45LC-Well that is a heavier barrel at muzzle than 12 ga slug
one I have here.Loading 585 bullets like sabots sounds great, and I think your rifling will work ok.Ed.

Hubel458,



Thanks for sticking around with this thread. I spoke to Dave Casey this morning. He seems to agree that the rifling is fine for paperpatch though a little fast (of course he deals with a lot of shooters who have 1 in 40 twist and such) but is interested in how the project goes.



I am still at a loss on what powder to use. It seems that it would be quite fun to do a few BPCR loads: that seems very fitting for paper patch aspect of this experiment. I don't like the mess, but is should be fun for a few shots. I am told that triple 7 does wierd things in very large capacities, so I won't go that way: if I do BP, it will be BP. I am thinking of getting Hodgdon's Xperimental Pack in the slow selections. I think it does H4350 to Retumbo.



I don't have the cases to figure capacity but it should be somewhat less that the .600 NE. Can anyone suggest powders good for 600 to 830 grain bullets at 17,000 PSI?

This is going to be a great experiment, with a lot of opportunity to learn things! As for powder, I think you are in "terra incognita", since very few people have done much with smokeless in a large-bore like yours at the pressure levels you must adhere to. My thought is that Ross Seyfried, and perhaps Ken Waters might be persons to contact since they seem to experiment with exotics a lot. Seyfried in particular seems to have frequent experience with big bore, large-capacity cases that operate at low pressure levels.



I think powders in the burning-rate zone between IMR 3031 up to IMR 4350 could provide the solution to propellant choices. One thing for sure is that the powder-burning chamber volume is going to multiply rapidly as the bullet moves down the bore, decreasing the probability of excessive peak pressures.



Please keep us informed of your progress and what you learn!

How long is the chamber on your barrel? How long of brass are you getting? Will it be for large rifle primers or shotgun primers?

I'll try some numbers through quickload.

This is not loading data, just what came out of quickload.

I took a 2 3/4" 20ga case and filled with water. It held 188gns. The fired case is 2.6" I went to www.mountainmolds.com and used his online bullet design to get approximate bullet lengths. I assumed a .4" nose. It seemed that RL-19 gave the highest velocities simulation. RL-22 was tried also, but took 10more gns of powder to get the same velocity and pressure. The quickload starting pressure was adjusted for lead bullets.

600gn .774"
136gns RL-19 1755fps at 17ksi

650gn .836"
130gns RL-19 1685fps at 17ksi

700gn .898"
125gns RL-19 1630fps at 17ksi

750gn .96"
120gns RL-19 1575fps at 17ksi

800gn 1.02"
115gns RL-19 1520fps at 17ksi

900gn 1.142"
106gns RL-19 1420fps at 17ksi

Hubel458 has stated before that the large straight cases give better performance than the paper ballistics would indicate.

Do you know what the 20ga barrel is made out of? Do they use 4140? We could use that for a pressure calculation for the barrel. A longer case would probably help to get more velocity.

!!Not load info, just a quickload estimation!!

The gun is a 3" chamber so I am getting 3" brass. I am going to shoot it for accuracy and shooting impressions when I get some range time. That will be with factory ammo. Plastic shells have a lot of material at the base, so I expect more than that along with the extra 1/4" 600 NE has just under 200 grains of water. What are we looking at, 195?



Before experimenting, I want to find out what my powders will do in large cases, I know from loading my moniker, the 45 Colt; that if you put too little H-110 in a case, things get nasty. Of course, we get warnings about that stuff when it is an issue. BP loads could be fun, I know how to handle that.



Looking to get a chronograph too, that will be in June.



I am glad to see more interest. I wonder how that fast twist will affect pressure....



As I move up to heavier loads, I will have to find some ways to add weight to the gun itself. The stock is in two peices and a larger forearm with added weight would be no problem. I can also the Survivor butstock and fill it with extra material.

Thanks for the Quickload data. Without any such data, I was thinking about using the slowest stuff I could get so 100% -capacity would not foul things up. I also thought about checking Ross Seyfried's nitro-for-black info for a base, after working up usable BPCR info. The upper end may be dictated by what I can tolerate recoil-wise rather than chamber pressure. Of course, this will be seeing plenty of light weight stuff at moderate velocities but 650 grains going over 16000 fps sure packs a whollop in North America.



