Prototype Portable Combination Pistol and Carbine (PCC) Machine Rest Build

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LiveLife

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GENERAL DISCLAIMER: This "unscientific" prototype project is being conducted by a "random guy on the internet"; therefore, use posted loads (based on published and unpublished load data) at your own risk. As always, since there are many reloading/shooting variables, your results from using different components, equipment and firearms may vary. Information posted on this thread is for educational/entertainment purposes only.

SAFETY DISCLAIMER: Always reference published load data for your load development.

ACCURACY/CONSISTENCY DISCLAIMER: This "unscientific" portable testing project obviously lacks ideal laboratory testing conditions. Accuracy and consistency claims expressed or demonstrated are likely by chance and may not be consistently repeatable or reproducible.

IMPARTIALITY DISCLAIMER: The "random guy on the internet" is in no way compensated by manufacturers/vendors of products tested which will include various headstamp brass, various brand projectiles, various powders, various primers, various firearms/barrels and various reloading equipment. Use of particular product or equipment in no way express endorsement. Any positive/negative comments expressed towards any product or equipment by the "random guy on the internet" is strictly personal opinion only.

A SPECIAL REQUEST FROM THE ORIGINAL POSTER (OP): Attempts will be made so in case the prototype project produces portable testing platform that successfully produces MORE CONSISTENT groups (not the best groups), focus will be made so cheaper/easier reproductions can be made and tested using readily available plywood and metal stock from THR members' local lumber/hardware stores. My ultimate goal for this project is to make available more consistent portable testing platform to other THR members so pursuit of "optimal" portable testing platform WILL NOT be made by intent. Please refrain from posting information deviating from this intent. Thank you in advance.

With those disclaimers out of the way, here we go with the prototype project. :)

NOTE: I will number my posts with descriptions for better tracking/referencing.
 
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Part 1 - History and progression towards machine rest

Thanks to retirement, I am finally able to start this project.

Reason for the project is obvious. Build a machine rest for pistol and carbine (PCC) load development so more consistent range testing can be done without human/shooter input as much as possible. If the machine rest is successful in producing more consistent shot groups, it will allow more definitive range testing of pistol loads at 25 and 50 yards.

Ideally, I would want a hard mount machine rest anchored to a large slab of concrete but that is not an option for me so I must make do with a portable testing platform to use on BLM land.

After conducting range tests at 25/50 yards using scopes and bipod on table, bipod from prone position and using 3 different plastic and metal rifle rests (Caldwell Steady Rest NXT, Caldwell Lead Sled Solo, etc.); I realized there were inherent shooting variables and shooter input that cannot be entirely removed from the shooting process.

Yes, many can argue my "optical" rests could be improved with better rests and shooting techniques but I am thinking about the "average" THR member/guest who won't/can't spend several hundred dollars on a rest - but could spend $100 on DIY supplies. ;)
 
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Part 2 - Machine rest inspiration

So with above reasons in mind, I initially obtained my inspiration from Bart B. mentioned machine rest that had the precision of consecutive 10-shot groups at 600 yards around 1 inch from the .308 Win. using full length sized cases (20 to 40 shot groups have been under 2 inches). Truly amazing. :eek::eek::eek::thumbup::thumbup::thumbup: - https://www.thehighroad.org/index.php?threads/rifle-rest.458493/#post-5724026

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I did mention "inspiration" as I do not anticipate coming nowhere near this level of precision with my DIY machine rest.

I studied various pictures of this rest in detail (Detailed pictures at above link) and focused on aspects that primarily contributed to shot-to-shot consistency along with other rail gun designs - https://www.google.com/search?q=ben...68jiAhWwHjQIHdo6D7gQ_AUIECgB&biw=1366&bih=609

While studying other rail gun designs, I began to compile factors and design features that increased consistent return to zero of these machine rests and rail guns. (Keep in mind, I am trying to build a simple machine rest that could be built/copied easily at low cost by other THR members)
 
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Part 3 - Material selection

I initially considered using various materials: Hardwood, plywood, no-void hardwood plywood, marine grade plywood, aluminum bars/blocks, aluminum sheets, steel, stainless steel, plastic/polymer, composite, etc.

After much thought, I decided on stainless steel. This is mainly because I live at the coast with salt mist being a concern for rust with wood/plywood with moisture swelling being another concern (Subsequent copies will be made out of plywood and moisture sealed for lower cost/ease of construction).

