Author Topic: No more GM barrels in Mrods? (Read 13943 times))

rsterne · « **Reply #40 on:** June 30, 2019, 02:43:24 PM »

Yep, and a 9/16" barrel would be (0.5625^4 - 0.25^4) = (0.1001-0.0039) = 0.0962.... That would make them 64% stiffer than a 1/2" OD barrel, and 163% stiffer than a 7/16" barrel.... over 2.5 times as stiff (all in .25 cal, same material and length).... A 16mm LW barrel would be (0.630^4 - 0.25^4) = (0.1575-0.0039) = 0.1536.... which is over 4 times as stiff as a 7/16" Crosman barrel....

When I sleeve my 14mm TJ's barrels up to 20mm, the stiffness also increases over 4 times....

Bob

K.O. · « **Reply #41 on:** June 30, 2019, 03:47:40 PM »

I guess treating wall thickness as a solid rectangular bar is way to simplistic... was just what I remembered off the top of my head... and it is basically the cube of the thickness... just did not think would be that far off as an estimate...

so found a calc cause was not sure you could treat as a solid round bar either... brain just does not remember right...

so hanging a 5# weight off of a 24" .4375 hollow tube with .09374 walls it deflects .478"

all same but .5 tube with .125 walls it deflects about half as much .267"...

so yep about 90% stiffer...

https://www.engineering.com/calculators/beams.htm

rsterne · « **Reply #42 on:** June 30, 2019, 07:17:11 PM »

Yep.... 0.478 / 0.267 = 1.79....

Once the bore is less than half the OD, you can almost ignore it.... and just use the 4th power of the ratio of the OD's.... (OD2 / OD1)^4.... close enough....

Bob

YEMX · « **Reply #43 on:** July 03, 2019, 01:25:00 PM »

GM barrels essentially told me to frak off.

the crosman spec would be handled as a "custom barrel" and therefore would require a minimum order of 100.

They said that the barrel specs are "proprietary" to Crosman, but I tried to counter with "since you're no longer supplying the barrels to crosman, couldn't you just add the barrel spec to your regular barrel selection?" so that GM could then offer the barrel as a normal (and inexpensive) blank. She came back with "it's proprietary, it's a custom order, minimum order size 100" in not so nice a tone. The contempt in her voice was palpable.

SMH, why do companies always do this once they hit a certain size?! I'll stick with TJ's barrels. Jeeze.

Machinist · « **Reply #44 on:** July 03, 2019, 01:26:00 PM »

I bought a 25 Mrod barrel from crosman in August of 2018, thinking that it was a GM barrel. It has 6 grooves and the last 1/2" of the bore on the muzzle end looks more like it was drilled, rather than reamed. I don't know if I can get a good picture of it.

I haven't shot it yet, but it sure ain't pretty. I paid $78.44 plus $10.63 shipping, plus tax.

Steve

moorepower · « **Reply #45 on:** July 03, 2019, 01:44:03 PM »

Green Mountain has never sold individual barrels, other than 10/22, 77/22 and AR barrels for the most part. I don't know how this can be a surprise to anyone. I am actually impressed that they stick to their agreement, unlike the Chinese than tell you it is your design and we will only make it for you, and then turn around and make it for anyone that pays them. Since they actually started reaming their barrels, instead of just buying tubing with I.D. specs they have been making quality barrels, so I hate to complain too much until I get one that won't shoot. Lots of old guns out there, for anyone that has to have a GM barrel. Might want to hold off on the panic until you see the fire. it might just be a quality barrel.

YEMX · « **Reply #46 on:** July 03, 2019, 02:07:31 PM »

Quote from: moorepower on July 03, 2019, 01:44:03 PM

Green Mountain has never sold individual barrels...

They offer barrels and blanks, sold to the individual... It's literally on their website... I'm confused as to why you say this...

I know we're not privy to the contract between crosman and GM, but I kinda feel like once you're contract is done, the product is good for sale on the open market- kind of like when a patent runs out. I'm sure I'm wrong, as I'm not a lawyer. But it makes sense to me.

