GM .62 Maximum Loads

Does anyone have published data on maximum loads for the Green Mountain .62 barrels?

Nope, and in my book it's theoretical at best. In reality when you move past 100 grains on a Hawken stock, you'll find your own personal max.... On the pain meter anyway. In a Renegade stock I've gone to 120 and decided that was powder aplenty. You could show me figures of 150 or 200 or 300 and I wouldn't care. I've found my own max.

Brownbear, you talking .595 or .600 round ball with double F?

Couldn't agree more with you about shoulder max. Tonight I swapped barrels and put the rifled .62 on the Hawken and the smooth on the Renegade. Already rethinking about whether or not that's the best move, putting the rifled barrel on the Hawken stock. Might be better to put it on another shotgun butt Renegade with the comb reworked.

It may be going into the ozone but I'm thinking about trying to see how far and flat I can make a rifled .62 hit. Or in the case of these GM's I should say .61. Hence I'm trying to find out where the upper limit on the equipment really is.
Needless to say, but this will definitely entail bedding the tang, breech and barrel. Got to go into the parts box and find a TC peep.

I use the .595 with a .018 patch. I tried .600 and had to go down to approx .010 patch, which is against my nature, but admittedly left over from rifle experience. Truth be known, I almost certainly have fired it more times with shot than ball. At the moment the barrel is sans rear sight and in a Renegade stock. Did some wing shooting with it that way, and certainly prefer it to a rear sight, even taped over as someone suggested. The front sight is awfully high for that, but I resisted the impulse to put on a low one in honor of my prominent cheekbone.

i have a GM 62 on the way.What are you using for your wing shooting loads brownbear? A talented buddy offered to make me a solid rib (that uses existing sight attachments)for the barrel for when i shoot shot.I may take him up on that.
My New Englander 12ga beats me up too much when i shoot ball.it likes 90g to shoot well but my neck says its too much.I hope this 32" heavier .62 cal is easier on me.

George

For ptarmigan I'm using a 70 grain measure of 1f and the same measure (1 oz) of #6 or #7 1/2 shot (see this chart). Wad is a Type A or "nitro" card lubed with olive oil. For snowshoe hare I move up to #5 shot for full penetration. BTW- That same volume charge of 1f patterns better than a 60 grain charge of 2f, the "classic" formula. I'm really liking 1f for shot.

Your rib sounds like a good idea. I like the high sight for my cheek bone, but it is kinda hanging way up there in space (0.5") above the barrel.

Folks that have not tried Fg in a large cal smoothbore do not know what they are missing. :thumbsup:

For reader information, your load is a 2 1/2 dram load of powder, and the equivalent volume of 1 oz. of shot. Using Fg powder reduces the velocity, and recoil, but how much depends on many other factors including wads used, wad diameter vs. bore diameter, etc. It should be below the Sound Barrier, however.

Is that a problem? NO!! At the short ranges that birds and rabbits are shot, time in flight is only a fraction of a second. Check Lyman's Charts in any of its Shotshell Reloading Manuals to get "time in flight" data. Since round pellets lose much of their velocity in the first 20 YARDS( 60 FEET!) You don't need 1200 fps. MV to kill small game. Its a waste of powder to try to do so.

I too am not concerned about any "Maximum Load" in any .62 cal bore- smooth nor rifled. Recoil tells You when enough is TOO MUCH, and ACCURACY tends to TALK TO YOU MUCH SOONER THAN THAT. :shocked2:

Trying to make any muzzle loader into a flat shooting 200 yard hunting gun is just SILLY, IMHO. :nono: The whole reason to use MLers for hunting game is to impose limitations that our forefathers had with the best firearms they had available- NOT to try to duplicate modern rifles for shoot game at longer ranges! Choosing to use a single-shot traditional MLers to hunt imposes a requirement that the hunter work on, and improve his hunting skills. Like archers, you need to learn how to get close to the game to take a successful shot. Accurate placement is the name of the game, and Large Round balls have a similar arcing trajectory to smaller caliber RBs. Their benefit is that they: 1) make much bigger holes in game, and 2)carry enough weigh to penetrate deeply at modest velocities.

