delisle carbine like rifle in .300 blackout

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Nov 9, 2009
so, i've been having the idea of taking a really compact 5.56 caliber bolt action, one that uses AR-15 mags like the mossberg MVP and converting it to .300 blackout probably using an 8 inch barrel with an 8 inch permanently attached suppressor and full shroud over the entire barrel for an integrally suppressed 16" .300 blackout delisle carbine type of rifle in .300 blackout giving me significantly improved distance and accuracy over the original

the idea of using a bolt action for this is of course the superior silencing characteristics of manually operated firearms vs those which use a gas system

what do you guys think about this idea?
so then, you like the idea of a delisle carbine firing 220 grain .30 cal bullets at 1100fps than 45acp?.. that said 230 grain 45acp only gets up to 900fps, 220 grains from the blackout can be pushed all the way up to 1100 giving you even more muzzle energy than the delisle
well, since it is a bolt action and im not constrained by an AR-15 action.. are there any other calibers that may make a better suppressed firearm that i could consider?.. even if theyre wildcats?.. more weight tends to lead to better kinetic energy and higher BC for more distance.. perhaps something using .375 or .416 bullets but is still smaller, lighter, and really only capable of pushing them at about 1100fps?
Whatever blows your skirts up.

Sounds like a neat idea to me. I might go with a 16.25 inch barrel just to avoid the SBR stamp and to allow me to hunt with it in places that do not take to suppressors, but sound fun if you have the bucks and the yen (that's a joke ,son, boy's got a mind like a steel trap. Sprung don't cha know)

Would certainly be "different" and in a caliber a lot of folks do not think is going away soon.

Less drop to account for than those big bores, I'd bet.

i cant help but thing there might be a cartridge or a wildcat designed for even better suppressed performance than 300 blackout?.. for example, you could probably stuff a 350 grain .416 projectile into a trimmed straight walled 7.62x39 case or something.. .300 blackout is better in an AR-15 sure, but we're not really limited by those restrictions with a bolt action
If you're going to do that much work pick a better cartridge than 300BO. When you're limiting yourself to subsonic velocities pick something that can provide the weight advantage to make it worthwhile. Something like a 458 Socom maybe, subsonics up to 500gr bullets.
I already went through this debate 10 years ago. Ended up building a 45 acp AR-15 with an integral can back in 2005-2006. I also considered 458 socom and 300 whisper at the time, but rejected them for reasons which I will explain below.

Under 3-400m, BC doesn't matter much, especially with subsonic rounds. BC simply indicates how quickly you lose velocity, and it only makes a big difference at longer ranges and higher velocities. This can easily be proved with any ballistic calculator. The biggest problem with 45 acp is that the low velocity of factory loadings noticeably increases drop, even at 100-200m. Come to think of it, this is the main problem with subsonic rounds in general- even at 1050 fps, you're heavily dependent on range estimation to hit anything, especially past 100-150m. Even if your BC was perfect and the round lost no velocity at any range, you're still being accelerated downward by gravity.

Assuming a 1.2 BC projectile at 1050 fps with no wind, estimating the range of a 475yard target to be 500m would cause you to miss by about 40 inches. With a generous .2 BC 45 acp round (really more like .16-.18), you would miss by 55 inches instead. It's like doing long range archery.

The reason I chose 45 acp is because it's always available everywhere in the US on a moments notice, at a cheap price. Not that I don't keep a few thousand rounds of everything on hand, but it's nice to know that I don't have to pay a buck a round or go hunting for exotic brass just to be able to go shooting.
IMO, unless you're already a seasoned reloader, stick with 300 BLK or the pistol calibers.

At the less practical end of things, you're going to be shooting wildcats based off rifle rounds, which means custom barrels.
It might mean going with a T/C contender/encore because there are no actions or magazines that fit your choice of round.
It definitely means handloading from day one.
It might mean that you need to form your own brass; the parent case might be expensive.