AlanMcD · « **Reply #47 on:** July 03, 2019, 02:28:23 PM »

Quote from: YEMX on July 03, 2019, 02:07:31 PM

I'm sure I'm wrong, as I'm not a lawyer. But it makes sense to me.

Tom - good thing you are sure you are wrong, because you are wrong

Unless the company that is doing the purchasing (Crosman here) is buying a standard spec item from the seller (Green Mountain), they define all the terms in the contract that they want. And if they have any input on specs, they can choose to keep them buried forever if they want. OF course the seller does not have to agree to that, but if they want the business they usually will as this is pretty standard practice.

If you think it is bad here, just imagine car and appliance parts - unless those parts were authorized by the original manufacturer, in most cases they are retro-engineered from the original physical parts , not the original specs or CAD data . . . . and since cars and appliances always need parts, and manufacturers eventually stop making parts, all the non-OEM parts out there were never validated to the original specs.

Obviously I have not seen the contract between Crosman and Green Mountain, but if Crosman wanted those specs kept hidden and forbade the sale of the barrels after the contract was done (as I expect they would have done), then Green Mountain would be opening themselves up to a guaranteed loss in a lawsuit that would likely follow.

YEMX · « **Reply #48 on:** July 03, 2019, 02:36:27 PM »

Quote from: AlanMcD on July 03, 2019, 02:28:23 PM

Quote from: YEMX on July 03, 2019, 02:07:31 PM
I'm sure I'm wrong, as I'm not a lawyer. But it makes sense to me.

Tom - good thing you are sure you are wrong, because you are wrong

Unless the company that is doing the purchasing (Crosman here) is buying a standard spec item from the seller (Green Mountain), they define all the terms in the contract that they want. And if they have any input on specs, they can choose to keep them buried forever if they want.

If you think it is bad here, just imagine car and appliance parts - unless those parts were authorized by the original manufacturer, in most cases they are retro-engineered from the original physical parts , not the original specs or CAD data . . . .

Obviously I have not seen the contract between Crosman and Green Mountain, but if Crosman wanted those specs kept hidden and forbade the sale of the barrels after the contract was done (as I expect they would have done), then Green Mountain would be opening themselves up to a guaranteed loss in a lawsuit that would likely follow.

I get all that- but the fact that they're willing to make/sell (in batches of 100) barrel blanks with the same barrel specs as the crosman barrel shows that this isn't necessarily the case. If the "crosman spec" is to be forever barred from sale, then they wouldn't entertain selling that barrel spec at all. Hence the confusion.

Bottom line, it's their policy/agreement w/Crosman. It's not THAT big a deal.

K.O. · « **Reply #49 on:** July 03, 2019, 02:59:36 PM »

I am sorry YEMX but I disagree... keeping your agreements is a big deal... Plus there are many ways to make a very good barrel that following Crosman Specs is not needed anyways...

I do think by not making some aftermarket air rifle barrel Blanks they are missing a good market...

K.O. · « **Reply #50 on:** July 03, 2019, 03:02:42 PM »

often when doing work for a corporation there is a no compete clause that says for a given period of time you can not make a competing product...

YEMX · « **Reply #51 on:** July 03, 2019, 03:40:47 PM »

Quote from: K.O. on July 03, 2019, 02:59:36 PM

I am sorry YEMX but I disagree... keeping your agreements is a big deal... Plus there are many ways to make a very good barrel that following Crosman Specs is not needed anyways...

I do think by not making some aftermarket air rifle barrel Blanks they are missing a good market...

I meant "it's not a big deal", as in "it's not a big deal that we can't buy crosman spec barrels direct from GM". I'm not saying GM honoring their contract w/crosman (whatever that entails) is a bad thing.

Quote from: K.O. on July 03, 2019, 03:02:42 PM

often when doing work for a corporation there is a no compete clause that says for a given period of time you can not make a competing product...

