300 yards with my 300 grain loads at 2400fps and in the right conditions could stretch that out to at least 400 yards. Sadly though I don't use the 45/70 much since moving to AR platforms for hunting, especially out West. I like the weatherproof and rugged design of my AR's much better. I've taken some pretty hard falls in rough terrain at high altitudes over the years and beat up my Marlin 45/70 some. I consider the 308-AR a better choice for that type of hunting and it's tough as nails and no worries at all when I go down hard and toss it into a snow-drift. I just pick it up, wipe it off and keep going........Cliff Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 25, 2020 Report Share Posted January 25, 2020 On 1/22/2020 at 5:56 AM, Cliff R said: The 45/70 has great potential in the right weapon. The problem with factory loads is that many older guns chambered for it will not take the heavy pounding of higher pressure "high performance" hand loads. ^^^ This right here, when looking up load data. There's 3 different types, and lord help you if you fuk it up. Trapdoor loads, modern Marlin loads, and Ruger No. 1 loads. Weakest action to strongest action. You load up a Ruger No. 1 load and shoot it through a trapdoor gun, and you'll hurt that gun, or blow yourself up. Gotta know what you have, and what the differences are in the loadings for each frame. Even when you have the right platform - there's a ton of data from different references for each, some "starting loads" from one reference are way above "max loads" for another reference - I found that, strictly researching modern Marlin load data, when I was getting started with this thing. Quote Link to comment Share on other sites More sharing options...
Cliff R Posted January 26, 2020 Report Share Posted January 26, 2020 I started with a Browning B-78 so was up at the top of the scale. Didn't like the rifle much, WAY too heavy and single shot so moved to the Marlin platform in the mid-1980's. Played around with several different powder/bullet combo's, even some home-made cast bullets (400 grains/gas checked), then settled on Reloader 7 and 300 grain Winchester hollow points (bought 1000 of them). I push that bullet with 55 grains of RL-7 where I used 60 grains in the B-78. Never had any issues and it goes across the chrony at 2400fps. That load is probably going to be considered +P in the Marlin platform so don't go out there are copy it. In recent years I've backed it off to 50 grains RL-7 and the same 300 grain jacketed hollow point bullet. Really didn't change much at any distance that I can tell and just a fuzz-nut easier on the shooter. Even so these loads are not for the faint of heart. As far as a hunting load...everything I've shot with them to date has been yanked straight to the ground without taking another step!.........Cliff Quote Link to comment Share on other sites More sharing options...
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