Advanced Marksmanship Differences shooting gas versus bolt guns?

[Sig685]

Re: Differences shooting gas versus bolt guns?

I still say the barrel is the issue and you should change that before you do anything else.

Just to be sure, take 10 rounds of the 175gr Fed GMM stuff you have and shoot them for group at 1 or 200 yards. Feed them manually, all the way into the chamber, not from the magazine. Your 1:10 twist should stabilize this bullet very nicely. This will remove all cycling issues, you are looking for the accuracy potential of your current rifle system.

And don't forget your follow through.

 

[Phylodog]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">Since the gas system is adjustable, I would adjust it for less gas until it fails to cycle reliably, the readjust it back just enough to get reliable cycling. </div></div>

That is the plan. I'm hoping to find a nice sweet spot in there somewhere.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sig685</div><div class="ubbcode-body">I still say the barrel is the issue and you should change that before you do anything else.

Just to be sure, take 10 rounds of the 175gr Fed GMM stuff you have and shoot them for group at 1 or 200 yards. Feed them manually, all the way into the chamber, not from the magazine. Your 1:10 twist should stabilize this bullet very nicely. This will remove all cycling issues, you are looking for the accuracy potential of your current rifle system.

And don't forget your follow through. </div></div>

I've already got the new scope, receiver and DD free float rail on the way. The barrel has been pulled and I'm going to thread it before putting everything back together. I'll find a PRS stock shortly to provide a solid cheek rest as well. All of these items should help to provide a more similar feel to what I am used to and therefore (hopefully) assist me in shooting this rifle more accurately. As the rifle sits now everything feels completely different than my bolt gun, the cheek rest I'm using isn't very solid and I'm shooting with a good bit less magnification than I'm used to. I realize it will never feel the same but the closer I bring it to what I'm used to the better off I'll be. I learned long ago that consistency was key and that's what I'm trying to accomplish with the mods. I want to give that a try before scrapping the barrel completely.

 

[Phylodog]

Re: Differences shooting gas versus bolt guns?

I don't think I've seen that grip before Sig, is that something available commercially or did you make it?

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

It's from David Tubb. It is the best grip I have ever used for shooting prone, or any other position for that matter and trust me when I say I've tried a bunch. As you can probably tell from the extension of the LOP adjustment on the PRS, I am pretty tall, 6'4", with hands to match. The regular AR-15 grip is way too small for me.

I have tried tactical grips, the cool-looking one with the palm shelves. All crap, they would actually hurt my hand after a few minutes on the ground. By the end of the first match, I took it off and it's on a shelf with other grips that failed me.

I've had the current one here for a few years now. I wish I could get the one in wood, but they don't make them any more. (Sigh). Look at davidtubb.com for info on this one. It's less than $40. Here's another picture of it.

 

[our gang]

Re: Differences shooting gas versus bolt guns?

Since I own 3 AR 10s (DPMS) let me make the following observations:
Your scope mount is probably too low (been there done that). I use Warne QD extra high rings now and they give a much better cheek weld and comfort.
Ignore all the BS about changing barrels, POI shifts and forward assist. None of my three show any POI shift whether single loaded, loaded from the magazine (first one) or during automatic cycling AS LONG AS YOU LET THE BOLT SLAM CLOSED BY PUSHING THE BOLT RELEASE LEVER.
All of my three are MOA or sub MOA capable. BiPods make that level of accuracy more difficult than a good bench rest setup.
The only meaningful accessories I have added are a target trigger and a new grip.
Spend your money on loading good ammo as that is the biggest non human factor. For example, my 16" TAC upper is a 2-3 MOA rifle with all the "normal" military or commercial ammo I have tried in it. With the load in the new Handloader with the exception of A Max 168s rather than Berger VLDs (VLDS wont fit and feed), it will shoot 5 shot one hole groups IF I do my part. I'm sure you LR will do even better.
Gettin a DPMS LR to shoot well is not a black art as some would have you believe. I own bolt rifles, falling blocks, gas port and gas impingment semi autos, percussion and flintlocks. In all cases the two biggest factors in accuracy are ammunition and "the nut behind the bolt". So load it up and shoot the Hell out of it and you'll find it does well by you.

