WV Brady
If you really like using the 7400, before you modify the rifle try as many different factory loads as are available in your area. You might find a load that shotts quite a bit better.
If your SKS is shooting 2 to 3 inch groups at 100 yards with iron sights, what is wrong with that?

I have a Rem 7400 and a couple of SKS's, which of course are semi-auto's, and which of course are not very accurate (2"-3", 5-shot groups at 100yds). Someone told me that the Yugo's have a selector switch that will block off the gas system for using a grenade launcher. I have wondered if it was possible to do something like that to a M7400 or other semi-auto's to change them into a sort of straight-pull repeater. Has anyone ever heard of someone doing this? If so, did it improve the accuracy? I thought it might be possible to improve the accuracy then by glass-bedding the action and either freefloating the barrel or using pressure at the end of the barrel in the manner used on bolt-action rifles.

Also, I know a couple of people who have extraction problems on their 7400's that this might help (one jerks the heads off the cases and the other one leaves the case in the chamber).

Another fellow told me that he got better accuracy with his SKS with a muzzle brake, because it reduced the muzzle rise (not talking full auto here ). I would think that any effect that the muzzle brake would have would be after the bullet had left the end of the barrel, and would thus not affect accuracy.

Anybody have any thoughts on these? TIA, Brady

WVBrady

First off let me say I�m by no means an expert on semi-autos. (Or any thing else for that matter) But the gas system is regulated more or less with the timing of the bolt. In other words if you block it off the best that will happen is your rifle will take a lot more of a beating than it should, and possibly your shoulder also.It also could just plain 'ol not work too. Or worse yet mess up the reciever some how.

As far as the stuck cases in your friends chambers it is most likely do to the chambers being pitted. They can be polished and sometimes made to function again. It is kind of a pain in the butt though.
Take a case that was in the rifle and drill and tap it for a piece of 3/8 or so all thread. Cut a piece about 5� long, and bend a 90 in it. Use a nut to tighten down next to the case head. Now you have a hone. You can use a little JB bore past as a grinding compound. It will take a lot of elbow grease but I have cleaned up chambers in this way before.

Shawn

One of the reasons that Rem autoloaders have accuracy problems is the method that the barrel is attached to the receiver. It attaches just like a Rem model 1100 shotgun where the barrel slides into the receiver and is locked down with a nut at the front of the forearm. Try taking the barrel off and hone the chamber then reassemble and lock down tight. As the barrel and action heat up the barrel tends to wander a bit. Shotguns take care of this problem by mounting the scopes to the barrel. If the chambers is not kept clean it will rust then pit and the only cure for a pitted barrel is to replace it. I went through all this with a friends Rem model 4 and we ended up replacing the barrel which was about $225 from Rem. They still shoot suprisingly well for a system that doesn't firmly attach the barrel. You can switch to the 7600 pump and they are generally more accurate than the auto's as I believe the barrel is screwed on. These are my experiences on one rifle so take it for what its worth.
Ralph
PS: You can always switch to a BAR

Bluetick,

"But the gas system is regulated more or less with the timing of the bolt. In other words if you block it off the best that will happen is your rifle will take a lot more of a beating than it should, and possibly your shoulder also.It also could just plain 'ol not work too. Or worse yet mess up the reciever some how."

Could you explain the physics or mechanics that led you to this conclusion?

Rick

If you are having extraction problems with handloads as opposed to factory loads, get a small base sizing die. It will probably make the problem go away.
I would guess most folks who have an autoloader use it in heavier cover where quick shots are the norm. Personally, I have used a Remington autoloading shotgun for decades and the 7400 is basically the same thing with a rifle barrel, so it is very quick for me in heavy cover where a deer, bear or elk jumps up and takes off.
I don't favor this action when I need better than 2 inches at 100 yards accuracy, not to say some 7400's would shoot better than 2". With the 7400, I am generally shooting less than 100 yards-- I even have a red dot on mine. So I don't use it for a target rifle. I think trying to make it a precision rifle would be an exercise in frustration. I use it for what it was designed for.

Rick

Like I said I'm know expert on semi autos. Nor am I Physicist. I dabble in mechanics a little on occasion though. Mostly my lawnmower and wore out Suburban.

