Breech bolt lock on 12 ga pump not working properly?

[CyberRon]

I need some expert advice - AND some home testing results with other brands of 12 ga pump action shotguns.

Here is the problem:
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I had purchased a Savage Arms 12 ga home security shotgun after last Christmas and I don't think it is working properly. I noticed when firing 3" magnum loads (the gun is chambered for both 2 3/4 and 3" shells), that the breech is blowing open and ejecting the shell "automatically" without any conscious effort from me. I can cycle through 2 3/4 field loads - a total of 5 or 6 shots - consecutively without a hitch. If I load up 3" buckshot, turkey loads (5 shot magnums), or rifled slugs, I can only get one shot off at a time, and have to click the trigger or release the breech bolt lock and cycle in another shell for the second shot.

I have complained to their service department and they have responded by sending an additional two weapons, one after the other, but both have the same issue as the first, and they claim that the operation is "typical" for all major brands of pump action shotguns.

Basically I believe that the breech bolt on a pump action shotgun should never "blow open" from recoil, but this is what is happening with the Savage. I noticed it more on 3" Magnum loads (turkey loads, 00 buckshot, and rifled slugs) when firing with my hand on the fore-end (pump "handle").

I devised a test to check the breech lock with different guns and different loads. My test is simple and I did this with the 12 ga pump from Savage and my old 16 ga pump from Westernfield (built by Nobel Arms around 1950's).

I put a field load - 2 3/4" shell in the chamber. I them use one hand to hold the butt to my shoulder and then the other (fingertips only) I use just in front of the magazine port and behind the fore-end so that my hand is not touching the slide of the pump, or the slide handle.

In this manner, I shoot the shotgun. My 16 ga shoots and the breech bolt stays locked until released by pulling back on the slide handle (fore-end). I even tried this with a 2 3/4" rifled slug. This is how I believe it should work.

On the 12 ga gun(s), the field loads (low brass and power) blows the slide, breech bolt, and fore-end handle all the way to the end of travel - not quite ejecting the shell, but within a 1/4 in of doing so. With a 2 3/4" rifled slug fired in this manner, the shell blows back enough to eject. In both cases, when I cycle the pump action (pulling back the remainder of travel, and then forward again to lock the breech bolt, a new shell is not loaded in the chamber - no second shot.

With 3" magnum loads the breech blow-back is worse - I have to concentrate on holding the fore-end with pressure in the forward direction to prevent it from opening the breech block. If I hold it lightly, it will blow back and eject the spent shell, and after cycling the pump (back and then forward - to make sure it goes full cycle), it will not load another shell until I release the breech lock and cycle the action again.

I don't thing this is correct, but the Director of Savage Customer Service says that ALL manufactures have this "trait" (they won't call this anything but normal). They said that Remington, Winchesters, and other brands they tried on their range, all show this same behavior. He an engineer, and the head of their quality department conducted my tests on their range and said that the recoil pushing the breech open is "normal behavior".

I am no gunsmith, but this not only seems wrong, but dangerous. This third gun blows back worse than the first two. If the pressure is high enough (magnum loads), the potential is there for the chamber gases to escape through the breech rather than through the barrel (like they are supposed to).

I was wondering what your thoughts are on this. Am I right in assuming that the breech locking block should stay put until I physically move the fore-end slide back? This is what happens with the 16 ga. - even the rifled slug. I don't have another 12 ga to compare to.

As it stands, even if the breech blow-back is "normal", what is not is the fact that I can't get a second shot off since this cycle leaves me with an empty chamber for the second shot. So much for a "home defense or security" weapon! I don't think the perp (or the bear) will wait for me to load up another round for the follow-up shot!

I wish they had gun ranges in the stores - to "test drive" a gun before purchasing!!! It would save a lot of hassles.