 

[j-huskey]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: our gang</div><div class="ubbcode-body">Since I own 3 AR 10s (DPMS) let me make the following observations:
Your scope mount is probably too low (been there done that). I use Warne QD extra high rings now and they give a much better cheek weld and comfort.
Ignore all the BS about changing barrels, POI shifts and forward assist. None of my three show any POI shift whether single loaded, loaded from the magazine (first one) or during automatic cycling AS LONG AS YOU LET THE BOLT SLAM CLOSED BY PUSHING THE BOLT RELEASE LEVER.
All of my three are MOA or sub MOA capable. BiPods make that level of accuracy more difficult than a good bench rest setup.
The only meaningful accessories I have added are a target trigger and a new grip.
Spend your money on loading good ammo as that is the biggest non human factor. For example, my 16" TAC upper is a 2-3 MOA rifle with all the "normal" military or commercial ammo I have tried in it. With the load in the new Handloader with the exception of A Max 168s rather than Berger VLDs (VLDS wont fit and feed), it will shoot 5 shot one hole groups IF I do my part. I'm sure you LR will do even better.
Gettin a DPMS LR to shoot well is not a black art as some would have you believe. I own bolt rifles, falling blocks, gas port and gas impingment semi autos, percussion and flintlocks. In all cases the two biggest factors in accuracy are ammunition and "the nut behind the bolt". So load it up and shoot the Hell out of it and you'll find it does well by you. </div></div>

AMEN BROTHER!!!!!
Continue to speak up.

 

[Lindy]

Re: Differences shooting gas versus bolt guns?

That Tubb grip may be great for target shooting. However, I'd not want one on a fighting rifle, as it doesn't look like you could use it from your support side. The ability to use a fighting weapon from either side is highly desirable.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">In all cases the two biggest factors in accuracy are ammunition and "the nut behind the bolt".</div></div>

I'll add an <span style="font-style: italic"><span style="font-weight: bold">AMEN</span></span> to that.

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

Lindy, I agree with you, but this is a target rifle. It weighs over 15 pounds in full dress and leave gouges in the grass on the firing line when I drag it up there from the back of my SUV.

 

[DTubb]

Re: Differences shooting gas versus bolt guns?


I have several tier one operators using this grip in the field and they seem to get along with it just fine.
Most users feel it allows more control over the weapon and the hand position allows quicker disengagement of the safety.

Most took the grip to a belt sander and cut the out edges down to give a more rounded appearance but overall the grip still functions as intended.

 

[Lindy]

Re: Differences shooting gas versus bolt guns?

A firearm with equipment which cannot be used from either side, whether that equipment is a stock, a grip, or a sling, is a handicap. Life in combat is hard enough without deliberately making it harder.

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DTubb</div><div class="ubbcode-body">
I have several tier one operators using this grip in the field and they seem to get along with it just fine.
Most users feel it allows more control over the weapon and the hand position allows quicker disengagement of the safety.

Most took the grip to a belt sander and cut the out edges down to give a more rounded appearance but overall the grip still functions as intended.

</div></div>

I like it just fine the way it is; as I said before of all the grips that I have tried, and that's quite a few, this one is the best for me and my purposes. If you ever make another run in wood, please let me know.

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

I know for a fact, the guys who come to classes with the Tubb rifles, either Spec Tac U Lars or otherwise have a very difficult time shooting from the weak side.

Not only is the pistol grip an issue, the stock is too, if we have them shooting from cover, or simply from the left on a right handed rifle they have issues. It's set up to shoot one way and one way only... it needs work as a tactical set up.

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

Be that as it may, I don't intend to shoot a match left-handed. As I said, it suits me just fine, for my purposes, none of which include shooting left-handed.