I do know this, unlike say an FAL that has an adjustable gas system, Remington autos are touchy suckers. Brand new ones will not cycle with all factory loads. Also if you block the gas port on one (Rem) the gun will take one heck of a beating that it was not designed for. Just like if you took a drill bit and hogged out the little hole to three times it size, then the gun is liable not cycle at all.
At least this is my understanding of how they work.

Shawn

First off, I suspect your accuracy problems with the Remington are more likely related to your ammo than to the semi-auto action. I have owned three Remington auto-loaders, 2 rifles and a carbine, all in .30-06, and all would shoot selected handloads within an 1" or less at 100 yards....and that with 200-gr Nosler Partition bullets, which aren't exactly target fodder.



Secondly, though I would not personally block the gas port on a Remington semi-auto (I bought mine BECAUSE they were semi-auto), I do not believe it would damage the rifle or beat it up in any way. After all, with the gas port blocked, the gas will NOT cause the bolt to open...which is why you would have to cycle it by hand. With the bolt not opening, what is there for the gases to pound? Recoil may be very slightly higher, but certainly not much. Putting the relatively small weight of the bolt (compared to the weight of the whole rifle) into motion uses very little of the gas energy which is causing the recoil.



AC

Closing the gas port on a semi won't harm the gun in the least. Witness the M14's spindle valve and many other mil-spec rifles with similar gas system features.

As far as timing of the mechanism, any closed-bolt, locking breech small arm will have the bolt locked shut until pressures within drop to a safe level, allowing unlocking and ejection. The mechanism is subjected to the full recoil force while locked, so turning off the gas system won't result in any additional battering over normal operation.

Some folks attribute an accuracy gain to muzzle devices for a couple reasons. First is harmonics (no, I don't node why). The second is the ability of some devices to evacuate the bore of turbulent gasses that precede the bullet.

Probably more'n you asked for, huh? My apologies.

Redial

I would think that it would recoil slightly less since the momentum of the bolt removing to the rear is taken out of the recoil equation.

Either way, I agree with you that it is not a real smart thing to do and there really is no practical reason to do it in the first place.

Rick

There is slightly less "felt" recoil when the gas system is working (open) for two reasons...



1 - Puttng the bolt in motion makes the gas "work", which uses up gas energy making the bolt travel back 3 or so inches BEFORE the bolt strkes anything...Like putting anything else in motion in other than a vacuum, that gives the bolt slightly less kinetic energy (in momentum) at the end of its travel than was used to start it in motion. The loss is mainly in the form of heat (friction generated), but there is danged little energy lost, even though it is used to move not only the bolt, but also the mechanism between the bolt and the gas port.



2. The momentum of the bolt is absorbed by a spring at the end of the bolt's travel....which then releases that energy by pushing the bolt back closed (forward), whereas, with the bolt locked closed (gas port closed too) all that energy left over after moving the bullet and heating the barrel is spent in the form of recoil. The force of the recoil is mainly absorbed by the shooter, not a spring.



And, of course, the important point is not the distribution of energy, but the time over which it is applied. With the gas port open, the rifle recoils at a slightly slower speed, due to some of the energy being "siphoned" off to move the bolt and op rod and to in turn load up the bolt return spring. So there is not as much energy available to put the body of the rifle into recoil. Then the rifle first "hits" the shooter and then a small secondary force, which is the energy expended by the bolt at the end of its travel, hits both the spring and the shooter. So, although the shooter gets almost all the energy of the explosion, he gets it over a longer time period, which also decreases very slightly the felt sensation of recoil.



AC

Thanks for all the replies. With regards to:

M7400:
I am not having any functioning problems, either with factory loads or handloads. I even loaded some with IMR4350 before I read that slower powders were not recommended for gas semi-autos (because the pressure might not drop enough when the extractor tried to withdraw the cartridge case). The friend that had the heads jerked off the cases may have been loading with slow powder, because when I mentioned the problem with loading with slow powder, he said "you may have answered why mine jerks the heads off the cases". The other fellow I just met at the rifle range one time, and I was interested in his problem , because I might have the same sort of problem in the future with mine (plus I might be able to help him out and look smart at the same time ). I never thought to take a look at his extractor to see what kind of condition it might be in (if it was indeed still there). He had to remove the fired casing with his knife and said it came out hard, so it could be that the chamber was corroded or dirty. I have read that this is common with this model, but don't know if is due to the type of metal or due to lack of cleaning ( you need an offset brush) He had killed a deer with it the previous season, so he probably made sure that his first shot counted!