PS I said I was no gunsmith, but I am a consulting product development engineer for an international technology company that makes high power equipment (motor drives - 500 to 50000 HP). I work with safety all the time. I used to work as a maintenance engineer in a steel mill, and after that worked in product development for people-mover trains (those unmanned units in a lot of airports). I am an excellent troubleshooter/problem solver with over 35 years experience, so I know how to devise reasonable tests for checking for defects. I also know a lot about physics, inertia, and other "control" type problems. I am not saying this to brag, but to buttress my logical tests and conclusions.

Ron

 

[Steve C]

Most likely the heavier recoil is moving the slide and your hand on it. Its most likely happening unconsciously so it appears to you that its "blowing' open. Its relatively common with pump actions for the bolt to open after firing due to the recoil and the shooters hand holding on to the slide applying pull. The heavier the load and the lighter the shotgun the slicker the action the more this happens.

If you want to test this, fire the weapon without holding on to the front slide. I'd bet it stays locked up.

 

[LJ-MosinFreak-Buck]

It doesn't take much for a fine working shotgun to unlock after firing. If your hand is on the slide (fore-end) just the affects from recoil going through your body are anough to move your hand enough to unlock the breech, and when it flies back it's because of the pressure still remaining in the barrel.

I wouldn't worry too much about it, because by that time, the pressure is already waaaayyyyy down there and won't hurt you. My Stevens Model 77F does the same thing, and it's a 20 ga. It'll only do it when I do exactly what you did in this test of yours. However, with a firm grip it wont, neither will it when you shoot it like a pistol.

 

[Virginian]

After pulling the trigger the bolt is unlocked, but the barrel and bolt are locked together until the handle comes to the rear. The gun recoils. Your shoulder stops the gun and the handle comes back. It's called inertia. If I shoot one handed, my Wingmaster will eject the empties all day. There is nothing wrong with your gun. That is how pump guns work.

 

[pikid89]

my 870 turkey gun does the exact same thing with 3" and 3.5"s.... pretty normal

 

[Hocka Louis]

I do see people fighting their guns have this happen. They are afraid of the recoil and pull hard on the forearm. When the gun fires and the action releases thee gun recoils, their body stops it, but the forearm wants to keep going through its momentum, your heavy hand is attached and recoiling, and you are pulling back to boot!

Yes, with a heavy load it might not open if you don't fight the recoil so much and kept your forward hand neutral or pushing forward. Pull the gun into your shoulder with the pistol hand. Hold it steady with the left -- firm, but don't fight it. Let your body move a little with the recoil -- again, stock pulled in tight from the (semi)pistol grip side.

 

[mnrivrat]

Without getting into a super lengthy explaination, I have dealt with a number of pump shotguns displaying what your complaint is about. I can tell you that I have worked on many Remington and Mossberg guns for this issue as well as a few other brands.

In all cases I was able to improve the gun to a significant degree. The issue is in the timing of the bolt release . Pump guns fire from a locked breech, but during the fall of the hammer the breech is unlocked so that the gun can be pumped to eject the empty and load another round.

If the mechanizim releases the bolt lock to early in the hammer stroke you will unlock the breech before all the pressure has cleared the barrel. This becomes more evident with heavier loads. Some designs, as in the Winchester speed pumps, they purposely did the earlier timing to speed up the process of pumping the action. So thereby you can see what the Savage rep was getting at.

It is not unusual, but on certain guns due to either design or by tolerances you can get the early blow back of the bolt. Due to tolerace stacking some guns can be quite severe in the blow back and cause the concern you have . The fix is to tune the system to prevent the earlier than desired bolt lock release. There are several ways to do just that depending on the design of the particular gun.

 

[CyberRon]

Thanks to all of you for your response. I did get a response back from Remington and they confirmed that older guns DID NOT have this issue.

Some of you missed the point - I didn't pull the fore-end back. Also the recoil (and inertia) would have pushed my arm and the slide mechanism forward (in relationship to the gun) while the rest of the gun was going backward with the recoil. (Not to get technical, but my inertia would have kept the arm and slide in a stationary position - the gun moving backward.)

Also my tests were performed with both guns with my hand off the fore-end altogether, so there was nothing but recoil force on the breech bolt forcing it open.