And if you think this rifle is not easily shot "other-handed," you should see some on the rifles on the F-class circuit; they make this one positively weak-handed friendly.

 

[Sterling Shooter]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">A firearm with equipment which cannot be used from either side, whether that equipment is a stock, a grip, or a sling, is a handicap. Life in combat is hard enough without deliberately making it harder.


</div></div>

I'm a left eye dominant shooter. The forward assist on my AR is my forward distraction when shooting from prone in low light. I need to crowd the rear sight in that scenerio, usually, causing the forward assist to hit my lip and upper teeth hard enough to draw blood. It's the kind of distraction that will break follow-though down, for sure.

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

Anything not capable of shooting from either side with the same ease has no purpose being discussed as tactical... if we were talking F Class or High Power in any other context except for similarities in marksmanship principals it is as well useless.

I have seen and shot F Class and contend it is a great training venue but has no serious value to me beyond basic marksmanship training, you're talking apples and avocados in this case, the only similarity lies in shape & skin color, maybe not even that much.

 

[Lindy]

Re: Differences shooting gas versus bolt guns?

I am a right-eye dominant shooter who is naturally left-handed. However, I have worked to develop ambidexterous skills with rifle, pistol, and carbine. The only thing that bothers me about switching hands with any of those is that my left index finger gets a bit sore from the mag release on my Glocks when I do extended shooting with my left hand.

Handed-ness is over rated.

A smart guy said, "The problem with arguing in favor of your limitations is that you get to keep them."

I prefer to overcome mine. Your mileage may vary.

 

[Sterling Shooter]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Anything not capable of shooting from either side with the same ease has no purpose being discussed as tactical... if we were talking F Class or High Power in any other context except for similarities in marksmanship principals it is as well useless.

I have seen and shot F Class and contend it is a great training venue but has no serious value to me beyond basic marksmanship training, you're talking apples and avocados in this case, the only similarity lies in shape & skin color, maybe not even that much. </div></div>

Hmmm... So, an AR isn't "tactical"?

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sterling Shooter</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Anything not capable of shooting from either side with the same ease has no purpose being discussed as tactical... if we were talking F Class or High Power in any other context except for similarities in marksmanship principals it is as well useless.

I have seen and shot F Class and contend it is a great training venue but has no serious value to me beyond basic marksmanship training, you're talking apples and avocados in this case, the only similarity lies in shape & skin color, maybe not even that much. </div></div>


Hmmm... So, an AR isn't "tactical"?</div></div>

Hmmm, you're not reading tactical, if you can't shoot it from the support side it's not. I have never had an AR I couldn't shoot from the Support side, so you mis-read something.

We were specifically talking about the Tubb guns, Because they are set up to work on one side only...

 

[Kix]

Re: Differences shooting gas versus bolt guns?

Here is a slow mo of the three impulses of a gas gun that was talked about earlier in the thread. Hope this helps out a bit. It's exactly 30 seconds into the vid. It's the M16 3 round burst in slow mo.

http://www.youtube.com/watch?v=g5aWFcxE30E&feature=related

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

That video is no longer available.

I found this one:
http://www.youtube.com/watch?v=d4S9f0D0THc

And this one:
http://www.youtube.com/watch?v=yQpldJaALU8

http://www.youtube.com/watch?v=FKLk6bhvfgU

 

[Kix]

Re: Differences shooting gas versus bolt guns?

What do you mean the video is no longer available? Click on the link and the m16 3 shot burst is exactly 30 seconds in. It shows the 3 impulses perfectly and hella slow.

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

Ok. thanks for updating the message and putting up a different link. Yes this one works but it only shows the bolt carrier moving and pulling out cartridges.

Nobody ever disputed the 3 impulses. Anyone who has ever fired an AR-15/M16 would know they exists and just disassembling the rifle will show you how it works. There are some rather sizable springs and big pieces of metals moving around there.