All of these factors will have to be considered BEFORE you begin.
If you build your 510 whisper carbine and then realize that you hate handloading, you've wasted a ton of effort making a gun that will sit in the back of your safe.
If you build a 45 acp carbine intending to get into reloading later but change your mind, you can still go shooting with WWB.
One part of the DeLisle was that being 45acp, it could be very compact, and lightly built. It was also very quiet by virtue of the small volume of gas produced by a pistol round, combined with a silencer that was even bigger than rifle-sized. To be honest, all 300BO suppressed jobs work similarly; the round has a small powder volume compared to most other AR loads, and the cans are still full rifle sized affairs. I suggest sticking to the same concept, at least, and leave more powerful rounds out of consideration.

I do think a bit more power than 45acp would be advisable, since the DeLisle was for people, and your gun is more likely for paper or game animals like hogs. They deserve a bit more 'authoritative' demise in the interest of avoiding needless suffering, even if it ultimately makes the gun a tad louder.

I think 45 Win Mag would be interesting; could be loaded down to ACP levels, as well as much heavier subsonics, as well as very powerful supersonics of various weights, and still be formed from common NATO brass like Blackout. You'd still retain a very short action, too.

As far as rounds better than Blackout for suppressing, of course there's better offerings; the BO was optimized for the AR platform, so if you aren't similarly constrained, it's compromises come into it. Generally, smaller caliber rounds suppress easier, but you also have a hard time getting them heavy enough to hit strongly as a fatter bullet, to say nothing of the increasing difficulty in stabilizing those super-long needles (and also ensuring they still remain effective upon impact). 30 cal seems to be the inflection point beyond which it gets really hard to make a subsonic projectile worth the bother, and above 45 that fat hole in the can and fat bullet start to be limiting factors in how quiet you can be at the muzzle and in flight. There's a similar inflection point regarding needed suppressor volume as well, that makes cans for rifle rounds with more volume than 223-variants get big really fast to attain the same decibel levels.

I'm sure somebody has charts that relate sonic-velocity max stabilized bullet weight by caliber to terminal effectiveness, and powder volume to suppressor volume for a set decibel level by caliber. I suspect they cross near, but not at, 45acp and 300 Blackout ;)

well here's some criteria, first and foremost it cannot be a pistol caliber or use a pistol bullet i want high ballistic coefficient to retain more of its energy at greater distances, i have ZERO interests in supersonic capabilities, with an internal suppressor i want something thats going to max out to just below supersonic levels.. any extra case volume at this point is just waste, so no, i wont go 300 blackout afterall because i could just as easily pack a 220 grain .308 projectile into a shortened 30 carbine case and increase its pressures as high as they would need to go to propel that at 1100fps and still be under 40mm COAL, so able to be fed from an M1 carbine mag which is going to save weight, save bulk and allow me to use even shorter actions and with a straight walled case it wont be hard to resize and i only need to go so deep with a .30 carbine reamer.. can we easily come up with another idea for a straight walled case, perhaps 7.62x39 brass straightwalled out to roughly .416? 308 maybe straightwalled out to .458?

the other criteria is it has to be a bolt action feeding from a box magazine, tube magazines arent going to work with the pointed bullets and ive considered a lever gun like the BLR but how much is this thing going to be used in the prone? it may actually be better to start with a lee enfield action as the delisle carbine did for the fact that its rear-locking and i would be able to push the barrel so much deeper in and shorten the bolt, just as delisle did


that said, i really think we may be able to do something like the 30 carbine idea above but with a larger diameter cartridge for longer, heavier bullets.. ive never tried this before, but if i cut the brass short at the shoulder, would feeding it through the original cartridges resizing die still properly resize the brass? and could the chamber reamer be cut short and used to chamber the shortened, straight-walled version

also, what exactly should our criteria be to determine effective range?.. how many ft/lbs of muzzle energy do we want to have at a given distance for something like this?.. a 300 grain .338 bullet for example will 550ft/lbs of energy all the way out to 1,000 yards, 550ft/lbs as we know can easily kill, id have no qualms about taking a deer with that much energy if i was reckless enough to attempt it at such range.. so how much energy and what kind of distance do you think we should aim for?

i ask this because then it really wouldnt cost me all that much to create a new straightwalled cartridge and chamber it in a barrel blank for a new suppressed-only cartridge superior in ballistics to 300 blackout, and also superior in its volumetric efficiency as well.. and lets keep that 30 carbine with a 220 grain bullet idea in mind if we cant find something else then i will go that route vs the 300 blackout
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well here's some criteria, first and foremost it cannot be a pistol caliber or use a pistol bullet i want high ballistic coefficient to retain more of its energy at greater distances, i have ZERO interests in supersonic capabilities,

I think you have unrealistic expectations. You mention you want an 8" barrel - so even at faster twist rates, you are going to get maybe one revolution on a long match bullet travelling at subsonic velocities. You also say you are only interested in subsonic.