So after several hours of treasure hunting at a metal salvage yard, I found these to start with the initial prototype build:
  • 26"x48" NSF stainless steel table with shelf
  • 11 gauge (1/8", 0.125" thick) 16"x25" platform with 1/2" bend on one side with two welded-on verticals that enhanced stiffness of the platform (And I will be using the bend as my slide track)
  • 10 gauge (9/64", 0.140" thick) 22"x28" plate to bend into triangle tube to hard mount pistols on one side and carbines on the other side
  • 3/8" steel plate (I have a large piece on hand, just in case)
I was also looking for aluminum plates and long bar stocks to use for my 18' Starcraft and found several aluminum pieces that could be used for the prototype project.

Here's the table with platform where it is anticipated to be used (without the bent plate or slide rail channel installed)

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Part 4 - Initial design/construction goals
  • Stability of platform - 26"x48" table will mount on top of spiked front legs.
  • Spikes will go into the ground with flat bar mount to distribute the weight and prevent/reduce sinking
  • Rear single blade leg with plate will incorporate a chair so my 250 lb body weight along with lead bullet filled bags (If necessary) on the front of table shelf will provide anticipated 400-500 lbs of push on the "tripod" legs. The ground area under the rear plate can be compacted to reduce/eliminate sinking and larger plate/base can be used if necessary.
  • Table top will be stiffened to reduce/eliminate deflection.
  • Bent edge along the platform will slide inside a tight fitting/lubricated channel for recoil with bungee cord/springs providing recoil reduction
  • "V" notched front stop will enhance platform return and along with tight fitting/lubricated slide channel provide more consistent zero
  • Pistol specific grip blocks for Glock 22/Sig 1911/GSG 1911 will be made for pistol testing (May incorporate additional hard mount to accessory rail)
  • PCC/Just Right carbine will essentially be barrel shroud hard mounted.
  • If copies of machine rest will be used on stable/anchored bench, different slide base can be considered
Here's a not-to-scale rough sketch of the prototype machine rest

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I am hoping to hear from mechanical/engineer/machinist/designer types who worked with close tolerance/metal work for feedback/suggestions/critique along the way to enhance the build. (Keep in mind the realistic limitations of working prototype copies that will be made from plywood and metal hardware to lower cost/ease of assembly with obvious reduction in tolerance)

Just like Myth Busters, I anticipate running into technical difficulties with the prototype.

Any thoughts on material selection and design/construction goals so far?
 
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Part 5 - Initial "rough" mock up

Here's the table with initial, very rough and approximate paper mock up of where bent triangle plate will go. Actual build will have smaller triangle so edges of the bent plate will be attached to the welded rails.

< Platform will be a bit more forward going towards left of picture to accommodate recoil travel >

Any thoughts or questions regarding the initial mock up?

< Can you picture a pistol hard mounted on this side of plate (to easily access mag release) with muzzle just past the left side of the plate? >

< Carbines will be hard mounted to the other side to better access the mag release >

< BTW, I anticipate the combined weight of table, platform and bent triangle plate to be about 100 lbs, certainly by the time I add the front legs and rear combo seat/leg >

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Here's close up of paper mock up showing welded rails and bent edge (on the right) that will be used as slide surface. Imagine smaller bent plate with edge joined to the two rails with pistol/carbine hard mounts on either sides of the triangle plate with "U" channel piece over the bent edge on the right to use as slide guide.

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I will be watching this with great interest.
I have a men's bathroom worth of plastic partions and steel supports with the intent of doing this same project.
(I feel my firearms would be more accurate if I didn't touch them.;))

I understand needing a place to sit. I thought of incorporating a seat onto mine, but now I am thinking of not touching the table either...

I have been stumped on how to make something to hold a pistol, as it needs to work with a Desert Eagle and smaller pocket guns. A series of bolt on blocks was my best (clunkiest) idea yet. Scrapped, still thinking.

I like the gliding triangle. A simple way to get dual positions. Maybe even place a rifle inside it if it is big enough, to remove scope cant error.
If the triangle piece is not too expensive, several different shapes could be bent up to accommodate differing profilles of firearms.

You now have a good recoil measurement system, too. A plastic slide foot on the mount and a clean metal rail, I feel, is better than lubricated metal to metal contact. There is more consistancy in the resistance to movement. Especially when environmental temperature is considered.


I appreciate all the work you do, done on our behalf. That you share it freely, with even more effort put into its concise nature, is a truly rare blessing. Thank you.

With kind regards,
D. Human
 
You may be able to use some high density foam (8#) to make the grip profile. Use it to make a exact casting of the grip. It's a 2 part mix. The bad thing is that foam chemicals have a very short shelf life span. This stuff is hard enough it's used for machine test setups. Has a super high compression strength.
 
I feel my firearms would be more accurate if I didn't touch them.

