How Was It Done -- Locking Cut?

[ThompsonCrazy]

Not only impossible but defeat the addition of the felt oiler too!

 

TC

[laurencen]

physics would lead me to believe the lock would slow it down but not fully prevent movement, having the larger radius in the slot would allow the bolt to retract quicker???

[buzz]

the principle of the blish lock is that the bronze rigidly sticks to the steel until the pressure drops

 

then it lets go and the bolt can retract freely

 

the lock is supposed to replace a mechanical lock, such as the way the bolt and barrel on a 1911 are locked together until the gun recoils enough for the link to draw the rear of the barrel downward and pull it free of the ridges on the bolt

 

or the way the turnbolt on a garand is locked until the bullet passes the gas port at the end of the barrel and makes the op-rod unlock the bolt.

 

 

it's a very clever design but it seems expensive and unnecessary for such a low pressure round.

 

if they would have started off with the M1 mechanism, they could have sold a lot more guns, at a lower cost

 

even 9mm subguns use a straight blowback operation, and that cartridge is a 35,000 psi round

[laurencen]

I understand the process but if you put a wooden dowel (soft wood) down the barrel of the 1928 and apply force there is about 1/2 inch movement before the lock clears the ramp and the only resistance then is the recoil spring, with the larger radius as in the pictures I would expect the movement to be considerably less as the lock almost instantly clears the ramp,

[mnshooter]

Very interesting photos. The rear ramp looks like a continuous curve, with no flat spot for the lock to "adhere" to.

Measured rates of fire can vary by 5% or so, in my limited experience. Same ammo, same magazine.

The big deal with the Blish (and their expensive WH rebuild) is how much it effects rear impact of the bolt against the receiver. If Reconbob ever gets time to finish his ballistic pendulum project, that should answer the question.

A more complicated test using pressure sensors and systems to time the actuator travel would likely only confirm whatever is learned from Bobs project.

Edited November 20, 2014 by mnshooter

[reconbob]

I have decided to ditch the pendulum and instead have a sliding weight on a rail. Picture a

a weight touching the back of the receiver, struck by a transfer block which has been struck by the

bolt when the bolt hits the back of the receiver - there will be no buffer. The weight will slide on the

rail and stop when it runs out of energy. The distance the block has moved along the rail can be exactly

measured. The weight of the block can be exactly measured.

The M1921 and M1928A1 bolt assemblies can be measured, then both with an H-lock from which

the "wings" have been removed. Of course, the wingless H-lock will have to be weighed and compared

to a standard lock.

I believe the rear of the receiver - and for this I am figuring a receiver that has a flat rear face - not

contoured like an M1921/28 or angled like an M1/M1A1 - can be rigged in such a way that M1 and

M1A1 bolts can be used as well. We don't need the buffer pilot to extend thru the back of the receiver,

but only to act as a pilot on the inside. So M1928A1, M1, and M1A1 can be fired in the same receiver

with the same recoil spring.

We should be able to get the recoil force for H-lock vs. no H-lock, and for all of the different bolt

assemblies. I was not planning on getting deep into the calculus for all this but just looking at how

far the weight slides on the rail. However, I can certainly provide all of the data for anyone who wants

to really get into it.

Unfortunately (for this project) I have been very busy so I don't have much "free" time. But I am

always thinking about it...

 

Bob

[laurencen]

Bob, could you not clamp the gun in place and use the inertia of the actuator knob,

[reconbob]

I am not sure how I would do that. The thing I am trying to determine is the force with which

the various bolts strike the back of the receiver. Now that I think about it, what relationship, if any,

is there between the rate of fire, and the force of the bolt striking the receiver?

I would think that at a higher rate of fire the bolt is moving faster and therefore would be striking

the back of the receiver harder...but maybe not.

I have no way of measuring rate of fire. It would be interesting to see how different buffers and

recoil springs (new, used, Wolff) increase or decrease the rate of fire.

For example - does a "hard" buffer like the standard military red fiber disk fire faster or slower

than a "soft" buffer like the one's sold by PK?

 

Bob

[gunhistorian]

As y'all know, this subject is being discussed in the '21 rate of fire thread, but I wanted to mention something to note about the so-called "adhesion principle" or the Blish principle and that is dissimilar metals are supposedly required - hence the bronze H piece rather than a steel H piece. It appears to give just a slight delay in the blowback operation to the tune of a little over 200 rounds per minute. If I did the math correctly (based on the figures given in the above mentioned thread), the Blish lock provides about an 18% reduction in the rate of fire. (NOTE: I was advised by my high school math teacher to NEVER take any additional math courses. . .so beware of the accuracy of my figgerin'.) That doesn't seem to be very "efficient" when comparing the cost in materials, machining, etc. as opposed to simply increasing the weight of the bolt and/or monkeying with the recoil spring. But, then again, we are talking about what might have been "the Golden Age" of automatic weapon design where new ideas were tried out. Besides, the '21 and '28 Thompsons simply "look" neat! Almost elegant. They have the same type of mechanical beauty that I associate with the Johnson rifle and l.m.g.s. Just MHO.

[reconbob]

I think it is safe to say that Auto-ordnance had the Blish lock on the brain. The

story is laid out in the Hill book. The intent of Auto-Ordnance was to design and

manufacture firearms using the Blish principle. When the high powered rifles failed

they turned their attention to the .45 ACP.