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My main concern now is the lack of a secondary shot.

mnrivrat ("Minnesota River Rat"?), you mentioned that this is timing related (which makes sense from what I am seeing) and can be "tuned out". As long as the gun design is sound (looks more like that from your feedback) then it comes down to timing - possibly due to stacked tolerances - as you suggest.

How would I adjust the "timing" of the trigger fall and the loading of the next shell? Does it require adjustments that can be made (screw tweeking), or filing and scraping to get the parts into tolerance?
Also, where do I get the schematics of the action? I'm pretty handy with mechanical devices, so if this is something that I can do easily, then I could try.

The gun is from Savage Arms, but is called a Stevens 350 pump (with both security and field barrels). The schematic would also go a long way in my understanding of the problem.

One thing that exacerbates the situation is that when I pump the gun, I have no visual indication of a loaded shell. There is no separate ejection port - it's on the bottom with the loading port (same opening). The only way of knowing that it didn't load is that the gun goes "click" instead of "bang" when I pull the trigger! This happens MOST of the time, but I had one field load shell (where I allowed the bolt to come back on it's own) that when cycled did put another round into the chamber. It surprised me when I pulled the trigger since I wasn't expecting it to fire (fortunately I was pointing downrange - as always - for safety).

Again - thanks all for your support. I'll keep you posted with a final solution.

 

[mnrivrat]

The Savage/Stevens M350 is a China copy of the old Ithaca Model 37 and should be near identical in design and build.

No screw to weak or easy adjustment built into the design. Adjustment require forming/bending and or filing to correct. On this design I think there is a lug on the right side of the hammer that controls the bolt lock arm. What you need to do is either increase the amount of contact on the front of the bolt lock arm to where it bears on the bolt slide to get breech lock up - or - delay the activation of the lock arm by adjusting the hammer lug that activates it.

Study the mechanism to see what you think. The lock arm being activated by hammer fall is the same one you activate by hand to unlock the breech when you want to cycle the action.

 

[CyberRon]

Where would I find a schematic? As I said, I'm no gunsmith...

The gun is new so I would only want it to clear it up in my mind what is happening. When I contact Savage again (after their 2 week hiatus) I will trade in for (yet) another gun - one they said they would hand select.

I'll make sure to add this additional insight into the mix. Hopefully I can get a good gun out of it. They said if the next one is still unsatisfactory, they will buy it back. Can't beat that - as long as I can find a good replacement. It is a good mix of ghost ring sights, 18.5 " barrel, and additional 26" field barrel.

Would like a "working" model though...

 

[mnrivrat]

Brownell's has a parts listing for the Model 37 with a diagram. The breech lock part (arm) is 92 . It is spring loaded by part 93 and the front of this part acts on the rear of the bolt carrier 79 to lock the breech. To unlock the breech the little bar at the bottom of part 92 can be pushed to rotate & bring the forend down manualy unlocking the gun . There is a lug on the right side of the hammer 88 (lugs doesn't show in this diagram)that acts on the part 92 to bring its forend down as the hammer rotates downward to unlock the breech when the gun is fired.

 

[Virginian]