The bone of contention, so to speak was that some stated all these moving pieces did their stuff while the bullet was still in the barrel. I, for one, disagreed with that assertion; the movement takes places after the bullet has left the barrel.

If you look closely at the videos to which I linked, you will see the muzzle blast occurs before the bolt carrier starts to move back; the bullet has left the barrel and the action is now underway. You will also notice the absence of the foot of sparks from the ejection port.

I am still waiting for the video promised by Lowlight.

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I am still waiting for the video promised by Lowlight.</div></div>

First off, I am still on the range working as I have been for months, not hours, months, doing this shit. And the internet connection is barely 2 bars on my aircard and the wifi on here has a 175MB transfer limit, so I' can't post the video yet.

As well, we already established the 5.56 model is different than the 7.62, and if in fact the gas moves 5X faster than the bullet as written by several other sources beyond this site, and if that is true, the bullet has to be still in the bore after the gas block unless the barrel infront of the block was 5X shorter than the barrel.... and they claim 5X faster than a 5.56, a 7.62 is heavier and slower.

If you disagree, no problem, prove how the bullet is moving faste than the gas and not just saying it isn't happening based on your limited experience with the system.

when I get home after the 15th I will post the video.

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

I look forward to the video.

I found this one on Youtube this morning. It's an SR-25 in Afghanistan at dusk, with supressor.

http://www.youtube.com/watch?v=r9d_P17LFdk

Also, I am writing an email to Knight Armament to see if they can settle the debate. I want to make sure I capture the full flavor of the argument so that they can give an unambiguous answer. I don't know that I will have time to finish it this morning, so it may not leave until this afternoon or even tomorrow.

 

[Sterling Shooter]

Re: Differences shooting gas versus bolt guns?

Who cares, follow-through is important no matter what the firearm's cycling scenario, as the brain, realizes the trigger pull is complete before the bullet is out of the bore; and, therefore, if the shooter does not consciencely continue to aim, until recoil subsides, a bad shot is certain.

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

Where's the shots at night ? If you are calling that night time I can see why you don't understand what is being said.

if you think calling Knights will answer, well another mistake, while you're on the phone ask them about broken bolt stops, out of spec bolt faces and the rest of the problems we see. I am sure you'll get an honest answer from them.

I love it, a case of finding someone, anyone, to agree with you because you have no personal experience to counter with, so you'll fish for an answer...

Sterling is correct follow through is key, all the fundamentals are and more so with a gas gun.

Well I am out the door to work the range, you be sure to get on those phones. No worries though, regardless what some twit at Knights' says, rest assured I have the video taken at night, you know in the dark, where the shit is flying out the chamber.

 

[Grump]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The trigger and especially the follow through in the gas gun is more important than with a bolt gun. In fact the gas gun is so different I can tell when the gas gun shooter has run out of ammo and fired his last round because I can usually see the impact change downrange. Why, the bolt is no longer, recoiling and then reloading but recoiling and stopping so it changes the unaware shooter's position slightly.</div></div>

I agree that the on-topic part of this threadzilla is careful attention to follow-through.

I also *suspect* that the traditionally-heavier trigger pulls on gas guns can expose bad shooter technique that does not arise with trigger pulls of 1.5 lbs or less. My official position is that, so long as the trigger pull is not so heavy that it causes muscle tremors, a good shooter can get equally good results with a variety of bad and/or heavy triggers.

However, if all or almost all of these Mark-whatever rifles are displaying this last-round flyer phenomenon, there's gotta be a design deficiency somewhere. I've fired over-the-course off an on since the 1980s and have NEVER seen a lock-open round go anywhere but randomly inside the rest of the group at 200 and 300 rapid. This has been with both M14 types and M16 types (the M1 Garand shooters I pulled targets for were not good enough to do those 98-100 point high X-count groups) and with some goofy .223 space gun.

