DYI Mrod Barrel tune-up

[ssscottg]

Thanks REARSPROCKET for posting this.

Has anyone followed this process to polish their Mrod barrel?

http://www.network54.com/Forum/79537/message/1259988439/The+Marauder+Barrel+Fix

It would be great to collect some before and after data.

Regards,
Scott

[REARSPROCKET]

[hawkeye]

Scott thanks for the post.

This is the kind of post that makes these forums so valuable. Great information on how to "fine tune" your air gun for maximum performance.

Thanks Again,

Tom

[ssscottg]

Hey Guys,

I am giving this a try with the Gamo Big Cat.

Scott

[oletom]

I just tried this mod on my mrod....didn't work out for me....spent 25 bucks in gas an materials an gun shoots worse than when I started....its headed for MAC1 tomorrow.....I think the crown work is more techinical than I'm capable of....I'm not saying it can't be done, it just didn't help me.....

[ssscottg]

Tom,

Sorry it didn't work out for your Mrod. I tried it on my Gamo Big Cat and noticed no significant difference than before shooting the H&N Baracuda match 10.6 pellets. It still shoots about 1 groups at 10 yards with a flyer about every 10 shots.

Scott

[Teryx]

Guys,
The only way to properly recut a crown or chamber inlead is with a piloted cutter. Crowns can be cut on a lathe if the barrel OD is concentric with the bore. All these shortcut fixes will do is (maybe) improve a severe problem. If no obvious problem is evident, the chances are for more likely that you will make the matter worse. Most of these barrels that have issues cannot be improved beyond a point because the problem is the bore itself. Try pushing a pellet down the bore with a thin wood dowel. If the pellet gives you resistance all the way through, you can probably make a shooter from that barrel. If the pellet is practically in a free fall by the 2/3 point, you will never make a tack driver from that barrel. I think most likely the good barrels are the ones cut on new tooling, and once the tooling begins to wear, the bore size increases. I've talked to Crosman about getting a barrel cut on fresh tooling but they say don't track that. The barrels get mixed up after drilling while waiting for further processing. It's luck of the draw.

Most of these barrels will shot better with hard lead pellets and with very large heads. The hard lead gets a better grip on the rifling, even if the head size is small. I just finished one part of my barrel work looking at this. I took a can of Crosman Premier HPs and fired groups at 35 yards. The extreme spread of a typical 10 shot group was 6 to 8". Then I took the same tin and started measuring heads. They ranged from .213 to .219 (terrible). Maybe 1 in 20 was below 215, and those are the crazy flyers. I sorted out 3 groups that were nominally .216, .217, .218. Shooting all 216's brought the group down to to 2". the 217's averaged 1" and the 218's averaged 3/4". From pie plate sized groups down to 3/4" from the same tin of pellets, same barrel. This was in one of my better barrels, but still oversized. The problem is that most pellets like the kodiaks are around .216. They do fairly well because they are pretty consistant and have hard lead. It takes a pretty tight barrel by crosman standards to shoot a soft pellet like a JSB. In most cases they are too small and too soft.

One other warning. The breech Orings can cause some real problems. The factory Oring is something like 40 durometer. Could be higher. They used that for a reason. I've tested the "40", 70 and 90 durometer in my test jig. I cut the chamber off of a barrel so I could cycle pellets through it and recover them for measurement after going through the oring. That was an eye openner. I would recommend against using the 90. It is hard enough that it will actually swage the skirts down on the softer pellets, making a bad situation way worse. The 70 polyurethane is a good tough Oring that isn't so compressive. The soft Buna Orings work fine but if you pull one out, just throw it away and get a new one. They are so soft that getting them out without damage is almost impossible. They are dirt cheap when bought by the 100. There are also people selling replacement Orings that may be oversized, especially in the .177 caliber. The .177 uses a metric oring I believe, not a standard profile Oring. If you use a standard size replacement you will be squeezing the pellets through a smaller hole and doing similar damage.

Teryx

[oletom]

Guys,
The only way to properly recut a crown or chamber inlead is with a piloted cutter. Crowns can be cut on a lathe if the barrel OD is concentric with the bore. All these shortcut fixes will do is (maybe) improve a severe problem. If no obvious problem is evident, the chances are for more likely that you will make the matter worse. Most of these barrels that have issues cannot be improved beyond a point because the problem is the bore itself. Try pushing a pellet down the bore with a thin wood dowel. If the pellet gives you resistance all the way through, you can probably make a shooter from that barrel. If the pellet is practically in a free fall by the 2/3 point, you will never make a tack driver from that barrel. I think most likely the good barrels are the ones cut on new tooling, and once the tooling begins to wear, the bore size increases. I've talked to Crosman about getting a barrel cut on fresh tooling but they say don't track that. The barrels get mixed up after drilling while waiting for further processing. It's luck of the draw.