 

Bob

[gunhistorian]

There is no question that Thompson wanted to exploit the Blish principle. Can't remember if he (J.T. Thompson) had money tied up in patent rights or other "arrangement" with Blish, but sometimes gun designers get really hung up on one idea and just won't let it go. Sometimes it works, sometimes it works only a little, sometimes it doesn't work at all. . .and years are invested in trying to make something work! Reconbob mentioned about the effect of the recoiling bolt on the rear of the receiver (if I interpreted that right -- haven't had enough coffee just yet!) and I am wondering if a part of the answer lies in the failure of the aluminum receiver guns. I can't remember how much detail Hill went into on these guns in the big book, but remember from his first little book written, with someone else -- Cannon? was that the co-author?, that there was a problem with the aluminum receivers. It might have been a "stretching" problem which probably would indicate some significant force being applied to the rear of the receiver (bolt battering?). I don't know if the buffer (and maybe even the oiler) spreads the recoil force sufficiently to prevent this stretching (thus demonstrating a elwrong choice of material) or if there is some bolt battering. Even though the aluminum used was probably not as tough or resistant as some of the alloys we have today, I have to wonder why the TSMG would demonstrate this problem while the comparatively cheap designs -- even of the day: the Hyde and the more "contemporary" Reising -- didn't need that massive block of steel for a receiver. Better yet, consider the bolt forces exerted on the M3 Grease Gun, the Sten, the Uzi, the MAC, all with relatively thin metal receiver rears. . . There is something that I'm missing here but it is too early for me to figure it out! LOL

[jim c 351]

GH,

The Reising used a delayed blowback, Blish like lock, in order to get by with lighter recoiling parts.

M3A1 SMGs and Uzis have been know to crack at the rear of the receiver.

Jim C

[james m]

My local gun club has a Model 28 that they used as a rental. They finish machined a partial receiver from Philadelphia Ordnance but didn't attempt to machine the Blish lock slots. The cut the ears off the Blish lock and basically ran it as a straight blowback gun for untold thousands of rounds.

The receiver never cracked but it was tough on actuators and I replaced more then one while servicing the gun. I tried multiple times to get them to send the receiver back and get the slots machined but to no avail.

Jim

[buzz]

don't forget that the purpose of the blish lock is to hold the bolt closed until the chamber pressure drops to a safe level

 

the fact that the bolt operation is slower is a side effect of the fact that the pressure is lower

 

if all they were trying to do is control the battering of the receiver, they could have accomplished that with a whole lot less work than making that fancy blish lock

[Paladin601]

Buzz, they finally did. We are a strange people we tend to like to complicate things

[buzz]

Can a Colt owner please do us a favor and post up pictures of the original Colt Blish slots?

 

Sure would be appreciated

Edited November 26, 2014 by buzz

[Banjo]

While we wait for Colt pics I have a few more of my early Savage that show a better view of the Blish Lock slots. You can see that even though they are rounded there seems to be enough of a flat spot for the lock to do its job. I would have posted these earlier in the thread but I was (maybe still) having issues with my computer. I can post or share Photobucket links the world over but when I try and post here, not so much. If they do not show up below, I will request another board members help.

 

 

 

 

 

[mnshooter]

While we wait for Colt pics I have a few more of my early Savage that show a better view of the Blish Lock slots. You can see that even though they are rounded there seems to be enough of a flat spot for the lock to do its job. I would have posted these earlier in the thread but I was (maybe still) having issues with my computer. I can post or share Photobucket links the world over but when I try and post here, not so much. If they do not show up below, I will request another board members help.

 

 

Lock Slots I.jpgLock Slots II.jpgLock Slots III.jpgLock Slots IV.jpg

You are pointing out a flat spot that has nothing to do with the lock function.

It is a bevel put there just to make it easier to drop the lock in during assembly.

It is found on all Colts and wartime 28 production; nice but not essential.

West Hurleys and some new production sample receivers do not have this at all.

 

But, thanks for your effort and participation on the board.

Edited December 1, 2014 by mnshooter

[ThompsonCrazy]

mn,

I think he is pointing out the right parts of the blish ramps. I don't think he is referring to the bevels but pointing out that the ramps are more radiused where some of the later have a complete flat ramp and angled intersection with the vertical rail inside the receiver. I though his concern was that due to this gradual radius and not a distinct flat that the lock function/principle could be compromised.

 

I could be way off but I thought that's what he was going after.

 

TC

[Banjo]

Sorry my first photo post and they are somewhat unclear. ThompsonCrazy is correct, I was going for the flat spot a little further down the slot. It just looked so rounded compared to drawings and other photographs I'd seen. I found it odd. Sorry about the confusion mnshooter my arrows could have been better placed.

[mnshooter]

Sorry my first photo post and they are somewhat unclear. ThompsonCrazy is correct, I was going for the flat spot a little further down the slot. It just looked so rounded compared to drawings and other photographs I'd seen. I found it odd. Sorry about the confusion mnshooter my arrows could have been better placed.

Knowing for sure where to look, it is clear what flat area you're referring to.

I have a West Hurley with nearly the identical pattern, and have wondered if that area is all that is really needed for the full benefit of the Blish effect principle. But, assuming they're parallel, square to the bolt, etc., the other important dimension (as mentioned in PKs excellent pinned post) is the distance the seated bolt assembly can move back and forth.

Edited December 1, 2014 by mnshooter