ar15 accuracy gas system "removal"

[rockwind1]

i read a while back that in some ar15 long distance matches, guys would somehow get rid of the gas system and cycle the charge handle manually,,,,,in order to improve accuracy, they didn't want the action cycling and either messing up the actual shot,,, or it helped with watching the shot hit. can't remember which.

i can't find the article or thread again. my question is, what did they do to nullify the gas system?

did they just put on a gas block that has no hole? since the rifle is designed to bleed off gas, could it cause to much pressure in the barrel, i wouldn't think so it would seem to just sort of turn it into a bolt gun (using the charging handle as a bolt)

also, was the goal in doing that to prevent the cycling bolt from messing up your shot,, or was it to help with watching the shot hit?

follow up question. when shooting a typical ar, will the bullet leave the barrel by the time the bolt slams back or forward again? where is the bolt in it's travel when the bullet actually leaves a typical 16" barrel?

 

[Richard Coody]

Well with an ajustable gas.block you can just cut the gas off if you like. I have tried this with precision ar's. My issue was cycling. With a bolt gun the first part of the cycling of the bolt is primary extraction. Same with the ar but with the bolt gun you have the leverage and caming action with the bolt. Not so with an ar. Now none of these were .223. Mine were 6.5 grendel and a wildcat 6mm grendel. Worked fine with the gas turned on but difficult cycling with the gas turned off.

I can tell you right now that even with the gas system ar's are capable of great accuracy but will never beat the accuracy or consistency of a benchrest bolt gun.

 

[skeeljc]

The bullet is several inches beyond the muzzle when the bolt carrier begins to move.

I do not know why you would want to run an AR manually. The only reasons I can think of is to eliminate any damage to the round during feeding from the mag to the chamber. There is a school of thought that rounds loaded from the right side and the left side of the mag will chamber differently.

The main reasons keeping an AR-15 from matching bolt gun performance are:

1. The fit of the barrel to the upper receiver.
2. The flexing of the upper receiver.
3. Looseness between the upper and lower receivers.
4. The lock time of the hammer fall.

 

[Robert Weidler]

i read a while back that in some ar15 long distance matches, guys would somehow get rid of the gas system and cycle the charge handle manually,,,,,in order to improve accuracy, they didn't want the action cycling and either messing up the actual shot,,, or it helped with watching the shot hit. can't remember which.

i can't find the article or thread again. my question is, what did they do to nullify the gas system?

did they just put on a gas block that has no hole? since the rifle is designed to bleed off gas, could it cause to much pressure in the barrel, i wouldn't think so it would seem to just sort of turn it into a bolt gun (using the charging handle as a bolt)

also, was the goal in doing that to prevent the cycling bolt from messing up your shot,, or was it to help with watching the shot hit?

follow up question. when shooting a typical ar, will the bullet leave the barrel by the time the bolt slams back or forward again? where is the bolt in it's travel when the bullet actually leaves a typical 16" barrel?

A few years back I put together a gasless gun built on the AR15 platform (no hole in the barrel and no gas block/tube). The idea was to eliminate the foibles of the gas system and also to slow down the shooting. The gun was built with a Bartlein 26" heavy palma and chambered for the 6 mm Grendle, looking to get 2800 fps at the muzzle. To mechanically actuate the bolt I added a straight pull bolt carrier and handle from Lantac USA (a British based company). The gun shot phenomenally well with sub-half minute groups at 200 yds and rang the bell consistently at 800 yards (could go no further due to scope limitations). While I did get my desired 2800 fps the cases had a sticking problem (could not unlock the bolt without knocking it back with a mallet handle) at that pressure and I had to drop back to 2760. Researching this problem led me to Target Shooter magazine where I learned the Brits, using a similar system, also had the sticking case problem when shooting hot loads. I should note here that in Britain, gas guns are outlawed and gasless ARs are common. My load was 107g SMK over H4895 and it did show signs of pressure. Switching to Varget improved things somewhat but could not reproduce the higher velocities. It's a great gun and I'm happy that I built it, but would not do it again.

 

[Oso]

The question of timing of when does the bullet leave the barrel and when does bolt begin moving is a point of contention in a number of threads on this forum. The bullet leaves the barrel in 0.0005 seconds (assuming 18" barrel and 3000fps: 1.5/3000) Someone is going to argue this in inaccurate because it assumes a constant velocity. Where in actuality the bullet is accelerating from 0fps to 3000fps.... so lets just use a average velocity of 1500fps...so call it 0.001 seconds. Basically, really fast.

There is some speculation that as the bullet begins traveling down the barrel some of the air in the barrel in front of bullet that is getting compressed may get captured/forced into gas system, but the bulk of the gas that operates the gas system is from exhaust gas resulting from the combustion of the gun powder that is behind the bullet. I am sure if you search there is a video somewhere on the internet that analyzes this event. Pragmatically, shooter can't feel the difference, but does the bullet??? Google It and get back to us on what the definitive answer is!

My guess is that they shut off the gas to make gun more accurate (single shot with no moving parts) or at least an attempt to limit the variable that could impact the shot. Even without the gas driving the BCG, the gun is still going to move from recoil (just like a bolt gun does) so there is still an issue with shot calling. At least this is my guess (could be wrong).

