Drop-free bolt incomplete?

[Lollygagger]

OKAY, listen up -this is going to be the first time most of you have really heard this:

As Marcus and I (and others) might have noted, there is some small issues with the "drop-free" bolt mod regarding feed.

Marcus has a disclaimer/info about it on his site. I note he has shown a pic of a bolt he has done some work to improve it in this matter.

I was thinking about this while out-of-town recently, where I store my firearms. So, I looked over some of my different military (semi-auto) rifle bolts pretty well.

Here is what I came to the conclusion about the matter -the SKS bolt mod for use of AK mags in the SKS "D"/"M" guns, adopted in standard rifles because of the drop-free feature is incomplete in it's modification -it was made as simple as possible, it seems. But incomplete in what needs/should have been done for the best function.

The modified SKS bolt just has the lower sides milled a bit -and, the "D"/"M" bolt bottoms are milled a little. It was kept simple.

There is alot of complex curves that would be best incorporated into it -a experienced Dremel guy should be able to do this.

A good example of what needs to be done can be seen in a FN/FAL bolt -which, BTW, uses the same locking system as a SKS. It, of course, is for a .308 round...the SKS bolt would have to be sized accordingly for it's cartridge length.

The FN/FAL bolt:


Bottom -note narrow ridge & it's curvature.

Another:

http://estore.websitepros.com/stores/832529/catalog/Bolt%20Carrier%20set%20inch%20used_thumb.JPG

Another (other side):

http://i39.photobucket.com/albums/e169/panzermk2/L1A1%20sale%20pics/P9050046.jpg

From the front:



While all of the other military bolts gave indications similar, I think the FN/FAL is most instructive for us SKS owners.

So, when I get around to it...plan to shortly, I will start to mimic this in my SKS drop-free bolts. I will, of course, do just one first & test it. I have little doubt it, despite the trouble and effort involved, *is* the best way to go.

Tapco, since they mfg'd a complete new bolt -should have figured this out in the process. They didn't -and it may have impaired their products marketability.

I suspected this was a issue and consideration to be made -took long enough for me to get to it...but I'm not in the business. Sorry 'bout that.

LG (My disclaimer: If this makes no sense to ya' -you don't need to be trying to do it.)

P.S -I  guess I have to do it and report back now, huh?

[martin08]

Did you get vibes about this or something?

I was contemplating PMing you about this exact situation.  Every third time or so that I load my mag into the well with the bolt closed, the first round will eject when I charge the handle.  It happens when the round hits the bottom of the bolt and pushes it out of the alignment from under the lip.

so.... here we go again!

[harleyrider]

So LG, specifically what is the problem with the bolt mod as done up till now (both sides straight milled)?

HR

[bill larry]

Weird. All three of the ones I did the bolt mod on have still NEVER had a feed issue. However, I removed the bolts from the carriers many times while I was grinding the bolts to check the fit of the tapco mags. I wonder if this may make a difference?

[Lollygagger]

This problem can be confusing, as maybe it takes place -maybe not...

Because, it is due to a FLAT bolt bottom contacting the cartridge when the mag is set (in the action with the bolt forward)...

Depressing a ROUND case, on top of a ROUND case...

Contained in place (before the bolt starts pushing it down into the mag when placed in the action) by a CURVED feed lip -that has OPEN space in the mag between each...that the cartridge can "roll" out of battery into, & "pop up" & out.

So, IT'S A BALANCING ACT -either it happens to balance -or, it has the flat FORCE IT TO ROLL OUT OF BATTERY to the lesser resistance (per power mechanics/physics 101). It is, at best, a tenuous situation -meaning that even if it seems to not be a current problem, there is not much to assume it won't be...mechanically, IT IS "ON THE LINE" of being a problem.

If you need a demonstration of this, walk around with two hard flat surfaces with marbles held by being forced between them -you'll get the idea after a while.

Get it?

LG (no...rubber cement & bubble gum will not maybe fix this)

[Lollygagger]

Did you get vibes about this or something?

You'll note I posted this AFTER a nap, after sleeping...

Where I somehow put together conclusions in my noodle while in dreamland after prior "on hands" observations. It's that weird habit of mine -it is more like something that demands my sleep attention.

LG (do other people do this?)

[ApexCypher]

I do some of my best thinking while I sleep....if that makes any since at all????

[martin08]

I'm going to work on one when I get a chance.

Like I said, I was getting a round popped out of the mag on the Drop-free insertion.  It just won't be today, as I'm going to my sister's big Five-O birthday party (which means I'm next in line!), but I will get it done before I'm too old!

[martin08]

Just another observation, LG.

You do mean to be referring to drop-free mag "insertion" and not "feed", don't you?

Because once a mag is inserted, the feed function should mimic the internal factory mag, and the feed has proven itself to be adequately reliable.  And I don't think it would be appropriate to pay a visit to Sergei at graveside to discuss his design flaw and initiate a recall on hundreds of millions of carbines??????   

Or maybe you do! 

But for my continued involvement in this intriguing observation, my concern will be for Drop-free mag insertion only.  That one out of twenty rounds that pops out unfired when I charge the handle is taking away 5% of my range fun, or it may be the deciding factor on life and death when 20 BG's show up instead of the standard 19. 