Most of these barrels will shot better with hard lead pellets and with very large heads. The hard lead gets a better grip on the rifling, even if the head size is small. I just finished one part of my barrel work looking at this. I took a can of Crosman Premier HPs and fired groups at 35 yards. The extreme spread of a typical 10 shot group was 6 to 8". Then I took the same tin and started measuring heads. They ranged from .213 to .219 (terrible). Maybe 1 in 20 was below 215, and those are the crazy flyers. I sorted out 3 groups that were nominally .216, .217, .218. Shooting all 216's brought the group down to to 2". the 217's averaged 1" and the 218's averaged 3/4". From pie plate sized groups down to 3/4" from the same tin of pellets, same barrel. This was in one of my better barrels, but still oversized. The problem is that most pellets like the kodiaks are around .216. They do fairly well because they are pretty consistant and have hard lead. It takes a pretty tight barrel by crosman standards to shoot a soft pellet like a JSB. In most cases they are too small and too soft.

One other warning. The breech Orings can cause some real problems. The factory Oring is something like 40 durometer. They used that for a reason. I've tested 40, 70 and 90 durometer in my test jig. I cut the chamber off of a barrel so I could cycle pellets through it and recover them for measurement after going through the oring. That was an eye openner. I would recommend against using the 90. It is hard enough that it will actually swage the skirts down on the softer pellets, making a bad situation way worse. The 70 polyurethane is a good tough Oring that isn't so compressive. The soft Buna Orings work fine but if you pull one out, just throw it away and get a new one. They are so soft that getting them out without damage is almost impossible. They are dirt cheap when bought by the 100. There are also people selling replacement Orings that may be oversized, especially in the .177 caliber. The .177 uses a metric oring I believe, not a standard profile Oring. If you use a standard size replacement you will be squeezing the pellets through a smaller hole and doing similar damage.

Teryx

I agree with this 100%...I found out the hard way....my mrod shot fairly well, I just felt there were to many flyers and that I may be able to decrease this by tampering with the barrel...I to noticed that the o-ring was unusual and felt weird, wasn't quite sure why . I may have even ruined the barrel an have to purchase a new one....MAC1 will determine this....I guess while I'm waiting for the return of my mrod I will refinish the terrible looking finish on my stock an do some pellet sorting... still lots of good info here....thanks, Tom

[Teryx]

Oletom,
I think Shamsher was the first guy to raise the flag about damaged Orings being an issue, and I agree with him. I've got an Oring pick that I've carefully polished to remove that breech Oring, and I still damage it more often than not just getting it out. It's hard to see the damage sometimes without a microscope. The nice thing about the polyurethane is that it's tougher, but it costs 10 - 15 times more. I'm beginning to think that a better strategy is to buy a bag of 100 buna Orings and just replace them every 1000 shots or every time you clean the rifle. If you don't have a good smooth pick, that is for sure the best route. I think they cost 5 or 6 cents each. Just for the record, I'm not sure what the durometer of the factory Orings is. I said "40" because it feels very soft to me but I could be wrong. Different materials feel different. Anything up to 70 or so should be OK with most pellets.

If all you did was work on the crown, you didn't ruin the barrel. Tim can recut it better than new. If you worked on the chamber you may have ruined it. it's harder to correct problems at that end because it's inside. Tim will know pretty quickly when he looks at it.
Teryx

[doctorvandermast]

Oletom,
I think Shamsher was the first guy to raise the flag about damaged Orings being an issue, and I agree with him. I've got an Oring pick that I've carefully polished to remove that breech Oring, and I still damage it more often than not just getting it out. It's hard to see the damage sometimes without a microscope. The nice thing about the polyurethane is that it's tougher, but it costs 10 - 15 times more. I'm beginning to think that a better strategy is to buy a bag of 100 buna Orings and just replace them every 1000 shots or every time you clean the rifle.
Teryx

What do you use for an Oring pick for the Mrod and do you have any tips for using it? Also, what's the best way to reinsert a new Oring?