I still contend that it is not blowing open. More like the recoil is throwing it open. Yes the initial inertia of the forend and your hand is forward against the recoil, but the recoil wins and then the inertia is rearward. You're trying to keep things forward and possibly short shucking the action is why you aren't loading a second shell in the chamber.
The action "lockup" is accomplished by the locking block in the bolt engaging the notch in the barrel extension or frame. Some raise, some rotate. The forearm slide lock has little to do with the bolt locking to the barrel to contain the shell. Even though the forearm slide release is activated by the trigger fall, the bolt is not unlocked until the forearm comes to the rear dropping the locking block or rotating the lugs. The bolt lock and recess are at a 90 degree angle so friction also keeps it in place under force from the shell going off. When the shell goes off, the recoil keeps the forend, action bar(s), and bolt carrier forward until you slow the recoil of the gun. By the time the forearm starts coming backwards unlocking the action the shot is long gone.
Most guns have an interrupter that prevents the hammer falling unless the action is locked shut. If you ever touched off a 12 gauge and the action wasn't locked and you truly got to experience real blowback, I wouldn't want to be in the vicinity.
I once had a guy who removed the side release trying to be able to pump faster, and it didn't really make any difference except his action kept falling open just handling the gun.
The Browning long recoil semi auto does "blowback", and the barrel and bolt are locked together until the whole works has recoiled to the rear against the force of the friction ring and the spring, and then the bolt unlocks from the barrel, at which time the barrel moves back forward. In that design as well by then the shot is long gone and the pressure has dropped by the time the bolt and barrel separate.
I sold guns for 25 years. I worked on a lot of them but I do not call myself a gunsmith because I have no artisanship in my whole body, but I am a pretty fair gun mechanic. A lot of newcomers to pump guns think they have a problem because the action on a lot of them will jump open after the shot from recoil. You are not alone; there are posts on every forum from people with the same concern that their pump guns are malfunctioning. The older smoother ones were worse about it than the new rougher ones.

 

[CyberRon]

Virginian
I have to respectfully disagree. If you saw the videos that I shot, you would have to change your opinion.

Like I said, I am not new to guns. I know how to handle a pump shotgun. My 16 ga doesn't even budge a fraction shooting a rifled slug single handed. This load is hotter than the low brass 12 ga in the Savage. If it was recoil alone, it wouldn't open AND pull the slide all the way open like it does.

The breech MUST be unlocking too soon, and the still pressurized chamber is causing the breech bolt to move backward. I call that blow-back. You can call it what you want - it is the gas pressure pushing the breech open.

If I can figure out what format to put the videos in, and how (and where) to upload them, I will attach a link. Then you can see for yourself. Until then, it's your opinion (with no evidence) versus my test results.

Until then....

 

[Virginian]

I'd like to see the videos. You can get in Guiness' for not only having the first malfunctioning pump, but three if I read you right. I have a feeling that if they had a malfunctioning design they would be addressing it in today's litigation environment.

 

[CyberRon]

"first malfunctioning pump" - Come on!!! You must either be joking or living beyond the cornfields in an extremely isolated hamlet somewhere!

If you search the internet (like I have - and just for a short time) I have turned up a lot of references to misfeeding pump action shotguns - a lot of them 870's (but probably because there are a lot of them out there). I have found a lot of cases where the breech bolt has come open slightly - but not to this extent (like I related with my brother's experience in duplicating my experiment). Also, I have heard of NO other cases where the next shell in the magazine failed to load after this - however, the misfeeds mentioned above may be related.

This Savage (Stevens) gun model was just introduced in 2010 - so it's possible that there are more out there that do this - but that the owners are not aware of this issue. I didn't become aware of the problem on my first gun until I tried shooting 3" rifled slugs out of it. It's quite possible that this is a bad design - or a bad manufacturing lot - that's what I intend to find out.

Also it takes time for a class-action lawsuit to be filed - let alone go to court - usually years. This gun has not been around that long. My whole point in bringing attention to it is that it appears to be "abnormal" and potentially dangerous.

Have you even TRIED to duplicate my testing - shooting a magnum round out of a pump with no hand on the fore-end to see how the gun reacts? - (not as a recommended shooting practice - but for experimental purposes)

Most people aren't as methodical at troubleshooting as I am - even in my own profession. Most would prefer to sit back and make guesses rather than gather facts. Others don't want to be bothered and just live with it. I am more proactive than that.

If there is anyone out there with this model? Have you tried shooting 3" magnum loads out of it? Any other similar experiences?

 

[Virginian]

Okay, sincere apologies, I mis-spoke. I have never seen a pump "blow" open. Shotshell pressures run above 7500 psi at the low end, and the pure force generated to the rear if the bolt was not locked on a 12 gauge would be in excess of 3,000 pounds. If your gun is truly blowing open I stand in awe of your physical prowess.
I don't have to shoot a magnum, my 870 will fully eject low powered loads shooting one handed.
I happen to be a professional troubleshooter by occupation for over 30 years, and I am more than a fair hand. I have tried my best to stay clear of lawyers and lawsuits, class action or otherwise, but I did stoop on occasion and have been paid for my time as an expert witness.
I wasn't kidding, I really would like to see the video. I own a Remington Wingmaster so small chance of buying a Savage/Stevens pump.