 

[forrestcav]

I think I see where your going with this. your kinda narrowing and rounding the bottom of the bolt instead of the wide flat bolt.
so does this mean the whiz bang mag release is on the back burner again?

[1mlt]

Joe, no it isn't on the back burner. If you have done the bolt mod already, the hard part is over. Take your Dremel tool using the reddish sanding drum and cut a 45d angel on the odd feed side of the bolt ONLY. You MUST stay behind the bolt face. See pix below. They look similar to LG's FAL bolt. It does not happen on the even side. As LG stated, I posted a disclaimer at my website and I even included instructions how to do this with the adapter install stuff. Below is a picture of my "extra" modified bolt. You can see were the sharp "edge" of the bolt has been "softened" by angle cutting. Notice the other side is still square at the edge. If you close the bolt and look into the mag well you can clearly see there is more clearance on the even side than the odd side with the edge of the bolt bottom to the side of the receiver. What happens is the bullet nose hits (sometimes) on the bolt bottom, is pushed inward toward the center of the mag, moving the front of the bullet out from under the feed lip and it goes "pop" out and is released to lay free on the top of the mag, preventing the mag from being latched. If you don't want to do the "angle" cut, you can ONLY load even numbers of rounds. It may or may NOT happen with your setup. But this is the easy fix. Marcus

[keymastr5912]

i understand exactly what you guys are talking about, but i have performed the standard bolt mod on two bolts and have not had this problem with well over 1000 rds through both. i normally store my loaded mags with 15-17 rds in them. if mine aint broke i aint gonna fix em. it looks like a pretty simple fix if i happen to run into this in the future. [ i had never even heard of this problem before reading this]. right when i think i have this stuff all figured out you guys throw something else at me. thanx

[1mlt]

i understand exactly what you guys are talking about, but i have performed the standard bolt mod on two bolts and have not had this problem with well over 1000 rds through both. i normally store my loaded mags with 15-17 rds in them. if mine aint broke i aint gonna fix em. it looks like a pretty simple fix if i happen to run into this in the future. [ i had never even heard of this problem before reading this]. right when i think i have this stuff all figured out you guys throw something else at me. thanx

It doesn't manifest itself very often using the Tapco duckbill mags as the loading angle is pretty flat when you go to latch up the mag. When you do my mag adapter mod, the mag approach angle is slightly steeper initially and the bullet tip is perhaps a few hundreds closer to the bolt bottom. In the gun world that can be a mile when clearances are measures in thousands. If the tip hits the bolt the bullet will "roll" inward and "pop" out as described above. Softening the edge of the bolt eliminates this from happening as the bullet tip now "clears' the bolt bottom. Marcus

[Lollygagger]

Just another observation, LG.

You do mean to be referring to drop-free mag "insertion" and not "feed", don't you?

Because once a mag is inserted, the feed function should mimic the internal factory mag, and the feed has proven itself to be adequately reliable.  And I don't think it would be appropriate to pay a visit to Sergei at graveside to discuss his design flaw and initiate a recall on hundreds of millions of carbines??????  

Or maybe you do! 

But for my continued involvement in this intriguing observation, my concern will be for Drop-free mag insertion only.  That one out of twenty rounds that pops out unfired when I charge the handle is taking away 5% of my range fun, or it may be the deciding factor on life and death when 20 BG's show up instead of the standard 19.  
 

I guess I meant both -I consider a round popping out of the mag and being loose in the action, a feed problem as well.

Just terminology.

LG

[Lollygagger]

Yeah...

That is the bolt pic from Marcus is what is basically needed...

Even if he used a HATCHET to do it, instead of a Dremel!

I know it was a experiement/prototype thing.

The FN/FAL bolt pretty much has the relief cut on both sides...despite it appearing critical only on the RIGHT side.

The rotating bolts, seem to do this only on the RIGHT side, with a milled angle cut that removes any material from contacting cartridges at the point...where it also rotates to a stop when locking. You see this on M14 & M1 weapons.

With a AK, also a rotating bolt, this is done NOT to the small bolt piece -but the right side of the carrier, serving the same purpose.

Because of the "dropping" bolt system on the SKS, I used the FN/FAL bolt to make observations because it locks up the same...as the french MAS semi-auto rifles do (which I did not have a sample of available at the time).

So. I'll get around to re-working one, testing it and getting a report/pics up here...which Marcus has actually effectively done.

My goal was to give you guys a "heads up" on something important that I did not think was commonly aware. It is now.

IN RETROSPECT:

I don't think you can make worthwhile comparisions as to why Simonov would have not done this in his original design...we have taken the SKS some ways in regard to detachable feed devices from that original design.

What was simple and workable with a low cap fixed box magazine that had the bolt trap the feed lips thru it's centerline -does not translate to modification to a modern system that is detachable regardless of the bolt condition...like any other modern military rifle.

While it is certainly in reason that a user might elect to remain with the original system (works fine) -the "I would never change anything on ma purfuct gun" & "I'm kung-fu with stripper clips" crowd...are missing the fact that there is NO downside issues (other than some cost & effort) -the gun is reversable to it's original functioning system, and, pretty quickly so.

I'll stop with my musings. Later, LG