Those rapid-fire (really sustained-fire) groups also had two last shots from separate magazines, and two shots fired from a fresh manual chambering.

So, LowLight, please describe and quantify this last-round effect you're seeing. Is it a constant MOA or Mils at all distances, and how much is it and in what direction(s)?

Just because what you're seeing doesn't match my experience does NOT mean it ain't happening. I've heard of different M14 magazines moving the group center a bit, but could never shoot mine tight enough to observe it in my own shooting. But within those limits, my last shots have always been with the rest of the group, whether in a fixed-round course of fire or shooting without knowing when the mag would empty.

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

Seeing how we don't shoot groups with them, and I am working an line in a different capacity, i can't say what the MOA variation is, I can just see it downrange when someone shoots the last round.

Basically they hit the target, hit it again, then a round goes way off and it's almost always the last shot when this happens.

It's far from scientific and as I explained it is more about not paying 100% attention to all 3 recoils than anything else. The triggers are not so heavy or awful, especially when properly reset to blame a heavy trigger pull on the problem... although trigger is the biggest problem with a gas gun shooter than anything else, it appears regardless... and none of this is happening during rapid fire, that isn't part of the program.

 

[Grump]

Re: Differences shooting gas versus bolt guns?

Any trends in the direction those last shots are off?

Same direction for any particular shooter, but different directions between different shooters?

I do see a possibility that the cadence and mindset of sustained-fire exercises could erase this tendency you're seeing on the line.

What proportion of shooters will display this, and for what percentage of their last shots?

Sounds like your training *does* reduce the frequency of it happening, am I right?

 

[esorensen]

Re: Differences shooting gas versus bolt guns?

I think what he meant to say was that the gas is moving 5x faster once it hits the ambient air, not in the confines of the weapon. Inside the barrel, the gas is only moving as fast as the projectile it is in contact with.

I'm also not sure of this, but i can SEE and watch an action cycle. I cannot see a bullet leave the muzzle. Barrel time is measured in micro seconds. Just the bolt unlocking probably takes more than a few thousandths of a second and the bullet is already on its merry way.

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

I have given some thought on and off to this issue and I have come up with some hypotheses. It would help if there was more data available such as the direction and amount of displacement experienced by the preponderance of the shooters.

What are the mechanical differences between the last shot and the others prior to it?

During the last loading cycle, the bolt coming forward will strip the last round from the magazine. This round will offer the least resistance to the moving BCG because it is under the least amount of spring tension and its friction is reduced since it is resting on the magazine follower and not another brass cartridge. In addition, the bolt itself will not experience the friction from the next round in the magazine as there is none there to slow the bolt down. So, it is quite conceivable the last round gets loaded and chambered more forcefully than the prior rounds.

This MAY have two consequences that taken separately or together may amount to a detectable difference to a trained observer looking at the target.

1- The cartridge, being chambered under greater force may allow the bullet to move slightly so the pressure may be reduced (bullet seated out a bit further) or bullet runout is introduced, or both.

2- The bolt carrier group on the SR-25 is pretty heavy, much heavier than on an AR-15. If the last cartridge in a magazine is loaded with more force than the others, this extra force may cause the rifle to shift and the relationship of the shooter’s eye, reticle and target may be offset by a small amount and unpredictably so, though to my mind there might be a bias towards shooting higher (and to the right for right handed shooters) on the last shot, but that may also depend on how the rifle is held so it could vary by shooter.

If the bullets are solidly crimped in place, 1- above will not occur. If the shooter has a good solid hold on the rifle and/or can detect minute differences in eye-sight-target alignment, 2- above can be avoided.

The reason I believe the last shot may go higher is that if the there is disturbance in holding the rifle, the added force of the carrier would cause the barrel to go forward and down and thus break the sight picture, the shooter would then simply aim higher but with an different sight picture and I think he or she may over-compensate not realizing there is a difference. After all the shooter has just put 19 rounds downrange with a similar hold, why should this next one be different?