Very few .62 caliber( .595 and larger)balls are recovered from any downed game, except possibly bears, wild boars, and moose. They are veritable FREIGHT CARS rolling downhill once fired. Remember that the ENTRANCE wound of these large RBs is LARGER than the EXIT wound of most modern rifle calibers. As the soft lead ball meets resistance of tissues inside the body cavity, or any bones, it expand to leave an even BIGGER EXIT wound. :hmm: :thumbsup: Death is caused by shock to internal organs and the central nervous system, as well as massive hemorrhage and the resultant-almost instant-- drop in blood pressure, starving the brain of oxygen.

The limiting factors for using any MLer of any caliber for longer range shooting at game has always been The very poor Ballistics Coefficient of any RB, and the use of open sights.

IdahoRon, a member here, has tackled the problem of hunting with MLers in mountains where Shots are likely to exceed 150 yards on your best day. He is shooting paper-patched, .45 cal. bullets and uses both tang peep, or scopes on his guns. His bullets weigh in excess of the typical 325 grain weight of a .62 cal RB. His accuracy is terrific, and he has had much success using a rifle most hunters in his area consider totally useless for that kind of hunting. :hmm: :hatsoff: :hatsoff:

If you are looking for a "solution" for flatter trajectory and longer range hitting powder, I suggest you sell that GM .62 cal. barrel, and spend some time reading back posts by Ron to show you how to achieve that goal w/o dislocating your shoulder. :grin:

My .40 (16" twist with 330 grain) and .458 (24" twist with 407 grain) rifles work very well thank you. As concerns the GM .62 smooth bore and rifled barrels, I prefer to actually know the limits before going there.

You might drop a PM to roundball. He shot the smooth barrel a lot and had one rifled and shot that quite a bit too. Flint, if I recall correctly. I don't know how high he pushed his loads or what he learned from GM about max, but he seemed to be in correspondence with them during that era. He's good about sticking to experience in his comments.

I agree. Recoil is not the issue. Internal pressure in the barrel is my concern.

I have a TC barrel in 56 SB that Bob Hoyt rifled to 62 cal. Land dia is .620. Groove dia is .644. The underlug dovetail is 8" from the breech plug and is .077 deep. This gives a minimum barrel wall thickness of .101 at this point.

Pressure data from Lyman for 58 cal bullets get to 10,000 psi range at 140 to 150 gr 2F so.....
Assuming pressure internally is 10,000 lbs/sq in, then the stress on a .101 wall with a .644 ID is 32,000 psi. I believe the steel in the TC barrel has a tensil strength much higher than this so 10,000 psi should be safe.

Next question is how much powder will it take pushing a .610 RB to generate 10,000 psi?

The only pressure date I have is my Lyman Black Powder Handbook, copyright 1975, that shows 20 ga. shot loads of 3 dram (82.0 gr.) and 7/8 oz shot (383 gr) generates 5740 LUP.

I believe my usual hunting load of 90 gr 2F or 3F should be safe but I would still like to see something from the TC engineers that gives a max load number for a .62 rifle. Even better, how do they calculate the max load for their barrels?

It's tough to find sources of published load data for big bores, at least ones that will go on record as recommending max loads of any real significance...and I guess no one can blame them as they have no idea of the condition of various firearms people would try to use them in...don't want any possible liability.

As one approach for shot load limits in my strong, modern steel smoothbore barrels, I try to draw parallels to the payload weight of a conical in a given caliber and keep the powder charge way down low...not highly scientific I'm sure but has been very workable for a few years now, with no noticeable recoil at all that you'd associate with an unusually heavy load or something.

Also, here's one example of a PRB load in a .62cal Zephyr underhammer using 175grns of powder...can't tell the size of the barrel in the photo but further research would dig it out.
Assuming the featured barrel is no stronger than a modern barrel like a Rice, GM, etc, in a strong 1+1/8" breeched .62cal smoothbore, it would seem the payload weight of a shot load should easily be able to double the PRB weight of the featured 344grn ball, with a powder charge way down only in the 70-80grn range, and not create unsafe pressures.