I have no data on the barrel aside from dimensions. Thank you for your info. I will give you bullet info as soon as I get the bullets. As for primers, I let Dave talk me into doing the shotgun primers. Now seeing that BPCR shooters go with the smallest primers that get consisent ignition, I may have goofed. Perhaps not: we are looking at low pressures and a fast increase in volume as the bullet goes down the bore, I may need as much initial fire as i can get.

I would think that the extra fire of the shotgun primer would help to light things off in a large case. Also what is the barrel length?



Quickload shows 211gns of H2O and 2.99" for the 600 Nitro.

45LC-Shotgun primers will be fine.Tom at Ballistic Research
found that 209A were a little hotter than Fed 215.As for loads if you don't want to use filler or have airspace. start out with 90% loads of real slow powders.On the 12GA
FH Iwill start with H-5010.Whicg is safest for you as you barrel is fairly heavy for 20 ga, but not overly heavy.Ed.

I am comforable with using 209 primers Dave is already turning the brass for that tho I did feel a little jumpy exploring the BPCR side of things. The concept of using ultra slow powders sounds right and you are the one here speaking from experience. It would be interesting to compare that to reduced loads of 4198 under a filler: Seyfried's formula. Has h-5010 been renamed H50BMG?

I will get case capacity as soon as I get a case back, my source for the NE might have used the shorter case. I will not worry about that now though I understand that it makes a difference. I had been thinking that barrel length was 22" like most rifles NEF makes but it is 24".

The worst part is that I don't have any suitable powders for when the brass comes. Even my black powder is FFF.

45LC-Yes it is called H50BMG.You can use Accurate 8700, and WC 872 surplus,and so on down the line.Have you got a
powder burn rate chart?Chart makes figuring out what to get a little easier.Ed.

Yes, I have one and often look at the one on The Reload Bench ( burn rates ). Too bad we don't still have H-870 around...

You once mentioned that you like spherical powders, I believe. Can you elaborate?

45LC-With right ball powders you can get more velocity
and less case stretching at the same time.IE, using a little slower ball and filling case, And most get to peak pressure slower, which give less pressure spike and thus case stretching, but they have larger overall area under the pressure curve.Ed.

45LC,

What's the latest on your project?

Sounds like an interesting project. My thoughts are free, maybe that's their worth:

Your twist rate will work with lead & paper patch, probably at velocities below 1600 fps. Size bullets at Bore diameter, patch to groove diameter, let the bullet obturate to take up the slack. In other words, don't get caught up in the hard cast theory. Marlin's microgroove barrels handle PP okay if they are properly sized. You may achieve higher velocities but I've no doubt that if you get to 1600 fps your flinch index will be off the scale anyway.

When you look at load data for straight wall cartridges, you'll notice mostly fast powders, seldom any real slow ones. There are sound reasons for this, and your ".600 Substitute" is no exception. Going with the slow burners is not a good idea, nor are huge charges necessary. You may be looking for a rifle, but load it like a shotgun. Use wads. The data that Lar45's Quickload offered will turn your NEF into schrapnel.

JMO

Well, I shot it today with factory ammo to sight in the scope I put on it. I know, I did not make the scope my first choice but the red dot sight that I had mounted was dead. Replacing the battery was not useful either. It was not a great loss, it had been given to me over a year ago and I thought about putting in on a Ruger .22 auto pistol but never got around to getting mounts. Still, I have plenty of eye relief on the scope and I will be working up in increments. I had only bought one box of premium sabot ammo and I used all five to get it sighted in at 45 meters. I was not shooting off a bench either. Though I did not shoot groups, the impression I got from this session is that it does what it was made to do quite well, that is shooting pistol bullets in plastic cups accurately. I will shoot groups when I get to a range with a bench.

I also happened across a small supply of Buffalo Bullet Co. .58, 505 grain minie ball slugs. That is close to 1 oz, which is a load in some 3� shells and standard in 12. If the brass comes in before the bullets, these will certainly be the first to go down the tube. They likely will anyway. The thought about putting them in a shot wad may not work. They were a little big for the one I had but may need to be fitted tight anyway. I patched them tonight and am very happy with the patches. I will have to pick up some art paper, maybe even watercolor paper, but for the moment I will get by with the Fabriano strips I trim off my stationary. I guess it is a good thing that I have envelopes too narrow for my paper.