 

[Sterling Shooter]

Re: Differences shooting gas versus bolt guns?

Sig,

Your ideas about it are food for thought. One thing is certain, recoil must be controlled until it subsides. Consistent contact with the rifle and ground is essential to good shooting. In HP, using an AR in both single load, as well as rapid fire events requires appointing a limit and pattern to recoil which encourages zeroing refinement for the particular event's entire string of fire, understanding last rounds out have a different recoil effect than rounds followed with another being chambered. I don't really understand it, but I do know when shooting from the standing position, or slow prone, should my gun short cycle, bolt closing rather than remaining open, my shot call will not be what I was shooting for and bullet strike will usually support the call. Of course, short cycling is a problem to good shooting for a multitude of reasons beyond, yet, still tangentially connected to, recoil issues.

I'm not such a good shooter that what I just described can be taken to the bank, I think that this esoteric stuff is sometimes masked by my less than perfect trigger control and sight alignment. As I recall, David Tubb touched on the matter a few years ago, but I don't remember his analysis.

Since I do know that the elements and factors of a steady position support trigger control and sight alignment, I try to make my position perfect. This gets me good results; plus, with a gas gun rather than a bolt gun, during rapid fire strings, I have the time to dress up my sight picture which may be more important than what other divergences exist between bolt and gas guns.

 

[esorensen]

Re: Differences shooting gas versus bolt guns?

I havn't personally found any difference in the last shot fired from the mag. I have however found the first shot fed from the mag shoots at 11 o'clock. All the rest group tightly. If I hand load the first round and push it into the chamber and then hit the bolt release, they all group together. This only happens on the AR10T in .308 not the .243 10T upper I have.

 

[sinister]

Re: Differences shooting gas versus bolt guns?

The difference between a single, hand-fed slow-fire round and a magazine-fed round or the last round of the magazine is the bolt catch pushing up from the bottom.

A trued/lapped turn bolt (for instance a Remington 700) won't have much bolt "Bow." In a gas-operated rifle (AR, Knight, DPMS) the bolt and carrier are two separate parts. There isn't much slop but it's got to be there (otherwise the carrier won't retract and the bolt won't turn). Although you can get it tight the lock-up between eight AR lugs will never be the same as a bolt-action and the bolt face may not be exactly plumb with the case head.

 

[boyanzhu]

Re: Differences shooting gas versus bolt guns?

Excellent discussion on the "last shot". I was kinda hoping to read more comments on the "first shot"

There was that comment made by Buford Boone in 2007 on another public forum:
"I have seen only two semi-auto rifles that would hold the CB to standard. I have seen many that would meet the requirement if allowed a couple of fouling shots"

He works for the FBI, one of the functions is training. By CB he means Cold Bore. The context of statement was .223 semi rifles, not the .308

What Cold Bore Shot behaviour do you gentlemen observe with these ultra-modern semi .308 ? Are they as good as better bolt guns?

Thanks

 

[sinister]

Re: Differences shooting gas versus bolt guns?

The hoo-hoo about the difference between the first round and the rest of a semi-auto group has been theorized for years.

You won't see it in hand-tuned and/or well-built rifles. It may be obvious in a production rifle.

Take a look at some of the rapid-fire groups fired from competition M16s from the service rifle teams -- those are normally fired from "Fouled" rifles (after they've fired between 10 and 22 rounds). The standard of excellence is to hold a minute or less 10-shot group from standing-to-sitting at 200 yards in 60 seconds (with a sling and irons) and standing-to-prone in 70 -- with a mag change between rounds two and three.

Listen to the shooters as they come off the line and report to the coach. If the shooter calls a "7X" it means he's shot a 100 with 7 X's. That is minute-of-angle performance (or better) and the difference between a good rifle/load/shooter combo and second place.

Too often folks want their rifles to give benchrest performance when a Soldier's goal is a center-of-mass hit on a fleeting target. Better to let the air outta bad guys quickly than argue how many angels dance on the head of a pin.

