[from a thread of mine elsewhere, that died out. Reposted here FYI]
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Has anyone done a scratchbuild with a roller locked bolt?
I've been looking at a book that covers the Enfield EM-1 prototype from the 1950s. It was a gas operated, roller locked setup. The bolt consisted of a tube that held two rollers, looks like they were about 5/16 x 3/8", and an inner wossname, firing pin carrier, with a wedge face to force the rollers out. The firing pin rode inside the carrier.
The gas system moved the firing pin carrier, which moved the outer sleeve. It looks like it was a very long stroke gas system.
From the drawings, it looked like about 1/3 of the roller was in the front trunnion when locked, so when the firing pin carrier moved back, the rollers just popped out of the trunnion of their own accord. There's no indication of anything like the fancy ramp angles a G3 or CETME uses. The trunnion otherwise looked pretty much like a G3 part.
The bolt tube carried the entire locking load; the carrier just kept the rollers pushed out. When in battery, the rollers were on a perpendicular surface on the carrier, so the camming action from the gas load just tried to pinch the bolt carrier; there was no angularity to move anything back.
The length of the carrier nose and the firing pin protrusion appear to be designed so that there's no chance of a firing pin strike until the bolt is fully locked.
I've been pondering this setup for a couple of weeks now. It looks like it would be easier to build than a turnbolt setup. The "lug" area of the bolt sleeve looks reasonable. You can buy proper roller bearing rollers from several sources; they're usually 8620 alloy or something similar.
The gas load on the locked bolt will try to spread the ears on the trunnion a bit. Theoretically, enough spread and you could blow the bolt right out. I found a G3 trunnion on GB for $15 to take a look at; it isn't here yet. The G3 is a roller-delayed setup instead of roller-locked, but I'd like to see how beefy they felt they needed to go with a .308.
Anyway, has anyone done this from scratch? Results? Comments?
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I found "Full Circle: A Treatise on Roller Locking" by R. Blake Stevens while searching for roller locking stuff on the web. The going price seems to be $80-ish, so I logged onto the local library's web site and ordered it via Inter-Library Loan. Hopefully some library out there has a copy to share. If not, I guess I'll buy it.
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10-4 I'm hoping it has some real information and not just pictures of guns that happened to use the system...
The EM-1 used an ordinary fixed barrel. I'm starting to get the impression that it was, if not unique, an unusual implementation of roller locking.
At the moment the only detailed roller locking information I have is the pictures in the book "EM-2 Concept and Design" by Dugelby, which has to go back to the library tomorrow. The EM-1 prototypes were roller locked, the EM-2 used lever locks. Doable, but way more complex to build than rollers. There was no explanation as to why they picked the EM-2 over the EM-1, but there was considerable politics involved. And as far as manufacture... the Brits were never afraid of complexity. Where an American car would join two parts together with a single coarse-thread bolt, a British car would use three fine-thread studs with flat washers, lock washers, castle nuts, and cotter pins...
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I discovered those while googling for roller stuff. I've seen some pictures of the bolt assembly, but just external pictures of the receivers. If you can point me to some detailed views I'd sure like to see them.
I'm guessing the backs of the flaps are shaped to cam out of their recesses, and do so when [a locking wedge?] releases them. I've managed to sketch a few designs that might work, but they would all be impossible to machine without building customer machinery to cut the flap recesses. Obviously the Russians and Germans had a better idea...
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The G3 trunnion showed up today. It's sitting on the desk next to a Yugo AK trunnion. They're about the same size, but the Yugo trunnion is noticeably beefier. They both use barrels of similar diameter, and the G3 barrel is pinned in place like (most) AKs.
The roller ramp area in the G3 is contained within "wings" off the back of the trunnion. They're joined by a flat web across the bottom. I guess you could also look at it as a 3/4 circle opened at the top; either way, the tops of the wings are unsupported.
There are marks from the rollers. They're much smaller than I expected.
There are machining marks on the outside of the G3 trunnion. I can't tell if it started off as an investment casting or bar stock, but the OD was finished off with dull tools. The roller ramps and inside areas of the trunnion are very smooth, apparently ground. The "wings" are tall enough to handle the roller tracks and sufficient overtravel for a small grinding wheel to finish the ramp area.
I *think* I see a pair of Rockwell dimples on the back of the right wing.
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The library emailed me back; that book is not available by Inter-Library Loan.
I've added it to the "discretionary budget" list, but it's pretty far down, considering the bits I need to finish various gun projects.
I'm still going to keep an eye out for roller locking stuff, though. It seems like such an elegant solution...
---
Has anyone done a scratchbuild with a roller locked bolt?
