Author Topic: No more GM barrels in Mrods? (Read 13952 times))

Machinist · « **Reply #60 on:** July 07, 2019, 03:16:11 AM »

Glad you like it.

vigilandy · « **Reply #61 on:** July 07, 2019, 04:39:07 AM »

I've got a couple .25 Mrods probably from late 2017, early 2018. Would be nice if Crosman could supply a more definite date the GM barrels were phased out. I'm a little surprised that no official announcement was made. Seems like this is the equivalent of dropping LW barrels from the Challenger and not mentioning it....

YEMX · « **Reply #62 on:** July 07, 2019, 10:54:33 AM »

Quote from: vigilandy on July 07, 2019, 04:39:07 AM

...Would be nice if Crosman could supply a more definite date the GM barrels were phased out... Seems like this is the equivalent of dropping LW barrels from the Challenger and not mentioning it....

Especially since Crosman changed the barrel spec...

BackStop · « **Reply #63 on:** July 07, 2019, 01:35:07 PM »

Quote from: YEMX on July 07, 2019, 10:54:33 AM

Quote from: vigilandy on July 07, 2019, 04:39:07 AM
...Would be nice if Crosman could supply a more definite date the GM barrels were phased out... Seems like this is the equivalent of dropping LW barrels from the Challenger and not mentioning it....

Especially since Crosman changed the barrel spec...

I may be wrong, but it seems Crosman would rather rely on anecdotal reviews on their barrels than actually provide the specs.

The AG community has become much more knowledgeable and "sophisticated"? in recent years and Crosman would be wise to make specs available. The competition will do so and that may drive sales away from Crosman.

JMHO and I am far from an expert on any of this. So, please, take my comments for what they are worth. (chuckle)

rsterne · « **Reply #64 on:** July 07, 2019, 02:20:25 PM »

Steve, nice job on measuring the twist.... I think Crosman went the right way on that for shooting .25 cal pellets.... slugs not so much.... However, even for pellets it seems to me that a 0.005" choke is way too much....

Bob

Machinist · « **Reply #65 on:** July 07, 2019, 10:08:57 PM »

Thanks Bob,

I want to look at a slice of the barrel on a comparator. I don't know if I can get a pic of the image, it might be too dark?

I can defiantly measure the groove dia, groove width, land width. Give everything a good look. There must be a radius in and on all the corners.

Steve

Machinist · « **Reply #66 on:** July 08, 2019, 08:52:28 PM »

I don't know if these pics will show details, so I'll post a few and see.

When you look at stuff on a comparator, not all the details are clear. Things are a little blurry. Then I take pics of the blurry images with a cell phone, and then resize the pics which doesn't help.

I did this on break, it could be done better, but not today.

This is under 20x magnification. If you start at the center, and work your way right, you see .1 a little above the horizontal line, that is .100"

Look further to the right, and there's a .2, that is .200"
The kinda bold line between the .1 and the .2 is .150"

The next bold line to the right of .2 is .250"

If you follow the .250" circle all the way around, it's pretty clear that the land diameter is a little bigger than .250" That's why a .250" diameter brass rod slid into the bore with no resistance.

You can also see that the groove diameter is almost one line further out than the land diameter.

The comparator also has a digital readout, and I used that to measure the groove diameter, which is about .255"
I could check it 10 times and get a slightly different size each time. Not a huge difference, just .0001" or .0002" maybe .00025" at worst. My eyes have gotten older, and I hardly ever use comparators. And the ones I used years ago, were different. But you get the idea, you can enlarge and measure an image.

Steve

Machinist · « **Reply #67 on:** July 08, 2019, 08:57:28 PM »

try this one

OK, this one is pretty clear, not the pic I was describing though. One of the grooves is blown up here. The info about the line applies here too.

Machinist · « **Reply #68 on:** July 08, 2019, 09:03:52 PM »

I think this is the pic I was describing

Yeah, this one is pretty good. I could measure the width of the grooves in inches or degrees. Other stuff too. No time today though. You can see that the grooves are more than twice as wide as the lands. It all could be measured pretty precisely with this gizmo. You can click on this pic and blow it up pretty big.

