AR wives tales

[budlight]

Lots of misinformation out there about felt recoil and the ejection system. So I went looking and came across this well written post. I have learned over time from my own experimentation and seeing what the pro's are doing. I've been blessed with enough resources to buy barrels and parts and modify them and if it doesn't work out, I throw them away. Life is about learning and not just trusted some gun shop owner that knows it all when you tell him that his 20 inch 7 twist throws every 55 or 62 grain bullet sideways through the paper at even 50 yards. Or an expensive FN ar10 that can only shoot "Service Rifle ammo" I also don't like using Adjustable gas blocks! when you can build a perfectly functional micro blocked rifle. I have two piston 15's with adjustable gas blocks. because of my rifle length and .072 gas ported SS barrel it's basically wide open to cycle right. Out shooting away 100's of miles from home and the adjustment came apart and quit firing. Luckily I always bring two or more rifles. Lesson learned from many years ago deer hunting when my buddy climbed into the pickup bed and upon coming out kick my rifle off the tail gate and internally broke my scope when it landed on a rocky two track road. The cross hairs were like 10 feet left and 8 feet high, so my hunt was done with a 800 mile round trip.

I machine dimples in my gas gun barrels, so the set screws don't allow the micro blocks forward over time and use high temp Permatex red inside the block to seal all gas from escaping between the block and the barrel.

On to the good read!

The Physics of AR-15 Recoil Reduction - AR15.COM

Firearm Discussion and Resources from AR-15, AK-47, Handguns and more! Buy, Sell, and Trade your Firearms and Gear.

www.ar15.com

 

[Bud H]

A good article and discussion on that page, I personally just tune it to work with several loads and not beat up the action. I have never thought of any gas gun as heavy recoiling. But then again, that is subjective as I shoot mostly light medium and big bore rifles and hand guns. The difference between a hunting gun and a three gun Is significant, kinda like cowboy action and the same guns for hunting.

 

[budlight]

Recoil is all what goes out the barrel. gas and a projectile. The air gap between the bolt and the buffer weight is a hammer. Fast high pressure is what damages the front of the buffer weight. Especially too heavy buffer weight, spring, and air compression. That is why I drilled out the buffer tube end hole to ease the cycle. I just figured that they were a cheap experiment and could go in the garbage like my other failed ideas. The spring strength is for the return cycle.

 

[Bud H]

Ok, but then doesn't the gas that moves the bolt back contribute to felt recoil? I suppose it would really only contribute to felt recoil, when the buffer is smashed the bottom of the tube. I wonder how much of a lapse their is between the bullet exiting the barrel and the buffer hitting bottom? I'm thinking that those two together would increase recoil. I don't know the actual science behind it, just a old gunsmith that has done some work on gas and recoil operated systems.

 

[budlight]

Did you read the article?

I don't think that the buffer weight can hit the bottom of the tube because of spring coil bind. I will measure that tomorrow.

 

[Bud H]

I did read the article, just thinking out loud. It would have to be a really over gased gun, or weak spring to achieve it. I have seen a messed up buffer on M-16's before, but not on AR's

 

[MSURunner]

My 2 cents that is worth even less than that... recoil on an AR is really only mitigated through a muzzle device for a given load. All of the items within the cycling system must work together to achieve their end goal; removing one round, and replacing it with another. If we lighten everything in the reciprocating mass and thus turn the gas way down and the spring rate gets lowered, we are getting ourselves closer and closer to a single shot rifle that would impart all of it's recoil through the one primary event (round firing). That recoil is only altered through the muzzle device.

3 Gunners go low mass for a couple of reasons. First, they can achieve a higher cyclic rate, which will allow for more time spent aiming between shots without the rifle moving. Second, they can run lower PF loads, which WILL decrease recoil. Less recoil + faster cyclic rate = quicker times between shots. Third, removing half a pound from the rifle's weight allows for quicker transitions between targets. So 3G gets "better" by having faster times between shots and between targets, but this is all 100% dependent on using that particular ammunition. If you throw a hot 77g load in there, the system starts falling out of cohesion.

 

[budlight]

My 3 gun was done with my full auto heavy bolt and 62 gr very high BC HPBT's. I also helped run events and people would try to sneek in ss109 for cheap shooting. We had to magnetic test rounds. Because they would tear up the ballistic targets. It's the total mass of the moving parts so it's the BCG, hammer, and the buffer weight. I don't know my cyclic rate. Full auto rifles are 700 - 950 round per minute. I do know from math that 600 is 10 shots per second. I do know that I was trying to improve my mil spec triggers by lightening the hammers and polishing the sear... That it turned my rifle into a double tap that was so fast that it almost sounded like a single shot. I ruined several sears before I made them really crisp and single shot.

So your statement about decreasing cyclic time between shots is not very valid. Who cares if it's .1 seconds or .08 seconds. You can't tell the difference because it's so fast.

One of my 1/2 weight hammers that works very well.

 

[D2wing]

A muzzle brake can redirect gases to reduce recoil. Rearward momentum of the gun minus any redirected gases is the same regardless. The rearward motion of the BCG, buffer and compression of the spring spreads out the recoil making it feel softer and the energy used to move the mass and compress the spring does take up some energy reducing the recoil. More mass of reciprocating parts does absorb some energy and does slow the recoil impulse making it feel like less recoil. That's the physics. Reducing the power and mass of the charge and bullet also reduces the recoil.

