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Author Topic: MDR/X Wildcat megathread  (Read 682 times)
WIndstorm
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« on: August 31, 2021, 04:40:46 PM »

Starting a thread in an attempt to collect what engineering information we have available regarding using non-factory calibers in the MDR/X

I know to date there have been successful conversions in .450BM and 6 ARC, and I believe Spector762 had some success with a large bore cartridge.

Questions that come to mind when looking at what is out there that fits AR/SR magazine lengths, and current cutting edge cartridge development:

  • What is the maximum safe bolt thrust that the system can handle? The SRS and HTI have a reputation for being beyond overbuilt in this arena, I was curious if the same was true here. This is a particularly important question with what I have taken to calling the "semi-magnum" family, the SIG .277 FURY and the True Velocity 6.8 TVCM. Both were developed for the NGSW program but both companies have committed to commercial release.
  • How much of a limiting factor is the fixed gas port position if accounted for with a suitable arrangement in the gas block adjustment? Will oprod spring replacement be required for certain calibers or suppressed wildcats?
  • Without breaking any terms of nondisclosure, what are the maximum barrel profile dimensions allowed by the receiver? What lengths are notable for those of us wanting to purchase a blank and then sacrifice an existing barrel kit?

@ColdBoreMiracle if you happen across the thread, since I know you are affiliated with DT, could you perhaps prevail on the company to have an option to buy the data package contained in the MDRX custom barrel listing as a standalone? Since that information would be invaluable to have for folks re-contouring or re-chambering existing barrel kits.

I'm hoping that this thread can become a repository of good info about who can create custom barrels, which calibers have had success, and any peculiarities relevant to others attempting the same thing.

For my part, I'm giving serious thought to having a kit made for .277 FURY I'll just have to make some sort of string snap trigger and a block for the barrel kit to test the bolt thrust question.

relevant information from another thread:

https://www.tvammo.com/68tvcm is the page for the True velocity cartridge,

https://gastatic.com/digest/wp-content/uploads/2019/12/Levi-Sim-7-768x576.jpg pic of a .277 FURY (center) next to 6.5CM and .308W

The biggest problem with potential use of it in a MDRX is that the bi metal case construction of .277 Fury allows both a MAP and bolt thrust that are substantially higher than .308/7.62x51.
« Last Edit: August 31, 2021, 05:06:51 PM by WIndstorm » Logged
spector762
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« Reply #1 on: August 31, 2021, 07:19:45 PM »

So I have some experience with this case pressure is not really a problem you can mitigate that with pre clambering the pressure to slow down the bolt dwell time and if you have enough pre chamber the pressure will be well within the alloted use case.    I used a carbon fiber barrel made my own gas block witch was around 5in forward of the block and modified the case holder so it is impossible to jam and take a lot less inertia so I made a huge pre chamber and have that bolt traveling significantly slower and the recoil is silk.  I say all this to say anything can be done with the right know how and the mdr is a perfect bullpup to do wild cats on
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WIndstorm
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« Reply #2 on: August 31, 2021, 07:30:01 PM »

So I have some experience with this case pressure is not really a problem you can mitigate that with pre clambering the pressure to slow down the bolt dwell time and if you have enough pre chamber the pressure will be well within the alloted use case.    I used a carbon fiber barrel made my own gas block witch was around 5in forward of the block and modified the case holder so it is impossible to jam and take a lot less inertia so I made a huge pre chamber and have that bolt traveling significantly slower and the recoil is silk.  I say all this to say anything can be done with the right know how and the mdr is a perfect bullpup to do wild cats on

Any thoughts on the bolt thrust issue? My gut feeling is the MDRX should be able to handle it, as the material and recoil lug surface area is on par with what we've seen of the MCX Spear, it would just be nice to get someone at DT to run the numbers and give us an idea of how feasible it is, obviously at our own risk.

I'll admit to the quite patently insane idea of reforming SIG .277 Fury brass into other designs with the same casehead, and from the few exploratory simulations I've done in QL, you'd be looking at something close to .300 Win Mag capability out of a standard .308 sized case, when loading to Fury's MAP and a burn rate powder appropriate to barrel length.
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« Reply #3 on: September 01, 2021, 10:59:09 AM »

In case you were wondering, Desert Tech did try to put together an NGSW submission for the same 6.8 projectile:

https://soldiersystems.net/2020/03/10/the-desert-tech-next-generation-squad-weapons-submissions/
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FrozenIceman
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« Reply #4 on: September 01, 2021, 11:56:50 AM »

You know, that kind of explains why the MDR has issues coming to market.  2013 to 2017 was the time frame for the big MDR ship/availability fiasco.  They may have been trying to delay adoption of the MDR to incorporate design improvements from their dev contract.

You should add a section on NGSW to the MDR Rifle wiki page and link that publication.
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WIndstorm
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« Reply #5 on: September 01, 2021, 12:43:19 PM »

In case you were wondering, Desert Tech did try to put together an NGSW submission for the same 6.8 projectile:

https://soldiersystems.net/2020/03/10/the-desert-tech-next-generation-squad-weapons-submissions/

Thanks for that link! From some careful looking and using that as a springboard, that gives me a lot more reason to think the current MDRX should have no issues handling the bolt thrust from .277 F or 6.8TVCM… or similar designs.