As Richard pointed out an Adjustable gas block is easiest way to turn on/off the gas by either opening or closing the gas port in gas block that allows the gas to flow back through the gas tube into the receiver to drive the BCG backwards. If you want to pursue this with your rifle, I suggest a quality adjustable gas block with positive clicks and a forward facing adjustment screw, such as SLR Rifleworks (gold standard) or something comparable (expect to spend $50-$100). Don't make mistake of buying an adjustable gas block with either a side adjusting screw or rear facing adjustment screw, because depending upon your forearm/rail you way not be able to access the adjustment screw without disassembling the rifle. If you go cheap then expect it to fail ($30 adjust gas block from Ebay isn't going to cut it).

Edit / Update: Sorry I was slow on typing and having breakfast so didn't see other posts before I submitted mine. Other posters have some good practical experience. Perhaps another answer as to "why turn off the gas"... if you close off the gas then you will maximize the velocity with all the energy/force of gas expansion being directed behind the bullet and none being redirected into the gas port to operate the BCG.

 

[rockwind1]

thanks to all, great answers. i was trying to apply this to a tavor x95 (of all things) and the gas block is not adjustable, similiar to an AK style. would need a custom job to do something with it i guess, i learned after posting this

 

[Laurie]

The gun was built with a Bartlein 26" heavy palma and chambered for the 6 mm Grendle, looking to get 2800 fps at the muzzle. To mechanically actuate the bolt I added a straight pull bolt carrier and handle from Lantac USA (a British based company). The gun shot phenomenally well with sub-half minute groups at 200 yds and rang the bell consistently at 800 yards (could go no further due to scope limitations). While I did get my desired 2800 fps the cases had a sticking problem (could not unlock the bolt without knocking it back with a mallet handle) at that pressure and I had to drop back to 2760. Researching this problem led me to Target Shooter magazine where I learned the Brits, using a similar system, also had the sticking case problem when shooting hot loads. I should note here that in Britain, gas guns are outlawed and gasless ARs are common.

I had such a rifle in 223 Rem some years ago - actually, it was my first long-range number in the dawn of F-Class. I won a fair number of short and mid-range comps with it. It wouldn't today given current states of F/TR play! To many Brits amazement, I shot it successfully in 800-1,000 yard matches with 80gn Sierra MKs. (When I say 'successfully', that means I could put 22 bullets into the frame and most into the standard NRA 1K 'black', but definitely not successfully in defeating people using cartridges like 6.5X55AI, nor a good 308 in terms of scores. This was a UK Southern Gun Company SSR-15 with extended manual handles on both sides built around a 24-inch Lilja match barrel with a modified Wylde chamber. The TS articles you refer to may have been mine.

This outfit would shoot genuine quarter-inch 5-round groups at 100 shot prone off a bipod and average somewhere in the 0.3-0.4" range - really quite astonishing. This was with fairly straightforward mild loads of VarGet or Re15 under the 80gn SMK in only basically prepped Winchester brass sized with an off the shelf - Hornady I think - FL sizer die and Redding Comp seater.

However, as Robert says, pressure and its effect on extraction/cycling are big issues. You didn't need pressure testing equipment to demonstrate how each 0.2gn step in charge weight increased chamber pressures and in turn the effort needed to get primary extraction. When I got QuickLOAD, I could see that calculated pressures of 55,000 psi were when things became (literally) sticky. I didn't have a chronograph then, but MVs were modest and the 80gn bullets were subsonic at 1,000 yards whispering silently through targets and confusing butts crews. As Robert also says, UK shooters lost access to semi-autos many years ago (with new legislation implemented in early 1989, the year after the Hungerford mass shooting using an AK47 type rifle), so I can't comment on how a built from scratch manual ('straight-pull') AR compares to the same rifle with gas operation in out and out precision terms.

With this type of AR being the dominant form in UK 'Tactical' and CSR (Civilian Service Rifle) competition, again as with Robert's experience, several people experimented with other cartridges, the Grendel and variations thereon being tried by some. Generally most people went back to 223 because of the manual operation / primary extraction issue as cartridges with cases with larger surface areas than the 6.8 Rem SPC tend to increase the pull needed on extraction and disrupt cycling. A friend, Dave Wylde, who is also a gunsmith and rifle builder and manual AR guru, CSR etc shooter, is now trying the 224 Valkyrie and reports very favourably on it, so this may at least partly replace 223 Rem over here in these rifles.

 

[Geno C]

My 300blk is a side charger that is usually run with the gas off. Even made a little extension so my 7 year old can cycle it easier. I run it with the gas off so subs are quieter. He runs it that way because it’s easier for him to concentrate on fundamentals without the bolt slamming back.

 

[divingin]

I do not know why you would want to run an AR manually. The only reasons I can think of is to eliminate any damage to the round during feeding from the mag to the chamber.

In my case, by doing so, I am no longer subject to California's Assault Weapon debacle. Since an AW is, by definition, a magazine-fed semi-auto rifle (with other identifying "features"), by removing the cycling of the firearm, you remove it from the entire debate.

Primary extraction is probably the biggest obstacle to running an AR in this configuration. You don't get a lot of assistance breaking the case free if you don't have gas helping out.

I removed the gas tube from my rifles and plugged the tube port; you probably don't even have to do the latter (I did to ensure there would be fewer questions about changing the config back to semi-auto. Don't know if that really made sense or not.)

 

[rockwind1]

so just an update, although i think i gained some (maybe 1/8 moa) by manually cycling, i went back to just turning the gas back on and it was a lot less of a hassle.