Steve

K.O. · « **Reply #69 on:** July 08, 2019, 09:17:49 PM »

Just to put the info and pic together did some copy/paste

"
This is under 20x magnification. The lines on the chart are .0025' apart. If you start at the center, and work your way right, you see .2 a little above the horizontal line that is .200"

Look further to the right, and there's a .4 that's .400" the kinda bold line between the .2 and the .4 is .300"

The next bold line to the right of .4 is .500"

If you follow the .500" circle all the way around, it's pretty clear that the land diameter is a little bigger than .500"

You can also see that the groove diameter is almost one line further out than the land diameter.

The comparator also has a digital readout, and I used that to measure the groove diameter, which is about .255"
I could check it 10 times and get a slightly different size each time. Not a huge difference , just .0001" or .0002" maybe .0003" on a bad day.
"

Machinist · « **Reply #70 on:** July 08, 2019, 09:52:44 PM »

Yeah Kirby,

But I typed in the wrong info initially. The bore is NOT .500" it's .250"

I put in the wrong numbers.

Steve

rsterne · « **Reply #71 on:** July 08, 2019, 10:18:19 PM »

So it looks like 0.251" land and 0.255" groove, right?.... with a 19.7" twist.... I assume that is NOT at the choke.... To me, that seems quite large for pellets.... It would barely touch the head of a JSB King, likely not even engrave it all the way around.... if you didn't push it into the choke....

Bob

Machinist · « **Reply #72 on:** July 08, 2019, 10:26:37 PM »

This section of barrel is from the breech end. A slice .115" thick. I was thinking about taking a sample from the muzzle end though, just for the heck of it.

I'm pretty sure the bore ID is .2502" max. Maybe .2503" but I don't think so. I turned a piece of stock .2502" and it was tight in the barrel.

The groove dia is .255"/.2553" give or take a few sub atomic particles.

Steve

Machinist · « **Reply #73 on:** July 08, 2019, 10:28:50 PM »

Yeah,

I was bummed out when the .250" brass rod slid right in. Woosh.... no resistance at all.

Machinist · « **Reply #74 on:** July 08, 2019, 10:36:24 PM »

I figured the sides of the lands wouldn't be square or sharp. A nice looking angle there.

All I need now is some really big pellets!!!!

Steve

rsterne · « **Reply #75 on:** July 08, 2019, 10:40:00 PM »

LW claim their barrels are 0.248"/0.254" (and smaller at the choke, obviously)….

Bob

Machinist · « **Reply #76 on:** July 08, 2019, 11:06:59 PM »

Yeah,

I checked the LW numbers a few times.

I wonder what their tolerances are?

Do they toss a barrel if it's .2477"

Probably not. What are their limits to make it out the door?

I wonder how wide their lands and grooves are compared to crossman?

Machinist · « **Reply #77 on:** July 09, 2019, 02:05:38 AM »

A pic of the optical comparator. It's about 2 feet wide by 3 feet high.

The light goes thru the part, and an image is projected on the screen. The little table you put the workpiece on, can move left and right and up and down. The screen can rotate to check angles. The digital readouts have something like 50 millionths resolution.

Steve

vigilandy · « **Reply #78 on:** July 09, 2019, 03:34:35 AM »

Quote from: Machinist on July 09, 2019, 02:05:38 AM

A pic of the optical comparator. It's about 2 feet wide by 3 feet high.

The light goes thru the part, and an image is projected on the screen. The little table you put the workpiece on, can move left and right and up and down. The screen can rotate to check angles. The digital readouts have something like 50 millionths resolution.

Steve

Thanks for sharing. I've never even heard of this device before, let alone seen one.

K.O. · « **Reply #79 on:** July 09, 2019, 04:39:17 AM »

I have had a few friends with pocket comparators 7x-10x...wonder how +/- they are good for... the one I looked thru was set up for thread pitch(metric) at the time...

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No more GM barrels in Mrods?

Author Topic: No more GM barrels in Mrods? (Read 13952 times))