Scroll about halfway down this page:
http://www.namlhunt.com/traditionalmldata3.html

And here, from the Pacific Rifle Company itself:

1) A load data table for their .62cal using 175grns of powder.
2) A write-up about Forsyth rifling using 200grns of powder.

By extension, using a smoothbore with no rifling at all, even further reduces the amount of resistance, and subsequently reduces the pressures.

( Maybe these links could be "stickys" or placed in the 'reference articles section'? )
http://pacificriflecompany.blogspot.com/
http://pacificriflecompany.blogspot.com/p/genuine-forsyth-rifling.html

Excellent info on the PRC. I've been tempted a few times by that page. 8)

My only gripe with their tables is that the 12-bore is sighted for 50 instead of 100 like the 20-bore. If sighted for 100, it would actually show that it has a flatter trajectory. (assuming you were willing to go to 250 gr of powder) Actually, it would shoot flatter at the same 1700 fps, but only by a gnat's whisker.

:v I have an early .62 PRC and have never been able to duplicate the advertised velocities with my Chrony at 15yards. I shot the 175 gr load for years but is not pleasant off the bench. Hunting conditions and you won't notice the recoil. The recomended maximum was 200gr of FFg, never tried that as the 175 gr load was more than enough. However, the literature with mine listed a twist of 144" and that checked out by measuring it. But groups started looking like a smooth-bore when reduced below 150 grs. My next move is to re-barrel with a 104" twist or so. I believe the faster twist will allow higher pressures with reduced powder loads and allows a wider range of usable loads. :v

MercerLake said:

I have an early .62 PRC

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Would you mind telling the size of barrel at the breech...ie: 1+1/8", etc

:v I'll be home by this Thursday and will post the measurements. :v

:v RoundBall, Here are the measurements.
Breech 1.084" flat to flat
Muzzle .925" flat to flat
Length 30"
Twist 1 in 144"
Land to land .610"
Groove to groove .625"
Narrow Lands 8
Wide Grooves 8
Recomended ball .600"-.610"
Max Charge recomended by manufacturer 200Grs FFg! :youcrazy:

This rifle was purchased new in 1996, later models have a 104" twist and a lower recomended maximum charge.
I found mine shot most accurately with 175grs FFg, the "knuckle-ball" effect started below 150grs. A 144" twist is so slow that one must push the limits to get the velocity required through that slow twist. Never tried the max charge as 175gr FFg is very uncomfortable on the bench and it shot through moose, bears, and most trees.
I would not recomend these charges to anyone as the barrel alloy is unknown, and there isn't much metal between a .625" bore and a .925" Muzzle. At best there is .150" holding disaster at bay. :shake: Which kind of bears on the original post regards a small diameter muzzle with a large hole.
Just because it doesn't blow up when everything is right doesn't mean it's safe, particularly if something goes wrong. Mr Murphy is always along waiting for an opportunity!!! :td:
My intent is to rebarrel to another .62" caliber barrel in a 96"/104" twist to allow more reasonable charges with sufficient velocity. :v

MercerLake said:

Never tried the max charge as 175gr FFg is very uncomfortable on the bench and it shot through moose, bears, and most trees.

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:grin: ...yeah, I suspect it would.

Surprised the breech wasn't a full 1&1/8" (1.125)...expected it would have been larger given the caliber and max load recommendation.
On the other hand, Pacific Rifle Company has specialized in such rifles and charges for quite some time and obviously know what they're doing.
Good information and thanks for sharing it.

My .62cal is a smooth rifle with a Rice barrel having a 1&1/8" breech...and doing load development for woods hunting on the east coast the most I ever tested was 120grns Goex 2F, settled on a moderate 110grn charge for whitetails.

roundball said:

My .62cal is a smooth rifle with a Rice barrel having a 1&1/8" breech...and doing load development for woods hunting on the east coast the most I ever tested was 120grns Goex 2F, settled on a moderate 110grn charge for whitetails.

Click to expand...

I am just working up loads for my .62 cal (.615) GM barrel.All i have is a .575 ball mold right now.With 90g of FF Goex and denim patch i am getting about 6" at 50 yards for 5 shots.How much better can i expect? Should i get a .590 to .600 ball mold and go with thinner patches?

George