The patches went on well and tucked back up into the hollow base. I could not resist penning �tag you�re it� on one of the finished bullets with my fine point sharpie. These are huge bullets compared to what I am accustomed to shooting. I used a 9mm FMJ to burnish the bottom of the patch in the hollow base. This will be a fun start and I will try to increase the weight gradually.

By the time I have loads assembled, my Chrony should be here. I would like to have gotten a premium unit but what I save here will get me that much closer to a strain gauge. I really don�t expect the scope to last long, so a William�s peep will be on the way as soon as the next paycheck comes in. I will have to get a gunsmith to mount a front sight.

Well the brass is in and it is quite impressive. I have been sitting on this announcement for a couple of days so I would not be pressed for extra info. They are not exactly 3 inches but 2.875 (that is 2 7/8) and that is no problem at all. Case capacity is 191.8 grains of water. ID is more than the plastic cases and it will accept a .58 caliber mini in a 20-gauge wad, I may give up paper patching the .58�s altogether. The paper patched minis were not a problem, though, and gave nostalgia to loading and shooting.

I ordered the brass without any chamfer to the mouth just so I could see how thick the case wall is. I will have to give you that info when I get my caliper back but they are certainly sufficient for what I am doing. I was going to chamfer the mouth on 9 cases so I could load them without damaging the patches and that is when I realized just what I had gotten into. Had the case been any larger, it would have swallowed my Lee chamfering tool. I came out better with the method I had adopted: I went into the woodshop and got a large roman ogee router bit, chucked it into the drill, and ran it in reverse to chamfer the case mouth. This put a chamfer on that was more like a bell than any I had done before. I was in a hurry to load but I did not want to go too quickly with any of the powders I had, so I ran by Wal-Mart and got some Pyrodex. First I loaded some Lee modified minis in shot-cups and worked up to 125 grains of Pyrodex RS. That went well and recoil was not too bad. I then loaded up some paper patched Buffalo Bullets 505 grain minis and worked them up to a max of roughly 160 grains Pyrodex by volume, being all it would hold while leaving enough bullet to seat straight and stay in place. I shot these to see if they were accurate enough to shoot over a Chrony and they seemed to be going close enough to where I aimed them not to worry about that. On the patched bullets, turned the patching back into the hollow base and the rest of the void was filled with CVA grease patch after and loaded over a card wad. The paper patch was lubed with Rooster Jacket and I have been happy with how that works on my 45-70. I am not sure if the grease patch was necessary on the Pyrodex load, but I wanted to make sure I had it loaded right. I will load up some more to chronograph and even try 4 wraps of thinner paper and see what that does. I did get some IMR 4198 to fool around with nitro-for-black loads until I get a better handle on what pressures I will be getting from different loads and until I get some more weight on the rifle. I am not having trouble yet, but I have not shot any really heavy bullets either.

While I was shopping around, I saw what I thought was a good price on some H-870. I may try this when I get some heavier bullets. I guess I could try in now; the rifling is pretty fast and wouldn�t likely allow the bullet to glide down the barrel outrunning the powder burn. I see that Re-15 is preferred for the 470 NE and wonder how this compares to my project.

45lcshooter;

got the whitworth's
thanks.

LC45--The H-870 would be good to see what she will do
as you work from lighter bullets to heavier. If they have a bunch extra let me know where it is, as I need to get more.
And let us know the vel of the 505 gr with full load of
pyrodex.Something to recheck, did you say your muzzle measured .960? Is that correct? If it is. that is a fairly heavy barrel, as most 12 ga for comparison measure about
.920.Did they say whether barrel is strong alloy like rifle barrels?.Ed.

Sorry, took that measurement maybe 1/4" from the muzzle, actual muzzle OD is .955. I have no clue on the alloy, maybe if I write them a letter....

I have a couple of decent photos but I don't have them online. I will have to do that and show the snapshots. I saw one other 1# canister of H-870 but they could have had more squirreled away in the back. It was selling for 13 and change and I picked up a pound just for the thought.I will call tomorrow and see if there is any more.

Brass thickness is .030" I feel I am doing pretty well without dies or expensive special tooling. I saw a Lee Classic loader for 20 ga that I picked up at the local nick nack store and use it for priming and depriming. That is basically it except that I tinker around with stuff in my press to seat the sabot bullets, as they are very tight.