I understand needing a place to sit. I thought of incorporating a seat onto mine, but now I am thinking of not touching the table either.
My focus is repeatable zero without moving the table.

I thought about not adding the chair at first.

But with the combined weight of table/platform/bent plate around 100 lbs, I wasn't sure if that was sufficient for zero movement.

So initially I thought of adding around 300-400 lbs of lead weight/sand bags to the bottom shelf of table but thought adding my 250 lb weight would reduce the need for lead weight and I have a place to seat.

Keep in mind the testing process will be:
  • Load the magazine
  • Seat down and be still
  • Remotely actuate the trigger 10 times
So me sitting on the rear table leg may not induce another variable. I can initially test the table without attached seat.

They make this for pistol and know this isn't what you want. The ones used for rifles you lock action in and can't do that with pistol
Precisely the reason for hybrid pistol and carbine machine rest. If I am going to spend time and effort to build a machine rest, I want it to be able to be usable for testing as many firearms as possible.

Another benefit of a portable machine rest - If repeatability is good, I can take it to other BLM land area for 300/600 yard rifle testing.

You may be able to use some high density foam (8#) to make the grip profile. Use it to make a exact casting of the grip. It's a 2 part mix. The bad thing is that foam chemicals have a very short shelf life span. This stuff is hard enough it's used for machine test setups. Has a super high compression strength.
Since this is a "hard mount" machine rest, I was thinking of making hard pistol grip mount out of custom cut plywood. I was thinking of using cut pieces of 2'x2' foam exercise mat but can test other padding materials to see which produces smallest groups.
 
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< Sorry about no sketch of machine rest. I got a request to share (as PIF) defensive point shooting for an older couple this morning and had to load up. I am leaving to meet them at the shooting area so will post the sketch later this afternoon (My initial session lasts 3-4 hours) >
 
I have always liked the one on Bart’s Flickr https://www.flickr.com/photos/12787226@N00/sets/72157594303093714/detail/, it wouldn’t take a lot to make it good for most rifles without messing up finish and such.

I have dabbled with a few using linear slides/rails and such but the cheapest one I have made that works pretty good is this one.



Like that the rifle is held pretty stable but is free to recoil in the rest.

I can also configure it like this.

D8E8D3E5-EF49-4E60-86DE-A3DD22483D59.jpeg

Makes for faster follow up shots.



But if you have a rifle with much recoil and it’s going to move.

Why the upper carriage on Bart’s linked photos moves with the rifle and the lower is c clamped in a number of spots to the bench.
 
Thank you for the posts and what I was looking for to help with problem identification and arriving at solution options.

I have dabbled with a few using linear slides/rails and such but the cheapest one I have made that works pretty good is this one.
I love it! Use of scissor jack is low tech but if it works, that's what I am talking about. :thumbup::thumbup::thumbup:

I have seen the "One shot zero" video before and pretty neat.


PROBLEM #1 (Pending evaluation) - Recoil management
Like that the rifle is held pretty stable but is free to recoil in the rest.

Why the upper carriage on Bart’s linked photos moves with the rifle and the lower is c clamped in a number of spots to the bench.
Yes, that's exactly what I am trying to do with the prototype build, a machine rest that "hard mounts" pistols and carbines yet allows recoil with precise return to zero for higher consistent repeatability.

Since this is a portable bench/table design, challenge for me is to overcome the stability factor. Maybe I am overthinking this. Maybe the 100 lb table will do OK with pistol/carbine recoil.

Once the platform with hard mounts are done, I can test fire and see how much recoil movement I have and work to address that movement.

Proposed Solution for Problem #1 - I had initially thought of using 2 thick rods with slide sleeves tensioned with springs over rods. But when I saw the platform with 1/2" bent on one edge, I thought of using the bend as slide guide with simple bungee as recoil reducer. Since the surface area of the platform against the table top is large, friction alone may be sufficient to manage recoil from pistol loads. But if machine rest is to be used for rifle loads (and I anticipate I may), then factoring in recoil management would be a must.


PROBLEM #2 (Pending evaluation) - Return to zero

It is my thinking that more precise return to zero will improve precision of the machine rest.

Proposed Solution for Problem #2 - I am thinking of using "V" notch cuts or Cone in Cone to return the platform to zero for repeatability. This will take the burden off the need to make recoil management (sleeved slide rail in my case) precise as return to zero will not be dependent on the recoil management system. This is of particular interest because subsequent copies of the machine rest made out of plywood/metal hardware will use slide guide rails or alternate slide system for recoil management.
 
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Would this automatically return to forward position? Perhaps under spring power?