At this end, the high ballistic coefficient is almost irrelevant - a giant .45 300gr wadcutter brick at subsonic speeds and a .300 BLK VLD match bullet have just a few inches of difference in drop at 200yds. There is only so much you can do when you start out that slow. Past 200yds, the high ballistic coefficient starts to help but by 300yds, you are looking at 10 feet of drop, plus wind dope (slower travel time means wind has more effect), plus a round that is kind of iffy out of such a short barrel to begin with.

Don't take my word for it though, bust out a ballistics computer and play around with it. At practical distances for subsonic shooting, the pistol calibers usually are cheaper, have bullets designed to expand at those velocities and frequently more energy as well.
thats why i said if i cant find anything better i would just cut a 30 carbine case down and load it with a 220 grain 30 caliber bullet, whether its getting 1100fps from an 8 inch barrel from a 30 carbine case or a 300 blackout case doesnt really matter, but doing it with the 30 carbine case would make the overall cartridge smaller, shorter, and lighter.. all that extra case capacity of the 300 blackout would just be a waste of space if the cartridge is never intended to go beyond 1100fps

but i will try it out with a big round nose bullet too, perhaps see what a huge 45 caliber bullet from a .45-70 can do, because a .308 case can be chopped down to straightwalled and made to fire that relatively easily, if the drop isnt too significant then it may be a better route

of course, you could go heavier than 230 grain in a 45ACP size case if you follow the 460 rowland.. cool think about that is if you did it with an enfield action youd end up with a final product that pretty much IS a delisle carbine, just improved with higher pressures and heavier bullets
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I think you'd be wasting your time with anything 30cal. Bullets in that caliber just don't have the weight to be effective at subsonic speeds. Compare a 240gr .308 SMK and a 500gr .458 Speer at 1100fps. The Speer has almost 359ft/lbs more energy retained at 250yds than the SMK has at the muzzle and drops less.
yeah, i know, weights more important, thats why im going to see whats available in 45 cal because i know a 308 case when the neck is cut off can fit that

hmm.. you know, i was looking at .50 beowulf for the AR-15?.. fits in AR-15 mags, has the same base diameter as .300 magnum, so magnum brass could be used, if magnum brass is being used then it would have pretty much the same rim diameter as the .303 british which means if we made .50 beowulf brass out of magnum brass it would actually fit the enfields bolt face without modification, and since we're not using it in an Ar-15, our limitation is the pressures the enfield action can handle, and the .50 cal bullets available, but we'd be able to use a 50 beowulf reamer, sizing dies, the enfield bolt, and im sure i could work up a way to add a magazine well to work with 5.56/223 magazines... this would actually be a pretty easy conversion i think

the question i have is just what is the bolt thrust limits of a lee enfield action?

i can also still just use the mossberg MVP with standard 50 beowulf brass

how are these for numbers?

.50 beowolf, 500 grain hornady XTP bullet

8" barrel; 30gr of winchester 296; 1104fps and 1352 ft/lbs of muzzle energy at 33359 PSI of pressure

this puts bolt thrust at 6550lbs, similar to .308 and .303 british, so there should be zero problems with using this in the lee enfield action, also 300 magnum brass is about 1/2 the price of 50 beowulf brass and the larger rim works perfectly with the enfield bolt face, so that kills two birds with one stone, cheaper brass and already have a bolt head for the enfield that works

you could easily hunt with this at 300 yards, though then we're looking at the problem of finding a 50 cal suppressor
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well ive decided what im going to do about bullets for this.. im going .458 cal.. whats REALLY cool is a 500 grain .458 bullet has a ballistic coefficient of .412