 

[MSURunner]

My 3 gun was done with my full auto heavy bolt and 62 gr very high BC HPBT's. I also helped run events and people would try to sneek in ss109 for cheap shooting. We had to magnetic test rounds. Because they would tear up the ballistic targets. It's the total mass of the moving parts so it's the BCG, hammer, and the buffer weight. I don't know my cyclic rate. Full auto rifles are 700 - 950 round per minute. I do know from math that 600 is 10 shots per second. I do know that I was trying to improve my mil spec triggers by lightening the hammers and polishing the sear... That it turned my rifle into a double tap that was so fast that it almost sounded like a single shot. I ruined several sears before I made them really crisp and single shot.

So your statement about decreasing cyclic time between shots is not very valid. Who cares if it's .1 seconds or .08 seconds. You can't tell the difference because it's so fast.

I think you're saying a lot of what I was, just differently. You are using a full power load, so if you lightened your reciprocating mass any, your cyclic rate would start becoming too fast or you would have to turn the gas down to a point of not getting consistent operation.

In lightening your hammer, you decreased your lock time, by a small margin. Increased cyclic rate is essentially doing the same thing with the "lock time" for the loading operation. There is only so far that it can go, though, before it becomes too fast and you don't have enough dwell time for the chamber to release to the spent cartridge. Your cyclic rate works for your rifle with your ammunition. Throw in a lower power load and you won't have the cyclic rate to operate the system and you'll now need to increase the cyclic rate. This is also based on a static gas port location. Changing this can change that dwell time more significantly than a lot of things, but people obviously can't change that after the rifle is built. I doubt the lightened hammer was the cause of the double tap, but more likely, incorrect geometry in the sear/disconnector from the polishing. Neither here, nor there...

Point being, if you want to decrease recoil, you should either decrease the recoil power of the load (and tune accordingly), or add a muzzle device.

 

[budlight]

A muzzle brake can redirect gases to reduce recoil. Rearward momentum of the gun minus any redirected gases is the same regardless. The rearward motion of the BCG, buffer and compression of the spring spreads out the recoil making it feel softer and the energy used to move the mass and compress the spring does take up some energy reducing the recoil. More mass of reciprocating parts does absorb some energy and does slow the recoil impulse making it feel like less recoil. That's the physics. Reducing the power and mass of the charge and bullet also reduces the recoil.

Totally agree all my AR's have brakes except for two a 20 and 24 inch with NON threaded 11 degree target crowns. All have full auto bolts. I have messed with springs and weights and never noticed much of a difference. Other than the flat wound springs being nearly silent instead of the bong when you have your cheek on the butt stock rest target shooting

I grew up shooting clay in the junior division and migratory bird hunting with 12 guage 3 mags. I went elk hunting with my dads friends and they would talk about how their 338 or 300 win mag or 7mm would just kick anyones butt. I saw one of them get the bleeding scope ring on his eye brow. I probably didn't weigh 100 pounds and I showed them how I could just pound away. Bunch of old wimps!

 

[budlight]

I doubt the lightened hammer was the cause of the double tap, but more likely, incorrect geometry in the sear/disconnector from the polishing. Neither here, nor there...

It was my overzealous polishing of the sear and front edge. It had so little to catch on that dry firing was very crisp, but live fire would fail to catch and fire a second or even third round. The sear block went in the garbage because I'm not getting arrested at some range firing a nearly full auto without a stamp. LOL I kept the light hammers and lighter springs. Most of my stuff has drop in 2- 3.5 pound single and dual stage triggers now

 

[JustMe2]

A slightly different question. My AR10 Armalite Target action takes a lot of effort to charge the first round. It is lubed well and throws the spent rounds at 2-3 o'clock. I have to place the rifle butt on my knee or against my belly and it takes a lot of force to pull the bolt back. It cannot be charged by holding the rifle in one hand and pulling the charge handle back with the other hand. That action will cause my rifle to swing wildly. I see a lot of videos of guys seemingly easily pulling an AR15 bolt back, not mine. Is this amount of force normal for a 308 AR10? If not, what is required to fix this to make charging less effort.

 

[MSURunner]

A slightly different question. My AR10 Armalite Target action takes a lot of effort to charge the first round. It is lubed well and throws the spent rounds at 2-3 o'clock. I have to place the rifle butt on my knee or against my belly and it takes a lot of force to pull the bolt back. It cannot be charged by holding the rifle in one hand and pulling the charge handle back with the other hand. That action will cause my rifle to swing wildly. I see a lot of videos of guys seemingly easily pulling an AR15 bolt back, not mine. Is this amount of force normal for a 308 AR10? If not, what is required to fix this to make charging less effort.

AR10's seem to require a bit more "break-in" time than 15's, but I would suspect you have excessive pressure on your carrier from a full magazine. If you strip a couple rounds out of the mag, does it still do that? One thing most people don't understand is that the bolt is not cycled by the gas impulse through the gas tube/piston. That impulse only unlocks the bolt, which is now being driven back by the pressure of the gasses still within the barrel. That pressure obviously dissipates very quickly as the action opens and the bullet exits, but is a very strong initial impulse.