I had a retail box of the True velocity .308 arrive yesterday, which I’ll be trying out in the MDRX, but also investigating if it can be reloaded, as it has a steel case head similar to the other NGSW cartridge entries….
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Wolvenhaven
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« Reply #6 on: September 01, 2021, 12:49:29 PM »

In case you were wondering, Desert Tech did try to put together an NGSW submission for the same 6.8 projectile:

https://soldiersystems.net/2020/03/10/the-desert-tech-next-generation-squad-weapons-submissions/

How can this work but 300blk can't?!  UGH!

It would be fun to have this as a caliber though.
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Chowwow
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« Reply #7 on: September 01, 2021, 01:21:20 PM »

On topic, what does everyone think about doing a 26" or longer .308 barrel for the MDRX? Would the gas port have to be moved further up the barrel or be modified in some other way in such a long barrel?

In case you were wondering, Desert Tech did try to put together an NGSW submission for the same 6.8 projectile:

https://soldiersystems.net/2020/03/10/the-desert-tech-next-generation-squad-weapons-submissions/

That's badass, and a good way to future proof the design in case 6.8 NGSW becomes commercially available. Though I'm not holding my breath, I would not be surprised if the Gov banned this particular round from being sold in civilian markets because it's a game changer and the military has had a very deep involvement with the development of this round.

How can this work but 300blk can't?!  UGH!

Who says that it's working? We've only seen a few shots in auto, it could be suffering the same piston-beating issues as the .300 BLK atm. Honestly though, the PCP rifle they are using here looks to be a modified MDR: the gas port appears hidden underneath the handguard somewhere. I suspect they spent significant time re-engineering the gas system to accommodate the 80K PSI chamber pressure that the 6.8 NGSW round generates. While it's a bummer that DT spent resources on this over .300 blk, it would be a great boon to the company if they can provide a 6.8 NGSW shooting bullpup to some military units and law enforcement at this point in time.
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WIndstorm
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« Reply #8 on: September 01, 2021, 01:42:36 PM »

On topic, what does everyone think about doing a 26" or longer .308 barrel for the MDRX? Would the gas port have to be moved further up the barrel or be modified in some other way in such a long barrel?

Probably moved up a bit, but perhaps not depending on the action timing.

I would not be surprised if the Gov banned this particular round from being sold in civilian markets because it's a game changer and the military has had a very deep involvement with the development of this round.

They have literally no legal authority to do so, except specific AP loadings already covered by existing legislation. In fact it would be in the military’s interest for widespread US civilian adoption of the cartridge in other projectile loadings as it creates extra manufacturing capacity and drives further development at no cost to the gov.

Don’t forget the Mk12 and Mk18 basically exist because of the US civilian AR market
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Wolvenhaven
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« Reply #9 on: September 01, 2021, 02:04:23 PM »

They have literally no legal authority to do so...

Have you met the ATF?  That's kinda their bread and butter.  They can also just force non-sale of it like the actually good 5.7 loadings that none of us are able to own even those that don't fall afoul of the AP pistol ammo ban.
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WIndstorm
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« Reply #10 on: September 01, 2021, 03:18:55 PM »

They have literally no legal authority to do so...

Have you met the ATF?  That's kinda their bread and butter.  They can also just force non-sale of it like the actually good 5.7 loadings that none of us are able to own even those that don't fall afoul of the AP pistol ammo ban.

The law is pretty clear cut when it comes to ammunition regulations, and as much as the ATF might like to, they don't make law. the most they can do is classify certain ammunition as "armor piercing" or not, and that has a very strict set of definitions that must be met.

The 5.7x28 the only stuff not commercially available is the SS190 loading, which is expressly AP, and even that is still legal to buy/sell/possess as a normal individual, the only unusual rules apply to FFLs and SOTs depending on type (it's slightly complicated, but you can't manufacture and sell AP, but you can buy gov/le surplus and sell it, and sell manufactured stuff to Gov/LE)

Case to make the point, in my ammo cabinet behind me is a small batch of .50 BMG mk211  Grin


back on thread topic, I've been trying to build up a list of known calibers that will feed from standard large frame mags with no or minimal modification, will edit this post with the list.
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« Reply #11 on: September 01, 2021, 06:17:16 PM »

I had a retail box of the True velocity .308 arrive yesterday, which I’ll be trying out in the MDRX, but also investigating if it can be reloaded, as it has a steel case head similar to the other NGSW cartridge entries….

Definitely looking forward to seeing your results with the TV .308.  Good luck with the reloading though...it's not something that True Velocity seems to think you'll be able to do easily--they're working on setting up their own rebate program where you ship back your spent cases.

Very reminiscent of printer companies now w/ ink toner cartridges Sad
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coldboremiracle
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« Reply #12 on: October 13, 2021, 02:11:49 PM »


@ColdBoreMiracle if you happen across the thread, since I know you are affiliated with DT, could you perhaps prevail on the company to have an option to buy the data package contained in the MDRX custom barrel listing as a standalone? Since that information would be invaluable to have for folks re-contouring or re-chambering existing barrel kits.