 

[CyberRon]

Fair enough.
I'm still not sure after all my research as to whether the breech bolt coming all the way open is a "problem" per se (seems to be mixed responses and opinions). My experience with the Westernfield 16 ga (also on the video) suggests that it is a problem. Maybe the design has changed in the last 50 years to allow the bolt to come open quicker - maybe this is "progress", but it doesn't seem right.

However, the fact that the next shell does not feed when this occurs, IS a problem. With low brass, I have never experienced this issue - unless allowing the breech bolt to come back on its own - this seems to be the key here. With magnums, it takes a concentrated effort to hold force on the fore-end to prevent this from occurring - not something done "in the heat of battle" when a second shot is needed.

I did find an allusion to this problem on an earlier model Mossberg (in Gun-Tests.com - a subscription forum). It was stated that:

"We previously had tested similar versions of two of these guns in the April 1997
issue. The Winchester Defender in wood/blued finish won a two-way test with the
wood/blued Mossberg 500 mainly because the latter showed some feeding
problems—a fatal flaw in a self-defense unit."

I am experiencing a similar issue with my Savage. I am working on the video - my first attempt caused the program to crash. I want to finish it and upload it before next Monday (that's when Savage gets off the two week shutdown) in order to show the CS director. I don't think he fully understands - or believes - the issue.

I will keep you posted. When the video is uploaded (I need to edit and combine 5 videos shot with my camera) I will post a link here. I'll have to contact my guru brother-in-law as to where to post it and how. I'm not a big web designer/user (other than for research). Been too busy the past week to work on it after the first botched attempt at editing.

As for experience - I spent some years out of college (BSEE 1975) in the steel mill - as a troubleshooter/designer, then as a Maintenance Electrical Engineer, before moving into the transportation industry (people-movers - Atlanta and Sea-Tac airports) as a troubleshooter/designer (safety-critical trainlines and door/stop control designs) for a couple years, and have been with the same company now for going on 29 years (4 different owners) now as a consulting control engineer for a large manufacturer of MV motor drives (500 to 50,000 HP). I have been involved heavily in investigating and resolving safety, control, and application issues for the oil and gas, power generation, sub-sea, and other industries. You could say that I am an expert in getting at root cause issues to problems (I then go on to fix them as well). This is not to boast - but for perspective. Haven't been called to court as an expert witness (don't really want to - but there were opportunities) but my insight affects jobs and sites that count down-time in the $millions per hour range of lost productivity. When a critical situation arises, I am always sought for involvement.

 

[mnrivrat]

If the mechanizim releases the bolt lock to early in the hammer stroke you will unlock the breech before all the pressure has cleared the barrel.

and/or ,all the recoil inertia has dissapated .

There ! I fixed it . It realy doesn't make any difference which one has the most effect, or any effect , the fix is the same. Modification of the slide latch release to delay release of the lock up is the only cure. The slide lock holds the bolt foward while the bolt lock being engaged takes the breech pressure. The bolt lock is unlocked by unlocking the slide lock to allow the bolt to travel rearward which unlocks the bolt lock.

As far as what's normal - no doubt that there is a "range" within this issue that effects pump guns . That range depends on the design and the tolerances of the parts contact in a given gun.

Most pump shotguns are built such that they will remain relatively closed no matter the magnum shells. Some will remain completely closed and some will crack open a little. Most should not fly to a complete open position.

Winchester used this issue to some degree to build their "Speed Pump" shotguns. The angle on the flat of their hammer pivot pin being tuned to somewhat early release of the slide lock to use this as an assist for speeding up the pump stroke. No particular harm caused by this.

Most pump shotgun users however find this a bit unsettling and different than what they are used to. On a specific design like the Remingtom 870, Mossberg 500, Ithaca 37 the ones that significantly open up in this manner are in fact different than what they were designed, and different than normal.