I've been looking at a book that covers the Enfield EM-1 prototype from the 1950s. It was a gas operated, roller locked setup. The bolt consisted of a tube that held two rollers, looks like they were about 5/16 x 3/8", and an inner wossname, firing pin carrier, with a wedge face to force the rollers out. The firing pin rode inside the carrier.
The gas system moved the firing pin carrier, which moved the outer sleeve. It looks like it was a very long stroke gas system.
From the drawings, it looked like about 1/3 of the roller was in the front trunnion when locked, so when the firing pin carrier moved back, the rollers just popped out of the trunnion of their own accord. There's no indication of anything like the fancy ramp angles a G3 or CETME uses. The trunnion otherwise looked pretty much like a G3 part.
The bolt tube carried the entire locking load; the carrier just kept the rollers pushed out. When in battery, the rollers were on a perpendicular surface on the carrier, so the camming action from the gas load just tried to pinch the bolt carrier; there was no angularity to move anything back.
The length of the carrier nose and the firing pin protrusion appear to be designed so that there's no chance of a firing pin strike until the bolt is fully locked.
I've been pondering this setup for a couple of weeks now. It looks like it would be easier to build than a turnbolt setup. The "lug" area of the bolt sleeve looks reasonable. You can buy proper roller bearing rollers from several sources; they're usually 8620 alloy or something similar.
The gas load on the locked bolt will try to spread the ears on the trunnion a bit. Theoretically, enough spread and you could blow the bolt right out. I found a G3 trunnion on GB for $15 to take a look at; it isn't here yet. The G3 is a roller-delayed setup instead of roller-locked, but I'd like to see how beefy they felt they needed to go with a .308.
Anyway, has anyone done this from scratch? Results? Comments?
---
I found "Full Circle: A Treatise on Roller Locking" by R. Blake Stevens while searching for roller locking stuff on the web. The going price seems to be $80-ish, so I logged onto the local library's web site and ordered it via Inter-Library Loan. Hopefully some library out there has a copy to share. If not, I guess I'll buy it.
---
10-4 I'm hoping it has some real information and not just pictures of guns that happened to use the system...
The EM-1 used an ordinary gas setup with a piston. It slotted into the firing pin sleeve, which formed the locking wedge. When the gas pushed the sleeve back, the rollers popped back in, and then the whole assembly moved back.
Yes, locked. I'm not sure about the G3 trunnion either; when I ordered it I didn't realize the G3 was just delayed and not locked. If nothing else I can get the roller size and send it off to a friend who has access to various testing equipment to get the hardness and alloy.
The EM-1 used an ordinary fixed barrel. I'm starting to get the impression that it was, if not unique, an unusual implementation of roller locking.
At the moment the only detailed roller locking information I have is the pictures in the book "EM-2 Concept and Design" by Dugelby, which has to go back to the library tomorrow. The EM-1 prototypes were roller locked, the EM-2 used lever locks. Doable, but way more complex to build than rollers. There was no explanation as to why they picked the EM-2 over the EM-1, but there was considerable politics involved. And as far as manufacture... the Brits were never afraid of complexity. Where an American car would join two parts together with a single coarse-thread bolt, a British car would use three fine-thread studs with flat washers, lock washers, castle nuts, and cotter pins...
---
I discovered those while googling for roller stuff. I've seen some pictures of the bolt assembly, but just external pictures of the receivers. If you can point me to some detailed views I'd sure like to see them.
I'm guessing the backs of the flaps are shaped to cam out of their recesses, and do so when [a locking wedge?] releases them. I've managed to sketch a few designs that might work, but they would all be impossible to machine without building customer machinery to cut the flap recesses. Obviously the Russians and Germans had a better idea...
---
The G3 trunnion showed up today. It's sitting on the desk next to a Yugo AK trunnion. They're about the same size, but the Yugo trunnion is noticeably beefier. They both use barrels of similar diameter, and the G3 barrel is pinned in place like (most) AKs.
The roller ramp area in the G3 is contained within "wings" off the back of the trunnion. They're joined by a flat web across the bottom. I guess you could also look at it as a 3/4 circle opened at the top; either way, the tops of the wings are unsupported.
There are marks from the rollers. They're much smaller than I expected.
There are machining marks on the outside of the G3 trunnion. I can't tell if it started off as an investment casting or bar stock, but the OD was finished off with dull tools. The roller ramps and inside areas of the trunnion are very smooth, apparently ground. The "wings" are tall enough to handle the roller tracks and sufficient overtravel for a small grinding wheel to finish the ramp area.
I *think* I see a pair of Rockwell dimples on the back of the right wing.
---
The library emailed me back; that book is not available by Inter-Library Loan.
I've added it to the "discretionary budget" list, but it's pretty far down, considering the bits I need to finish various gun projects.
I'm still going to keep an eye out for roller locking stuff, though. It seems like such an elegant solution...