Well, it rained today and I did not get in a shooting session. I did, however, get off a shot with my first smokeless load in the new brass. Using Ross Seyfried�s formula of loading IMR 4198 at 40% to 60% charge weight of black powder under a wad of dacron, I started out at 64 grains of powder and about 15 grains of dacron. I did fire it today into my sand trap and it was fast enough for the bullets to flatten and even grow some holes. That was quite something, and recoil was negligible. I found some similar load data for the .585 Nyati that lists 72 grains of 4198 for a 545 grain lead patched bullet producing 1641 fps, and 73 grains for a 650 grain bullet at 1660. These were reduced loads, of course; but right in the area I want to be. I did not want to get the Chrony wet, so it stayed inside; but I will try to clock some loads as soon as I can.

I am still waiting on bullets from Liberty Shooting Supplies, but they cast items like this per order (it would be foolish to try to stock everything and I am sure that these are not commonly ordered items) and I have not asked them how busy they might be. I have a few samples and am thinking of a Lee mini-ball mould, they are inexpensive and the base plug is can be machined down to add weight. I can get a wadcutter for target work and one of the others for hunting (the improved looks best for solids but the original looks good hollow-pointed and paper patched). I am getting one from a one of the guys over in the Cast Bullets forum and will see how heavy a bullet they can make when given a solid base.

I have found some other bullet makers who are working in the range I am looking for and will be contacting them soon.

Concerning the primers, I am getting great fire and it is really lighting up that pyrodex, but I looked at one of the primers from a fired cartridge and my rifle firing pin really punches that soft primer. At the pressures I am shooting, I am sure it is of no concern, but it certaily looks funny with that skinny, deep impression on those spent primers.

Well, I have been waiting to post again until after contacting Simmons about that powder; Hubel, I will have to PM you with that.

With full case of pyrodex but not compressed, velocity averaged 1521 fps. Due to my not being much of a BPCR shooter and loading it more like nitro except for a card over the powder and some lube in the hollow base, I did not expect consistency...nor did I get it. Lowest was 1490 fps and highest was 1575 fps.

Using the rest of my little sample of 505 grainers, I worked up Seyfried's nitro-for-black and got as far as 70 grain loads of IMR 4198 under a good sized tuft of dacron which gets about 1560 fps. 1600 is not far away (and I hope to do better), but I now have a Lee improved mini mould and can do much more testing with it. I am loading these in Federal shot cups over the same load (as this bullet is lighter) and I am shielding my Chrony before I resume testing so those shot cups, sabots, and filler does not become a problem. Recoil is noticeable but not bad at all... the little Bushnell 4x scope I swiped off my 10/22 is still working too. It is loud but most of the impulse goes away from the gun: shooting without hearing protection (in field situations) will not be a problem.

I am still very early in load development and was starting to feel that I had not achieved much, but I grabbed Ballistic Products Inc, slug loading manual and I have most of their published 12 and under loads beat in both mass and velocity, which I find rather exciting now that I think of it. If I do any more development with black powder or pyrodex, I will probably use paper hulls and consider them disposable, as I do not like the extra steps cleaning up the brass. I tested some smokeless sabot loads and I am getting very complete burn with 4198 and a fairly clean and shiny barrel.

Load Tech predicts 2075 fps with 57.6 grains of XMP-5744 for my 450 grain .451" Lyman Volunteer (sort of a Whitworth) in a sabot, at 17500 PSI. It will be interesting to work that one up.

I am wondering whether I really need filler using those shotgun primers, I may just have to look at load density a little closer and check it out.

Excellent, sounds like alot of fun. You might try dropping Seyfriend a letter and ask his opinion on this one.

Very interesting information here. This is a great project, something along the lines of which has always interested me, but I have never gotten to the point of doing it. Please keep us updated!

1720 fps with Lee modern mini in shotcup over 72 gr IMR 4198 and dacron filler, only one firing, so I do not have any average or sense of consistency; but I will shoot a string whenever I get a chance to shoot groups. The mini is lighter than I expected to be shooting but an excellent toy to last me while I wait for the heavies. Recoil is finally something to acknowledge though still no concern. There is a part of me wanting to push it on up to 1800 fps but I really want to get an idea of what the pressures really are. It would be nice to have a strain gauge The current load does not bother me, but I will play around with it and see what the accuracy is. There are some things I can do in the meantime: I have some .270 loads to work up (90 gr Speer and 110 Hornady v-max) for coyotes, anyway. I also plan to make a heavy full-length style front stock for testing the heavies with.