If the 350 gun was designed to function simular to the Winchester Speed Pumps then the opening up is relatively normal. If it was suppose to be near identical to the Ithaca 37 function, then their guns may need a little tweaking .

 

[Virginian]

However, the fact that the next shell does not feed when this occurs, IS a problem.

I would certainly agree 100% with that part.
I have the edge on you experience wise... barely. BSME 1973. PE since 1978. Been in maintenance, engineering, and plant management in pulp and paper, steel, and transformer manufacturing, and was a consultant for a while - bought a briefcase and worked more than 50 miles from home.
Now involved in making cellulosic alcohol for BP. Took it on on a lark and it has been great. Had to do an RCFA just today. Interesting in that it is a totally new industry with unique equipment, so there is no where to go for help, and zero experience. Proving an old dog can learn some new tricks though.

 

[RX-178]

I've experienced this with multiple guns, and multiple high-recoil loads. Slugs, etc.

In the shotgun episode on my show (check sigline), you can even see it happening to me when I fire a Black Magic Magnum slug.

And I've also shouldered the gun with one hand (just holding it by the grip and without a hand on the forend), fired off a slug, and had it automatically eject the shell too.

I'm POSITIVE that this is normal behaviour.

 

[barnetmill]

I use to have a very old stevens shotgun that if fired w/o holding the forearm upon firing it would partially unlock. When hand was on the forearm this did not happen. It was due to the recoil causing the forearm to come back with enough force to unlock the action. There are some semiauto shotguns that function due to part of bolt recoiling free of the rest of the gun that unlock the bolt and function the gun. See: http://en.wikipedia.org/wiki/Recoil_operation#Inertia_operation see diagram: Block diagram of inertia operation cycle
Perhaps you might gain some insight as to what is happening.

Also have someone else with a lot of pumpgun experience fire the gun and see if they have the same experience.

 

[CyberRon]

Here it is - Finally! I was able to get the video together edited, and converted for YouTube.

This is the comparison between my 60 year-old Westernfield 16 ga (the way I think a pump-action shotgun SHOULD work) and the new Stevens 350 (Savage Arms) tactical shotgun.

I could live with the breech opening (although after seeing other videos recently, still think it excessive on this gun), BUT I cannot live with the failure to feed the second round!

Check it out at http://www.youtube.com/watch?v=c-dNUZIGylY

Now you can comment on the real facts!

 

[Virginian]

Nope, that's definitely not blowback in my opinion. You'd never be able to hold on to the fore end at all if it was truly blowing back.
Obviously there is something wrong with the feed mechanism in that it is not releasing the next round out of the magazine when the fore end comes to the rear quickly.

 

[mnrivrat]

Nope, that's definitely not blowback in my opinion. You'd never be able to hold on to the fore end at all if it was truly blowing back.

I don't think you are accounting for the dissipated pressure at the time the bolt comes out of its locked position. Chamber pressure at the time of ignition, when the bolt is locked may be 15K , but that's mostly absorbed by the breech bolt lock.

We're not talking about a straight blow back gun , it is a locked breech mechanism . The question is in the timing of the bolt unlocking and how much pressure is left at that point , or how much recoil inertia is left at that point.

 

[barnetmill]

The reason the gun is not feeding a second shot is that the shells in magazine tube are not recoiling to the rear at the same time as the gun. The shells in the tube mag will travel relatively a little forward in the magazine tube until the spring and follower stop them and push them to the rear. The gun is unlocking due to the recoil impulse of the forearm and perhaps other parts of the mechanism that are unlocking the gun prior to shells in magazine being in a position to feed.
I and most others would have no problem with that gun. Sir that model shotgun is not for you. Try some other 3 inch model 12 ga's and see if they work better for you. Not all people hold guns the same way and there are some that cannot get for example many autoloading pistols to function due their handgrip. This is the first time I have seen this with a pumpgun. What ever the cause, it is happening to you and that is what is important.