with a 500 grain bullet with .412 BC at 1100fps muzzle energy, we're getting 1343 ft/lbs of muzzle energy, at 1,000 yards were still at 663ft/lbs of muzzle energy so over 1000 yards we're barely losing half our energy and a 500 grain bullet even at 663 will EASILY kill big game and anything else its fired at... granted your bullet drop is 1,943 inches which is about 50 yards, with the right optics and some practice you could easily make shots in excess of 500 yards

also, looking at the 458 lott it would appear to have a neck diameter of about 12mm so my plan here to keep it cheap is to use .308 winchester brass, shoulders chopped off and converted into a 12mm diameter straight walled case

i think this will be the best idea.. it gives us more kinetic energy than a 5.56 at close range, it gives us more than enough energy at ANY length of its travel to be effective, its just a matter of if you can actually hit or not, kinetic energy will never come into question, 458 bullets are rather inexpensive when compared to things like .416, .50 cal, etc, and im fairly certain this could be made from common, cheap, once-fired .308 brass, and use the most common bolt face in rifles

i think the closest cartridge to what i'll be doing is the .45 raptor
If you're going to do that much work pick a better cartridge than 300BO. When you're limiting yourself to subsonic velocities pick something that can provide the weight advantage to make it worthwhile. Something like a 458 Socom maybe, subsonics up to 500gr bullets.
Make that 600 grains.

the real question is, what kind of barrel length and twist rates are we looking at to stabilize something like that?.. it would seem i would be looking at a pretty fast twist rate
Here you go, 170$ for a 1:7 twist barrel --not like you won't have a bunch of holes in it by the time you're done, so don't mind the gas port ;)

should i really do this with an enfield action though?
Any reason not to? You clearly like the action, so why not use it? I like straight-pull bolt actions more than lever guns, so my "Thumper*" build is a Steyr M95 rebarreld to 50 Alaskan (laterally-stretched 45-70). Unlike the Steyr, the Enfield is a very well designed setup for high pressure rounds with immense bolt thrusts (Alaskan runs fairly low pressures) and should work nicely.


*the rabbit, not the stupid Cooper invention
actually, the steyr M1895 is actually one of my favorite actions.. right up there with mausers, lee enfields are lower on the list however enfields are rear lugged which means i can actually shorten the bolt and push the barrel as far in as it would need to go so i can really shorten up the bolt and travel if i need to, but it all depends.. im going to sketch up a .308 case, a .458 500 grain bullet with the necessary dimensions and determine how much case capacity im going to have and how much i need to shorten it to determine just how much action length i'm going to need for this

but with the enfield i can customize the action length to what i need.. are there any other rear lugged bolt actions out there that'll allow me to do the same thing?
did some more playing around in quickload, using 45 win mag brass with standard 40,000 PSI pressure limits, i put in the data for the 500 grain .458 woodleigh bullet, if i extend the COAL to about 56mm (same as the 5.56), the seating depth for the woodleigh bullet is pretty close to what the .458 bullet was designed for and staying within standard pressures, 19.7 grains of winchester 296 powder gives me 1103fps, 1351 ft/lbs of energy at the muzzle, this would allow me to use .45 win mag loading dies, chamber reamers and potentially 5.56 size mags

and these numbers are assuming an 8 inch barrel.. plus any 45 cal suppressor should work.. i should end up with something that looks like a delisle, is a 45 cal like a delisle, im just juicing it up to give us almost 3x more muzzle energy and a considerably higher ballistic coefficient

cool think about it is if i use .308 brass and up the pressure to about 50-55k PSI, i can actually get the 1100fps with H4895 powder.. my primary go-to caliber is .308 and i reload with H4895.. so using the same brass i already have after it gets work out around the case mouth, and using the powder i already have all i need is some .458 bullets to feed this rifle when its finished.. so whats really cool about going this route is not only does it stick closer to the delisle roots using the enfield action, and a straight walled 45 cal cartridge, but the logistics of using brass and powder i already have... its a no brainer, this HAS to be the route i go for this project and it all falls together so perfectly
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