I now envision the triangle mounted to two full extension, soft close drawer slides. With one long and weak spring to return the whole apparatus to battery, slowly, while also absorbing the recoil. Allowing movment only straight rearward.

And a long armed trigger actuator with a return spring. Mounted to the board in a way to go through the trigger guard, sprung forward. A spring on the end to attach a string to, to avoid any jarring from pulling on the string past trigger stop.

This could be fixed to the "rail plate" and clamped on the table.
 
Would this automatically return to forward position? Perhaps under spring power?

I now envision the triangle mounted to two full extension, soft close drawer slides. With one long and weak spring to return the whole apparatus to battery, slowly, while also absorbing the recoil. Allowing movment only straight rearward.
Great idea. We are problem solving already. :thumbup::thumbup::thumbup:

I was thinking of a manual return to zero system (like the Ransom Rest) for more precision but I need to chew on considering an automatic return to zero option. Whether a manual or automatic return to zero, focus would be made on final "lock up" for utmost repeatability (and why I am thinking of "V" notches or Cone on cone design).

And use of drawer slides would be good for subsequent copies that will be made from plywood and metal hardware.

See, that's why I solicited feedback. I am sure, many brains are much better than my foggy tired single brain. :eek:

And a long armed trigger actuator with a return spring. Mounted to the board in a way to go through the trigger guard, sprung forward. A spring on the end to attach a string to, to avoid any jarring from pulling on the string past trigger stop.
The pistol frame will be hard mounted to the bent "triangle" plate but the slide and trigger will cycle and reset normally for remote trigger to actuate again.

Carbine will be hard mounted to bent "triangle" plate by free-float tube and bolt will cycle and reset normally for remote trigger to actuate again.
 
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All of my ARs/PCCs have rails: Quad, Keymod, MLok (Only thing that doesn't have a rail is Ruger 10/22 Take Down).

And pistols I plan to use for testing are railed (Glock 22/23 and Sig 1911)
 
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That makes it infinitely easier, provided the Glock pistol rails can take recoil while mounted.

My Eagle and others have rails as well, which got me to thinking that would be a way to fix them in the apparatus.
IF that was enough purchase on them to keep them perfectly aimed.
(I am having serious doubts about the Eagle staying put...)

Time for me to get my sketch pad and straight edge out.
 
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I am thinking the "hard mounted" pistols will stay put as movable platform will transfer the recoil energy away from the hard mount points.

Rough sketch of the machine rest shows pistol mounted to the bent plate that's attached to the platform and bent edge on right side will slide inside the "U" channel rail attached to the table.

If bottom of platform friction with top of table is not sufficient to absorb the recoil energy, I can add bungee or spring.

Question is whether weight of 100 lb table is heavy enough to provide stability for repeat zero and I could add lead filled bags on the bottom shelf (I am sure initial testing firing of pistol will indicate if that's the case). For carbine/rifle testing, I may need to address greater recoil energy issue but I will start with pistol recoil energy first.
 
Yes, that's exactly what I am trying to do with the prototype build, a machine rest that "hard mounts" pistols and carbines yet allows recoil with precise return to zero for higher consistent repeatability.

Since this is a portable bench/table design, challenge for me is to overcome the stability factor. Maybe I am overthinking this. Maybe the 100 lb table will do OK with pistol/carbine recoil.

What surface do you have to set the 100 lb table on and to what repeatability are you looking for?
 
I have nothing constructive to add, other than to provide a link for inspiration:




(there's a little bit of language towards the end).
 
LOL. Thanks for infusing some sense of reality to the thread.


I am not going to be pursuing precision rabbit holes. I will be taking step by step while maximizing the precision of what I have on hand as much as possible.
  • My next step will be to bend the hard mount plate and attach to the platform.
  • Then work on universal hard mount system for pistol.
  • Then work on slide/channel rail for recoil management.
  • Then work on return to zero system (still pondering "V" notch vs cone on cone).
  • Then test fire just with the weight of 100 lb table/platform and add weight to lower bench shelf as necessary to reduce movement.
  • If successful (Repeatability acceptable to THR peanut gallery), then work on universal hard mount for carbines on the other side of the plate.
  • Then test fire with necessary revision to recoil management system if inadequate.
  • If successful at 100 yards, conduct 300/600 yard testing.
  • Then make copy from plywood/metal hardware using different recoil management system (maybe drawer slides) and test fire.
  • If successful, make more copes for THR PIF/detailed plan distribution for members wanting their own machine rest.
 
BLM land dirt surface.

Depending on how much repeatability you are looking for that could be difficult for something that light on that kind of a surface, without having to re aim each shot.
 
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