The question has crossed my mind of how does the plastic wads used for sabots (or jackets depending on your POV) affect pressure? I have been thinking about a letter to Mr. Seyfried, I am sure he would be amused at least.

I wrote hime a letter about my 70 cal pinfire Howda and was suprized when I got a quick and informative reply. I was even more suprized when he printed it in the Handloader magazine.

45LC. The 16yo Son and I are looking into a moose hunt in a short range weapon area. Muzzle loaders, shotguns, archery. This has me thinking lots more about your 20 Express. Have you tried any accuracy tests on it with your Minnies in the wads?

Time has been pretty tight lately and I have not done much shooting. I had sighted it in for shooting over the chrony and but shot at a clay pigeon sitting by a stump when shooting clays with some friends from church. I was dead on at the 30 yards from which I shot it...small comfort, I know. I will shoot some groups Monday, I need to do that with the .270 anyway.

Thanks, I understand the time thing. I'm takeing some summer classes and it has been crazy. I'm done after today until the fall semsester. I have 2 finals done so far and a psyc test this afternoon.

On another thought. I was out looking for 10 ga doubles yesterday and one shop had some Siaga? Russion AK47 variants in 20 ga. It has the 3 lug rotating bolt with adjustable gas chamber for 2 3/4" or 3" shells, adjustable rib for elevation, 2 5 round magazines for both sizes and sells for $189. it's all black with synthetic stock. I was thinking that this might be an interesting option.
I may not take it moose hunting, but I may have to get one just for a toy.

The Lee modern mini is a flat nose and does not affect COAL too much in these brass cases (even with the nose exposed) and could even be happy in a tube mag for those with conventional shotguns. Sized down to .470, it should fit in plastic hulls and roll or star crimps according to what I have done with .470 ball. I am sure you could find some 3" data that would have a heavy enough shot load to work with this at conventional pressures. Cation makes rifled choke tubes that have a 1 in 36" twist if I recall correctly, a lot better with the round ball and even better for the Lees.

Well, I finally punched some holes in a target... I did not shoot off a bench so I will blame the 3" at 50 yards on myself. These were the 1720 fps loads tho this string was not chronographed so i don't know if the fact that i did not weight the dacron for consistency affected velocity and accuracy either. It was a quick opportunity and I had already shot the loads that i had intended to use for some friends who wanted to see the gun in action.

I appologize for not having better-executed test session to report on, but this is the first load i even tried to shoot groups with, more on the way.

I think on my next run i will fill the bases of the minnis with epoxy or such to make sure they are not deforming upon firing. a flat base may be better using the shot cups and if so, altering the plug on my mold will fix it (and give me more lead to play with). I cannot wait until the other bullets get here. I will try a few without filler and see if there is any hangfire: the 209's may negate the usual need for such.

I have a box of old CIL composition wads which would allow filling the case and shooting full sized 20 ga. bullets. Your project sounds very interesting.
About the closest in terms of weirdness was a .577 Snider I used to shoot at BPCR matches. My friend that owned the old rifle was of the opinion that the price of .577 brass was comparable to a few cases of beer and a blow job so he devised an alternative. He made a mold for the lead and then i used cut down 20 ga. hulls loaded with black powder and capped off with bees wax and parafin mix. Loading was done by shoving in a bullet and jamming the 20 Ga hull behind sort of progreesive loading as in a Percussion sahrps. The slugs were straight bore size with no round nose just a inch and a quarter length of lead. Surprisingly accuracey at 50 yards was good but by 100 they were begining to keyhole. AT 200 they often hit sideways to the target. It was real interesting to listen to the scorers try and figure out just how 5 shots could rip such a hole in the target.

45LC:
Fabulous thread. I had thought of trying this with the 12-gauge Ultra Slug, but based on your experience, it seems the 20 is a great choice, too.
I just thought I would mention that a fellow who goes by Coyote sells .590 moulds and bondo base plugs for loading the .577 Snider. Not sure if these would work for you, but his base plug system may be quite useful. Here's the URL: http://www.oldyoti.com/moulds.htm

Anything new going on with this project?

For some reason, all the posts are seperated to the point I can't seem to read the whole thread.

