Thought on endcap design

[L1A1Rocker]

I know aesthetics dictate an endcap screws into the tube. But what about having an endcap screw ONTO the tube. It won't look as pretty but wouldn't it be a bit stronger that way? I would think that heat and pressure expansion would be pushing the peaces together rather than apart.

Has anyone done this?

[Dr.K]

I've seen some cans like this, and I believe your thoughts are all correct.

Just doesn't seem as pleasing to the eye for me. Kinda looks like a pipe bomb.

[Bendersquint]

There is a reason why no commercial manufacturer makes endcaps like this.


What this does is fix a problem that doesn't exist.

[Capt. Link.]

I know aesthetics dictate an endcap screws into the tube. But what about having an endcap screw ONTO the tube. It won't look as pretty but wouldn't it be a bit stronger that way? I would think that heat and pressure expansion would be pushing the peaces together rather than apart.

Has anyone done this?

The only technical reason to do that would be with the use of thin Ti as its very elastic.I personally don't like the ascetics and elasticity is best handled with welding which will be much lighter and stronger.

[CThomas]

It is on the outside to hold wipes

[Fulmen]

Only problem I see is that it adds to the diameter. We usually strive for a large diameter to keep a decent volume without adding too much length, but a larger diameter can obscure the sights so it's often a compromise. If you can afford the extra diameter why not use it for volume?

[CMV]

One advantage I can think of doing it that way is you could make it much easier to grip for taking apart by hand & tool-less. Can't think of other positives, but I'm sure there are some.

[ghostdog662]

Endcaps that are not the same diameter as the tube just look bad and will certainly weigh more. No thank you.

[Fulmen]

Structurally I don't see any real problems. I don't care for the look, and I think it adds to the diameter without freeing much volume, but that's mostly a matter of taste. I also think it makes more sense to let the thrust act directly on the threads rather than transferring it through the front of the end cap.

[pnl2012]

I see some benefits on Caps threading onto the Tube and no need for an increase in OD and/or multi OD’s (ugly look): Shorter Cans, no wasted space, more contact surface for hand-screwing, easier to Machine for MiniLathes. no need for “special” Baffles to fit into the end cap, easier for building complex reflex/integral Cans, … Tubing can be the same. A Pic follows; this one is 1 inch OD, 0.065 walls and 32 tpi.

[Capt. Link.]

If it must be as short as possible that is a good idea in the low pressure muzzle end of a can +1 Paul.

[Fulmen]

low pressure muzzle end of a can

The pressure might be low, but the end cap has to distribute all the axial load back onto the tube. And that load is not something to be taken lightly, it represents all the drop in recoil which can be substantial, try calculating the forces involved and you'd be surprised.

[pnl2012]

Mechanical elongations (deformation) are exactly the same as long as thickness and materials are the same for in & on. Now, of course, with “in to” caps you can go thicker ergo you can go stronger. So, this is not a better or worse matter; it’s just another available “option” and for sure not related to “look and feel” at all anyway. The balance is the key.

[Capt. Link.]

low pressure muzzle end of a can

The pressure might be low, but the end cap has to distribute all the axial load back onto the tube. And that load is not something to be taken lightly, it represents all the drop in recoil which can be substantial, try calculating the forces involved and you'd be surprised.

My take apart .308 cans have but .200" muzzle cap thread engagement and I don't need spares figure that one out.

+1 Paul I give credit where its due I don't like the pipe bomb look and that cap will look nice on a magnum can I need.

[Fulmen]

I'm just pointing out that a can is subjected to much more than pressure. Pnl2012s sketch would not be a good solution as there is almost no material left to handle the axial load. I had a 22 can with K's that were too thin for pistol use, it had a strong first baffle to handle the high pressures but the front baffles collapsed due to axial load.

[Capt. Link.]

I'm just pointing out that a can is subjected to much more than pressure. Pnl2012s sketch would not be a good solution as there is almost no material left to handle the axial load.

How much material is required to handle the axial load

[Fulmen]

That is a very good question, and I suspect the answer is the same as for "how long is a rubber band?"

I'll admit I haven't done any calculations as it's hard to get an exact figure, so I just use experience and other working designs as a reference. That probably means they are seriously over-engineered, but better safe than sorry.

[pnl2012]

OK, i understand what Fulmen says. My comments: Axial pressure is related to threads engagement and tolerances while radial pressure is related to net wall thicknesses at threading peaks (Note: Axial pressure is the bullet flight and radial pressure is the pressure pulse expansion to the Baffles/Tube/Caps in a “sideways” way). Obviously, my example is 32 tpi (not really strong) and we have a system with two parts (Tube and Cap) so Axial & Radial are directly related and constrained to the weakest point (Note: A s--t threading plenty of walling thickness is going to fail – due to axial forces - while perfect threading with extremely thin wall will also collapse – due to radial forces -). In order to design a VERY STRONG Can with “onto” Caps, you have to either accept the “pipe bomb look” or just work with thicker Tubes and Mill the outside of the Tube - in between the Caps - to lighten the Can without compromising the look and feel and the overall ID. Remember: Cheap, Good and Safe, … pick two; that’s the Law.

[Fulmen]

In order to design a VERY STRONG Can with “onto” Caps, you have to either accept the “pipe bomb look” or just work with thicker Tubes.

That's my sentiment as well.

[CThomas]

I realize that the AAC Element is not an "outside" end cap design but I would think such a design could be made to look nice if edges were machined at angles to flow into the tube

[delta9mda]

stop making this harder than it has to be.

bender- spot on

[Shift1]

If memory serves, there have been a couple OPs who have posted an external cap design project to the pages. I think that it was done due to running with a mini lathe and not having the room to do otherwise. Bender is correct...you do not see them commercially made this way. Why....Bender may know the answer, I do not. You see some that have a reduced center between the caps as illustrated by CThomas. Personally... keep the threads on the inside of the tube.