 

[Sig685]

Re: Differences shooting gas versus bolt guns?

Sinister, I need your help. You have just confused the heck out of me. I admit that it has been some years since I competed in Service Rifle, so I had to go back to the rule book to verify. The SR target used at 200 yards, its X-ring is 3 inches, the 10-ring is 7 inches and the 9-ring (last black ring,) is 13 inches in diameter (Rule 4.3 200 Yard Targets.)

Correct me if I'm wrong (and be gentle about it,) but 3 inches at 200 yards is about 1.5MOA. The 10 ring is about 3.5MOA and the 9-ring is about 6.5MOA.

If the above is all correct, I would say that someone putting 7 shots out of 10 in 1.5 MOA and the other 3 shots within 3.5 MOAs, while being an excellent score for that discipline, is not what I would call minute-of-angle performance. I would qualify it more as two-minutes-of-angle performance which is still excellent going from standing to sitting in 60 seconds with slings and iron and a mag change.

Please help me understand.

 

[sinister]

Re: Differences shooting gas versus bolt guns?

Yup, a 3-inch X-ring is 1.5 MOA at 200. Same X-ring for 300 yards (MOA).

5-inches for 500, 6-inches for 600.

It gets even trickier when you start using reduced targets (the 200 and 300 rapids targets fired at 100 or 200 -- then the X- and 10-rings are scale reduced.

Not unusual to see a young AMU shooter fire a 200-10X or better at 200 or 300.

Even old, fat, blind guys like me can do it every once in a while.

 

[marduk185]

Re: Differences shooting gas versus bolt guns?

my m1a prints the same sub moa that my heavy barrel savage with accutrigger using the same ammo. no difference in fundamentals required. the main difference is about 100fps loss of muzzle velocity at the chronograph which makes the bolt gun inherently flatter. im sure the longer lock time could throw some shooters off as well. as far as final round variation, im sure its like another poster mentioned i.e. increased bolt travel vigor due to less friction stripping in the final round. i note a minor shift in poi if i single feed versus use the mag probably due to same phenomenon.

 

[2156SMK]

Re: Differences shooting gas versus bolt guns?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">So if they are saying gas moves 5X faster than the bullet, the bullet has 7 inches in front of the gas key, and 13 inches of suppressor, the gas is moving about 13" back to the bolt on a Mk11 , 5X faster means the bullet hasn't left the muzzle before the unlocking operations has started. </div></div>

I just bumped into this while searching for my name and it still warrants more explanation.
Gas moves 5-7x faster than a bullet in FREE AIR.
This is mostly in relation to the gas coming around the back of the bullet when the bullet leaves the muzzle.
At the time that gas first starts moving down the gas tube, it's also free air, but as soon as it starts to pressurize the carrier and gas tube, the speed of the gas is drastically slowed down.
Also note that the gas tube and carrier need to come "up to pressure" before the carrier can start moving and that the carrier unlocks the bolt.
The mass of the carrier and the mass of the buffer are the two primary delaying agents BEYOND the gas port size and gas tube length.

Randall Rausch
ar15barrels.com

 

[jwoolf]

Re: Differences shooting gas versus bolt guns?

I don't want to argue with anyone but, I was under the impression that "exit timing" is exactly the idea of making damned sure that the bullet has left the rifle before anything on a gas gun moves whatsoever and, it's always taken into consideration, for example, when someone tunes the gas piston on an M14 match rifle to shoot 190gr pills instead of being limited to the 175gr pills.

This is what I've always been taught but, I'd like to hear more.

I shot a LOT of service rifle over the years and still own my supermatch but, the mechanics of the exit timing of the bullet and the gas system is above my pay grade.

I know that I have to say to a certain burn rate in powder and 175gr pills are as heavy as I can go with that rifle without jacking with the gas system.

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

The bolt carrier absolutely starts to move before the bullet leaves the bore, it moves back to unlock the lugs, and that movement still takes place before the round has completely left the bore.