Several things going on, i have almost all my cases loaded but haven't shot anything amost all summer. Found out that the barrels are made from a lesser alloy than many rifle barrels so i have toned down the heavy loading. I may refer to this as the .62-160. I did not have the usually suggested powder for duplex loading but what i used was a little slower and i wasn't worried. 5477 seems to do well in this one but i have not completely worked loads up. I will be looking at buying some Swiss 1.5f. Here are some notes i kept in Word. By the way, my new bullets are paper patched.

I finally gave up on my ordered bullets coming in and started trolling for a mould. Again, there is not much on the market and I did not want to get a .58 this time but a .62. Now, there are not many makers that offer .62 caliber moulds and those are probably hollow-base. I could not afford a custom mould but there is one maker that offers moulds on a semi-custom basis. Dan at Mountain Mould, LLC makes moulds on a CNC machine to your order, providing he can make the mould without excessive programming; that means some profiles are not available, but unless you want round nose, you are probably alright. Of course, any profile that you can create on his on-line program can be made relatively quickly, and thus made quickly enough to not be expensive. My design had a smaller metplat than I would normally use (so I could hollow-point the bullets with a decent profile) but a larger metplat than on many older conicals. The bullets weigh in at 900 grains. I can cut the bullet down until the metplat is half an inch and 800 grains or I can hollow-point them to get 700 grains. I nearly omitted the grooves completely but thought I might use them as reference points to shorten them from the base.
Pyrodex loads with the 900 grain bullets were a pleasant surprise: velocities were just below 1300 fps; which, at least on this continent, is plenty within close ranges. Recoil was not terrible though it was considerable. Mindset is important to managing recoil: when I first shot the heavies, I had shot about 50-65 rounds blasting (at) clays, no big deal with target loads. It did loosen me up because I had been shooting and was in good humor. Shooting was almost pleasant when we shot the big heavies. But when I was chronographing loads I was really tense and took a beating.

Duplex loads with Re 7 boosting black powder pushing a 700 grain bullet yields 1447 fps on a single shot chronographed the other day when I was in a hurry. My sizing die is not in yet and the case stretched enough for it to jam. This is a common occurrence but not a bad one. I have put several loads through much of the brass and it has not come out bad. In fact, I have gone through a number of duplex loads with the 800 grain, .5†metplat bullet. I am very pleased with this as I do not have to worry about getting a hole perfectly centered on the bullet. I just set the depth of my drill press with a large router bit chucked in it. I did not get a chance to chronograph any of these loads but my BP duplexes were not harsh to shoot. They seem to be pretty accurate too, though I have not shot at any great range.

I have a TCR-87 with a fully rifled 20-guage barrel. That is the break-over single shot hammerless rifle which Thompson Center no longer makes. I have a number of rifle barrels for it and also shotgun barrels. A 12-guage barrel was pulled from its monoblock and replaced with a fully rifled 20-guage barrel and it was chamered for 2-3/4-inch shells. It was turned to the outside conture of a 10-guage. That is strait 1.03 inches and is 23 inches long. The gun weighs 8-1/2 pounds with a 1.5-4X leupold scope. I had Rocky Mountain Cartridge turn some brass cases for it and got a 720 grain mold which was a shortened 900 grain 600 nitro bullet. Anyway, with 45 grains of AA5744 it shoots the 720 grain bullet at 1000 fps. At 50 yards that load shoots 1-inch groups. I had some bullets hollow pointed in a lathe which reduced the weight to 550 grains. With 60 grains of AA5744 they go 1330 fps and recoil is about like a 12-guage with regular birdshot loads. That load put 4 of 5 bullets in a 2-1/2 inch group at 100 meters. For pressure this load has a case about as long as a .45-90 and a 550-grain .62 bullet has about the same sectional density as a 300 grain .45 bullet. So I think the pressure would be about the same as a AA5744 load in a .45-90 with a 300 grain bullet at 1300 fps. An advisor at Accurate Arms agreed it would be close and such a load is about 12,000 psi. A 1500 fps load would be about 15,000 psi, too high for a regular shotgun. Mine has the outside conture of a 10-guage and will take the back thrust of a belted magun so I figure its good for 20,000 psi maximum based on hoop stress in the barrel, but want to be conservative so will stick with the 1300 fps limit. I plan on shooting a deer with it just to see how it works, but my regular deer load is the Winchester sabot 260 pistol bullets at 1900 fps. The work good past 150 yards. - DON