I have always been looking forward to making new and other caliber conversion kits. I've been working out my own plans for a 9mm kit, but there's quite a bit of work to be done first. 

I had a retail box of the True velocity .308 arrive yesterday, which I’ll be trying out in the MDRX, but also investigating if it can be reloaded, as it has a steel case head similar to the other NGSW cartridge entries….

Definitely looking forward to seeing your results with the TV .308. 
I've already shot the TV 308 ammo thru the MDRX, it worked pretty good for the first few rounds, but problems develop shortly thereafter. The problem is that the plastic cases once warmed up are quite pliable, and the soft case doesn't snap into the ejection chute pawl as well as the more rigid brass cases do. So you will see malfunctions of the front of the spent cases not getting deep enough into the chute to be ejected properly. The problem was easily remedied by removing the chute, where it worked just fine.
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« Reply #13 on: October 13, 2021, 02:38:21 PM »

I've already shot the TV 308 ammo thru the MDRX, it worked pretty good for the first few rounds, but problems develop shortly thereafter. The problem is that the plastic cases once warmed up are quite pliable, and the soft case doesn't snap into the ejection chute pawl as well as the more rigid brass cases do. So you will see malfunctions of the front of the spent cases not getting deep enough into the chute to be ejected properly. The problem was easily remedied by removing the chute, where it worked just fine.
Yeah, that'd make sense for the chute that was designed for brass cases to not be compatible with composite.

Do you suppose a polymer version of the ejection chute would solve this problem?
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WIndstorm
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« Reply #14 on: October 13, 2021, 04:08:23 PM »

I had a retail box of the True velocity .308 arrive yesterday, which I’ll be trying out in the MDRX, but also investigating if it can be reloaded, as it has a steel case head similar to the other NGSW cartridge entries….

Definitely looking forward to seeing your results with the TV .308.  Good luck with the reloading though...it's not something that True Velocity seems to think you'll be able to do easily--they're working on setting up their own rebate program where you ship back your spent cases.

Very reminiscent of printer companies now w/ ink toner cartridges Sad

They're actually quite easily reloadable, with two important things to know over brass cases. 1) they have lesser case capacity, so care must be taken to compensate for that. and 2) the friction hold on the bullet is not strong like in a brass case, so the sealant is important for maintaining seating depth during handling after loading. fortunately a bit of slightly thinned nail polish does the job quite well.

So far I'm experiementing with a bolt rifle that I don't care about as much as my MDRX for load development, but once I have something I like, I'll be willing to potentially destroy a few cases to test it with the MDR.

The image below are Reloaded TV308 using 175gr SMKs, and 41.3gr of CFE223 with a COAL of 2.83" to give effectively a polymer-case M118LR clone. Blue OPI nail polish thinned with acetone for sealant.

I have always been looking forward to making new and other caliber conversion kits. I've been working out my own plans for a 9mm kit, but there's quite a bit of work to be done first. 

I've already shot the TV 308 ammo thru the MDRX, it worked pretty good for the first few rounds, but problems develop shortly thereafter. The problem is that the plastic cases once warmed up are quite pliable, and the soft case doesn't snap into the ejection chute pawl as well as the more rigid brass cases do. So you will see malfunctions of the front of the spent cases not getting deep enough into the chute to be ejected properly. The problem was easily remedied by removing the chute, where it worked just fine.

That's about what I was expecting to happen, I figured it would probably require some modification of the ejection chute to handle the polycase, but I think it could be done in such a way to handle brass and poly reliably. Thankfully I have a spare ejection chute because of my 6.5 Creed barrel, so I'll be experimenting with that if I run into the same issues.

Don't know if you can say or not about the data package for custom barrels available separately, would be nice to hear if that's in the works.

Sadly busy season at work hasn't left me much time for tinkering.


* image046511589.jpg (385.38 KB, 2291x1741 - viewed 15 times.)
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coldboremiracle
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« Reply #15 on: October 18, 2021, 01:33:13 PM »



They're actually quite easily reloadable, with two important things to know over brass cases. 1) they have lesser case capacity, so care must be taken to compensate for that. and 2) the friction hold on the bullet is not strong like in a brass case, so the sealant is important for maintaining seating depth during handling after loading. fortunately a bit of slightly thinned nail polish does the job quite well.


The cases I fired were definitely not reloadable, they deformed and had heat damage.
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WIndstorm
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« Reply #16 on: October 18, 2021, 03:13:43 PM »


The cases I fired were definitely not reloadable, they deformed and had heat damage.

I find that a bit surprising actually, were they run through an already hot chamber? So far I've not had any of the ~30 I've fired deformed by heat, since they're thermoset polymer they should return to original state after elastic deformation, which is also why they theoretically have no upper limit to number of times reloaded either as the plastic does not work itself thinner like brass.

Would you mind providing some pictures at some stage if possible? would love to have a point of comparison once I'm able to get out and do my own testing  Grin
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