I figure its something like that, but again, why the ability to sell "a custom barrel" with the same exact specs as the crosman?

Never mind, I'm just gonna drop it. There's other options out there. The GM barrel isn't the be-all end-all of .25 barrels.

Machinist · « **Reply #52 on:** July 05, 2019, 02:00:06 AM »

I bought my 25 Mrod barrel directly from crosman in August 2018. I thought the bore looked kinda rough, but figured it would be ok. The GM barrels were supposed to be good right?

I just measured it today. I've been measuring stuff for a living for 30 years. I've used all kinds if gages and have absolute faith in my measurements.

The bore at the muzzle is .245"

The bore at the breech is .250"/.2501"

In the pic, there is a .2498" pin gage in the breech end. It's a loose fit. The 9 inch long brass bar in the pic is .250" and it slides in freely, to within 1.550" of the muzzle. Almost the entire barrel is .250" !!!!!

I cast a lead slug in the barrel to measure the twist rate. It's between 1:18 and 1:19 there is some slop and the barrel isn't long enough to get a full revolution, so I did half a rev and multiplied by 2. I held the barrel in the lathe, secured the aluminum clamp/wrench pointing straight up, and pulled the slug through until the wrench pointed straight down. Never did this before.

There are 6 grooves. I can cut off a slice of the barrel and get a pic from the optical comparator at work.

SMH
Steve

Machinist · « **Reply #53 on:** July 05, 2019, 02:11:32 AM »

This pic might be better.

Frank in Fairfield · « **Reply #54 on:** July 05, 2019, 09:59:35 AM »

My .50 caliber Hawken had a Green Mountain barrel..

Machinist · « **Reply #55 on:** July 05, 2019, 12:46:38 PM »

The lead slug has some play in the barrel, it turns freely maybe 2 or 3 degrees? The lead slug also turns on the brass adapter a couple of degrees. Need to eliminate that. Seems like the lead was a bad idea. Oh well.

I'm gonna try a jag and a piece of cloth later. Also gonna lock a collar on the rod and measure movement with a 12" dial caliper.

If I lock the aluminum wrench thing in the horizontal, I could indicate it perfectly level. Get exactly 180 degrees of rotation. Might be overkill, I don't know yet. Maybe just use a square, I only eyeballed it last night.

I can check the groove diameter and other details at work. Gonna dissect this thing.

Steve

Machinist · « **Reply #56 on:** July 07, 2019, 01:15:00 AM »

I measured the twist rate on the 25 Mrod barrel again today. The results I got the other day were inconsistent. There were pretty big voids in the 1st lead slug. I cast another lead slug today, this time I heated the barrel more. I also made the flats bigger on the brass piece that the slug is cast around (to keep the slug from turning) Put a few drops of oil in the bore to keep the lead slug from binding. Didn't do that the other day.

I positioned the wrench with a 1-2-3 block when the wrench was pointing down, and positioned the wrench with a square when it was pointing up. So now I'm getting very close to 180 degrees of rotation. Way better than just eyeballing it. I also locked a stop on the 3/16 dia rod, so I could check the movement with a dial caliper.

The system repeats pretty well now. Every time I push the rod home, the wrench is pointing straight down. I measured the twist rate 7 times. I rounded off the results to the nearest .005"

9.855"
9.800"
9.820"
9.860"
9.845"
9.870"
9.850"

The average was 9.843" per 180 degrees X 2 = a twist rate of approx. 1:19.7
I have confidence in this number.

Steve

Machinist · « **Reply #57 on:** July 07, 2019, 01:16:07 AM »

Pic b

Machinist · « **Reply #58 on:** July 07, 2019, 01:16:58 AM »

Pic c

YEMX · « **Reply #59 on:** July 07, 2019, 02:34:03 AM »

That is good stuff! Very interesting!

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No more GM barrels in Mrods?

Author Topic: No more GM barrels in Mrods? (Read 13943 times))