You can argue it, and say nothing moves, but the fact the Point of Impact changes when things like the last round is fired clearly shows the movement has happened.

Speaking with the guys who test it using high speed film, the carrier is moving.

There is plenty of distance to move the bolt carrier before the locking lugs unlock... that movement is why follow through is important, especially in a 308, because the bolt is so big and heavy compared to a 5.56.

The gases reach the bolt carrier in plenty of time, starting the movement back, which then unlocks the bolt after the bolt carrier "travels' the prescribed distance in order to turn the bolt to unlock the lugs.

I think this needed to be clarified -- the bolt versus the carrier

 

[1917]

Re: Differences shooting gas versus bolt guns?

Just finished reading all of this and it's funny how sincere people can be without realizing they can be sincerely wrong. I have the Tubb CWS on my tight built AR15 and is running cleaner now able to go longer round counts between cleaning.

 

[Chris F]

Re: Differences shooting gas versus bolt guns?

I don't have a dog in this fight, but I do play with high speed video on occasion. I also play with AR's quite a bit, though I haven't thought of combining the two until reading through this.

I used a shortcut and found a decent high speed video (600fps) of an AR in action;
http://www.youtube.com/watch?v=N_bdg60HjcY

I then used video editing software so I could advance it a single frame at a time so I could observe the the firing sequence.

Here's what I saw;
1) Gas exits the muzzle first.
2) about 5 frame later, gas begins exiting the ejection port.
3) about 8 frames after 2), the Carrier starts to move rearwards.

I'll see if I can figure out a way to share this, so ya'll can see it for yourselves.
Then you can fight over whether the bullet is exiting with the visible gas at the muzzle and whether the bolt has started to move before the gas at the ejection port is seen exiting.

 

[Chris F]

Re: Differences shooting gas versus bolt guns?

Alrighty...I turned the video clip into an animated gif with the frame advance slowed way down. You should be able to see the timing well enough.

Warning: the file is a good sized one (5meg) so give it some time to load before it starts animating.

 

[Sterling Shooter]

Re: Differences shooting gas versus bolt guns?

Very good video, that's to say, to show the sequence of events to perhaps better understand what's going on as a shooter is following through. However, even with an understanding, I don't know what a shooter's response would be other than to follow through. It is what it is, and, based on a highly qualified Service Rifle shooter's ability to shoot such rifle with results as what would be possible with a bolt gun, I'm not sure the action's cycling, whether the bullet is, or is not in the bore during the process, is meaningful. I certainly don't think it means a gas gun is less accurate than a bolt gun. With either type it's possible to recognize where the barrel is pointed, and maintain recognition until recoil has subsided.

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

As Sterling says, don't follow through and see what happens. Where the bullet is can be debated but the results speak for themselves.

Also, not that I need to, but my context has always been with that of a 308 in this system. Nobody sees these things in the 5.56 platform, at least not in my experience.

Heavier bullets, more powder, slower MV as well as more barrel beyond the gas block... makes a difference, maybe, maybe not, but the results downrange are unmistakeable.

I will have to video it and slow it down in FCP maybe it will shed some light.

 

[Chris F]

Re: Differences shooting gas versus bolt guns?

Lowlight, send me a Mk11 and some LR and I'll do the high speed video and editing!

When you say the last round is out of the group, how far out? Any consistency on where it is going?

 

[Chris F]

Re: Differences shooting gas versus bolt guns?

I found some 308 AR Slow motion footage (amazing what you can find on youtube!). Unknown manufacturer. Working on processing, but it looks like the same sequence.

 

[Lowlight]

Re: Differences shooting gas versus bolt guns?

Knock yourself out, it's an old topic and a non-issue for me at this point shoot the rifle anyway you like.

I'm sure thanks to the delay the bullet wins every time. There is a reason we get 1/2 MOA out of them, your results will definitely vary.