I have tried several powders at different weights and likewise with bullets. The reason I was interested in investigating blocking the gas port is that no load seemed to be much better or worse than any other. I do have a M7600 and it shows a marked preference for 140 gr. pointed bullets, and a fairly slow powder (don't remember right now, I am not at home).

I don't think that blocking the gas port would cause any stress on the action, because the bolt rotates into the locked position just like the pumpaction M7600. Maybe I mislead some people into thinking that I wanted to block the piston or other part of the mechanism; sorry if I misled you.

I no longer hunt, so I am just interested in getting the most accuracy out of it that I can. I have thought about taking some sort of flexible compound to put between the barrel and forend to dampen the vibrations. Has anyone done that? I have read that silicone rubber is hard on bluing.

SKS:
The same as for the M7400; I just want to see what the best accuracy I can get out of it. Again, I don't think that blocking the gas port would damage the action. The locking mechanism not rotary, but it is still locked until the bolt is forced back by the gas piston mechanism.

The technician at Centerfire Systems also recommended putting in a "buffer", which they sell, evidently just to reduce the stress on the action. I have read that the gas system is deliberately violent to ensure reliability under battle conditions. You (all ) may have seen the History Channel program where an American Officer had an AK-47 that he kept in a locker. About every three months he would take it out of the locker. It would be rusted shut. He would take it out to the range, stomp the bolt open with his boot, load it and proceed to fire off a clip!

The accuracy that I am getting with the SKS is with a Leepers scope mount that replaces the dust cover. I have found that it is secure only if I tighten the four screws tightly against the reciever, which mars it slightly. The problem is that I have to loosen these screws to remove the dust cover for cleaning and need to re-zero afterwards.
With a mount that fastened only to the receiver, I could remove the dust cover and not lose my zero.

I did read someplace that a gunsmith had installed a conventional guard screw in place of the frontsight/clamp and maybe at the back end of the action in place of the triggerguard/clamp there too, and got significant improvement.

Thanks again, Brady

The fella you met at the range probably was not correctly lubing his 7400. Despite what anyone may tell you, keeping these rifles lubed (both bolt and barrel extension) is an absolute necessity over the long haul. If they are operated without sufficient lubrication, they WILL wear excessively, gall, and yield exactly the kind of malfunction you describe,



That doesn't mean the action has to be constantly soaked in oil...various dry lubes such as Dri-Slide will do the job as well.



AC

I will start this off by stating that I am not now, nor have I ever been a reloader.

Having said that...it has been my experience that semi-auto firearms are normally far more picky when it comes to reloads than are other types of weapons.

Their systems are designed to operate within certain pressures and with certain bullet weights and when you start varying these you really need to know what you are doing if you want the weapon to function reliably and safely.

Obviously, this is true for any reloading but I believe that you have far less "wiggle-room" when reloading for semi-autos.

Rick

Rick -



I believe you are exactly correct. It is also true that powders have varying specific ranges of pressures in which they are each designed to burn for consistent results. (Consistent burning is necessary for top accuracy.) So, to get the best out of any particular powder, it is best to operate somewhere near the midpoint of the pressure range within which it is designed to burn. Not too high a pressure. nor too low. Either exess will result in erratic and/or incomplete powder burning, which in turn will lead to erratic and/or incomplete rifle action operation.



With my various Remington semi-autos and the old version of IMR-4350, IIRC, that proved to be about 53.5 grains behind the 200 gr. Nosler Partition in G.I. brass, which gave a velocity of just almost exactly 2,500 fps with my "lot(s)" of powder. That's not the flattest shooting load by any means, but it was the best for accuracy and rifle life, and would shoot end-wise through a moose. It was plenty good enough.



You are exactly correct...to get the best use of those guns, one has to select a loading which operates well within the design parameters of both the rifle and the powder being used.



Best wishes,



AC

That is the primary reason I don't reload!

It all sounds "greek" to me no matter how well it is explained so I just stay the hell away from it and shoot nothing but factory ammunition in all my firearms.

I have no argument with people who want to get into reloading but I really believe that it is a practice that should be approached very carefully with a great deal of understanding of the intended use... and with a huge amount of "adult supervision!"

Rick